Anatomy PDF

The Body What is anatomy? Anatomy includes those structures that can be seen grossly are studied at the same time. For example, if the thorax (without the aid of magnification) and microscopically is to be studied, all of its structures are examined. (with...

The Body What is anatomy? Anatomy includes those structures that can be seen grossly are studied at the same time. For example, if the thorax (without the aid of magnification) and microscopically is to be studied, all of its structures are examined. (with the aid of magnification). Typically, when used by This includes the vasculature, the nerves, the bones, itself, the term anatomy tends to mean gross or macroscopic the muscles, and all other structures and organs anatomy—that is, the study of structures that can be seen located in the region of the body defined as the without using a microscopic. Microscopic anatomy, also thorax. After studying this region, the other regions of called histology, is the study of cells and tissues using a the body (i.e., the abdomen, pelvis, lower limb, upper microscope. limb, back, head, and neck) are studied in a similar Anatomy forms the basis for the practice of medicine. fashion. Anatomy leads the physician toward an understanding of In contrast, in a systemic approach, each system of a patient’s disease, whether he or she is carrying out a the body is studied and followed throughout the entire physical examination or using the most advanced imaging body. For example, a study of the cardiovascular system techniques. Anatomy is also important for dentists, chiro- looks at the heart and all of the blood vessels in the body. practors, physical therapists, and all others involved in any When this is completed, the nervous system (brain, aspect of patient treatment that begins with an analysis of spinal cord, and all the nerves) might be examined in clinical signs. The ability to interpret a clinical observation detail. This approach continues for the whole body until correctly is therefore the endpoint of a sound anatomical every system, including the nervous, skeletal, muscular, understanding. gastrointestinal, respiratory, lymphatic, and reproduc- Observation and visualization are the primary tech- tive systems, has been studied. niques a student should use to learn anatomy. Anatomy is much more than just memorization of lists of names. Each of these approaches has benefits and deficiencies. Although the language of anatomy is important, the The regional approach works very well if the anatomy network of information needed to visualize the position of course involves cadaver dissection but falls short when physical structures in a patient goes far beyond simple it comes to understanding the continuity of an entire memorization. Knowing the names of the various branches system throughout the body. Similarly, the systemic of the external carotid artery is not the same as being able approach fosters an understanding of an entire system to visualize the course of the lingual artery from its origin throughout the body, but it is very difficult to coordinate in the neck to its termination in the tongue. Similarly, this directly with a cadaver dissection or to acquire suffi- understanding the organization of the soft palate, how it is cient detail. related to the oral and nasal cavities, and how it moves during swallowing is very different from being able to recite the names of its individual muscles and nerves. An under- Important anatomical terms standing of anatomy requires an understanding of the The anatomical position context in which the terminology can be remembered. The anatomical position is the standard reference position of the body used to describe the location of structures (Fig. 1.1). The body is in the anatomical position when standing How can gross anatomy be studied? upright with feet together, hands by the side and face The term anatomy is derived from the Greek word temnein, looking forward. The mouth is closed and the facial expres- meaning “to cut.” Clearly, therefore, the study of anatomy sion is neutral. The rim of bone under the eyes is in the is linked, at its root, to dissection, although dissection of same horizontal plane as the top of the opening to the cadavers by students is now augmented, or even in some ear, and the eyes are open and focused on something in cases replaced, by viewing prosected (previously dissected) the distance. The palms of the hands face forward with the material and plastic models, or using computer teaching fingers straight and together and with the pad of the thumb modules and other learning aids. turned 90° to the pads of the fingers. The toes point Anatomy can be studied following either a regional or a forward. systemic approach. Anatomical planes With a regional approach, each region of the body Three major groups of planes pass through the body in the 2 is studied separately and all aspects of that region anatomical position (Fig. 1.1).  What Is Anatomy Important Anatomical Terms 1 Superior Coronal plane Inferior margin of orbit level with top of external auditory meatus Face looking forward Sagittal plane Anterior Posterior Medial Transverse, horizontal, or axial plane Hands by sides palms forward Lateral Feet together toes forward Inferior Fig. 1.1 The anatomical position, planes, and terms of location and orientation. 3  The Body Coronal planes are oriented vertically and divide the Proximal and distal are used with reference to being body into anterior and posterior parts. closer to or farther from a structure’s origin, particu- Sagittal planes also are oriented vertically but are at larly in the limbs. For example, the hand is distal to the right angles to the coronal planes and divide the body elbow joint. The glenohumeral joint is proximal to into right and left parts. The plane that passes through the elbow joint. These terms are also used to describe the center of the body dividing it into equal right and the relative positions of branches along the course of left halves is termed the median sagittal plane. linear structures, such as airways, vessels, and nerves. Transverse, horizontal, or axial planes divide the For example, distal branches occur farther away toward body into superior and inferior parts. the ends of the system, whereas proximal branches occur closer to and toward the origin of the system. Terms to describe location Cranial (toward the head) and caudal (toward the tail) Anterior (ventral) and posterior (dorsal), are sometimes used instead of superior and inferior, medial and lateral, superior and inferior respectively. Three major pairs of terms are used to describe the location Rostral is used, particularly in the head, to describe the of structures relative to the body as a whole or to other position of a structure with reference to the nose. For structures (Fig. 1.1). example, the forebrain is rostral to the hindbrain. Anterior (or ventral) and posterior (or dorsal) Superficial and deep describe the position of structures relative to the “front” Two other terms used to describe the position of structures and “back” of the body. For example, the nose is an in the body are superficial and deep. These terms are anterior (ventral) structure, whereas the vertebral used to describe the relative positions of two structures column is a posterior (dorsal) structure. Also, the nose with respect to the surface of the body. For example, the is anterior to the ears and the vertebral column is pos- sternum is superficial to the heart, and the stomach is deep terior to the sternum. to the abdominal wall. Medial and lateral describe the position of structures Superficial and deep can also be used in a more absolute relative to the median sagittal plane and the sides of fashion to define two major regions of the body. The super- the body. For example, the thumb is lateral to the little ficial region of the body is external to the outer layer of finger. The nose is in the median sagittal plane and deep fascia. Deep structures are enclosed by this layer. is medial to the eyes, which are in turn medial to the Structures in the superficial region of the body include the external ears. skin, superficial fascia, and mammary glands. Deep struc- Superior and inferior describe structures in reference tures include most skeletal muscles and viscera. Superficial to the vertical axis of the body. For example, the head is wounds are external to the outer layer of deep fascia, superior to the shoulders and the knee joint is inferior whereas deep wounds penetrate through it. to the hip joint. Proximal and distal, cranial and caudal, and rostral Other terms used to describe positions include proximal and distal, cranial and caudal, and rostral. 4  Body Systems Skeletal System 1 Bone Bone is a calcified, living, connective tissue that forms the majority of the skeleton. It consists of an intercellular calcified matrix, which also contains collagen fibers, and several types of cells within the matrix. Bones function as: supportive structures for the body, protectors of vital organs, reservoirs of calcium and phosphorus, levers on which muscles act to produce movement, and containers for blood-producing cells. Os trigonum There are two types of bone, compact and spongy (tra- becular or cancellous). Compact bone is dense bone that forms the outer shell of all bones and surrounds spongy bone. Spongy bone consists of spicules of bone enclosing cavities containing blood-forming cells (marrow). Classifi- cation of bones is by shape. Long bones are tubular (e.g., humerus in upper limb; femur in lower limb). A Short bones are cuboidal (e.g., bones of the wrist and ankle). Sesamoid bones Flat bones consist of two compact bone plates separated by spongy bone (e.g., skull). Irregular bones are bones with various shapes (e.g., bones of the face). Sesamoid bones are round or oval bones that develop in tendons. In the clinic Accessory and sesamoid bones These are extra bones that are not usually found as part of the normal skeleton, but can exist as a normal variant in many people. They are typically found in multiple locations in the wrist and hands, ankles and feet (Fig. 1.13). These should not be mistaken for fractures on imaging. Sesamoid bones are embedded within tendons, the largest of which is the patella. There are many other sesamoids in the body particularly in tendons of the hands and feet, and most frequently in flexor tendons of the thumb and big toe. Degenerative and inflammatory changes of, as well as Os naviculare B mechanical stresses on, the accessory bones and sesamoids can cause pain, which can be treated with Fig. 1.13 Accessory and sesamoid bones. A. Radiograph of physiotherapy and targeted steroid injections, but in some the ankle region showing an accessory bone (os trigonum). severe cases it may be necessary to surgically remove the B. Radiograph of the feet showing numerous sesamoid bones and an accessory bone (os naviculare). bone. 13  The Body Bones are vascular and are innervated. Generally, an vessels that supply the bone and the periosteum. Most of adjacent artery gives off a nutrient artery, usually one per the nerves passing into the internal cavity with the nutrient bone, that directly enters the internal cavity of the bone artery are vasomotor fibers that regulate blood flow. Bone and supplies the marrow, spongy bone, and inner layers of itself has few sensory nerve fibers. On the other hand, the compact bone. In addition, all bones are covered externally, periosteum is supplied with numerous sensory nerve fibers except in the area of a joint where articular cartilage is and is very sensitive to any type of injury. present, by a fibrous connective tissue membrane called the Developmentally, all bones come from mesenchyme by periosteum, which has the unique capability of forming new either intramembranous ossification, in which mesenchy- bone. This membrane receives blood vessels whose branches mal models of bones undergo ossification, or endochondral supply the outer layers of compact bone. A bone stripped ossification, in which cartilaginous models of bones form of its periosteum will not survive. Nerves accompany the from mesenchyme and undergo ossification. In the clinic Determination of skeletal age Throughout life the bones develop in a predictable way to form the skeletally mature adult at the end of puberty. In western countries skeletal maturity tends to occur between the ages of 20 and 25 years. However, this may well vary according to geography and socioeconomic conditions. Skeletal maturity will also be determined by genetic factors and disease states. Up until the age of skeletal maturity, bony growth and development follows a typically predictable ordered state, which can be measured through either ultrasound, plain radiographs, or MRI scanning. Typically, the nondominant (left) hand is radiographed, and the radiograph is compared A B to a series of standard radiographs. From these images the bone age can be determined (Fig. 1.14). In certain disease states, such as malnutrition and hypothyroidism, bony maturity may be slow. If the skeletal bone age is significantly reduced from the patient’s true age, treatment may be required. In the healthy individual the bone age accurately represents the true age of the patient. This is important in determining the true age of the subject. This may also have medicolegal importance. Carpal bones C D Fig. 1.14 A developmental series of radiographs showing the progressive ossification of carpal (wrist) bones from 3 (A) to 10 (D) years of age. 14  Body Systems Skeletal System 1 In the clinic Epiphyseal fractures As the skeleton develops, there are stages of intense growth typically around the ages of 7 to 10 years and later in puberty. These growth spurts are associated with increased cellular activity around the growth plate between the head and shaft of a bone. This increase in activity renders the growth plates more vulnerable to injuries, which may occur from dislocation across a Bone Articular cavity Bone growth plate or fracture through a growth plate. A Synovial joint Occasionally an injury may result in growth plate compression, destroying that region of the growth plate, which may result in asymmetrical growth across that joint region. All fractures across the growth plate must be treated with care and expediency, requiring fracture reduction. Bone Connective tissue Bone B Solid joint Joints Fig. 1.18 Joints. A. Synovial joint. B. Solid joint. The sites where two skeletal elements come together are termed joints. The two general categories of joints The synovial membrane attaches to the margins of the (Fig. 1.18) are those in which: joint surfaces at the interface between the cartilage and bone and encloses the articular cavity. The synovial the skeletal elements are separated by a cavity (i.e., membrane is highly vascular and produces synovial synovial joints), and fluid, which percolates into the articular cavity and there is no cavity and the components are held together lubricates the articulating surfaces. Closed sacs of by connective tissue (i.e., solid joints). synovial membrane also occur outside joints, where they form synovial bursae or tendon sheaths. Bursae Blood vessels that cross over a joint and nerves that often intervene between structures, such as tendons innervate muscles acting on a joint usually contribute and bone, tendons and joints, or skin and bone, and articular branches to that joint. reduce the friction of one structure moving over the other. Tendon sheaths surround tendons and also Synovial joints reduce friction. Synovial joints are connections between skeletal compo- The fibrous membrane is formed by dense connective nents where the elements involved are separated by a tissue and surrounds and stabilizes the joint. Parts of narrow articular cavity (Fig. 1.19). In addition to contain- the fibrous membrane may thicken to form ligaments, ing an articular cavity, these joints have a number of which further stabilize the joint. Ligaments outside the characteristic features. capsule usually provide additional reinforcement. First, a layer of cartilage, usually hyaline cartilage, covers the articulating surfaces of the skeletal elements. In other words, bony surfaces do not normally contact one Another common but not universal feature of synovial another directly. As a consequence, when these joints are joints is the presence of additional structures within the viewed in normal radiographs, a wide gap seems to sepa- area enclosed by the capsule or synovial membrane, such rate the adjacent bones because the cartilage that covers as articular discs (usually composed of fibrocartilage), the articulating surfaces is more transparent to X-rays fat pads, and tendons. Articular discs absorb compres- than bone. sion forces, adjust to changes in the contours of joint sur- A second characteristic feature of synovial joints is the faces during movements, and increase the range of presence of a joint capsule consisting of an inner syno- movements that can occur at joints. Fat pads usually occur vial membrane and an outer fibrous membrane. between the synovial membrane and the capsule and move 17  The Body Tendon Sheath Synovial Hyaline cartilage membrane Fat pad Joint capsule Articular cavity Fibrous Articular membrane disc Bone Bone Hyaline cartilage Bone Articular cavity Bone Fibrous membrane Synovial Skin Bursa membrane A B Fig. 1.19 Synovial joints. A. Major features of a synovial joint. B. Accessory structures associated with synovial joints. into and out of regions as joint contours change during bicondylar (two sets of contact points), condylar (ellip- movement. Redundant regions of the synovial membrane soid), saddle, and ball and socket; and fibrous membrane allow for large movements at joints. based on movement, synovial joints are described as uniaxial (movement in one plane), biaxial (movement Descriptions of synovial joints based on shape in two planes), and multiaxial (movement in three and movement planes). Synovial joints are described based on shape and movement: Hinge joints are uniaxial, whereas ball and socket joints are multiaxial. based on the shape of their articular surfaces, synovial joints are described as plane (flat), hinge, pivot, 18  Body Systems Skeletal System 1 adduction, circumduction, and rotation (e.g., hip Specific types of synovial joints joint) (Fig. 1.20) Plane joints—allow sliding or gliding movements when Solid joints one bone moves across the surface of another (e.g., Solid joints are connections between skeletal elements acromioclavicular joint) where the adjacent surfaces are linked together either Hinge joints—allow movement around one axis that by fibrous connective tissue or by cartilage, usually fibro- passes transversely through the joint; permit flexion and cartilage (Fig. 1.21). Movements at these joints are more extension (e.g., elbow [humero-ulnar] joint) restricted than at synovial joints. Pivot joints—allow movement around one axis that Fibrous joints include sutures, gomphoses, and passes longitudinally along the shaft of the bone; permit syndesmoses. rotation (e.g., atlanto-axial joint) Bicondylar joints—allow movement mostly in one axis Sutures occur only in the skull where adjacent bones with limited rotation around a second axis; formed by are linked by a thin layer of connective tissue termed a two convex condyles that articulate with concave or flat sutural ligament. surfaces (e.g., knee joint) Gomphoses occur only between the teeth and adjacent Condylar (ellipsoid) joints—allow movement around bone. In these joints, short collagen tissue fibers in the two axes that are at right angles to each other; permit periodontal ligament run between the root of the tooth flexion, extension, abduction, adduction, and circum- and the bony socket. duction (limited) (e.g., wrist joint) Syndesmoses are joints in which two adjacent bones Saddle joints—allow movement around two axes that are linked by a ligament. Examples are the ligamentum are at right angles to each other; the articular surfaces flavum, which connects adjacent vertebral laminae, are saddle shaped; permit flexion, extension, abduction, and an interosseous membrane, which links, for adduction, and circumduction (e.g., carpometacarpal example, the radius and ulna in the forearm. joint of the thumb) Ball and socket joints—allow movement around Cartilaginous joints include synchondroses and multiple axes; permit flexion, extension, abduction, symphyses. B Humerus Ulna Radius Synovial membrane Wrist joint Articular disc Radius Olecranon A Synovial cavity C Ulna Odontoid process Cartilage of axis Trapezium Synovial membrane Atlas Metacarpal I Synovial Femur membrane D E F Fig. 1.20 Various types of synovial joints. A. Condylar (wrist). B. Gliding (radio-ulnar). C. Hinge (elbow). D. Ball and socket (hip). E. Saddle 19 (carpometacarpal of thumb). F. Pivot (atlanto-axial).  The Body SOLID JOINTS Fibrous Cartilaginous Sutures Sutural ligament Skull Synchondrosis Head Gomphosis Cartilage of growth plate Tooth Long bone Shaft Periodontal ligament Bone Symphysis Intervertebral Syndesmosis discs Radius Ulna Interosseous membrane Pubic symphysis Fig. 1.21 Solid joints. Synchondroses occur where two ossification centers Symphyses occur where two separate bones are inter- in a developing bone remain separated by a layer of connected by cartilage. Most of these types of joints cartilage, for example, the growth plate that occurs occur in the midline and include the pubic symphysis between the head and shaft of developing long bones. between the two pelvic bones, and intervertebral discs These joints allow bone growth and eventually become between adjacent vertebrae. 20 completely ossified.  Back FUNCTIONS Early embryo Support The skeletal and muscular elements of the back support the body’s weight, transmit forces through the pelvis to the lower limbs, carry and position the head, and brace and help maneuver the upper limbs. The verte- Somites bral column is positioned posteriorly in the body at the midline. When viewed laterally, it has a number of curva- tures (Fig. 2.2): The primary curvature of the vertebral column is Concave primary curvature of back concave anteriorly, reflecting the original shape of the embryo, and is retained in the thoracic and sacral regions in adults. Secondary curvatures, which are concave posteriorly, Adult form in the cervical and lumbar regions and bring the center of gravity into a vertical line, which allows the body’s weight to be balanced on the vertebral column in a way that expends the least amount of muscular energy to maintain an upright bipedal stance. Cervical curvature (secondary curvature) As stresses on the back increase from the cervical to lumbar regions, lower back problems are common. Movement Thoracic curvature Muscles of the back consist of extrinsic and intrinsic (primary curvature) groups: The extrinsic muscles of the back move the upper limbs and the ribs. Lumbar curvature The intrinsic muscles of the back maintain posture and (secondary curvature) move the vertebral column; these movements include flexion (anterior bending), extension, lateral flexion, Sacral/coccygeal curvature (primary curvature) and rotation (Fig. 2.3). Although the amount of movement between any two vertebrae is limited, the effects between vertebrae are addi- tive along the length of the vertebral column. Also, freedom Gravity line of movement and extension are limited in the thoracic region relative to the lumbar part of the vertebral column. Muscles in more anterior regions flex the vertebral column. 52 Fig. 2.2 Curvatures of the vertebral column.  Conceptual Overview Functions 2 Extension Flexion Lateral flexion Rotation Fig. 2.3 Back movements. Brain In the cervical region, the first two vertebrae and associ- Cranial nerve ated muscles are specifically modified to support and posi- tion the head. The head flexes and extends, in the nodding motion, on vertebra CI, and rotation of the head occurs as Spinal cord vertebra CI moves on vertebra CII (Fig. 2.3). Spinal nerve Protection of the nervous system The vertebral column and associated soft tissues of the back contain the spinal cord and proximal parts of the spinal nerves (Fig. 2.4). The more distal parts of the spinal nerves pass into all other regions of the body, including certain regions of the head. Fig. 2.4 Nervous system. 53  Back COMPONENT PARTS are associated. There are seven cervical, twelve thoracic, five lumbar, five sacral, and three to four coccygeal verte- Bones brae. The sacral vertebrae fuse into a single bony element, The major bones of the back are the 33 vertebrae (Fig. the sacrum. The coccygeal vertebrae are rudimentary in 2.5). The number and specific characteristics of the verte- structure, vary in number from three to four, and often fuse brae vary depending on the body region with which they into a single coccyx. 7 cervical vertebrae (CI–CVII) 12 thoracic vertebrae (TI–TXII) 5 lumbar vertebrae (LI–LV) Sacrum (5 fused sacral vertebrae I-V) Coccyx (3–4 fused coccygeal vertebrae I-IV) Fig. 2.5 Vertebrae. 54  Conceptual Overview Component Parts 2 On each side of the vertebral arch, a transverse process Typical vertebra extends laterally from the region where a lamina meets a A typical vertebra consists of a vertebral body and a verte- pedicle. From the same region, a superior articular process bral arch (Fig. 2.6). and an inferior articular process articulate with similar The vertebral body is anterior and is the major weight- processes on adjacent vertebrae. bearing component of the bone. It increases in size Each vertebra also contains rib elements. In the thorax, from vertebra CII to vertebra LV. Fibrocartilaginous inter- these costal elements are large and form ribs, which articu- vertebral discs separate the vertebral bodies of adjacent late with the vertebral bodies and transverse processes. vertebrae. In all other regions, these rib elements are small and are The vertebral arch is firmly anchored to the posterior incorporated into the transverse processes. Occasionally, surface of the vertebral body by two pedicles, which form they develop into ribs in regions other than the thorax, the lateral pillars of the vertebral arch. The roof of the usually in the lower cervical and upper lumbar regions. vertebral arch is formed by right and left laminae, which fuse at the midline. The vertebral arches of the vertebrae are aligned to Muscles form the lateral and posterior walls of the vertebral canal, Muscles in the back can be classified as extrinsic or intrinsic which extends from the first cervical vertebra (CI) to the based on their embryological origin and type of innerva- last sacral vertebra (vertebra SV). This bony canal contains tion (Fig. 2.7). the spinal cord and its protective membranes, together The extrinsic muscles are involved with movements of with blood vessels, connective tissue, fat, and proximal the upper limbs and thoracic wall and, in general, are parts of spinal nerves. innervated by anterior rami of spinal nerves. The superfi- The vertebral arch of a typical vertebra has a number cial group of these muscles is related to the upper limbs, of characteristic projections, which serve as: while the intermediate layer of muscles is associated with the thoracic wall. attachments for muscles and ligaments, All of the intrinsic muscles of the back are deep in levers for the action of muscles, and position and are innervated by the posterior rami of sites of articulation with adjacent vertebrae. spinal nerves. They support and move the vertebral column and participate in moving the head. One group A spinous process projects posteriorly and generally of intrinsic muscles also moves the ribs relative to the inferiorly from the roof of the vertebral arch. vertebral column. Anterior Superior articular process Superior Pedicle Superior vertebral Transverse process notch Transverse Vertebral Pedicle Spinous process process body Anterior Posterior Fused costal (rib) element Vertebral Lamina Lamina Inferior arch Vertebral body Inferior articular Spinous process process Inferior vertebral notch A Posterior B Fig. 2.6 A typical vertebra. A. Superior view. B. Lateral view. 55  Back Levator scapulae Serratus posterior superior Trapezius Rhomboid minor Rhomboid major Latissimus Serratus posterior dorsi inferior Superficial group Intermediate group Extrinsic muscles A Innervated by anterior rami of spinal nerves or cranial nerve XI (trapezius) Suboccipital Splenius Longissimus Erector spinae Iliocostalis Spinalis Deep group Intrinsic muscles B True back muscles innervated by posterior rami of spinal nerves Fig. 2.7 Back muscles. A. Extrinsic muscles. B. Intrinsic muscles. 56  Back Vertebrae Regional anatomy There are approximately 33 vertebrae, which are subdi- SKELETAL FRAMEWORK vided into five groups based on morphology and location (Fig. 2.14): Skeletal components of the back consist mainly of the vertebrae and associated intervertebral discs. The skull, ¥ The seven cervical vertebrae between the thorax and scapulae, pelvic bones, and ribs also contribute to the bony skull are characterized mainly by their small size and framework of the back and provide sites for muscle the presence of a foramen in each transverse process attachment. (Figs. 2.14 and 2.15). Anterior Fused costal Foramen (rib) element transversarium 7 Cervical vertebrae Cervical vertebra 12 Thoracic vertebrae Rib Thoracic vertebra 5 Lumbar vertebrae Sacrum Fused costal Coccyx (rib) element Lumbar vertebra Posterior Fig. 2.14 Vertebrae. 62  Regional Anatomy Skeletal Framework 2 CII Vertebral Posterior tubercle body of CIII of CI (atlas) A B Location of Vertebra prominens Rib II Spinous process of CVII intervertebral disc (spinous process of CVII) Fig. 2.15 Radiograph of cervical region of vertebral column. A. Anteroposterior view. B. Lateral view. 63  Back The 12 thoracic vertebrae are characterized by their Next are five sacral vertebrae fused into one single bone articulated ribs (Figs. 2.14 and 2.16); although all called the sacrum, which articulates on each side with vertebrae have rib elements, these elements are small a pelvic bone and is a component of the pelvic wall. and are incorporated into the transverse processes in Inferior to the sacrum is a variable number, usually four, regions other than the thorax; but in the thorax, the ribs of coccygeal vertebrae, which fuse into a single small are separate bones and articulate via synovial joints triangular bone called the coccyx. with the vertebral bodies and transverse processes of the associated vertebrae. In the embryo, the vertebrae are formed intersegmen- Inferior to the thoracic vertebrae are five lumbar verte- tally from cells called sclerotomes, which originate from brae, which form the skeletal support for the posterior adjacent somites (Fig. 2.18). Each vertebra is derived from abdominal wall and are characterized by their large size the cranial parts of the two somites below, one on each (Figs. 2.14 and 2.17). side, and the caudal parts of the two somites above. The Pedicle Vertebral body Location of intervertebral disc Rib A B Transverse process Vertebral body Spinous process Intervertebral foramen Location of intervertebral disc Fig. 2.16 Radiograph of thoracic region of vertebral column. A. Anteroposterior view. B. Lateral view. 64  Regional Anatomy Skeletal Framework 2 Location of Transverse process intervertebral disc Rib A B Spinous process of LIV Pedicle Intervertebral foramen Vertebral body of LIII Fig. 2.17 Radiograph of lumbar region of vertebral column. A. Anteroposterior view. B. Lateral view. Developing Caudal spinal nerve Somites Developing spinal nerve Neural tube Cranial Forming vertebra Somites Migrating sclerotome cells Sclerotome Fig. 2.18 Development of the vertebrae. 65  Back spinal nerves develop segmentally and pass between the The vertebral arch of each vertebra consists of pedicles forming vertebrae. and laminae (Fig. 2.19): Typical vertebra The two pedicles are bony pillars that attach the verte- A typical vertebra consists of a vertebral body and a poste- bral arch to the vertebral body. rior vertebral arch (Fig. 2.19). Extending from the vertebral The two laminae are flat sheets of bone that extend arch are a number of processes for muscle attachment and from each pedicle to meet in the midline and form the articulation with adjacent bone. roof of the vertebral arch. The vertebral body is the weight-bearing part of the vertebra and is linked to adjacent vertebral bodies by A spinous process projects posteriorly and inferiorly intervertebral discs and ligaments. The size of vertebral from the junction of the two laminae and is a site for bodies increases inferiorly as the amount of weight sup- muscle and ligament attachment. ported increases. A transverse process extends posterolaterally from The vertebral arch forms the lateral and posterior the junction of the pedicle and lamina on each side and is parts of the vertebral foramen. a site for muscle and ligament attachment, and for articu- The vertebral foramina of all the vertebrae together lation with ribs in the thoracic region. form the vertebral canal, which contains and protects Also projecting from the region where the pedicles join the the spinal cord. Superiorly, the vertebral canal is continu- laminae are superior and inferior articular processes ous, through the foramen magnum of the skull, with the (Fig. 2.19), which articulate with the inferior and superior cranial cavity of the head. articular processes, respectively, of adjacent vertebrae. Superior articular process Superior vertebral notch Vertebral body Pedicle Transverse process Vertebral arch Lamina Spinous process Inferior articular process Inferior vertebral notch Superior view Superolateral oblique view Fig. 2.19 Typical vertebra. 66  Regional Anatomy Skeletal Framework 2 Between the vertebral body and the origin of the The vertebral body is short in height and square shaped articular processes, each pedicle is notched on its superior when viewed from above and has a concave superior and inferior surfaces. These superior and inferior ver- surface and a convex inferior surface. tebral notches participate in forming intervertebral Each transverse process is trough shaped and perforated foramina. by a round foramen transversarium. The spinous process is short and bifid. Cervical vertebrae The vertebral foramen is triangular. The seven cervical vertebrae are characterized by their small size and by the presence of a foramen in each trans- The first and second cervical vertebrae—the atlas verse process. A typical cervical vertebra has the following and axis—are specialized to accommodate movement of features (Fig. 2.20A): the head. Superior view Anterior view Foramen transversarium Vertebral body Uncinate process Transverse process Vertebral canal Foramen Spinous process transversarium Spinous process A Fig. 2.20 Regional vertebrae. A. Typical cervical vertebra. Continued 67  Back Atlas (CI vertebra) Atlas (CI vertebra) and Axis (CII vertebra) Anterior tubercle Transverse ligament of atlas Facet for dens Anterior arch Lateral mass Transverse process Impressions for alar ligaments Foramen transversarium Facet for occipital condyle Posterior arch Posterior tubercle Superior view Superior view Tectorial membrane (upper part Apical ligament of posterior longitudinal ligament) of dens Transverse ligament of atlas Dens Atlas (CI Inferior longitudinal vertebra) Axis (CII vertebra) band of cruciform and Axis ligament (CII vertebra) Dens and base of skull Facets for attachment of alar ligaments Alar ligaments Posterior longitudinal ligament B Superior view Posterior view Posterosuperior view Demifacet for articulation Vertebral body with head of its own rib Facet for articulation with tubercle of its own rib Demifacet for articulation Mammillary with head of rib below Transverse process Transverse process process Spinous Spinous process process C Superior view Lateral view D Superior view Fig. 2.20, cont’d B. Atlas and axis. C. Typical thoracic vertebra. D. Typical lumbar vertebra. 68  Regional Anatomy Skeletal Framework 2 Posterior sacral foramina Coccygeal cornu Anterior sacral Facet for articulation Incomplete foramina with pelvic bone sacral canal E Anterior view Dorsolateral view F Posterior view Fig. 2.20, cont’d E. Sacrum. F. Coccyx. between CI and CII. When viewed from above, the atlas is Atlas and axis ring shaped and composed of two lateral masses inter- Vertebra CI (the atlas) articulates with the head (Fig. connected by an anterior arch and a posterior arch. 2.21). Its major distinguishing feature is that it lacks a Each lateral mass articulates above with an occipital vertebral body (Fig. 2.20B). In fact, the vertebral body of condyle of the skull and below with the superior articular CI fuses onto the body of CII during development to become process of vertebra CII (the axis). The superior articular the dens of CII. As a result, there is no intervertebral disc surfaces are bean shaped and concave, whereas the infe- rior articular surfaces are almost circular and flat. Inferior articular facet The atlanto-occipital joint allows the head to nod up on lateral mass of CI and down on the vertebral column. The posterior surface of the anterior arch has an articu- lar facet for the dens, which projects superiorly from the vertebral body of the axis. The dens is held in position by a strong transverse ligament of atlas posterior to it and spanning the distance between the oval attachment facets on the medial surfaces of the lateral masses of the atlas. The dens acts as a pivot that allows the atlas and attached head to rotate on the axis, side to side. The transverse processes of the atlas are large and protrude further laterally than those of the other cervical vertebrae and act as levers for muscle action, particularly for muscles that move the head at the atlanto-axial joints. The axis is characterized by the large tooth-like dens, which extends superiorly from the vertebral body (Figs. 2.20B and 2.21). The anterior surface of the dens has an oval facet for articulation with the anterior arch of the atlas. The two superolateral surfaces of the dens possess cir- cular impressions that serve as attachment sites for strong Superior articular facet of CII Dens alar ligaments, one on each side, which connect the dens to the medial surfaces of the occipital condyles. These alar Fig. 2.21 Radiograph showing CI (atlas) and CII (axis) vertebrae. ligaments check excessive rotation of the head and atlas Open mouth, anteroposterior (odontoid peg) view. relative to the axis. 69  Back Thoracic vertebrae and below with the coccyx. It has two large L-shaped The twelve thoracic vertebrae are all characterized by their facets, one on each lateral surface, for articulation with the articulation with ribs. A typical thoracic vertebra has two pelvic bones. partial facets (superior and inferior costal facets) on each The posterior surface of the sacrum has four pairs of side of the vertebral body for articulation with the head posterior sacral foramina, and the anterior surface has of its own rib and the head of the rib below (Fig. 2.20C). four pairs of anterior sacral foramina for the passage of The superior costal facet is much larger than the inferior the posterior and anterior rami, respectively, of S1 to S4 costal facet. spinal nerves. Each transverse process also has a facet (transverse The posterior wall of the vertebral canal may be incom- costal facet) for articulation with the tubercle of its own plete near the inferior end of the sacrum. rib. The vertebral body of the vertebra is somewhat heart shaped when viewed from above, and the vertebral foramen Coccyx is circular. The coccyx is a small triangular bone that articulates with the inferior end of the sacrum and represents three to four Lumbar vertebrae fused coccygeal vertebrae (Fig. 2.20F). It is characterized The five lumbar vertebrae are distinguished from vertebrae by its small size and by the absence of vertebral arches and in other regions by their large size (Fig. 2.20D). Also, they therefore a vertebral canal. lack facets for articulation with ribs. The transverse proc- esses are generally thin and long, with the exception of those on vertebra LV, which are massive and somewhat Intervertebral foramina cone shaped for the attachment of iliolumbar ligaments Intervertebral foramina are formed on each side between to connect the transverse processes to the pelvic bones. adjacent parts of vertebrae and associated intervertebral The vertebral body of a typical lumbar vertebra is cylin- discs (Fig. 2.22). The foramina allow structures, such as drical and the vertebral foramen is triangular in shape and spinal nerves and blood vessels, to pass in and out of the larger than in the thoracic vertebrae. vertebral canal. An intervertebral foramen is formed by the inferior Sacrum vertebral notch on the pedicle of the vertebra above and The sacrum is a single bone that represents the five fused the superior vertebral notch on the pedicle of the vertebra sacral vertebrae (Fig. 2.20E). It is triangular in shape with below. The foramen is bordered: the apex pointed inferiorly, and is curved so that it has a concave anterior surface and a correspondingly convex posteriorly by the zygapophysial joint between the posterior surface. It articulates above with vertebra LV articular processes of the two vertebrae, and Inferior vertebral notch Intervertebral foramen Zygapophysial joint Intervertebral disc Superior vertebral notch Fig. 2.22 Intervertebral foramen. 70  Regional Anatomy Skeletal Framework 2 anteriorly by the intervertebral disc and adjacent verte- reasonably complete bony dorsal wall for the vertebral bral bodies. canal. However, in the lumbar region, large gaps exist between the posterior components of adjacent vertebral Each intervertebral foramen is a confined space sur- arches (Fig. 2.23). These gaps between adjacent laminae rounded by bone and ligament, and by joints. Pathology in and spinous processes become increasingly wide from any of these structures, and in the surrounding muscles, vertebra LI to vertebra LV. The spaces can be widened can affect structures within the foramen. further by flexion of the vertebral column. These gaps allow relatively easy access to the vertebral canal for clini- Posterior spaces between vertebral arches cal procedures. In most regions of the vertebral column, the laminae and spinous processes of adjacent vertebrae overlap to form a Thoracic vertebrae Lamina Spinous process Lumbar vertebrae Spinous process Lamina Space between adjacent laminae Fig. 2.23 Spaces between adjacent vertebral arches in the lumbar region. 71  Back In the clinic Osteoporosis With increasing age and poor-quality bone, patients are Osteoporosis is a pathophysiologic condition in which more susceptible to fracture. Healing tends to be impaired in bone quality is normal but the quantity of bone is these elderly patients, who consequently require long deficient. It is a metabolic bone disorder that commonly hospital stays and prolonged rehabilitation. occurs in women in their 50s and 60s and in men in Patients likely to develop osteoporosis can be identified their 70s. by dual-photon X-ray absorptiometry (DXA) scanning. Many factors influence the development of osteoporosis, Low-dose X-rays are passed through the bone, and by including genetic predetermination, level of activity and counting the number of photons detected and knowing the nutritional status, and, in particular, estrogen levels in dose given, the number of X-rays absorbed by the bone can women. be calculated. The amount of X-ray absorption can be Typical complications of osteoporosis include “crush” directly correlated with the bone mass, and this can be used vertebral body fractures, distal fractures of the radius, and to predict whether a patient is at risk for osteoporotic hip fractures. fractures. JOINTS Anulus fibrosus Nucleus pulposus Joints between vertebrae in the back The two major types of joints between vertebrae are: symphyses between vertebral bodies (Fig. 2.31), and synovial joints between articular processes (Fig. 2.32). Layer of A typical vertebra has a total of six joints with adjacent hyaline vertebrae: four synovial joints (two above and two below) cartilage and two symphyses (one above and one below). Each symphysis includes an intervertebral disc. Although the movement between any two vertebrae is limited, the summation of movement among all vertebrae Fig. 2.31 Intervertebral joints. results in a large range of movement by the vertebral column. Movements by the vertebral column include flexion, extension, lateral flexion, rotation, and circumduction. Movements by vertebrae in a specific region (cervical, thoracic, and lumbar) are determined by the shape and orientation of joint surfaces on the articular processes and on the vertebral bodies. 78  Regional Anatomy Joints 2 Cervical Symphyses between vertebral bodies “Sloped from anterior (intervertebral discs) to posterior” The symphysis between adjacent vertebral bodies is formed Zygapophysial joint by a layer of hyaline cartilage on each vertebral body and an intervertebral disc, which lies between the layers. The intervertebral disc consists of an outer anulus Lateral view fibrosus, which surrounds a central nucleus pulposus (Fig. 2.31). The anulus fibrosus consists of an outer ring of col- Thoracic lagen surrounding a wider zone of fibrocartilage “Vertical” arranged in a lamellar configuration. This arrangement Zygapophysial joint of fibers limits rotation between vertebrae. The nucleus pulposus fills the center of the interver- tebral disc, is gelatinous, and absorbs compression forces between vertebrae. Degenerative changes in the anulus fibrosus can lead to herniation of the nucleus pulposus. Posterolateral hernia- Lateral view tion can impinge on the roots of a spinal nerve in the intervertebral foramen. Joints between vertebral arches (zygapophysial joints) Lumbar The synovial joints between superior and inferior articular “Wrapped” processes on adjacent vertebrae are the zygapophysial joints (Fig. 2.32). A thin articular capsule attached to the margins of the articular facets encloses each joint. In cervical regions, the zygapophysial joints slope infe- riorly from anterior to posterior and their shape facilitates flexion and extension. In thoracic regions, the joints are oriented vertically and their shape limits flexion and exten- Lateral view Zygapophysial joint sion, but facilitates rotation. In lumbar regions, the joint surfaces are curved and adjacent processes interlock, thereby limiting range of movement, though flexion and extension are still major movements in the lumbar region. “Uncovertebral” joints The lateral margins of the upper surfaces of typical cervi- cal vertebrae are elevated into crests or lips termed uncinate processes. These may articulate with the body of the ver- tebra above to form small “uncovertebral” synovial joints (Fig. 2.33). Superior view Fig. 2.32 Zygapophysial joints. 79  Back In the clinic Back pain Back pain is an extremely common disorder. It can be CIV related to mechanical problems or to disc protrusion impinging on a nerve. In cases involving discs, it may be necessary to operate and remove the disc that is pressing on the nerve. CV Not infrequently, patients complain of pain and no immediate cause is found; the pain is therefore attributed to mechanical discomfort, which may be caused by Uncovertebral joint degenerative disease. One of the treatments is to pass a needle into the facet joint and inject it with local Uncinate process anesthetic and corticosteroid. Fig. 2.33 Uncovertebral joint. In the clinic Herniation of intervertebral discs (Fig. 2.34). This is a common cause of back pain. A disc may The discs between the vertebrae are made up of a central protrude posteriorly to directly impinge on the cord or the portion (the nucleus pulposus) and a complex series of roots of the lumbar nerves, depending on the level, or may fibrous rings (anulus fibrosus). A tear can occur within protrude posterolaterally adjacent to the pedicle and impinge the anulus fibrosus through which the material of the on the descending root. nucleus pulposus can track. After a period of time, this In cervical regions of the vertebral column, cervical disc material may track into the vertebral canal or into the protrusions often become ossified and are termed disc intervertebral foramen to impinge on neural structures osteophyte bars. Vertebral canal containing CSF Meningeal sac containing and cauda equina Psoas CSF and cauda equina A B LIV vertebra Disc protrusion Disc protrusion Facet Fig. 2.34 Disc protrusion. T2-weighted magnetic resonance images of the lumbar region of the vertebral column. A. Sagittal plane. B. Axial plane. 80  Regional Anatomy Ligaments 2 Posterior longitudinal ligament In the clinic Joint diseases Some diseases have a predilection for synovial joints rather than symphyses. A typical example is rheumatoid arthritis, which primarily affects synovial joints and synovial bursae, resulting in destruction of the joint and its lining. Symphyses are usually preserved. LIGAMENTS Joints between vertebrae are reinforced and supported by numerous ligaments, which pass between vertebral bodies and interconnect components of the vertebral arches. Anterior and posterior longitudinal ligaments The anterior and posterior longitudinal ligaments are on the anterior and posterior surfaces of the vertebral bodies and extend along most of the vertebral column (Fig. 2.35). The anterior longitudinal ligament is attached superiorly to the base of the skull and extends inferiorly to attach to the anterior surface of the sacrum. Along its Anterior longitudinal ligament length it is attached to the vertebral bodies and interverte- bral discs. Fig. 2.35 Anterior and posterior longitudinal ligaments of vertebral column. The posterior longitudinal ligament is on the poste- rior surfaces of the vertebral bodies and lines the anterior surface of the vertebral canal. Like the anterior longitudi- nal ligament, it is attached along its length to the vertebral canal. Each ligamentum flavum runs between the posterior bodies and intervertebral discs. The upper part of the pos- surface of the lamina on the vertebra below to the anterior terior longitudinal ligament that connects CII to the intra- surface of the lamina of the vertebra above. The ligamenta cranial aspect of the base of the skull is termed the tectorial flava resist separation of the laminae in flexion and assist membrane (see Fig. 2.20B). in extension back to the anatomical position. Ligamenta flava The ligamenta flava, on each side, pass between the Supraspinous ligament laminae of adjacent vertebrae (Fig. 2.36). These thin, and ligamentum nuchae broad ligaments consist predominantly of elastic tissue The supraspinous ligament connects and passes along and form part of the posterior surface of the vertebral the tips of the vertebral spinous processes from vertebra 81  Back Superior Superior Ligamenta flava Ligamenta flava Posterior Inferior Inferior Vertebral canal Fig. 2.36 Ligamenta flava. CVII to the sacrum (Fig. 2.37). From vertebra CVII to the skull, the ligament becomes structurally distinct External occipital from more caudal parts of the ligament and is called the protuberance ligamentum nuchae. The ligamentum nuchae is a triangular, sheet-like structure in the median sagittal plane: Ligamentum nuchae The base of the triangle is attached to the skull, from the external occipital protuberance to the foramen magnum. Spinous process of The apex is attached to the tip of the spinous process of vertebra CVII vertebra CVII. The deep side of the triangle is attached to the posterior tubercle of vertebra CI and the spinous processes of the other cervical vertebrae. The ligamentum nuchae supports the head. It resists Supraspinous ligament flexion and facilitates returning the head to the anatomi- cal position. The broad lateral surfaces and the posterior edge of the ligament provide attachment for adjacent muscles. Interspinous ligaments Interspinous ligaments pass between adjacent vertebral spinous processes (Fig. 2.38). They attach from the base to the apex of each spinous process and blend with the supra- spinous ligament posteriorly and the ligamenta flava Fig. 2.37 Supraspinous ligament and ligamentum nuchae. 82 anteriorly on each side.  Regional Anatomy Ligaments 2 In the clinic Ligamenta flava The ligamenta flava are important structures associated with the vertebral canal (Fig. 2.39). In degenerative conditions of the vertebral column, the ligamenta flava may hypertrophy. This is often associated with hypertrophy and arthritic change of the zygapophysial joints. In combination, zygapophysial joint hypertrophy, ligamenta flava hypertrophy, and a mild disc protrusion can reduce the dimensions of the vertebral canal, Ligamentum flavum producing the syndrome of spinal stenosis. Supraspinous ligament Interspinous ligament Ligamentum flavum Fig. 2.39 Axial slice MRI through the lumbar spine demonstrating bilateral hypertrophy of the ligamentum flavum. Ligamentum flavum Supraspinous ligament Fig. 2.38 Interspinous ligaments. In the clinic Vertebral fractures analgesia. Disruption of two columns is highly likely to be Vertebral fractures can occur anywhere along the vertebral unstable and requires fixation and immobilization. A column. In most instances, the fracture will heal under three-column spinal injury usually results in a significant appropriate circumstances. At the time of injury, it is not the neurological event and requires fixation to prevent further fracture itself but related damage to the contents of the extension of the neurological defect and to create vertebral vertebral canal and the surrounding tissues that determines column stability. the severity of the patient’s condition. At the craniocervical junction, a complex series of Vertebral column stability is divided into three arbitrary ligaments create stability. If the traumatic incident disrupts clinical “columns”: the anterior column consists of the craniocervical stability, the chances of a significant spinal vertebral bodies and the anterior longitudinal ligament; the cord injury are extremely high. The consequences are middle column comprises the vertebral body and the quadriplegia. In addition, respiratory function may be posterior longitudinal ligament; and the posterior column is compromised by paralysis of the phrenic nerve (which arises made up of the ligamenta flava, interspinous ligaments, from spinal nerves C