Principal Human anatomy : the definitive visual guide
Human anatomy : the definitive visual guideAlice M Roberts
Offers a complete overview of the development, form, function, and disorders of the human body, from muscle structure and activity to motor pathways within the brain.
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HUMAN ANATOMY THE DEFINITIVE VISUAL GUIDE CONTENT PREVIOUSLY PUBLISHED IN THE COMPLETE HUMAN BODY HUMAN ANATOMY THE DEFINITIVE VISUAL GUIDE HUMAN ANATOMY THE DEFINITIVE VISUAL GUIDE CONTENTS LONDON, NEW YORK, MELBOURNE, MUNICH, AND DELHI DK LONDON Project Art Editor Duncan Turner Jacket Designer Duncan Turner Pre-Production Producer Vikki Nousiainen Managing Art Editor Michelle Baxter Production Editor Rachel Ng Art Director Philip Ormerod Associate Publishing Director Liz Wheeler DK DELHI Project Editor Ruth O’Rourke-Jones US Editor Cheryl Ehrlich Editor Lili Bryant Jacket Editor Manisha Majithia Managing Editor Angeles Gavira Publisher Sarah Larter Publishing Director Jonathan Metcalf Senior Editor Anita Kakkar Art Editors Suhita Dharamjit, Amit Malhotra Deputy Managing Art Editor Sudakshina Basu DTP Designer Vishal Bhatia Production Manager Pankaj Sharma Editor Pallavi Singh Design Assistant Anjali Sachar Managing Editor Rohan Sinha Pre-Production Manager Balwant Singh Picture Researcher Sumedha Chopra Illustrators Medi-Mation (Creative Director: Rajeev Doshi) Antbits Ltd. (Richard Tibbitts) Dotnamestudios (Andrew Kerr) Deborah Maizels Editor-in-Chief Professor Alice Roberts Authors Consultants THE INTEGRATED BODY THE INTEGRATED BODY Linda Geddes Professor Mark Hanson, University of Southampton, UK BODY SYSTEMS, IMAGING THE BODY BODY SYSTEMS, IMAGING THE BODY Professor Alice Roberts Professor Harold Ellis, King’s College, London Professor Susan Standring, King’s College, London 006 Foreword 01 008 THE INTEGRATED BODY 010 012 014 016 018 Human genetic formula Cell Body composition Body systems Terminology and planes Content previously published in The Complete Human Body First American Edition, 2010 This American Edition, 2014 02 Published in the United States by DK Publishing 4th floor, 345 Hudson Street New York, New York 10014 14 15 16 17 18 10 9 8 7 6 5 4 3 2 1 256502—05/14 Copyright © 2010, 2014 Dorling Kindersley Limited Foreword copyright © Alice Roberts All rights reserved Without limiting the rights under copyright reserved above, no part of this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted, in any form, or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of both the copyright owner and the above publisher of this book. Published in Great Britain by Dorling Kindersley Limited. 020 BODY SYSTEMS 022 SKIN, HAIR, AND NAIL A catalog record for this book is available from the Library of Congress. ISBN 978-1-4654-1954-5 DK books are available at special discounts when purchased in bulk for sales promotions, premiums, fund-raising, or educational use. For details, contact: DK Publishing Special Markets, 345 Hudson Street, New York, New York 10014 or SpecialSales@dk.com. Printed and bound in China by South China Discover more at www.dk.com 024 026 036 040 042 046 SKELETAL SYSTEM OVERVIEW Head and neck Thorax Spine Abdomen and pelvis Pelvis 048 054 056 058 062 064 066 Shoulder and upper arm Lower arm and hand Hand and wrist joints Hip and thigh Hip and knee Lower leg and foot Foot and ankle 068 MUSCULAR SYSTEM OVERVIEW 070 Head and neck 076 Thorax 082 Abdomen and pelvis 086 Shoulder and upper arm 094 Lower arm and hand 098 Hip and thigh 106 Lower leg and foot 110 NERVOUS SYSTEM OVERVIEW 112 Brain 118 Head and neck 120 Brain (transverse and coronal sections) 122 Head and neck (cranial nerves) 124 Eye 126 Ear 128 Neck 130 Thorax 132 Abdomen and pelvis 134 Shoulder and upper arm 138 Lower arm and hand 140 Hip and thigh 144 Lower leg and foot 180 LYMPHATIC AND IMMUNE SYSTEM OVERVIEW 182 Head and neck 184 Thorax 186 Abdomen and pelvis 188 Shoulder and upper arm 190 Hip and thigh 192 194 196 198 200 202 DIGESTIVE SYSTEM OVERVIEW Head and neck Thorax Abdomen and pelvis Stomach and intestines Liver, pancreas, and gallbladder 204 URINARY SYSTEM OVERVIEW 206 Abdomen and pelvis 208 REPRODUCTIVE SYSTEM OVERVIEW 210 Thorax 212 Abdomen and pelvis 216 ENDOCRINE SYSTEM OVERVIEW 218 Head and neck 03 146 RESPIRATORY SYSTEM OVERVIEW 148 Head and neck 150 Thorax 152 Lungs 154 CARDIOVASCULAR SYSTEM OVERVIEW 156 Head and neck 160 Thorax 162 Heart 166 Abdomen and pelvis 168 Shoulder and upper arm 172 Lower arm and hand 174 Hip and thigh 178 Lower leg and foot 220 IMAGING THE BODY 222 224 226 228 Imaging techniques Head and neck Thorax Abdomen and pelvis 230 Lower arm and hand 232 Lower limb and foot 234 GLOSSARY 241 INDEX 255 ACKNOWLEDGMENTS FOREWORD Anatomy is a very visual subject, and illustrated anatomy books have been around for centuries. In the same way that a map must represent the physical features of a landscape, anatomical illustrations must convey the detailed layout of the human body. The mapmaker is concerned with the topography of a landscape, while the anatomist focuses on the topography of the body. The maps—whether of landscapes or the body—are collected into books known as atlases. The ﬁrst anatomical atlases appeared in the Renaissance period, but students of anatomy today still rely heavily on visual media. Plenty of students still use atlases, alongside electronic resources. Anatomical depictions have changed through time, reﬂecting the development of anatomical knowledge, changing styles and taste, and the constraints of different media. One of the earliest and most well-known atlases is Andreas Vesalius’ De humani corporis fabrica (On the structure of the human body), published in 1543. The anatomical illustrations in this book took the form of a series of posed, dissected ﬁgures standing against a landscape. It was a book intended not just for medical students, but for a general readership. The heavy use of images to convey information made sense for this visual subject, and also helped to make anatomy accessible. The late seventeenth century saw a striking change in anatomical depictions. Flayed ﬁgures, gracefully arranged against landscapes, gave way to brutally realistic illustrations of cadaveric specimens in the dissection room. The connection between anatomy and death was impossible to ignore in these pictures. The style of anatomy illustration has also been inﬂuenced by the methods available to capture and print images. As lithography replaced woodcut printing, it was possible to render anatomy in ﬁner detail. Anatomical illustrators leaped on the potential offered by color printing, using different colors to pick out arteries, veins, and nerves. More recently, the advent of photography meant that anatomy could be captured more objectively. It would be reasonable to suppose that photography would offer the best solution to the challenges facing the medical illustrator, but the task requires more than objectivity and ﬁdelity. Images need to be uncluttered, and sometimes a simple line drawing can convey information better than a photograph of an actual dissection. The challenge facing the medical illustrator has always centered on what to keep in and what to leave out. The development of medical imaging, including the use of X-rays, ultrasound, and MRI (magnetic resonance imaging), has had a huge impact on medicine, and has also had a profound effect on the way we visualize and conceptualize the body. Some anatomy atlases are still based on photographic or drawn representations of dissected, cadaveric specimens, and these have their place. But a new style has emerged, heavily inﬂuenced by medical imaging, featuring living anatomy. The supernatural, reanimated skeletons and musclemen of the Renaissance anatomy atlases, and the later, somewhat brutal illustrations of dissected specimens, have been replaced with representations of the inner structure of a living woman or man. Historically, and by necessity, anatomy has been a morbid subject. The general reader may understandably have been put off by opening an atlas to be confronted with images of dead ﬂesh, slightly shrunken eyeballs resting in dissected sockets, and dead guts spilling out of opened abdomens. But the depiction of living anatomy, informed by medical imaging techniques, reveals anatomy in all its glory, without the gore. The illustrations in this atlas are all about living anatomy. Most of the images in this book are founded on a 3-D reconstruction of the anatomy of a whole body, drawn up in digital media and based on scans. We have grappled with the challenge of what to keep in and what to leave out. It’s overwhelming to see all the elements at the same time, so the anatomy of this idealized living human is stripped down, revealing the bones, muscles, nerves, blood vessels, and organs of the body in turn. The result is, I hope, an anatomy atlas that will be useful to any student of anatomy as well as appealing to anyone with an interest in the structure of the human body. PROFESSOR ALICE ROBERTS The body piece by piece A series of MRI scans show horizontal slices through the body, starting with the head and working downward, through the thorax and upper limbs, to the lower limbs and ﬁnally the feet. The Integrated Body 01 The human body comprises trillions of cells, each one a complex unit with intricate workings in itself. Cells are the building blocks of tissues, organs, and eventually, the integrated body systems that all interact—allowing us to function and survive. 010 Human genetic formula 012 Cell 014 Body composition 016 Body systems 018 Terminology and planes INTEGRATED BODY 010 HUMAN GENETIC FORMULA DNA (deoxyribonucleic acid) is the blueprint for all life, from the humblest yeast to human beings. It provides a set of instructions for how to assemble the many thousands of different proteins that make us who we are. It also tightly regulates this assembly, ensuring that the components of the assemby do not run out of control. THE MOLECULE OF LIFE Although we all look different, the basic structure of our DNA is identical. It consists of chemical building blocks called bases, or nucleotides. What varies between individuals is the precise order in which these bases connect into pairs. When base pairs are strung together they can form functional units called genes, which “spell out” the instructions for making a protein. Each gene encodes a single protein, although some complex proteins are encoded by more than one gene. Proteins have a wide range of vital functions in the body. They form structures such as skin or hair, carry signals around the body, and ﬁght off infectious agents such as bacteria. Proteins also make up cells, the basic units of the body, and carry out the thousands of basic biochemical processes needed to sustain life. However, only about 1.5 per cent of our DNA encodes genes. The rest consists of regulatory sequences, structural DNA, or has no obvious purpose – so-called “junk DNA”. DNA double helix In the vast majority of organisms, including humans, long strands of DNA twist around each other to form a right-handed spiral structure called a double helix. The helix consists of a sugar (deoxyribose) and phosphate backbone and complementary base pairs that stick together in the middle. Each twist of the helix contains around ten base pairs. Cytosine Guanine Thymine Adenine DNA backbone Formed of alternating units of phosphate and a sugar called deoxyribose PACKAGING DNA MAKING PROTEINS The human genome is composed of approximately 3 billion bases of DNA— about 61/2ft (2m) of DNA in every cell if it were stretched from end to end. So our DNA must be packaged in order to ﬁt inside each cell. DNA is concentrated into dense structures called chromosomes. Each cell has 23 pairs of chromosomes (46 in total)—one set from each parent. To package DNA, the double helix must ﬁrst be coiled around histone proteins, forming a structure that looks like a string of beads. These histone “beads” wind around and lock together into densely coiled “chromatin”, which, when a cell prepares to divide, further winds back on itself into tightly coiled chromosomes. Proteins consist of building blocks called amino acids, strung together in chains and folded. Every three base pairs of DNA codes for one amino acid. The body makes 20 different amino acids—others are obtained from the diet. Protein synthesis occurs in two steps: transcription and translation. In transcription, the DNA double helix unwinds, exposing single-stranded DNA. Complementary sequences of a related molecule called RNA (ribonucleic acid) then create a copy of the DNA sequence that locks into the exposed DNA bases to be translated into protein. This “messenger RNA” travels to ribosomes, where it is translated into strings of amino acids. These are then folded into the 3D structure of a particular protein. Histone COILED Histone Chromatin Nondividing cell DNA double helix Supercoiled region Cell prepared for division SUPERCOILED Chromosome BASE PAIRS GENES DNA consists of building blocks called bases. There are four types: adenine (A), thymine (T), cytosine (C), and guanine (G). Each base is attached to a phosphate group and a deoxyribose sugar ring to form a nucleotide. In humans, bases pair up to form a double-stranded helix in which adenine pairs with thymine, and cytosine with guanine. The two strands are “complementary” to each other. Even if they are unwound and unzipped, they can realign and rejoin. A gene is a unit of DNA needed to make a protein. Genes range in size from just a few hundred to millions of base pairs. They control our development, but are also switched on and off in response to environmental factors. For example, when an immune cell encounters a bacterium, genes are switched on that produce antibodies to destroy it. Gene expression is regulated by proteins that bind to regulatory sequences within each gene. Genes contain regions that are translated into protein (exons) and non-coding regions (introns). 011 Supercoiled DNA Coils of DNA double-helix are themselves twisted into a supercoil Guanine–cytosine link Guanine always forms a base pair with cytosine Core unit Package of proteins around which 2–5 turns of DNA is wrapped; also known as a nucleosome Histone Ball-shaped protein Adenine– thymine link Adenine and thymine always form base pairs together Helical repeat Helix turns 360° for every 10.4 base pairs THE HUMAN GENOME Different organisms contain different genes, but a surprisingly large proportion of genes are shared between organisms. For example, roughly half of the genes found in humans are also found in bananas. However, it would not be possible to substitute the banana version of a gene for a human one because variations in the order of the base pairs within each gene also distinguish us. Humans possess more or less the same genes, but many of the differences between individuals can be explained by subtle variations within each gene. In humans, DNA differs by only about 0.2 per cent, while human DNA differs from chimpanzee DNA by around 5 per cent. Human genes are divided unevenly between 23 pairs of chromosomes, and each chromosome consists of gene-rich and gene-poor sections. When chromosomes are stained, differences in these regions show up as light and dark bands, giving chromosomes a striped appearance. We still don’t know the exact number of protein-coding genes in the human genome, but researchers currently estimate between 20,000 and 25,000. Karyotype This is an organized proﬁle of the chromosomes in someone’s cells, arranged by size. Studying someone’s karyotype enables doctors to determine whether any chromosomes are missing or abnormal. GENETIC ENGINEERING This form of gene manipulation enables us to substitute a defective gene with a functional one, or introduce new genes. Glow-in-the-dark mice were created by introducing a jellyﬁsh gene that encodes a ﬂuorescent protein into the mouse genome. Finding safe ways of delivering replacement genes to the correct cells in humans could lead to cures for many types of inherited diseases—so-called gene therapy. HUMAN GENETIC FORMULA Chromosome X-shaped structure composed of DNA molecules INTEGRATED BODY 012 CELL It is hard to comprehend what 75 trillion cells looks like, but observing yourself in a mirror would be a good start. That is how many cells exist in the average human body – and we replace millions of these cells every single day. Nucleus The cell’s control centre, containing chromatin and most of the cell’s DNA CELL ANATOMY The cell is the basic functional unit of the human body. Cells are extremely small, typically only about 0.01mm across – even our largest cells are no bigger than the width of a human hair. They are also immensely versatile: some can form sheets like those in your skin or lining your mouth, while others can store or generate energy, such as fat and muscle cells. Despite their amazing diversity, there are certain features that all cells have in common, including an outer membrane, a control center called a nucleus, and tiny powerhouses called mitochondria. Nuclear membrane A two-layered membrane with pores for substances to enter and leave the nucleus Nucleolus The region at the centre of the nucleus; plays a vital role in ribosome production Nucleoplasm Fluid within the nucleus, in which nucleolus and chromosomes ﬂoat Microtubules Part of cell’s cytoskeleton, these aid movement of substances through the watery cytoplasm Centriole Composed of two cylinders of tubules; essential to cell reproduction Liver cell These cells make protein, cholesterol, and bile, and detoxify and modify substances from the blood. This requires lots of energy, so liver cells are packed with mitochondria (orange). Microvilli These projections increase the cell’s surface area, aiding absorption of nutrients CELL METABOLISM When a cell breaks down nutrients to generate energy for building new proteins or nucleic acids, it is known as cell metabolism. Cells use a variety of fuels to generate energy, but the most common one is glucose, which is transformed into adenosine triphosphate (ATP). This takes place in structures called mitochondria through a process called cellular respiration: enzymes within the mitochondria react with oxygen and glucose to produce ATP, carbon dioxide, and water. Energy is released when ATP is converted into adenoside diphosphate (ADP) via the loss of a phosphate group. Mitochondrion While the number of mitochondria varies between different cells, all have the same basic structure: an outer membrane and a highly folded inner membrane, where the production of energy actually takes place. Golgi complex A structure that processes and repackages proteins produced in the rough endoplasmic reticulum for release at the cell membrane Released secretions Secretions are released from the cell by exocytosis, in which a vesicle merges with the cell membrane and releases its contents Secretory vesicle Sac containing various substances, such as enzymes, that are produced by the cell and secreted at the cell membrane Lysosome Produces powerful enzymes that aid in digestion and excretion of substances and worn-out organelles CELL TRANSPORT At a cell’s heart is the nucleus, where the genetic material is stored and the ﬁrst stages of protein synthesis occur. Cells also contain other structures for assembling proteins, including ribosomes, the endoplasmic reticulum, and the Golgi apparatus. The mitochondria provide the cell with energy. Vacuole Sac that stores and transports ingested materials, waste products, and water Cell interior Fluid outside cell Diffusion Molecules passively cross the membrane from areas of high to low concentration. Water and oxygen both cross by diffusion. Cell interior Cytoskeleton Internal framework of the cell, made up of microﬁlaments and hollow microtubules Microﬁlament Provides support for the cell; sometimes linked to the cell’s outer membrane Mitochondrion Site of fat and sugar digestion in the cell; produces energy Rough endoplasmic reticulum Consists of folded membranes, studded with ribosomes, that extend throughout the cell Molecule at receptor site Carrier protein Protein forms channel Molecule Facilitated diffusion Active transport A carrier protein, or protein pore, binds with a molecule outside the cell, then changes shape and ejects the molecule into the cell. Molecules bind to a receptor site on the cell membrane, triggering a protein, which changes into a channel that molecules travel through. MAKING NEW BODY CELLS While the cells lining the mouth are replaced every couple of days, some of the nerve cells in the brain have been there since before birth. Stem cells are specialized cells that constantly divide and give rise to new cells, such as blood cells. Cell division requires that a cell’s DNA is accurately copied and then shared equally between two “daughter” cells, by a process called mitosis. The chromosomes are ﬁrst replicated before being pulled to opposite ends of the cell. The cell then divides to produce two daughter cells, with the cytoplasm and organelles being shared between the two cells. Centromere Nuclear membrane Cytoplasm Jellylike ﬂuid in which organelles ﬂoat; primarily water, but also contains enzymes and amino acids Single chromosome Centromere Spindle Duplicated chromosome Nucleus Ribosome Tiny structure that assists with protein assembly (see p.10) Cell membrane Encloses contents of the cell and maintains the cell’s shape; regulates ﬂow of substances in and out of the cell 1 Preparation 2 Alignment 3 Separation The cell produces proteins and new organelles, and duplicates its DNA. The DNA condenses into X-shaped chromosomes. The chromosomes line up along a network of ﬁlaments – spindle – linked to a larger network, called the cytoskeleton. The chromosomes are pulled apart and move to opposite ends of the cell. Each end has an identical set of chromosomes. Single chromosome Peroxisome Makes enzymes that oxidize some toxic chemicals Smooth endoplasmic reticulum Network of tubes and ﬂat, curved sacs that helps to transport materials through the cell; site of calcium storage; main location of fat metabolism Nucleus Chromosome Nuclear membrane 4 Splitting 5 Offspring The cell now splits into two, with the cytoplasm, cell membrane, and remaining organelles being shared roughly equally between the two daughter cells. Each daughter cell contains a complete copy of the DNA from the parent cell; this enables it to continue growing, and eventually divide itself. 013 CELL Generic cell Materials are constantly being transported in and out of the cell via the cell membrane. Such materials include fuel for generating energy, or building blocks for protein assembly. Some cells secrete signalling molecules to communicate with the rest of the body. The cell membrane is studded with proteins that help transport, allow cells to communicate, and identify a cell to other cells. The membrane is permeable to some molecules, but others need active transport through special channels in the membrane. Cells have three methods of transport: diffusion, facilitated diffusion, and active transport. Cell membrane INTEGRATED BODY 014 BODY COMPOSITION Cells are building blocks from which the human body is made. Some cells work alone—such as red blood cells, which carry oxygen—but many are organized into tissues. These tissues form organs, which in turn form speciﬁc body systems, where cells with various functions join forces to accomplish one or more tasks. CELL TYPES There are more than 200 types of cells in the body, each type specially adapted to its own particular function. Every cell contains the same genetic information, but not all of the genes are “switched on” in every cell. It is this pattern of gene expression that dictates the cell’s appearance, its behavior, and its role in the body. A cell’s fate is largely determined before birth, inﬂuenced by its position in the body and the cocktail of chemical messengers that it is exposed to in that environment. Early during development, stem cells begin to differentiate into three layers of specialized cells called the ectoderm, endoderm, and mesoderm. Cells of the ectoderm will form the skin and nails, the epithelial lining of the nose, mouth, and anus, the eyes, and the brain and spinal cord. Cells of the endoderm will become the inner linings of the digestive tract, the respiratory linings, and glandular organs. Mesoderm cells will develop into muscles, and the circulatory and excretory systems. STEM CELLS A few days after fertilization, an embryo consists of a ball of “embryonic stem cells” (ESCs). These cells have the potential to develop into any type of cell in the body. Scientists are trying to harness this property to grow replacement body parts. As the embryo grows, the stem cells become increasingly restricted in their potential and most are fully differentiated by the time we are born. Only a small number of stem cells remain in parts of the adult body, including in the bone marrow. Scientists believe that these cells could also be used to help cure diseases. Adult stem cells Adult stem cells, such as the large white cell in this image, are present in bone marrow, where they multiply and produce millions of blood cells, including red blood cells, also seen here. Red blood cells Unlike other cells, red blood cells lack a nucleus and organelles. Instead, they have an oxygen-carrying protein (hemoglobin), which gives blood its red color. Epithelial cells The skin cells and the cells lining the lungs and reproductive tracts are among the barrier cells, called epithelial cells, which line the cavities and surfaces of the body. Adipose (fat) cells These cells are highly adapted for storing fat – the bulk of their interior is taken up by a large droplet of semi-liquid fat. When we gain weight, they ﬁll up with more fat. Nerve cells These electrically excitable cells transmit electrical signals down an extended stem called an axon. Found throughout the body, they enable us to feel sensations. Photoreceptor cells Located in the eye, these areof two types— cone and rod (left). Both have a lightsensitive pigment and generate electrical signals when struck by light, helping us see. Smooth muscle cells One of three types of muscle cell, smooth muscle cells are spindle-shaped cells found in the arteries and the digestive tract that produce contractions. Ovum (egg) cells The largest cells in the female human body, eggs are female reproductive cells. Like sperm, they have just 23 chromosomes. Sperm cells Sperm are male reproductive cells, with tails that enable them to swim up the female reproductive tract and fertilize an egg. LEVELS OF ORGANIZATION The overall organization of the human body can be visualized as a hierarchy of levels. At its lowest are the body’s basic chemical constituents, forming organic molecules, such as DNA, the key to life. As the hierarchy ascends, the number of components in each of its levels —cells, tissues, organs, and systems—decreases, culminating in a single being at its apex. Cells are the smallest living units, with each adapted to carry out a speciﬁc role, but not in isolation. Groups of similar cells form tissues, which in turn form organs with a speciﬁc role. Organs with a common purpose are linked within a system, such as the cardiovascular system, shown right. These interdependent systems combine to produce a human body (see pp.16–17). TISSUE TYPES 015 Skeletal muscle Smooth muscle Spongy bone Able to contract involuntarily in long, wavelike motions, smooth muscle is found in sheets on the walls of speciﬁc organs. It is vital for maintaining blood pressure and for pushing food through the system. Spongy bone is found in the center of bones (see p.24) and is softer and weaker than compact bone. The latticelike spaces in spongy bone are ﬁlled with bone marrow or connective tissue. Cartilage Loose connective tissue Its high water-content makes this tissue rubbery yet stiff. It is composed of cells, called chondrocytes, set in a matrix of gel-like materials secreted by the cells. Cartilage is found in the bone joints and in the ear and nose. This tissue type also contains cells called ﬁbroblasts, which secrete loosely-organized ﬁbers that make the tissue pliable. Loose connective tissue holds organs in place and provides support. Dense connective tissue Adipose tissue This contains ﬁbroblast cells, which secrete the ﬁbrous protein called type 1 collagen. The ﬁbers are organized into a regular parallel pattern, making the tissue very strong. This tissue type occurs in the base layer of skin. A type of connective tissue, adipose tissue is composed of fat cells called adipocytes, as well as some immune cells, ﬁbroblast cells, and blood vessels. Its main task is to store energy, and to protect and insulate the body. Epithelial tissue Nervous tissue This tissue forms a covering or lining for internal and external body surfaces. Some epithelial tissues can secrete substances such as digestive enzymes; others can absorb substances like food or water. This forms the brain, spinal cord, and the nerves that control movement, transmit sensation, and regulate many body functions. It is mainly made up of networks of nerve cells (see opposite). This tissue enables voluntary limb movements. Its cells are arranged into bundles of ﬁbers that connect to bones via tendons. They are packed with ﬁlaments that slide over one another to produce contractions. 1. CHEMICALS 2. CELLS 3. HEART TISSUE 4. HEART Key among the chemicals inside all cells is DNA (see pp.10–11). Its long molecules provide the instructions for making proteins. These, in turn, perform many roles, such as building cells. While cells may differ in size and shape, all have the same basic features: an outer membrane; organelles ﬂoating within jellylike cytoplasm; and a nucleus containing DNA (see pp.12–13). One of the three types of muscle tissue, cardiac muscle is found only in the walls of the heart. Its cells contract together, as a network, to make the heart squeeze and pump blood. Like other organs, the heart is made of several types of tissue, including cardiac muscle tissue. Among the others are connective and epithelial tissues, found in the chambers and valves. 5. CARDIOVASCULAR SYSTEM The heart, blood, and blood vessels form the cardiovascular system. Its main tasks are to pump blood, deliver nutrients, and remove waste from the tissue cells. BODY COMPOSITION Cells of the same kind often group together to form tissues that carry out a speciﬁc function. However, not all cells within a tissue are necessarily identical. The four main types of tissue in the human body are muscle, connective tissue, nervous tissue, and epithelial tissue. Within these groups, different forms of these tissues can have very different appearances and functions. For example, blood, bone, and cartilage are all types of connective tissue, but so are fat layers, tendons, ligaments, and the ﬁbrous tissue that holds organs and epithelial layers in place. Organs such as the heart and lungs are composed of several different kinds of tissue. INTEGRATED BODY 016 BODY SYSTEMS The human body can do many different things. It can digest food, think, move, even reproduce and create new life. Each of these tasks is performed by a different body system—a group of organs and tissues working together to complete that task. However, good health and body efﬁciency rely on the different body systems working together in harmony. SYSTEM INTERACTION Think about what your body is doing right now. You are breathing, your heart is beating, and your blood pressure is under control. You are also conscious and alert. If you were to start running, specialized cells called chemoreceptors would detect a change in your body’s metabolic requirements and signal to the brain to release adrenaline. This would in turn signal the heart to beat faster, boosting blood circulation and providing more oxygen to the muscles. After a while, cells in the hypothalamus might detect an increase in temperature and send a signal to the skin to produce sweat, which would evaporate and cool you down. The individual body systems are linked together by a vast network of positive and negative feedback loops. These use signalling molecules such as hormones and electrical impulses from nerves to maintain equilibrium. Here, the basic components and functions of each system are described, and examples of system interactions are examined. LYMPHATIC AND IMMUNE SYSTEM The lymphatic system includes a network of vessels and nodes, which drain tissue ﬂuid and return it to the veins. Its main functions are to maintain ﬂuid balance within the cardiovascular system and to distribute immune cells around the body. Movement of lymphatic ﬂuid relies on the muscles within the muscular system. ENDOCRINE SYSTEM The endocrine system communicates with the other systems, enabling them to be monitored and controlled. It uses chemical messengers, called hormones, which are secreted into the blood by specialized glands. BREATHING IN AND OUT The mechanics of breathing rely upon an interaction between the respiratory and muscular systems. Together with three accessory muscles, the intercostal muscles and the diaphragm contract to increase the volume of the chest cavity. This draws air down into the lungs. A different set of muscles is used during forced exhalation. These rapidly compress the chest cavity, forcing air out of the lungs. Accessory and intercostal muscles RESPIRATORY SYSTEM Every cell in the body needs oxygen and must dispel carbon dioxide in order to function. The respiratory system ensures this by breathing air into the lungs, where the exchange of these molecules occurs between the air and blood. The cardiovascular system transports oxygen and carbon dioxide between the cells and the lungs. NERVOUS SYSTEM Diaphragm The brain, spinal cord, and nerves collect, process, and disseminate information from the body’s internal and external environments. The nervous system communicates through networks of nerve cells, which connect with other systems. The brain controls and monitors all the other systems to ensure they are performing normally. DIGESTIVE SYSTEM MUSCULAR SYSTEM 017 As well as oxygen, every cell needs energy in order to function. The digestive system processes and breaks down the food we eat so that a variety of nutrients can be absorbed from the intestines into the circulatory system. These are then delivered to the cells of every body system in order to provide them with energy. The muscular system is made up of three types of muscle: skeletal, smooth, and cardiac. It is responsible for generating movement – both in the limbs and within the other body systems. For example, smooth muscle aids the digestive system by helping to propel food down the esophagus and through the stomach, intestines, and rectum. The respiratory system needs the thoracic muscles to contract to ﬁll the lungs with air (see opposite). BODY SYSTEMS SKELETAL SYSTEM This system uses bones, cartilage, ligaments, and tendons to provide the body with structural support and protection. It encases much of the nervous system within a skull and vertebrae, and the vital organs of the respiratory and circulatory systems within the ribcage. The skeletal system also supports our immune and the circulatory systems by manufacturing red and white blood cells. REPRODUCTIVE SYSTEM CARDIOVASCULAR SYSTEM The cardiovascular system uses blood to carry oxygen from the respiratory system and nutrients from the digestive system to cells of all the body’s systems. It also removes waste products from these cells. At the center of the cardiovascular system lies the muscular heart, which pumps blood through the blood vessels. Although the reproductive system is not essential for maintaining life, it is needed to propagate it. Both the testes of the male and the ovaries of the female produce gametes in the form of sperm and eggs, which fuse to create an embryo. The testes and ovaries also produce hormones including estrogen and testosterone, thus forming part of the endocrine system. URINARY SYSTEM The urinary system ﬁlters and removes many of the waste products generated by cells of the body. It does this by ﬁltering blood through the kidneys and producing urine, which is collected in the bladder and then excreted through the urethra. The kidneys also help regulate blood pressure within the cardiovascular system by ensuring that the correct amount of water is reabsorbed by the blood. INTEGRATED BODY 018 Midclavicular line A vertical line running down from the midpoint of each clavicle Pectoral region The chest; sometimes refers to just the upper chest, where the pectoral muscles lie Epigastric region Area of the abdominal wall above the transpyloric plane, and framed by the diverging margins of the ribcage Axilla The armpit; more precisely, the pyramidshaped part of the body between the upper arm and the side of the thorax. Floored by the skin of the armpit, it reaches up to the level of the clavicle, top of the scapula, and ﬁrst rib Occipital region The back of the head Anterior surface of arm “Anterior” means front, and refers to the body when it is in this “anatomical position”. “Arm” relates to the part of the upper limb between the shoulder and the elbow Posterior surface of arm Hypochondrial region The abdominal region under the ribs on each side Umbilical region Central region of the abdomen, around the umbilicus (navel) Lumbar region On the back of the body it refers to the part between the thorax and the pelvis Cubital fossa Triangular area anterior to the elbow, bounded above by a line between the epicondyles of the humerus on each side, and framed below by the pronator teres and brachioradialis muscles Transpyloric plane Horizontal plane joining tips of the ninth costal cartilages, at the margins of the ribcage; level with the ﬁrst lumbar vertebra and pylorus of the stomach Posterior surface of forearm Dorsum of hand The back of the hand Anterior surface of forearm The part of the body between the elbow and the wrist Lumbar region The side of the abdominal wall Palmar surface of hand Anterior surface of the hand Intertubercular plane This plane passes through the iliac tubercles—bony landmarks on the pelvis —and lies at the level of the ﬁfth lumbar vertebra Iliac region The area below the intertubercular plane and lateral to (to the side of) the midclavicular line; may also be referred to as the “iliac fossa” Gluteal region Refers to the buttock, and extends from the iliac crest (the top of the bony pelvis) above, to the gluteal fold (the furrow between the buttock and thigh) below Suprapubic region The part of the abdomen that lies just above the pubic bones of the pelvis Inguinal region Refers to the groin area, where the thigh meets the trunk Posterior surface of thigh Anterior surface of thigh Part of the body between the hip and the knee Popliteal fossa A diamond-shaped cavity at the back of the knee, between the diverging hamstring muscles above and the converging calf muscles below Anterior surface of knee Anterior surface of leg Anatomically, “leg” just refers to the part between the knee and ankle, and the term “lower limb” is used for the whole limb Calf This common term is also used anatomically, to describe the ﬂeshy back of the leg Dorsum of foot Standing upright, this is the upper surface of the foot Anterior surface regions Posterior surface regions The anterior surface of the body is divided into general anatomical areas by imaginary lines drawn on the body. The location of many of these lines is deﬁned by reference to underlying features such as muscles or bony prominences; for example, the cubital fossa is deﬁned by reference to epicondyles of the humerus, and the pronator teres and brachioradialis muscles. Many of the regions may be divided into smaller areas. For instance, the upper part of the anterior thigh contains the femoral triangle. As with the anterior surface, the posterior surface can also be divided into anatomical regions. The anterior surface of the abdomen is divided by planes and mapped into nine regions—allowing doctors to describe precisely where areas of tenderness or lumps are felt on abdominal examination. The back is not divided into as many regions. This illustration shows some of the terms used for the broader regions of back of the body. TERMINOLOGY AND PLANES 019 TERMINOLOGY AND PLANES Anatomical language allows us to describe the structure of the body accurately and unambiguously. The illustrations here show the main regions of the anterior (front) and posterior (back) surfaces of the body. Sometimes it is easier to understand anatomy by dividing the body into two dimensional slices. The orientation of these planes through the body also have speciﬁc anatomical names. There are also terms to describe the relative position of structures within the body. Superior Medial Lateral Sagittal plane Coronal plane Transverse plane Promixal Medial Lateral Flexion Distal Extension Promixal Adduction Abduction Distal Inferior Directions and relative positions As well as deﬁning parts of the body, anatomical terminology also allows us to precisely and concisely describe the relative positions of various structures. These terms always refer back to relative positions of structures when the body is in the “anatomical position” (shown above). Medial and lateral describe positions of structures toward the midline, or toward the side of the body, respectively. Superior and inferior refer to vertical position—toward the top or bottom of the body. Proximal and distal are useful terms, describing a relative position toward the center or periphery of the body. Anatomical terms for planes and movement The diagram above shows the three planes—sagittal, coronal, and transverse—cutting through a body. It also illustrates some medical terms that are used to describe certain movements of body parts: ﬂexion decreases the angle of a joint, such as the elbow, while extension increases it; adduction draws a limb closer to the sagittal plane, while abduction moves it further away from that plane. 02 Body Systems The human body is made up of eleven functional systems. No one system works in isolation: for example the endocrine and nervous systems work closely to keep the body regulated, while the respiratory and cardiovascular systems combine to deliver vital oxygen to cells. To build the clearest picture of how the body is put together it is, however, helpful to strip back our anatomy and consider it system by system. This chapter gives an overview of the basic structure of each system before looking at each region in detail. 022 024 068 110 Skin, hair, and nail Skeletal system Muscular system Nervous system 146 154 180 192 Respiratory system Cardiovascular system Lymphatic and immune system Digestive system 204 Urinary system 208 Reproductive system 216 Endocrine system Medulla 022 Cortex INTEGUMENTARY SYSTEM Hair Cuticle Visible hair A hair in section A strand of hair has a multilayered structure, from its root to the tip. Hair’s color is determined by melanin within the cortex; the medulla reﬂects light so the different tones of color are seen. Epithelial root sheath Internal root sheath Sebaceous gland External root sheath Dermal root sheath Together with the epithelial root sheath, makes the hair follicle Hair matrix Melanocyte Cell that makes the pigment (melanin) that gives hair its color Bulb Base of hair root Papilla Directs growth of the hair follicle Blood vessels Bring nourishment to the cells of the matrix SECTION THROUGH A HAIR SKIN, HAIR, AND NAIL The skin is our largest organ, weighing about 9lb (4kg) and covering an area of about 21 square feet (2 square meters). It forms a tough, waterproof layer, which protects us from the elements. However, it offers much more than protection: the skin lets us appreciate the texture and temperature of our environment; it regulates body temperature; it allows excretion in sweat; communication through blushing; gripping thanks to ridges on our ﬁngertips, and vitamin D production in sunlight. Thick head hairs and ﬁne body hairs help to keep us warm and dry. All visible hair is in fact dead; hairs are only alive at their root. Constantly growing and self-repairing, nails protect ﬁngers and toes but also enhance their sensitivity. Nail matrix Adds keratinized cells to nail root Nail root Cuticle Lunula Crescent shape on nail Nail Hard plate made of keratin Nail bed Distal phalanx Fat SECTION THROUGH A NAIL 023 Hair Hairs cover most of the body, apart from the palms of the hands, soles of the feet, nipples, glans penis, and vulva Touch sensor Epidermal surface Skin in section In just one square centimeter ( 1⁄6 in2) of the skin, there are, on average, 211⁄2in (55cm) of nerve ﬁbers, 27 1⁄2in (70cm) of blood vessels, 15 sebaceous glands, 100 sweat glands, and over 200 sensory receptors. Arrector pili muscle Tiny bundles of smooth muscle, these contract to raise the hairs in response to cold Basal epidermal layer New skin cells are made here Sweat droplet Epidermis Outermost layer of the skin, comprising constantly renewing layers of cells called keratinocytes Dermis Inner layer, composed of dense connective tissue, containing the nerves and blood vessels that supply the skin Hypodermis Layer of loose connective tissue under the skin; also known as superﬁcial fascia Hair follicle Cuplike structure in the dermis or hypodermis forms a socket for a hair Sebaceous gland Secretes sebum into the hair follicle; this oily secretion helps to waterproof the skin and keep it supple, and also has an antibacterial effect Sweat gland Coiled tube extend upward from the dermis to open at a pore on the surface of the epidermis Arteriole Venule SKIN, HAIR, AND NAIL SECTION THROUGH SKIN SKELETAL SYSTEM 024 SKELETAL SYSTEM OVERVIEW The human skeleton gives the body its shape, supports the weight of all our other tissues, provides attachment for muscles, and forms a system of linked levers that the muscles can move. It also protects delicate organs and tissues, such as the brain within the skull, the spinal cord within the arches of the vertebrae, and the heart and lungs within the ribcage. The skeletal system differs between the sexes. This is most obvious in the pelvis, which is usually wider in a woman than in a man. The skull also varies, with men having a larger brow and more prominent areas for muscle attachment on the back of the head. The entire skeleton tends to be larger and more robust in a man. Cranium Contains and protects the brain and the organs of special sense – the eyes, ears, and nose – and provides the supporting framework of the face Vertebral column Comprises stacked vertebrae and forms a strong, ﬂexible backbone for the skeleton Mandible A single bone, the jaw contains the lower teeth and provides attachment for the chewing muscles Clavicle Manubrium Scapula Sternum Gladiolus Xiphoid process Humerus Costal cartilages Attach the upper ribs to the sternum, and lower ribs to each other, and give the ribcage ﬂexibility Ribs Ulna BONE STRUCTURE Most of the human skeleton develops ﬁrst as cartilage, which is later replaced by bone throughout fetal development and childhood. Both bone and cartilage are connective tissues. Bone tissue consists of cells that are embedded in a mineralized matrix, making it extremely hard and strong. Bone is full of blood vessels and repairs easily. Diaphysis Line of fusion of growth plate Medullary (marrow) cavity Periosteum Compact bone Osteocyte Epiphysis Articular surface Sacrum Formed from ﬁve fused vertebrae; it provides a strong connection between the pelvis and the spine Femur The largest bone in the body at around 18in (45cm) long Patella The kneecap. This bone lies embedded in the tendon of the quadriceps muscle Tibia The shinbone. Its sharp anterior edge can be felt along the front of the shin Osteon Periosteal blood vessels Endosteal blood vessels Medullary (marrow) cavity Radius Spongy (cancellous) bone Long bone Long bones are found in the limbs, and include the femur (shown above), humerus, radius, ulna, tibia, ﬁbula, metatarsals, metacarpals, and phalanges. A long bone has ﬂared ends (epiphyses), which narrow to form a neck (metaphysis), tapering down into a cylindrical shaft (diaphysis). Cartilage growth plates near the ends of bones allow rapid growth in childhood, but disappear by adulthood. Central osteonal canal (Haversian canal) Pelvis Oddly shaped bone also called the innominate bone (“bone without a name”) Lymphatic vessel Compact bone Also called cortical bone, compact bone is made up of osteons: concentric cylinders of bone tissue, each around 0.1–0.4mm in diameter, with a central vascular canal. Bone is full of blood vessels: those in the osteons connect to blood vessels within the medullary cavity of the bone as well as to vessels in the periosteum on the outside. Tarsals A group of seven bones, including the talus; contributes to the ankle joint, and the heel bone or calcaneus Fibula Contributes to the ankle joint and provides a surface for muscle attachment Metatarsals Five bones in the foot; the equivalent of the metacarpals in the hand Phalanges Fourteen phalanges form the toes of each foot ANTERIOR (FRONT) 025 Clavicle Traces a sinuous curve at the base of the neck; it acts as a strut supporting the shoulder Nasal bone Temporal bone Hyoid bone U-shaped bone; provides attachments for muscles of the tongue, as well as the ligaments suspending the larynx in the neck Occipital bone Occipital bone Atlas Axis Cervical vertebrae Cranium Cervical vertebra Clavicle Acromion Thoracic vertebrae Scapula Connects the arm to the trunk, and provides a secure but mobile anchor for the arm, allowing the shoulders to be retracted backward, protracted forward, and elevated Scapula Ribs Twelve pairs of curving bones form the ribcage Thoracic vertebra Humerus Ulna Wide at its proximal end, where it articulates with the humerus at the elbow, this bone tapers down to a pointed styloid process near the wrist Humerus Latin for shoulder Epicondyles Lumbar vertebra Lumbar vertebrae Radius Forearm bone; it can rotate around the ulna to alter the orientation of the hand Ulna Pelvis Ilium Named after the Latin for hip Carpals Eight small bones in the base of the hand. Two articulate with the radius to form the wrist joint Carpal Phalanges Fourteen bones in each hand: two form the thumb, with three (proximal, middle, and distal) in each ﬁnger Metacarpal Radius Coccyx Phalanges Femur Coccyx End of the spine made up of three to ﬁve tiny vertebrae; means cuckoo in Greek Metacarpals Five slender bones, hidden in the base of the thumb and the palm of the hand Femur Patella Fibula Tibia Tibia Fibula Tarsals Metatarsals Phalanx Calcaneus Heel bone POSTERIOR (BACK) SIDE OVERVIEW Frontal bone Parietal bone Nasal crest Where the two maxillae meet; the vomer (part of the septum) sits on the crest Infraorbital foramen Hole for infraorbital branch of maxillary nerve to supply sensation to the cheek Inferior orbital ﬁssure Gap between the maxilla and the greater wing of the sphenoid bone, opening into the back of the orbit Superior orbital ﬁssure Gap between the sphenoid bone’s greater and lesser wings, opening into the orbit TOP Parietal bone From the Latin for wall Zygomatic process of maxilla Part of the maxilla that projects laterally (to the side) Inferior nasal concha Lowest of the three curled protrusions on the lateral wall of the nasal cavity Piriform aperture Pear-shaped (piriform) opening; also called the anterior nasal aperture Frontal process of maxilla Rises up on the medial (inner) side of the orbit Orbit Technical term for the eye-socket, from the Latin for wheel track Nasal bone Two small bones form the bony bridge of the nose Superciliary arch Also called the supraorbital ridge, or brow ridge; from the Latin for eyebrow The skull comprises the cranium and mandible. It houses and protects the brain and the eyes, ears, nose, and mouth. It encloses the ﬁrst parts of the airway and of the alimentary canal, and provides attachment for the muscles of the head and neck. The cranium itself comprises more than 20 bones that meet each other at ﬁbrous joints called sutures. In addition to the main bones labeled on these pages, there are sometimes extra bones along the sutures. In a young adult skull, the sutures are visible as tortuous lines between the cranial bones; they gradually fuse with age. The mandible of a newborn baby is in two halves, with a ﬁbrous joint in the middle. The joint fuses during early infancy, so that the mandible becomes a single bone. Zygomatic process of frontal bone Runs down to join the frontal process of the zygomatic bone Occipital bone Sagittal suture Joint on the midline (sagittal plane) where parietal bones meet Bregma Where the sagittal and coronal sutures meet Coronal suture Where the frontal and parietal bones meet; crosses the skull’s highest part (the crown) Frontal bone HEAD AND NECK Supraorbital foramen The supraorbital nerve passes through this hole to supply sensation to the forehead Glabella Area between the two superciliary arches; glabella comes from the Latin for smooth, and refers to the bare area between the eyebrows Frontal bone BACK Occipital bone Forms lower part of back of skull, and back of cranial base Lambda Point where the sagittal suture meets the lambdoid suture Lambdoid suture Joint between occipital and parietal bones Sagittal suture Parietal bones Paired bones forming most of the roof and sides of skull SKELETAL SYSTEM 026 ANTERIOR (FRONT) Maxilla Latin word for jaw; the maxilla bears the upper teeth and also encloses the nasal cavity Ramus of mandible Part of the mandible, named after the Latin for branch First rib Several small muscles in the neck attach to the small, C-shaped ﬁrst rib Cervical vertebra There are seven vertebrae in the neck region of the spine Clavicle Bone that supports the shoulder and gives attachment to the trapezius and sternocleidomastoid muscles Mental protuberance The chin’s projecting lower edge—more pronounced in men than in women Mental foramen Hole that transmits branches of the mandibular nerve; mental can refer to the chin (mentum in Latin) Mandible The jawbone; its name comes from the Latin verb meaning to chew Alveolar process of maxilla Part of the maxilla that holds the upper teeth; alveolus (meaning small cavity) refers to a tooth socket Temporal bone Zygomatic bone From the Greek for yoke; it forms a link between the bones of the face and the side of the skull Nasal bone Lacrimal bone Tears drain from the surface of the eye into the nasolacrimal duct, which lies in a groove in this bone Coronoid process of mandible This is where the temporalis muscle attaches to the jawbone Greater wing of sphenoid bone Pterion Area on side of skull where the frontal, parietal, temporal, and sphenoid bones come close together; it is a key surgical landmark as the middle meningeal artery runs up inside the skull at this point and may be damaged by a fracture to this area Frontal bone The cervical spine includes seven vertebrae, the top two of which have speciﬁc names. The ﬁrst vertebra, which supports the skull, is called the atlas, after the Greek god who carried the sky on his shoulders. Nodding movements of the head occur at the joint between the atlas and the skull. The second cervical vertebra is the axis, from the Greek word for axle, so-called because when you shake your head from side to side, the atlas rotates on the axis. In this side view, we can also see more of the bones that make up the cranium, as well as the temporomandibular ( jaw) joint between the mandible and the skull. The hyoid bone is also visible. This small bone is a very important anchor for the muscles that form the tongue and the ﬂoor of the mouth, as well as muscles that attach to the larynx and pharynx. Asterion From the Greek for star; it is where the lambdoid, occipitomastoid, and parietomastoid sutures meet Condyle Condylar process projects upwards to end as the condyle, or head of the mandible, which articulates with the cranium at the temporomandibular ( jaw) joint Zygomatic arch Formed by the zygomatic process of the temporal bone projecting forward to meet the temporal process of the zygomatic bone Coronal suture HEAD AND NECK Occipital bone Lambdoid suture Occipitomastoid suture Fibrous joint between the occipital bone and the mastoid part of the temporal bone Parietomastoid suture Here the parietal bone meets the posterior, mastoid part of the temporal bone Squamosal suture The articulation between squamous part of temporal bone and parietal bone Parietal bone Tympanic part of temporal bone Forms ﬂoor of the external acoustic meatus, at the inner end of which lies the tympanic membrane, or eardrum SKELETAL SYSTEM 028 Angle of mandible Where the body of the mandible turns a corner to become the ramus Mastoid process The name of this conical projection under the skull comes from the Greek for breast SIDE Hyoid bone Takes its name from the Greek for U-shaped; it is a separate bone, lying just under the mandible, which provides an anchor for muscles forming the ﬂoor of the mouth and the tongue; the larynx hangs below it Ramus of mandible Body of mandible Mental foramen Alveolar process of mandible The part of the jawbone bearing the lower teeth Maxilla HEAD AND NECK Styloid process Named after the Greek for pillar, this pointed projection sticks out under the skull and forms an anchor for several slender muscles and ligaments 029 SKELETAL SYSTEM 030 HEAD AND NECK The most striking features of the skull viewed from these angles are the holes in it. In the middle, there is one large hole—the foramen magnum—through which the brain stem emerges to become the spinal cord. But there are also many smaller holes, most of them paired. Through these holes, the cranial nerves from the brain escape to supply the muscles, skin, and mucosa, and the glands of the head and neck. Blood vessels also pass through some holes, on their way to and from the brain. At the front, we can also see the upper teeth sitting in their sockets in the maxillae, and the bony, hard palate. Foramen magnum Latin for large hole; the brain stem emerges here Internal occipital protuberance Located near the conﬂuence of the sinuses, where the superior sagittal, transverse, and straight sinuses (the large veins in the dura mater) meet Hypoglossal canal The hypoglossal nerve, supplying the tongue muscles, exits here Mastoid foramen An emissary (valveless) vein passes out through this hole Basiocciput Part of the occipital bone, in front of the foramen magnum, which fuses with the body of the sphenoid bone Jugular foramen The internal jugular vein and the glossopharyngeal, vagus, and accessory nerves emerge from this hole Internal acoustic meatus The facial and vestibulocochlear nerves pass through this hole Petrous part of temporal bone Foramen lacerum Foramen ovale Foramen spinosum Entry point of the middle meningeal artery, which supplies the dura mater and the bones of the skull Pituitary fossa Foramen rotundum The maxillary division of the trigeminal nerve passes through this round hole Lesser wing of sphenoid bone Optic canal Orbital part of frontal bone Part of the frontal bone that forms the roof of the orbit, and also the ﬂoor at the front of the cranial cavity Cribriform plate of ethmoid Area of the ethmoid bone pierced by holes, through which the olfactory nerves pass. Cribriform is Latin for sievelike; ethmoid, taken from Greek, also means sievelike Foramen caecum Named after the Latin for blind, this is a blind-ended pit INTERNAL SURFACE OF BASE OF SKULL Crista galli Vertical crest on the ethmoid bone that takes its name from the Latin for cock’s comb; it provides attachment for the falx cerebri—the membrane between the two cerebral hemispheres 031 Occipital bone External occipital protuberance Inferior nuchal line Slight ridge lying between the attachments of some of the deeper neck muscles Foramen magnum Hypoglossal canal Lambdoid suture Occipital condyle Where the skull articulates with the atlas (ﬁrst cervical vertebra) Pharyngeal tubercle Foramen lacerum Fibrocartilage-ﬁlled hole between the body of the phenoid bone and the petrous part of the temporal bone Jugular foramen Carotid canal The internal carotid artery enters here Digastric notch The posterior belly of the digastric muscle attaches to this pit Stylomastoid foramen The facial nerve emerges through this hole Styloid process Foramen spinosum Foramen ovale The mandibular division of the trigeminal nerve goes through this hole Mastoid process Tympanic part of temporal bone Lateral pterygoid plate An anchor point for jaw muscles Mandibular fossa Socket for the temporomandibular ( jaw) joint Pterygoid hamulus The word hamulus means small hook in Latin Articular eminence The condyle of the mandible moves forward onto this area as the jaw opens Zygomatic arch Medial pterygoid plate Forms the back of the side wall of the nasal cavity Lesser palatine foramina The lesser palatine arteries and nerves pass through this hole and run backward to supply the soft palate Zygomatic process of maxilla Choana Opening of the nasal cavity into the pharynx; from funnel in Greek Vomer Interpalatine suture Joint between the horizontal plates of the two palatine bones Posterior nasal spine Palatomaxillary suture Palate Intermaxillary suture UNDERSIDE OF SKULL Greater palatine foramen This hole transmits the greater palatine artery and nerve, which supply the hard palate Incisive fossa The nasopalatine nerve emerges here to supply sensation to the front of the palate HEAD AND NECK Superior nuchal line The trapezius and sternocleidomastoid muscles attach to this ridge SKELETAL SYSTEM 032 HEAD AND NECK This section—right through the middle of the skull—lets us in on some secrets. We can clearly appreciate the size of the cranial cavity, which is almost completely ﬁlled by the brain, with just a small gap for membranes, ﬂuid, and blood vessels. Some of those blood vessels leave deep grooves on the inner surface of the skull: we can trace the course of the large venous sinuses and the branches of the middle meningeal artery. We can also see that the skull bones are not solid, but contain trabecular bone (or diploe), which itself contains red marrow. Some skull bones also contain air spaces, like the sphenoidal sinus visible here. We can also appreciate the large size of the nasal cavity, hidden away inside the skull. Frontal bone Forms the anterior cranial fossa, where the frontal lobes of the brain lie, inside the skull Frontal sinus One of the paranasal air sinuses that drain into the nasal cavity, this is an air space within the frontal bone Nasal bone Pituitary fossa Fossa is the Latin word for ditch; the pituitary gland occupies this small cavity on the upper surface of the sphenoid bone Sphenoidal sinus Another paranasal air sinus; it lies within the body of the sphenoid bone Superior nasal concha Part of the ethmoid bone, which forms the roof and upper side walls of the nasal cavity Middle nasal concha Like the superior nasal concha, this is also part of the ethmoid bone Inferior nasal concha A separate bone, attached to the inner surface of the maxilla; the conchae increase the surface area of the nasal cavity Anterior nasal crest Palatine bone Joins to the maxilla and forms the back of the hard palate Pterygoid process Sticking down from the greater wing of the sphenoid bone, this process ﬂanks the back of the nasal cavity and provides attachment for muscles of the palate and jaw 033 HEAD AND NECK Parietal bone Grooves for arteries Meningeal arteries branch on the inside of the skull and leave grooves on the bones Squamous part of the temporal bone Squamosal suture Lambdoid suture Internal acoustic meatus Hole in petrous part of the temporal bone that transmits both the facial and vestibulocochlear nerves Occipital bone External occipital protuberance Projection from occipital bone that gives attachment to the nuchal ligament of the neck; much more pronounced in men than in women Hypoglossal canal Hole through occipital bone, in the cranial base, which transmits the hypoglossal nerve supplying the tongue muscles Styloid process INTERIOR OF SKULL Frontal bone Forms joints with the parietal and sphenoid bones on the top and sides of the skull, and with the maxilla, nasal, lacrimal, and ethmoid bones below In this view of the skull, we can clearly see that it is not one single bone, and we can also see how the various cranial bones ﬁt together to produce the shape we are more familiar with. The butterﬂy-shaped sphenoid bone is right in the middle of the action—it forms part of the skull base, the orbits, and the side walls of the skull, and it articulates with many of the other bones of the skull. The temporal bones also form part of the skull’s base and side walls. The extremely dense petrous parts of the temporal bones contain and protect the delicate workings of the ear, including the tiny ossicles (malleus, incus, and stapes) that transmit vibrations from the eardrum to the inner ear. FIBROUS JOINTS In places, the connective tissue between developing bones solidiﬁes to create ﬁbrous joints. Linked by microscopic ﬁbers of collagen, these ﬁxed joints anchor the edges of adjacent bones, or bone and tooth, so that they are locked together. Such joints include the sutures of the skull, the teeth sockets (gomphoses), and the lower joint between the tibia and ﬁbula. Periodontal ligament Dense connective tissue anchoring the tooth in the socket Cement Covers the roots of the tooth Alveolar bone Bone of the maxilla or mandible forming the tooth socket (alveolus) Gomphosis This name comes from the Greek word for bolted together. The ﬁbrous tissue of the periodontal ligament connects the cement of the tooth to the bone of the socket. TOOTH Capsular layer Middle layer Cambial layer Bone Occipital bone Uniting layer SKULL Suture These joints exist between ﬂat bones of the skull. They are ﬂexible in the skull of a newborn baby, and allow growth of the skull throughout childhood. The sutures in the adult skull are interlocking, practically immovable joints, and eventually fuse completely in later adulthood. Parietal bone Forms the roof and side of the skull SKELETAL SYSTEM Parietal bone HEAD AND NECK 034 Zygomatic bone Occipital bone Forms the lower part of the back of the skull Frontal bone Zygomatic bone This roughly triangular bone connects the frontal bone, maxilla, and temporal bone Temporal bone Articulates with the parietal, sphenoid, and occipital bones and contains the ear apparatus, including the ossicles Mastoid process ARTICULATED VIEW Maxilla Nasal bones Two bones, attaching to the frontal bone above and the maxillae to the side, form the bridge of the nose Angle of mandible The masseter muscle attaches down to this angle, which tends to be slightly ﬂared outward in men Ramus of mandible Orbital surface of maxilla Body of mandible The mandible develops as two separate bones, which fuse in infancy DISARTICULATED VIEW MALLEUS STAPES INCUS OSSICLES OF THE EAR Alveolar process of mandible Projects up from the mandible and forms the sockets for the lower teeth Alveolar process of maxilla Projects down from the maxilla and forms the sockets for the upper teeth Maxilla Articulates with the opposite maxilla in the midline, with the nasal, frontal, and lacrimal bones above, and the sphenoid, ethmoid, and palatine bones Vomer Zygomatic bone Zygomatic process Lacrimal bone Nasal bone Orbital plate of ethmoid bone Petrous part of temporal bone HEAD AND NECK Sphenoid bone 035 036 SKELETAL SYSTEM T1 (ﬁrst thoracic) vertebra Clavicle First rib Smaller and more curved than all the other ribs; the thoracic inlet is formed by the ﬁrst rib on each side, together with the manubrium sterni and the body of the T1 vertebra Scapula Second costal cartilage The upper seven ribs are true ribs, and all attach directly to the sternum via costal cartilages Third rib Fourth rib Fifth rib Sixth rib Seventh rib Eighth to tenth ribs The costal cartilages of these ribs each attach to the costal cartilage above Eleventh and twelfth ribs These are also called ﬂoating ribs because they do not attach to any others 037 THORAX Transverse process of T1 Each rib articulates with the transverse processes of the corresponding thoracic vertebra Head of ﬁrst rib The heads of the ribs articulate with the bodies of vertebrae Manubrium sterni The sternum is shaped like a dagger or short sword; manubrium means handle or hilt in Latin Manubriosternal joint Body of sternum Sternum comes from the Greek for breastbone Xiphisternal joint Xiphoid process The tip of the sternum takes its name from the Greek word for sword THORAX ANTERIOR (FRONT) The skeleton of the thorax plays several extremely important roles. It not only acts as an anchor for muscle attachment, but during breathing the ribs move up and out to increase the volume inside the thoracic cavity and draw air into the lungs. It also forms a protective cage around the precious organs inside: the heart and lungs. The bony thorax includes the 12 thoracic vertebrae, 12 pairs of ribs and costal cartilages, and the breastbone, or sternum. The upper seven ribs all articulate with the sternum via their costal cartilages. The eighth to the tenth costal cartilages each join to the cartilage above, creating the sweeping curve of the ribcage below the sternum on each side. The eleventh and twelfth ribs are short and do not join any other ribs—they are sometimes referred to as free or ﬂoating ribs. SKELETAL SYSTEM 038 First rib Third rib Fifth rib Seventh rib Ninth rib Tenth rib Eleventh rib With your ﬁngers tracing down the edge of the ribcage, you may be able to feel the end of the eleventh rib in your side Twelfth rib The twelfth rib is even shorter than the eleventh, and tucked underneath muscles, so it cannot be felt. Unlike most ribs, the twelfth has no costal groove 039 C7 (seventh cervical vertebra) THORAX Costal groove POSTERIOR (BACK) There are cartilaginous joints between the vertebrae at the back of the thorax, and between the parts of the sternum at the front. The joints between the ribs and the vertebrae at the back are synovial, allowing the ribs to move during breathing. When taking a breath, the anterior (front) ends of the upper ribs, along with the sternum, lift up and forward to increase the chest’s front-to-back diameter, while the lower ribs move up and out, increasing the side-to-side diameter. Most ribs have a costal groove marking the lower border, on the inner surface, where nerves and vessels of the thoracic wall lie. THORAX Transverse process of T1 Cervical spine (Seven vertebrae make up the spine in the neck) Thoracic spine (Twelve vertebrae, providing attachment for twelve pairs of ribs) T10 T9 T8 T7 T6 T5 T4 Thoracic curvature This dorsally convex type of curvature is technically known as a kyphosis, from the Greek for crooked Intervertebral disc Weight-bearing cartilaginous joint composed of an outer annulus ﬁbrosus (ﬁbrous ring) and an inner nucleus pulposus (pulpy nucleus) Demifacet for rib joint Vertebral foramen Large compared with the size of the body; contains the spinal cord Transverse foramen The vertebral artery passes through here Vertebral foramen Body Superior articular facet Vertebral foramen Lateral mass Superior articular facet Articulates with the condyle of the occipital bone, on the base of the skull CERVICAL Lamina AXIS (C2) ATLAS (C1) Spinous process Tends to be small and forked; for the attachment of back muscles Superior articular facet Transverse process For neck muscle attachment Body Made of cancellous bone containing blood-making bone marrow Spinous process Transverse foramen Transverse process Dens (odontoid peg) This projection sticks up to articulate with the atlas Posterior arch Transverse foramen Anterior arch The atlas has no body, but it has an anterior arch that forms a joint with the dens of the axis The spine, or vertebral column, occupies a central position in the skeleton, and plays several extremely important roles: it supports the trunk, encloses and protects the spinal cord, provides sites for muscle attachment, and contains blood-forming bone marrow. The entire vertebral column is about 28in (70cm) long in men, and 24in (60cm) long in women. About a quarter of this length is made up by the cartilaginous intervertebral discs between the vertebrae. The number of vertebrae varies from 32 to 35, mostly due to variation in the number of small vertebrae that make up the coccyx. Although there is a general pattern for a vertebra —most possess a body, a neural arch, and spinous and transverse processes—there are recognizable features that mark out the vertebrae of each section of the spine. T3 Cervical curvature A dorsally concave curvature, or lordosis (from a Greek word meaning bent backward) Superior articular process Intervertebral foramen These are the holes between adjacent vertebrae through which spinal nerves emerge SPINE T2 T1 C7 C6 C5 C4 C3 C2 (axis) C1 (atlas) SKELETAL SYSTEM 040 Lumbar spine (Five vertebrae) Sacrum (Five fused vertebrae) Coccyx (Three to ﬁve vertebrae) ANTERIOR (FRONT) L5 L4 L3 L2 L1 T12 T11 Lumbar curvature Appears about a year after birth, when an infant starts to walk co3 co2 co1 S5 S4 S3 S2 S1 Sacral curvature SIDE Transverse process Long and thin Coccygeal cornu Articulates with sacral cornu Anterior sacral foramen Anterior branches of sacral spinal nerves pass through these holes; posterior branches emerge through the posterior foramina Body Five vertebrae fuse during development to form the sacrum Lateral part Formed from fused lateral parts of the sacral segments; articulates with the pelvis at the sacroiliac joint Inferior articular process Superior articular facet Pedicle Vertebral foramen Zygapophyseal (facet) joint Synovial joints between the adjacent articular processes allow variable degrees of movement in different sections of the spine; in disk degeneration, these joints end up bearing more weight and may be a source of back pain Transverse process Forms a joint with the ribs on each side COCCYX SACRUM LUMBAR Lamina THORACIC Facet for apex of sacrum Facet for coccyx Spinous process Large and square in the lumbar spine Body Vertebral bodies are larger at lower spinal levels— they have progressively more weight to bear; bodies of lumbar vertebrae are kidneyshaped, and large compared with the size of the vertebral foramen Spinous process Long and sloping in the thoracic spine Lamina Superior articular facet Vertebral foramen Body Thoracic vertebrae have heart-shaped bodies SKELETAL SYSTEM 042 ABDOMEN AND PELVIS The bony boundaries of the abdomen include the ﬁve lumbar vertebrae at the back, the lower margin of the ribs above, and the pubic bones and iliac crest of the pelvic bones below. The abdominal cavity itself extends up under the ribcage, as high as the gap between the ﬁfth and sixth ribs, due to the domed shape of the diaphragm. This means that some abdominal organs, such as the liver, stomach, and spleen are, in fact, largely tucked up under the ribs. The pelvis is a basin shape, and is enclosed by the two pelvic (or innominate) bones, at the front and sides, and by the sacrum at the back. Each pelvic bone is made of three fused bones: the ilium at the rear, the ischium at the lower front, and the pubis above it. Twelfth rib Lumbar vertebrae The lumbar section of the spine forms part of the posterior abdominal wall Iliac crest Upper edge of the ilium—one of the three bones that make up the bony pelvis; it can be felt easily through the skin Sacroiliac joint A synovial joint between the sacrum and ilium Iliac fossa The concavity (concave surface) of the ilium gives attachment to the iliacus muscle and supports the intestines Sacrum Pelvic bone Each of the two large pelvic bones is made up of ilium, pubis, and ischium Coccyx Superior pubic ramus The upper branch of the pubic bone Body of ischium Ischiopubic ramus Ischial tuberosity Femur ANTERIOR (FRONT) CARTILAGINOUS JOINTS 043 Pubic bone Forms the front of the bony pelvis Pubic symphysis PELVIS Pubic symphysis At the front of the bony pelvis, the two pubic bones meet each other. The articular surface of each is covered with hyaline cartilage, with a pad of ﬁbrocartilage joining them in the middle. Atlas (ﬁrst cervical vertebra) Hyaline cartilage Zygapophyseal joint Small synovial joints between the neural arches at the back of the spine Nucleus pulposus Inner, gel-like center of the disk Axis (second cervical vertebra) Annulus ﬁbrosus Outer, ﬁbrous ring of the disk SPINE Intervertebral disc Each ﬁbrocartilage pad or disk between vertebrae is organized into an outer annulus ﬁbrosus and an inner nucleus pulposus. Anterior superior iliac spine This is the anterior (front) end of the iliac crest Ala of sacrum The bony masses to the sides of the sacrum are called the alae, which means wings in Latin Anterior sacral foramina Anterior (frontal) branches of the sacral spinal nerves pass out through these holes Pubic symphysis A cartilaginous joint between the two pubic bones Pubic tubercle This small bony projection provides an attachment point for the inguinal ligament Obturator foramen This hole is largely closed over by a membrane, with muscles attaching on either side; its name comes from the Latin for stopped up ABDOMEN AND PELVIS Semi-movable cartilaginous joints are formed by bones separated by a disc of resilient and compressible ﬁbrocartilage, which allows limited movement. Cartilaginous joints include the junctions between ribs and costal cartilages, joints between the components of the sternum, and the pubic symphysis. The intervertebral discs are also specialized cartilaginous joints. SKELETAL SYSTEM 044 ABDOMEN AND PELVIS The orientation of the facet joints (the joints between the vertebrae) of the lumbar spine means that rotation of the vertebrae is limited, but ﬂexion and extension can occur freely. There is, however, rotation at the lumbosacral joint, which allows the pelvis to swing during walking. The sacroiliac joints are unusual in that they are synovial joints (which are usually very movable), yet they are particularly limited in their movement. This is because strong sacroiliac ligaments around the joints bind the ilium (part of the pelvic bone) tightly to the sacrum on each side. Lower down, the sacrospinous and sacrotuberous ligaments, stretching from the sacrum and coccyx to the ilium, provide additional support and stability. Iliac crest Gluteal surface of ilium The gluteal muscles attach to the pelvis here Posterior superior iliac spine This is the back end of the iliac crest Sacroiliac joint Sacrum Body of pubis The wide, ﬂat portion of the pubic bone Ischial spine This projection from the ischium forms the attachment point for the sacrospinous ligament of the pelvis Greater trochanter Gluteal muscles attach here Coccyx Lesser trochanter Attachment point for the psoas muscle Femur 045 ABDOMEN AND PELVIS Twelfth rib Lumbar vertebrae Five vertebrae make up the lumbar spine Lumbosacral joint Where the ﬁfth lumbar vertebra meets the sacrum Posterior sacral foramina Posterior branches of the sacral spinal nerves pass through these holes Superior pubic ramus This extension of the pubic bone is named after the Latin for branch Obturator foramen Ischiopubic ramus Ischial tuberosity (POSTERIOR) BACK Sacral promontory The upper margin of the sacrum projects forward less in the female SKELETAL SYSTEM 046 Iliiac crest Sacroiliac joint Smaller in the female pelvis Greater sciatic notch Superior pubic ramus Ischiopubic ramus Thinner in the female pelvis PELVIS Pubic symphysis FEMALE PELVIS ANTERIOR (FRONT) Subpubic angle Much wider in the female pelvis The bony pelvis is the part of the skeleton that is most different between the sexes, because the pelvis in the female has to accommodate the birth canal, unlike the male pelvis. Comparing the pelvic bones of a man and a woman, there are obvious differences between the two. The shape of the ring formed by the sacrum and the two pelvic bones —the pelvic brim—tends to be a wide oval in the woman and much narrower and heart-shaped in a man. The subpubic angle, underneath the joint between the two pubic bones, is much narrower in a man than it is in with a woman. As with the rest of the skeleton, the pelvic bone also tends to be more chunky or robust in a man, with more obvious ridges where muscles attach. Pelvic brim This forms the inlet into the pelvis, and is wider in the female FEMALE PELVIS VIEWED FROM ABOVE Sacral promontory The upper margin of the sacrum projects into the heart-shaped pelvic brim 047 Greater sciatic notch Superior pubic ramus Ischiopubic ramus Thicker in the male pelvis, with a turned-out edge where the crus of the penis attaches Pubic symphysis Subpubic angle MALE PELVIS ANTERIOR (FRONT) Pelvic brim Heart-shaped in the male and narrower than in the female pelvis MALE PELVIS VIEWED FROM ABOVE PELVIS Iliac crest Gives attachment to the muscles of the abdominal wall and is more robust or chunky in the male Sacroiliac joint Male joints tend to be larger than those of the female, and this one is no exception Greater tubercle Forms an attachment site for some of the muscles coming to the neck of the humerus from the scapula Acromion Clavicle Neck of humerus Lesser tubercle Point at which the subscapularis muscle attaches from the inner surface of the scapula to the humerus Scapula Coracoid process The name for this hooked, beaklike structure found on the scapula derives from the Greek word for raven SKELETAL SYSTEM 048 The scapula and clavicle make up the shoulder girdle, which anchors the arm to the thorax. This is a very mobile attachment—the scapula “ﬂoats” on the ribcage, attached to it by muscles only (rather than by a true joint) that pull the scapula around on the underlying ribs, altering the position of the shoulder joint. The clavicle has joints—it articulates with the acromion of the scapula laterally (at the side) and the sternum at the other end—and helps hold the shoulder out to the side while allowing the scapula to move around. The shoulder joint, the most mobile joint in the body, is a ball-and-socket joint, but the socket is small and shallow, allowing the ball-shaped head of the humerus to move freely. Glenoid fossa Shallow area that articulates with the head of the humerus, forming part of the shoulder socket SHOULDER AND UPPER ARM Radius Capitulum of humerus Ball-like part of the humerus that articulates with the head of the radius; its name comes from the Latin for little head Lateral epicondyle Forms an anchor for the extensor muscles of the forearm Radial fossa The head of the radius swings around to occupy this shallow cavity when the elbow is ﬂexed Coronoid fossa This depression accommodates the coronoid process of the ulna when the elbow is fully ﬂexed Shaft of humerus Like other long bones, this is a cylinder of compact (or cortical) bone, containing a marrow cavity Ulna Coronoid process Trochlea of humerus Forms a joint with the ulna; its name comes from the Latin for pulley Medial epicondyle Flexor muscles of the forearm attach to this projection from the inner side of the humerus ANTERIOR (FRONT) Glenoid cavity Spine of scapula Acromion Clavicle Supraspinous fossa This is the depression above the spine of the scapula, where the supraspinatus muscle is attached Spiral groove This faint line marks where the radial nerve spirals around the posterior aspect of the humerus Inferior angle SKELETAL SYSTEM The back of the scapula is divided into two sections by its spine. The muscles that attach above this spine are called supraspinatus; those that attach below are called infraspinatus. They are part of the rotator cuff muscle group, which enables shoulder movements and stabilizes the shoulder joint. The spine of the scapula runs to the side and projects out above the shoulder joint to form the acromion, which can be easily felt on the top of the shoulder. The scapula rests in the position shown here when the arm is hanging at the side of the body. If the arm is abducted (raised to the side), the entire scapula rotates so that the glenoid cavity points upward and the inferior angle moves outward. Infraspinous fossa The infraspinatus muscle attaches to this part of the scapula—below its spine SHOULDER AND UPPER ARM 050 POSTERIOR (BACK) Shaft of ulna Shaft of radius Radial tuberosity Head of radius Olecranon of ulna Olecranon fossa A deep cavity on the posterior surface of the humerus; it accommodates the olecranon of ulna when the elbow is fully extended—as shown here Shaft of humerus SKELETAL SYSTEM 052 Coracoacromial ligament Tendon of supraspinatus muscle runs under this ligament, and may become compressed in impingement syndrome Acromioclavicular ligament Strengthens the ﬁbrous capsule of the acromioclavicular joint, between the lateral end of the clavicle and the acromion of the scapula Coracoclavicular ligament Coracoid process Acromion Glenohumeral ligaments Reinforce the front of the ﬁbrous capsule of the shoulder joint Humerus SHOULDER JOINT (ANTERIOR /FRONT) Scapula Transverse scapular ligament Clavicle SHOULDER AND UPPER ARM 053 In any joint, there is always a play off between mobility and stability. The extremely mobile shoulder joint is therefore naturally unstable, and so it is not surprising that this is the most commonly dislocated joint in the body. The coracoacromial arch, formed by the acromion and coracoid process of the scapula with the strong coracoacromial ligament stretching between them, prevents upward dislocation; when the head of the humerus dislocates, it usually does so in a downward direction. The elbow joint is formed by the articulation of the humerus with the forearm bones: the trochlea articulates with the ulna, and the capitulum with the head of the radius. The elbow is a hinge joint, stabilized by collateral ligaments on each side. Fibrous capsule Attaches to the front of the humerus above the radial and coronoid fossae, and to the ulna and annular ligament below Medial epicondyle Lateral epicondyle Radial collateral ligament Attaches from the lateral epicondyle to the annular ligament Annular ligament Ulnar collateral ligament Attaches from the medial epicondyle to the ulna Neck of radius Humerus Oblique cord Ulna Annular ligament of the radius Encircling the head of the radius, this allows the bone to rotate during pronation and supination movements in the forearm Medial epicondyle Also forms the common ﬂexor origin—the attachment of many of the forearm ﬂexor muscles ELBOW (ANTERIOR /FRONT) Biceps tendon Inserts on the radial tuberosity. A powerful ﬂexor of the elbow joint and also acts to supinate the forearm Radius Olecranon of ulna Ulnar collateral ligament Ulna ELBOW (LATERAL / OUTER SIDE) SHOULDER AND UPPER ARM Humerus Styloid process of radius Lunate Articulates with scaphoid and radius to form wrist joint; this is the most commonly dislocated carpal (wrist) bone Scaphoid The most commonly fractured wrist bone Trapezium Articulates with ﬁrst metacarpal of thumb Trapezoid Articulates with second metacarpal of index ﬁnger First metacarpal Proximal phalanx Distal phalanx Scaphoid Convex bone named after the Greek for boat-shaped Trapezoid Also four-sided, this bone’s name means tableshaped in Greek Pisiform Latin for pea-shaped; articulates with the triquetral, and receives the tendon Styloid process of the ﬂexor carpi of radius ulnaris muscle The radial collateral ligament of the Styloid process wrist attaches to of ulna this sharp point Pointed projection taking its name Trapezium from the Greek Four-sided bone for pillar-shaped named after the Head of ulna Greek for table Triquetral Latin for three-cornered Hamate Articulates with fourth and ﬁfth metacarpals Capitate Articulates with third and fourth metacarpals Fifth metacarpal Proximal phalanx Middle phalanx Distal phalanx Radial tuberosity Biceps tendon attaches here Trochlea of humerus Head of radius Bowl-shaped surface articulates with the capitulum of humerus Capitulum of humerus Lateral epicondyle Hamate One of the carpal bones, along with the other bones between the radius and ulna Triquetral Pisiform Styloid process of ulna Where the ulnar collateral ligament attaches Head of ulna Articulates with lower end of the radius, at the distal radioulnar joint Lunate Crescent-shaped bone named after the Latin for moon Shaft of ulna Interosseous border of ulna Shaft of radius Like the ulna, this is triangular in cross section Interosseous border of radius Sharp ridges on facing edges of the radius and ulna provide attachment for the forearm’s interosseous membrane Tuberosity of ulna Brachialis muscle attaches here Radial notch of ulna This concave surface articulates with the head of the radius, forming the proximal radioulnar joint Coronoid process Forms anterior margin of the trochlear notch of the ulna, which accommodates the trochlea of the humerus Medial epicondyle 054 POSTERIOR (BACK) Humerus Olecranon fossa of humerus Olecranon of ulna Lateral epicondyle of humerus Head of radius Medial epicondyle of humerus Radial tuberosity Interosseous border of ulna Interosseous border of radius Proximal phalanx Shaft of ulna First metacarpal Shaft of radius The shafts of the radius and ulna contain marrow cavities Distal phalanx of thumb The thumb has just two phalanges: proximal and distal ANTERIOR (FRONT) Supinator crest Middle phalanx Proximal phalanx Each ﬁnger has three phalanges: proximal, middle, and distal Fifth metacarpal Metacarpals in the palm link carpals to phalanges Capitate Meaning headed in Latin, this bone looks like a tiny head on a neck Distal phalanx The two forearm bones, the radius and ulna, are bound together by a ﬂat sheet of ligament called the interosseous membrane, and by synovial joints between the ends of the two bones. Known as radioulnar joints, these joints allow the radius to move around the ulna. Hold your hand out in front of you, palm upward. Now turn your hand so that the palm faces the ground. This movement is called pronation, and is achieved by bringing the radius to cross over the ulna. The movement that returns the palm to an upward-facing position is called supination. Since the forearm bones are bound together by ligaments, joints, and muscles, it is common for both bones to be involved in a serious forearm injury. Often, one bone is fractured and the other dislocated. The skeleton of the hand comprises the eight carpal bones (bones between the radius and ulna), ﬁve metacarpals, and fourteen phalanges. 055 LOWER ARM AND HAND LOWER ARM AND HAND SKELETAL SYSTEM 056 HAND AND WRIST JOINTS The radius widens out at its distal (lower) end to form the wrist joint with the closest two carpal bones, the lunate and scaphoid. This joint allows ﬂexion, extension, adduction, and abduction (see pp.16–17). There are also synovial joints (see p.60) between the carpal bones in the wrist, which increase the range of motion during wrist ﬂexion and extension. Synovial joints between metacarpals and phalanges allow us to spread or close our Proximal ﬁngers, as well as ﬂexing or extending the interphalangeal whole ﬁnger. Joints between the individual joint The interphalangeal ﬁnger bones, or phalanges, enable ﬁngers joints have a to bend and straighten. In common with ﬁbrous capsule, strengthened by many other primates, humans have palmar and opposable thumbs. The joints at the base collateral ligaments of the thumb are shaped differently from Proximal those of the ﬁngers. The joint between the phalanx metacarpal of the thumb and the wrist bones is especially mobile and allows the thumb to be brought across the palm of the hand so that the tip of the thumb can touch the other ﬁngertips. Distal phalanx Middle phalanx Distal interphalangeal joint Second metacarpophalangeal joint These joints allow about 90 degrees of ﬂexion, a very small amount of extension, and about 30 degrees of abduction and adduction of the metacarpals First metacarpophalangeal joint Allows about 60 degrees of ﬂexion, a little extension, as well as abduction and adduction Joint capsule Collateral ligament First metacarpal The shortest and thickest of the metacarpals Metacarpophalangeal joint Fifth metacarpal First carpometacarpal joint The ﬁrst metacarpal lies at right angles to the metacarpals of the ﬁngers, so that ﬂexion and extension of the thumb occur in the same plane as abduction and adduction of the ﬁngers Proximal interphalangeal joint Dorsal carpometacarpal ligament Hamate Capitate Triquetrum Dorsal intercarpal ligament Styloid process of radius Scaphoid Distal interphalangeal joint Radius Dorsal radiocarpal ligament Styloid process of ulna Ulna FINGER (SAGITTAL SECTION) DORSAL /POSTERIOR (BACK) 057 HAND AND WRIST JOINTS Distal phalanx Distal interphalangeal joint Like the proximal interphalangeal joint, this is a simple hinge joint and can move in ﬂexion and extension only Palmar ligament Middle phalanx Proximal interphalangeal joint Deep transverse metacarpal ligament These ligaments bind together the metacarpophalangeal joints of the ﬁngers Distal phalanx Proximal phalanx Palmar ligament Metacarpophalangeal joint First metacarpal Palmar metacarpal ligament Carpometacarpal joint of the thumb Hook of hamate Pisiform Ulnar radiocarpal ligament Joins the ulna to the carpal bones Capitate bone Radiate carpal ligament Fibers radiate from the head of the capitate to other carpal bones Palmar radiocarpal ligament Joins the radius to the carpal bones Lunate Radius Hand X-ray Styloid process of ulna Ulna PALMAR /ANTERIOR (FRONT) This X-ray of the hand clearly shows the carpal bones in the wrist and the joints between them. Near the metacarpophalangeal joint of the thumb, the thumb’s tiny sesamoid bones, embedded in tendons, are also visible. Femur Lesser trochanter The psoas muscle, which ﬂexes the hip, attaches to this bony projection; trochanter comes from the Greek word for running Intertrochanteric line Runs between the greater and lesser trochanters; the ﬁbrous capsule of the hip joint attaches to the front of the femur along this line Neck of femur Head of femur Ball-shaped head articulates with the acetabulum to form the hip socket Acetabulum Receives the head of the femur to form the hip socket; its name comes from the Latin for vinegar cup Greater trochanter A projection onto which some gluteal muscles attach ANTERIOR (FRONT) Ischial tuberosity Obturator foramen The obturator nerve and vessels pass through this hole to enter the inner compartment of the thigh Ischiopubic ramus The leg or, to be anatomically precise, the lower limb, is attached to the spine by the pelvic bones. This is a much more stable arrangement than that of the shoulder girdle, which anchors the arm, because the legs and pelvis must bear our body weight as we stand or move around. The sacroiliac joint provides a strong attachment between the ilium of the pelvis and the sacrum, and the hip joint is a much deeper and more stable ball-and-socket joint than that in the shoulder. The neck of the femur joins the head at an obtuse angle. A slightly raised diagonal line on the front of the neck (the intertrochanteric line) shows where the ﬁbrous capsule of the hip joint attaches to the bone. Tibia Medial condyle Patella The technical name for the kneecap comes from the Latin for small dish Apex of patella Lateral condyle of the femur Condyle comes from the Greek word for knuckle; the term describes parts of the ends of bones that form joints Lateral epicondyle The term epicondyle (meaning close to the condyle) describes a projecting part of bone near a joint that provides a point of attachment for muscles HIP AND THIGH Patellar surface of the femur Base of patella Shaft of femur This is not vertical, but angled inward slightly, to bring the knees under the body Medial epicondyle HIP AND THIGH Adductor tubercle The point at which the tendon of adductor magnus attaches to the femur 059 Acetabulum The three bones that comprise the pelvic bones—the ilium, ischium, and pubis (which fuse toward the end of puberty to form a single bone)—all come together in the base of the acetabulum POSTERIOR (BACK) Linea aspera The adductor muscles of the thigh attach to the femur along this line Gluteal tuberosity The lower part of the gluteus maximus muscle attaches here Lesser trochanter Intertrochanteric crest This smooth ridge joins the two trochanters Neck of femur Joins the femoral shaft at an angle of around 125º Greater trochanter Head of femur Medial condyle of tibia Medial condyle of femur Rests on the medial condyle of the tibia Adductor tubercle Popliteal surface This smooth area forms the base of the popliteal fossa at the back of the knee Lateral supracondylar line Medial supracondylar line The adductor magnus muscle attaches to the femur at the linea aspera and medial supracondylar line, all the way down to the adductor tubercle Shaft of femur Lateral condyle of tibia Lateral condyle of femur Articulates with the slightly concave lateral condyle of the tibia Intercondylar fossa Cruciate ligaments attach to the femur in this depression between the condyles Lateral epicondyle The shaft of the femur (thighbone) is cylindrical, with a marrow cavity. The linea aspera runs down along the back of the femoral shaft. This line is where the inner thigh’s adductor muscles attach to the femur. Parts of the quadriceps muscle also wrap right around the back of the femur to attach to the linea aspera. At the bottom—or distal—end, toward the knee, the femur widens to form the knee joint with the tibia and the patella. From the back, the distal end of the femur has a distinct double-knuckle shape, with two condyles (rounded projections) that articulate with the tibia. HIP AND THIGH HIP AND THIGH 061 HIP AND KNEE SKELETAL SYSTEM 062 Ilium Ilium, pubis, and ischium of the pelvis all meet in the acetabulum or hip socket Tendon of rectus femoris Attaches to the anterior inferior iliac spine The hip joint is very stable. Its ﬁbrous capsule is strengthened by ligaments that attach from the neck of the femur to the pelvic bone. These are the iliofemoral and pubofemoral ligaments at the front and the ischiofemoral ligament at the back. Inside the joint capsule, a small ligament attaches from the edge of the acetabulum (hip socket) to the head of the femur. The knee joint is formed by the articulation of the femur with the tibia and patella. Although primarily a hinge joint, the knee also permits some rotation to occur. These complex movements are reﬂected by the complexity of the joint: there are crescent-shaped articular disks (menisci) inside the joint, powerful collateral ligaments on either side of the joint, as well as crossed-over cruciate ligaments binding the femur to the tibia, and numerous extra pockets of synovial ﬂuid, called bursae, that lubricate tendons around the joint. Pubofemoral ligament Blends with the inner side of the hip capsule Iliofemoral ligament This strong ligament strengthens the front of the ﬁbrous capsule of the hip joint Superior pubic ramus Forms the upper border of the obturator foramen Body of pubic bone Ischiopubic ramus Forms the lower border of the obturator foramen Greater trochanter of femur Ischium Ischial tuberosity Hamstring muscles of the thigh attach here Intertrochanteric line of the femur The iliofemoral ligament attaches to the femur along this line Lesser trochanter of femur HIP (ANTERIOR/FRONT) Obturator membrane Covers over the obturator foramen, leaving just a small gap at the top where the obturator nerve and vessels pass out of the pelvis into the thigh SYNOVIAL JOINTS 063 Vastus lateralis muscle Suprapatellar bursa Rectus femoris muscle HIP AND KNEE The majority of the body’s 320 or so joints, including those in the ﬁnger, knee, and shoulder, are free-moving synovial joints. The joint surfaces are lined with smooth hyaline cartilage to reduce friction, and contain lubricating synovial ﬂuid. Vastus medialis muscle Femur Tendon of quadriceps femoris muscle Articular cartilage of patella Bursa under head of gastrocnemius muscle Patella Prepatellar bursa Femoral condyle Synovial cavity Articular cartilage Infrapatellar fat pad Fibrous capsule Articular cartilage Hyaline cartilage covers the articular surfaces of the tibia, femur, and patella Subcutaneous infrapatellar bursa Meniscus Deep infrapatellar bursa Tibial plateau Tibia KNEE Complex joint A complex synovial joint, such as the knee, has articular discs or menisci inside the synovial cavity. The knee is also a compound hinge joint, as it involves more than two bones. Its complex anatomy allows it to move in ﬂexion and extension, but some sliding and axial rotation of the femur on the tibia also occurs. Quadriceps tendon Iliotibial tract Patella Patella Shown in cross section Femur Lateral condyle Posterior cruciate ligament Anterior cruciate ligament Cruciate means crosslike in Latin Medial condyle Medial meniscus Meniscus comes from the Greek for little moon—the menisci are crescent-shaped Lateral meniscu