Back and Vertebral Column I.pptx PDF

BACK REGION AND VERTEBRAL COLUMN Structure and function of Vertebrae; Regional characteristics of vertebrae; Vertebral column ; Joints of vertebral column; Curvature of vertebral column ; Vasculature and nerves of vertebral column Pg 44...

BACK REGION AND VERTEBRAL COLUMN Structure and function of Vertebrae; Regional characteristics of vertebrae; Vertebral column ; Joints of vertebral column; Curvature of vertebral column ; Vasculature and nerves of vertebral column Pg 440-482 Overview of Back The back comprises the posterior aspect of the trunk, inferior to the neck and superior to the buttocks (L. nates). It is the region of the body to which the head, neck, and limbs are attached. The back includes the: Skin and subcutaneous tissue. Muscles: a superficial layer, primarily concerned with positioning and moving the upper limbs, and deeper layers (“true back muscles”), specifically concerned with moving or maintaining the position of the axial skeleton (posture). Vertebral column: the vertebrae, intervertebral (IV) discs, and associated ligaments) Ribs (in the thoracic region): particularly their posterior portions, medial to the angles of the ribs. Spinal cord and meninges (membranes that cover the spinal cord). Various segmental nerves and vessels.  Overview of Vertebral column The vertebrae and IV discs collectively make up the vertebral column(spine), the skeleton of the neck and back that is the main part of the axial skeleton (i.e., articulated bones of the cranium, vertebral column, ribs, and sternum). The vertebral column extends from the cranium (skull) to the apex of the coccyx. In the adult it is 72–75 cm long, of which approximately one quarter is formed by the IV discs that separate and bind the vertebrae together. The vertebral column: Protects the spinal cord and spinal nerves. Supports the weight of the body superior to the level of the pelvis. Provides a partly rigid and flexible axis for the body and an extended base on which the head is placed and pivots. Plays an important role in posture and locomotion (the movement from one place to another).  Vertebrae The vertebral column in an adult typically consists of 33 vertebrae arranged in five regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal Significant motion occurs only between the 25 superior vertebrae. Of the 9 inferior vertebrae, the 5 sacral vertebrae are fused in adults to form the sacrum, and after approximately age 30, the 4 coccygeal vertebrae fuse to form the coccyx. The lumbosacral angle occurs at the junction of the long axes of the lumbar region of the vertebral column and the sacrum. The vertebrae gradually become larger as the vertebral column descends to the sacrum and then become progressively smaller toward the apex of the coccyx. The vertebral column is flexible because it consists of many relatively small bones, called vertebrae (singular = vertebra), that are separated by resilient IV discs. 25 cervical, thoracic, lumbar, and first sacral vertebrae also articulate at synovial zygapophysial joints, which facilitate and control the vertebral column’s flexibility. Although the movement between two adjacent vertebrae is small, in aggregate the vertebrae and IV discs uniting them form a remarkably flexible yet rigid column that protects the spinal cord they surround. Structure and function of vertebrae Vertebrae vary in size and other characteristics from one region of the vertebral column to another, however, their basic structure is the same A typical vertebra consists of a vertebral body, a vertebral arch, and seven processes. The vertebral body is the more massive, roughly cylindrical, anterior part of the bone that gives strength to the vertebral column and supports body weight. The size of the vertebral bodies increases as the column descends, most markedly from T4 inferiorly, as each bears progressively greater body weight. The vertebral body consists of vascular, trabecular (spongy, cancellous) bone enclosed by a thin external layer of compact bone. The trabecular bone has spaces between these trabeculae are occupied by red bone marrow that is among the most actively hematopoietic (blood-forming) tissues of the mature individual. One or more large foramina in the posterior surface of the body accommodate basivertebral veins that drain the marrow. The superior and inferior surfaces of the vertebral body are covered with discs of hyaline cartilage (vertebral “end plates”), which are remnants of the cartilaginous model from which the bone develops.  Structure and function of vertebrae In addition to serving as growth zones, the anular epiphyses and their cartilaginous remnants provide some protection to the vertebral bodies and permit some diffusion of fluid between the IV disc and the blood vessels (capillaries) in the vertebral body. The superior and inferior epiphyses usually unite with the centrum, the primary ossification center for the central mass of the vertebral body, early in adult life (at approximately age 25).  Structure and function of vertebrae The vertebral arch is posterior to the vertebral body and consists of two (right and left) pedicles and laminae. The vertebral arch and the posterior surface of the vertebral body form the walls of the vertebral foramen. The succession of vertebral foramina in the articulated vertebral column forms the vertebral canal (spinal canal), which contains the spinal cord and the roots of the spinal nerves that emerge from it, along with the membranes (meninges), fat, and vessels that surround and serve them. Structure and function of vertebrae The vertebral notches are indentations observed in lateral views of the vertebrae superior and inferior to each pedicle between the superior and inferior articular processes posteriorly and the corresponding projections of the body anteriorly. The superior and inferior vertebral notches of adjacent vertebrae and the IV discs connecting them form intervertebral foramina, in which the spinal (posterior root) ganglia are located and through which the spinal nerves emerge from the vertebral column with their accompanying vessels. Structure And Function Of Vertebrae Seven processes arise from the vertebral arch of a typical vertebra One median spinous process projects posteriorly (and usually inferiorly, typically overlapping the vertebra below) from the vertebral arch at the junction of the laminae. Two transverse processes project posterolaterally from the junctions of the pedicles and laminae Four articular processes(G. zygapophyses)—two superior and two inferior—also arise from the junctions of the pedicles and laminae, each bearing an articular surface (facet). The spinous and transverse processes provide attachment for deep back muscles and serve as levers, facilitating the muscles that fix or change the position of the  Structure and function of vertebrae The articular processes are in apposition with corresponding processes of vertebrae adjacent (superior and inferior) to them, forming zygapophysial (facet) joints. Through their participation in these joints, these processes determine the types of movement permitted and restricted between the adjacent vertebrae of each region. The articular processes also assist in keeping adjacent vertebrae aligned, particularly preventing one vertebra from slipping anteriorly on the vertebra below. Generally, the articular processes bear weight only temporarily, as when one rises from the flexed position, and unilaterally when the cervical vertebrae are laterally flexed to their limit. However, the inferior articular processes of the L5 vertebra bear weight even in the erect posture.  Regional characteristics of vertebrae Although each of the 33 vertebrae is unique, most of the vertebrae demonstrate characteristic features identifying them as belonging to one of the five regions of the vertebral column For example; vertebrae having foramina in their transverse processes are cervical vertebrae). In addition, certain individual vertebrae have distinguishing features; the C7 vertebra, for example, has the longest spinous process and forms a prominence under the skin at the back of the neck, especially when the neck is flexed. In each region, the articular facets are oriented on the articular processes of the vertebrae in a characteristic direction that determines the type of movement permitted between the adjacent vertebrae and, in aggregate, for the region. For example, the articular facets of thoracic vertebrae are nearly vertical, and together define an arc centered in the IV disc; this arrangement permits rotation and lateral flexion of the vertebral column in this region. Regional variations in the size and shape of the vertebral canal accommodate the varying thickness of the spinal cord.  Cervical Vertebrae Cervical vertebrae form the skeleton of the neck. The smallest of the 24 movable vertebrae, the cervical vertebrae are located between the cranium and the thoracic vertebrae. Their smaller size reflects the fact that they bear less weight than do the larger inferior vertebrae. Although the cervical IV discs are thinner than those of inferior regions, they are relatively thick compared to the size of the vertebral bodies they connect. The relative thickness of the discs, the nearly horizontal orientation of the articular facets, and the small amount of surrounding body mass give the cervical region the greatest range and variety of movement of all the vertebral regions.  Cervical Vertebrae The most distinctive feature of each cervical vertebra is the oval foramen transversarium(transverse foramen) in the transverse process. The vertebral arteries and their accompanying veins pass through the transverse foramina, except those in C7, which transmit only small accessory veins. Thus the foramina are smaller in C7 than those in other cervical vertebrae, and occasionally they are absent. The transverse processes of cervical vertebrae end laterally in two projections: an anterior tubercle and a posterior tubercle. The tubercles provide attachment for a laterally placed group of cervical muscles (levator scapulae and scalenes). The anterior rami of the cervical spinal nerves course initially on the transverse processes in grooves for spinal nerves between the tubercles. The anterior tubercles of vertebra C6 are called carotid tubercles because the common carotid arteries may be compressed here, in the groove between the tubercle and body, to control bleeding from these vessels. Bleeding may continue because of the carotid’s multiple anastomoses of distal branches with adjacent and contralateral branches, but at a slower rate. Cervical Vertebrae Vertebrae C3–C7 are the typical cervical vertebrae. They have large vertebral foramina to accommodate the cervical enlargement of the spinal cord as a consequence of this region’s role in the innervation of the upper limbs. Cervical Vertebrae The spinous processes of the C3–C6 vertebrae are short and usually bifid in white people, especially males, but usually not as commonly in people of African descent or in females. C7 is a prominent vertebra that is characterized by a long spinous process. Because of this prominent process, C7 is called the vertebra prominens. It is the most prominent spinous process in 70% of people.  Cervical vertebrae The first two cervical vertebrae are the atlas (C1) and the axis (C2). These two vertebrae are unusual: No intervertebral disc lies between them. The atlas lacks a body and a spinous process. Essentially, it is a ring of bone consisting of anterior and posterior arches, plus a lateral mass on each side. These joints participate in flexion and extension of the head on the neck, as when you nod “yes.” The axis, which has a body, a spinous process, and the other typical vertebral processes. It also have knoblike dens (“tooth”) projecting superiorly from its body. The dens acts as a pivot for the rotation of the atlas and skull. Hence, this joint participates in rotating the head from side to side to indicate “no.” The dens is held in position against the posterior aspect of the anterior arch of the atlas by the transverse ligament of the atlas  Thoracic Vertebrae The thoracic vertebrae are in the upper back and provide attachment for the ribs Primary characteristic features of thoracic vertebrae are the costal facets for articulation with ribs. The middle four thoracic vertebrae (T5–T8) demonstrate all the features typical of thoracic vertebrae. The articular processes of thoracic vertebrae extend vertically with paired, nearly coronally oriented articular facets that define an arc centered in the IV disc. This arc permits rotation and some lateral flexion of the vertebral column in this region, permitting greatest degree of rotation. Attachment of the rib cage combined with the vertical orientation of articular facets and overlapping spinous processes limits flexion and extension as well as lateral flexion.  Thoracic Vertebrae The T1–T4 vertebrae share some features of cervical vertebrae. T1 is atypical of thoracic vertebrae in that it has a long, almost horizontal spinous process that may be nearly as prominent as that of the vertebra prominens. T1 also has a complete costal facet on the superior edge of its body for the 1st rib and a demifacet on its inferior edge that contributes to the articular surface for the 2nd rib. The T9–T12 vertebrae have some features of lumbar-vertebrae (e.g., tubercles similar to the accessory processes). Mammillary processes also occur. However, most of the transition in characteristics of vertebrae from the thoracic to the lumbar region occurs over the length of a single vertebra: vertebra T12. Generally, its superior half is thoracic in character, having costal facets and articular processes that permit primarily rotatory movement, whereas its inferior half is lumbar in character, devoid of costal facets and having articular processes that permit only flexion and extension. Consequently, vertebra T12 is subject to transitional stresses that cause it to be the most commonly fractured vertebra. Surface Anatomy of Cervical and Thoracic Vertebrae Several of the spinous processes can usually be observed, especially when the back is flexed and the scapulae are protracted most of them can be palpated—even in an obese patient—because fat does not normally accumulate in the midline. The tip of the C7 spinous process is the most evident superficially. Often, when the patient stands erect, it is the only spinous process visible hence the name vertebra prominens. The spinous process of C2 can be felt deeply in the midline inferior to the external occipital protuberance, a median projection located at the junction of the head and neck. C1 has no spinous process, and its small posterior tubercle is neither visible nor palpable.  Surface Anatomy of Cervical and Thoracic Vertebrae The short bifid spinous processes of the C3–C5 vertebrae may be felt in the nuchal groove between the neck muscles, but they are not easy to palpate because the cervical lordosis, which is concave posteriorly, places them deep to the surface from which they are separated by the nuchal ligament. However, because it is considerably longer, the bifid spinous process of C6 vertebra is easily felt superior to the visible tip of the C7 process when the neck is flexed. When the neck and back are flexed, the spinous processes of the upper thoracic vertebra may also be seen. If the individual is especially lean, a continuous ridge appears linking their tips—the supraspinous ligament. Although C7 is the most superior process that is visible and readily palpable, the spinous process of T1 may actually be more prominent. Spinous processes of the other thoracic vertebrae may be obvious in thin people and in others can be identified by superior to inferior palpation beginning at the C7 spinous process. The tips of the thoracic spinous processes do not indicate the level of the corresponding vertebral bodies because they overlap.  Surface Anatomy of Cervical and Thoracic Vertebrae When the back is not being flexed or the scapulae are not protracted, the tips of the thoracic spinous processes lie deep to a median longitudinal furrow. A sudden shift in the alignment of adjacent spinous processes may be the result of a unilateral dislocation of a zygapophysial joint; however, slight irregular misalignments may also result from a fracture of the spinous process. The short 12th rib, the lateral end of which can be palpated in the posterior axillary line, can be used to confirm identity of the T12 spinous process. Lumbar Vertebrae Lumbar vertebrae are in the lower back between the thorax and sacrum. Because the weight they support increases toward the inferior end of the vertebral column, lumbar vertebrae have massive bodies, accounting for much of the thickness of the lower trunk in the median plane. Their articular processes extend vertically, with articular facets sagittally oriented initially (beginning abruptly with the T12–L1 joints), but becoming more coronally oriented as the column descends. The L5–S1 facets are distinctly coronal in orientation. In the more sagittally oriented superior joints, the laterally facing facets of the inferior articular processes of the vertebra above are “gripped” by the medially facing facets of the superior processes of the vertebra below, in a manner that facilitates flexion and extension and allows lateral flexion, but prohibits rotation.  Lumbar Vertebrae Vertebra L5, distinguished by its massive body and transverse processes, is the largest of all movable vertebrae. It carries the weight of the whole upper body. The L5 body is markedly deeper anteriorly; therefore, it is largely responsible for the lumbosacral angle between the long axis of the lumbar region of the vertebral column and that of the sacrum. Body weight is transmitted from L5 vertebra to the base of the sacrum, formed by the superior surface of S1 vertebra.  Sacrum The wedged-shaped sacrum (L. sacred) is usually composed of five fused sacral vertebrae in adults. It is located between the hip bones and forms the roof and posterosuperior wall of the posterior half of the pelvic cavity. The triangular shape of the sacrum results from the rapid decrease in the size of the lateral masses of the sacral vertebrae during development. The inferior half of the sacrum is not weightbearing; therefore, its bulk is diminished considerably. The sacrum provides strength and stability to the pelvis and transmits the weight of the body to the pelvic girdle, the bony ring formed by the hip bones and sacrum, to which the lower limbs are attached.  Sacrum The sacral canal is the continuation of the vertebral canal in the sacrum. It contains the bundle of spinal nerve roots arising inferior to the L1 vertebra, known as the cauda equina (L. horse tail), that descend past the termination of the spinal cord. On the pelvic and posterior surfaces of the sacrum between its vertebral components are typically four pairs of sacral foramina for the exit of the posterior and anterior rami of the spinal nerves. The anterior (pelvic) sacral foramina are larger than the posterior (dorsal) ones. The base of the sacrum is formed by the superior surface of the S1 vertebra. Its superior articular processes articulate with the inferior articular processes of the L5 vertebra. The anterior projecting edge of the body of the S1 vertebra is the sacral promontory (L. mountain ridge), an important obstetrical landmark. The apex of the sacrum, its tapering inferior end, has an oval facet for articulation with the coccyx.  The sacrum is tilted so that it articulates with the L5 vertebra at the lumbosacral angle which varies from 130° to 160°. The sacrum is often wider in proportion to length in the female than in the male, but the body of the S1 vertebra is usually larger in males. The pelvic surface of the sacrum is smooth and concave. During childhood, the individual sacral vertebrae are connected by hyaline cartilage and separated by IV discs. Fusion of the sacral vertebrae starts after age 20; however, most of the IV discs remain unossified up to or beyond middle life.  Sacrum The dorsal surface of the sacrum is rough, convex, and marked by five prominent longitudinal ridges. The central ridge, the median sacral crest, represents the fused rudimentary spinous processes of the superior three or four sacral vertebra; S5 has no spinous process. The intermediate sacral crests represent the fused articular processes, and the lateral sacral crests are the tips of the transverse processes of the fused sacral vertebrae. The clinically important features of the dorsal surface of the sacrum are the inverted U-shaped sacral hiatus and the sacral cornua (L. horns). The sacral hiatus results from the absence of the laminae and spinous process of S5 and sometimes S4. The sacral hiatus leads into the sacral canal. Its depth varies, depending on how much of the spinous process and laminae of S4 are present. The sacral cornua, representing the inferior articular processes of S5 vertebra, project inferiorly on each side of the sacral hiatus and are a helpful guide to its location. The superior part of the lateral surface of the sacrum looks somewhat like an auricle (L. external ear); because of its shape, this area is called the auricular surface. It is the site of the synovial part of the sacroiliac joint between the sacrum and ilium. During life, the auricular surface is covered with hyaline cartilage.  Coccyx The coccyx (tail bone) is a small triangular bone that is usually formed by fusion of the four rudimentary coccygeal vertebrae, although in some people, there may be one less or one more. Coccygeal vertebra 1 (Co1) may remain separate from the fused group. The coccyx is the remnant of the skeleton of the embryonic tail-like caudal eminence, which is present th in human embryos from the end of the 4 week until the beginning of the 8th week. The pelvic surface of the coccyx is concave and relatively smooth, and the posterior surface has rudimentary articular processes. Co1 is the largest and broadest of all the coccygeal vertebrae. Its short transverse processes are connected to the sacrum, and its rudimentary articular processes form coccygeal cornua, which articulate with the sacral cornua.  Coccyx The last three coccygeal vertebrae often fuse during middle life, forming a beak-like coccyx; hence the name (G. coccyx, cuckoo). With increasing age, Co1 often fuses with the sacrum, and the remaining coccygeal vertebrae usually fuse to form a single bone. The coccyx does not participate with the other vertebrae in support of the body weight when standing; however, when sitting it may flex anteriorly somewhat, indicating that it is receiving some weight. The coccyx provides attachments for parts of the gluteus maximus and coccygeus muscles and the anococcygeal ligament, the median fibrous band of the pubococcygeus muscles. Surface Anatomy of Lumbar Vertebrae, Sacrum and Coccyx The spinous processes of lumbar vertebrae are large and easy to observe when the trunk is flexed. They can also be palpated in the posterior median furrow. The L2 spinous process provides an estimate of the position of the inferior end of the spinal cord. A horizontal line joining the highest points of the iliac crests passes through the tip of the L4 spinous process and the L4–L5 IV disc. This is a useful landmark when performing a lumbar puncture to obtain a sample of cerebrospinal fluid (CSF). The S2 spinous process lies at the middle of a line drawn between the posterior superior iliac spines, indicated by the skin dimples formed by the attachment of skin and deep fascia to these spines.  Surface Anatomy of Lumbar Vertebrae, Sacrum and Coccyx The median sacral crest can be felt inferior to the L5 spinous process. The sacral triangle is formed by the lines joining the two posterior superior iliac spines and the superior part of the intergluteal (natal) cleft between the buttocks. The sacral triangle outlining the sacrum is a common area of pain resulting from low back sprains. The sacral hiatus can be palpated at the inferior end of the sacrum located in the superior part of the intergluteal cleft. The transverse processes of thoracic and lumbar vertebrae are covered with thick muscles and may or may not be palpable. The coccyx can be palpated in the intergluteal cleft, inferior to the apex of the sacral triangle. The tip (apex) of the coccyx can be palpated approximately 2.5 cm posterosuperior to the anus. Clinically, the coccyx is examined with a gloved finger in the anal canal. Ossification of Vertebrae Vertebrae begin to develop during the embryonic period as mesenchymal condensations around the notochord. Later, these mesenchymal bone models chondrify and cartilaginous vertebrae form. Typically, vertebrae begin to ossify toward the end of the embryonic period (8th week), with three primary ossification centers developing in each cartilaginous vertebra: an endochondral centrum, which will eventually constitute most of the body of the vertebra, and two perichondral centers, one in each half of the neural arch. Ossification continues throughout the fetal period. At birth, each typical vertebra and the superior most sacral vertebrae consists of three bony parts united by hyaline cartilage. The inferior sacral vertebrae and all the coccygeal vertebrae are still entirely cartilaginous; they ossify during infancy.  Ossification of Vertebrae Five secondary ossification centers develop during puberty in each typical vertebra: one at the tip of the spinous process; one at the tip of each transverse process; and two anular epiphyses (ring epiphyses), one on the superior and one on the inferior edges of each vertebral body (i.e., around the margins of the superior and inferior surfaces of the vertebral body). The hyaline anular epiphyses, to which the IV discs attach, are sometimes referred to as epiphysial growth plates and form the zone from which the vertebral body grows in height. When growth ceases early in the adult period, the epiphyses usually unite with the vertebral body. This union results in the characteristic smooth raised margin, the epiphysial rim, around the edges of the superior and inferior surfaces of the body of the adult vertebra. All secondary ossification centers have usually united with the vertebrae by age 25; however, the ages at which specific unions are made vary.  Variations in Vertebrae Most people have 33 vertebrae, but developmental errors may result in 32 or 34 vertebrae. Estimates of the frequency of abnormal numbers of vertebrae superior to the sacrum (the normal number is 24) range between 5% and 12%. Variations in vertebrae are affected by race, gender, and developmental factors (genetic and environmental). An increased number of vertebrae occurs more often in males and a reduced number occurs more frequently in females. Variations in the number of vertebrae may be clinically important: An increased length of the presacral region of the vertebral column increases the strain on the inferior part of the lumbar region of the column owing to the increased leverage. Most numerical variations are incidental findings diagnostic medical imaging studies being performed for other reasons during dissections and autopsies of persons with no history of back problems.  Caution is necessary when describing an injury Variations in E.g. when reporting the site of a vertebral fracture When counting the vertebrae, begin at the base of Vertebrae the neck. The number of cervical vertebrae (seven) is remarkably constant. Numerical variation of thoracic and lumbar vertebrae Persons with >5 Lumbar vertebrae = compensatory decrease in thoracic vertebrae. Variations in vertebrae also involve: Relationship between the vertebrae and ribs, and the number of vertebrae that fuse to form the sacrum Presacral vertebrae to ribs and/or sacrum may occur higher (cranial shift) or lower (caudal shift) than normal. A C7 vertebra articulating with a rudimentary cervical rib(s) is still considered a cervical vertebra, same for lumbar vertebrae and lumbar ribs An L5 vertebra fused to the sacrum is referred to as a “sacralized 5th lumbar vertebra”  Vertebral Column Generally made up of 33 vertebrae and the components that unite them into a single structural, functional entity—the “axis” of the axial skeleton. It provides the semirigid, central “core” about which movements of the trunk occur “soft” or hollow structures that run a longitudinal course are subject to damage or kinking (e.g., the spinal cord, descending aorta, venae cavae, thoracic duct, and esophagus). Hence they lie in close proximity to the vertebral axis, where they receive its semirigid support and torsional stresses on them are minimized. Joints of Vertebral Column Joints of the vertebral bodies. Joints of the vertebral arches Craniovertebral (atlanto-axial and atlanto-occipital) joints. Costovertebral joints. Sacroiliac joints. Joints of Vertebral Bodies The joints of the vertebral bodies are symphyses (secondary cartilaginous joints) designed for weight-bearing and strength. Articulating surfaces of adjacent vertebrae connected by IV discs and ligaments.  Intervertebral Discs The IV discs provide strong attachments between the vertebral bodies, uniting them into a continuous semirigid column and forming the inferior half of the anterior border of the IV foramen. ▪ IV disc is a cushionlike pad composed of an inner sphere, the nucleus pulposus (pul-posus; “pulp”), and an outer collar of about 12 concentric rings, the anulus fibrosus (an u-lus fi-bro sus; “fibrous ring”). ▪ Each nucleus pulposus is gelatinous and acts like a rubber ball, enabling the spine to absorb compressive stress. ▪ In the anulus fibrosus, the outer rings consist of ligament and the inner ones consist of fibrocartilage. ▪ The discs are thickest in the lumbar (lower back) and cervical (neck) regions of the vertebral column. ▪ It permits movement between adjacent vertebrae, their resilient deformability allows them to serve as shock absorbers.  Joints of Vertebrae The anulus becomes decreasingly vascularized centrally, and only the outer third of the anulus receives sensory innervation. At birth, these pulpy nuclei are about 88% water and are initially more cartilaginous than fibrous. The pulpy nuclei become broader when compressed and thinner when tensed or stretched (as when hanging or suspended). Compression and tension occur simultaneously in the same disc during anterior and lateral flexion and extension of the vertebral column. The nucleus pulposus is avascular; it receives its nourishment by diffusion from blood vessels at the periphery of the anulus fibrosus and vertebral body. There is no IV disc between C1 and C2 vertebrae; the most inferior functional disc is between L5 and S1 vertebrae.  Uncovertebral Joints Uncovertebral “joints” or clefts (of Luschka) commonly develop between the unci of the bodies of C3 or 4–C6 or 7 vertebrae and the beveled inferolateral surfaces of the vertebral bodies superior to them after 10 years of age. The joints are at the lateral and posterolateral margins of the IV discs. The articulating surfaces of these joint-like structures are covered with cartilage moistened by fluid contained within an interposed potential space, or “capsule.” They are considered synovial joints by some; others consider them to be degenerative spaces (clefts) in the discs occupied by extracellular fluid. The uncovertebral joints are frequent sites of bone spur formation in later years, which may cause neck pain. Ligaments of the Vertebral Column The anterior longitudinal ligament is a strong, broad fibrous band that covers and connects the anterolateral aspects of the vertebral bodies and IV discs. It extends longitudinally from the pelvic surface of the sacrum to the anterior tubercle of vertebra C1 and the occipital bone anterior to the foramen magnum, the superior most parts specified as the anterior atlanto-axial and atlanto-occipital ligaments. Although thickest on the anterior aspect of the vertebral bodies it also covers the lateral aspects of the bodies to the IV foramen. It functions in prevention of hyperextension of the vertebral column, maintaining stability of the joints between the vertebral bodies. It is the only ligament that limits extension; all other IV ligaments limit forms of flexion. Ligaments of the Vertebral Column The posterior longitudinal ligament is a much narrower, somewhat weaker band than the anterior longitudinal ligament Runs within the vertebral canal along the posterior aspect of the vertebral bodies. It is attached mainly to the IV discs and less so to the posterior aspects of the vertebral bodies from C2 to the sacrum, often bridging fat and vessels between the ligament and the bony surface. This ligament weakly resists hyperflexion of the vertebral column and helps prevent or redirect posterior herniation of the nucleus pulposus. It is well provided with nociceptive (pain) nerve endings.  Joints of Vertebral Arches Zygapophysial joints The joints of the vertebral arches are the zygapophysial joints (often called facet joints). These articulations are plane synovial joints between the superior and inferior articular processes (G. zygapophyses) of adjacent vertebrae. Each joint is surrounded by a thin joint capsule. Those in the cervical region are especially thin and loose, reflecting the wide range of movement. The capsule is attached to the margins of the articular surfaces of the articular processes of adjacent vertebrae. Accessory ligaments unite the laminae, transverse processes, and spinous processes and help stabilize the joints. The zygapophysial joints permit gliding movements between the articular processes; the shape and disposition of the articular surfaces determine the types of movement possible. The range (amount) of movement is determined by the size of the IV disc relative to that of the vertebral body. In the cervical and lumbar regions, these joints bear some weight, sharing this function with the IV discs, particularly during lateral flexion. The zygapophysial joints are innervated by articular branches that arise from the medial  Accessory Ligaments Of Intervertebral Joints The laminae of adjacent vertebral arches are joined by broad, pale yellow bands of elastic tissue called the ligamenta flava (L. flavus, yellow). Long, thin, and broad in the cervical region, thicker in the thoracic region, and thickest in the lumbar region. Resist separation of the vertebral lamina by limiting abrupt flexion of the vertebral column, and thereby prevent injury to the IV discs. The strong elastic flaval ligaments help preserve the normal curvatures of the vertebral column and assist with straightening of the column after flexing. Accessory Ligaments Of Intervertebral Joints Adjoining spinous processes are united by weak, often membranous interspinous ligaments and strong fibrous supraspinous ligaments. The thin interspinous ligaments connect adjoining spinous processes, attaching from the root to the apex of each process. The cord-like supraspinous ligaments, which connect the tips of the spinous processes from C7 to the sacrum, merge superiorly with the nuchal ligament at the back of the neck (Fr. nuque, back of neck). Unlike the interspinous and supraspinous ligaments, the strong, broad, nuchal ligament (L. ligamentum nuchae) is composed of thickened fibroelastic tissue, extending as a median band from the external occipital protuberance and posterior border of the foramen magnum to the spinous processes of the cervical vertebrae. Because of the shortness and depth of the C3–C5 spinous processes, the nuchal ligament provides attachment for muscles that attach to the spinous processes of vertebrae at other levels. Accessory Ligaments Of Intervertebral Joints The intertransverse ligaments, connecting adjacent transverse processes, consist of scattered fibers in the cervical region and fibrous cords in the thoracic region. In the lumbar region these ligaments are thin and membranous. Craniovertebral Joints There are two sets of craniovertebral joints, the atlantooccipital joints, formed between the atlas (C1 vertebra), and the occipital bone of the cranium, and the atlanto-axial joints, formed between the atlas and axis (C2 vertebra). The craniovertebral joints are synovial joints that have no IV discs. The articulations involve the occipital condyles, atlas, and axis. Membranes of craniovertebral joints. A. Only the thicker, most anterior part of the anterior longitudinal ligament is included here to demonstrate its superior continuation as the anterior atlanto-axial membrane and anterior atlanto-occipital membrane. Laterally, the membranes blend with the joint capsules of the lateral atlanto-axial and atlantooccipital joints. B. The posterior atlanto-occipital and atlanto-axial membranes span the gaps between the posterior arch of the atlas (C1) and the occipital bone (posterior margin of the foramen magnum) superiorly, and the laminae of the axis (C2) inferiorly. The vertebral arteries penetrate the atlanto-occipital membrane before traversing the foramen magnum C. The articulated atlas and axis  Movements of the Vertebral Column The range of movement of the vertebral column varies according to the region and the individual. Contortionists, who begin their training during early childhood, become capable of extraordinary movements. The normal range of movement possible in healthy young adults is typically reduced by 50% or more as they age. The mobility of the vertebral column results primarily from the compressibility and elasticity of the IV discs. The vertebral column is capable of flexion, extension, lateral flexion and extension, and rotation (torsion). Bending of the vertebral column to the right or left from the neutral (erect) position is lateral flexion; returning to the erect posture from a position of lateral flexion is lateral extension.  Movements of the Vertebral Column The range of movement of the vertebral column is limited by the: Thickness, elasticity, and compressibility of the IV discs. Shape and orientation of the zygapophysial joints. Tension of the joint capsules of the zygapophysial joints. Resistance of the back muscles and ligaments (e.g., the ligamenta flava and the posterior longitudinal ligament). Attachment to the thoracic (rib) cage. Bulk of surrounding tissue. Movements are not produced exclusively by the back muscles. They are assisted by gravity and the action of the anterolateral abdominal muscles. Movements between adjacent vertebrae occur at the resilient nuclei pulposi of the IV discs (serving as the axis of movement) and at the zygapophysial joints. Except in C1–C2, movement never occurs at a single segment of the column. Movements of the Vertebral Column Movements of the vertebral column are freer in the cervical and lumbar regions than elsewhere. Flexion, extension, lateral flexion, and rotation of the neck are especially free because the: IV discs, although thin relative to most other discs, are thick relative to the size of the vertebral bodies at this level. Articular surfaces of the zygapophysial joints are relatively large and the joint planes are almost horizontal. Joint capsules of the zygapophysial joints are loose. Neck is relatively slender (with less surrounding soft tissue bulk compared with the trunk).  Movements of the Vertebral Column Flexion of the vertebral column is greatest in the cervical region. The sagittally oriented joint planes of the lumbar region are conducive to flexion and extension. Extension of the vertebral column is most marked in the lumbar region and is usually more extensive than flexion; however, the interlocking articular processes here prevent rotation The lumbar region, like the cervical region, has IV discs that are large relative to the size of the vertebral bodies. Lateral flexion of the vertebral column is greatest in the cervical and lumbar regions.  Movements of the Vertebral Column The thoracic region The thoracic region, in contrast, has IV discs that are thin relative to the size of the vertebral bodies. Relative stability is also conferred on this part of the vertebral column through its connection to the sternum by the ribs and costal cartilages. The joint planes here lie on an arc that is centered on the vertebral body, permitting rotation in the thoracic region. This rotation of the upper trunk, in combination with the rotation permitted in the cervical region and that at the atlanto-axial joints, enables the torsion of the axial skeleton that occurs as one looks back over the shoulder. However, flexion is limited in the thoracic region, including lateral flexion Curvatures of the Vertebral Column The vertebral column in adults has four curvatures that occur in the cervical, thoracic, lumbar, and sacral regions. The thoracic and sacral kyphoses (singular = kyphosis) are concave anteriorly, whereas the cervical and lumbar lordoses (singular = lordosis) are concave posteriorly. When the posterior surface of the trunk is observed, especially in a lateral view, the normal curvatures of the vertebral column are especially apparent. The thoracic and sacral kyphoses are primary curvatures that develop during the fetal period in relationship to the (flexed) fetal position. Curvatures of the Vertebral Column The Primary Curvatures are retained throughout life as a consequence of differences in height between the anterior and posterior parts of the vertebrae. The cervical and lumbar lordoses are secondary curvatures that result from extension from the flexed fetal position. They begin to appear during the late fetal period but do not become obvious until infancy. Secondary curvatures are maintained primarily by differences in thickness between the anterior and the posterior parts of the IV discs. The cervical lordosis becomes fully evident when an infant begins to raise (extend) its head while prone and to hold its head erect while sitting. The lumbar lordosis becomes apparent when toddlers begin to assume the upright posture, standing and walking. This curvature, generally more pronounced in females, ends at the lumbosacral angle formed at the junction of L5 vertebra with the sacrum. The sacral kyphosis also differs in males and females, that of the female reduced so that the coccyx protrudes less into the pelvic outlet. Curvatures of the Vertebral Column The curvatures of the vertebral column provide additional flexibility (shock-absorbing resilience), further augmenting that provided by the IV discs. Carrying additional weight anterior to the body’s normal gravitational axis (e.g., abnormally large breasts, a pendulous abdomen in men or during late pregnancy, or carrying a young child) also tends to increase these curvatures. When sitting, especially in the absence of back support for long periods of time, one usually “cycles” between back flexion (slumping) and extension (sitting up straight) to minimize stiffness and fatigue. This allows alternation between the active support provided by the extensor muscles of the back and the passive resistance to flexion provided by ligaments. Vasculature of Vertebral Column Vertebrae are supplied by periosteal and equatorial branches of the major cervical and segmental arteries and their spinal branches. Parent arteries of periosteal, equatorial, and spinal branches occur at all levels of the vertebral column, in close association with it, and include the following arteries: Vertebral and ascending cervical arteries in the neck The major segmental arteries of the trunk: Posterior intercostal arteries in the thoracic region, Subcostal and lumbar arteries in the abdomen and Iliolumbar, lateral and medial sacral arteries in the pelvis. Vasculature of Vertebral Column Periosteal and equatorial branches arise from these arteries as they cross the external (anterolateral) surfaces of the vertebrae. Spinal branches enter the IV foramina and divide. Smaller anterior and posterior vertebral canal branches pass to the vertebral body and vertebral arch, respectively, and give rise to ascending and descending branches that anastomose with the spinal canal branches of adjacent levels. Anterior vertebral canal branches send nutrient arteries anteriorly into the vertebral bodies that supply most of the red marrow of the central vertebral body. The larger branches of the spinal branches continue as terminal radicular or segmental medullary arteries distributed to the posterior and anterior roots of the spinal nerves and their coverings and to the spinal cord, respectively.  Vasculature of Vertebral Column Spinal veins form venous plexuses along the vertebral column(inside and outside the vertebral canal) Internal vertebral venous plexuses (epidural venous plexuses) and external vertebral venous plexuses. These plexuses communicate through the intervertebral foramina. Both plexuses are densest anteriorly and posteriorly and relatively sparse laterally. The large, tortuous basivertebral veins form within the vertebral bodies. emerge from foramina on the surfaces of the vertebral bodies (mostly the posterior aspect) and drain into the anterior external and especially the anterior internal vertebral venous plexuses, which may form large longitudinal sinuses. The intervertebral veins receive veins from the spinal cord and vertebral venous plexuses as they accompany the spinal nerves through the IV foramina to drain into the vertebral veins of the neck and segmental (intercostal, lumbar, and sacral) veins of the trunk.  Nerves of Vertebral Column Other than the zygapophysial joints (innervated by articular branches of the medial branches of the posterior rami, as described with these joints), the vertebral column is innervated by (recurrent) meningeal branches of the spinal nerves. These rarely described or depicted branches are the only branches to arise from the mixed spinal nerve, arising immediately after it is formed and before its division into anterior and posterior rami, or from the anterior ramus immediately after its formation.  Nerves of Vertebral Column As the spinal nerves exit the IV foramina, most of the meningeal branches run back through the foramina into the vertebral canal (hence the alternate term recurrent). However, some branches remain outside the canal and are distributed to the anterolateral aspect of the vertebral bodies and IV discs.  Nerves of Vertebral Column They also supply the periosteum and especially the annuli fibrosi and anterior longitudinal ligament. Inside the vertebral canal, transverse, ascending, and descending branches distribute nerve fibers to the: Periosteum (covering the surface of the posterior vertebral bodies, pedicles, and laminae). Ligamenta flava. Anuli fibrosi of the posterior and posterolateral aspect of the IV discs. Posterior longitudinal ligament. Spinal dura mater. Blood vessels within the vertebral canal. Nerve fibers to the periosteum, anuli fibrosi, and ligaments supply pain receptors. Those to the anuli fibrosi and ligaments also supply receptors for proprioception (the sense of one’s position). Sympathetic fibers to the blood vessels stimulate vasoconstriction The End!