Vertebral Column & Spinal Cord Lecture PDF

Vertebral Column and Spinal Cord DPM Program Learning Objectives: 1. Identify the major surface features and anatomical landmarks of the back. 4.0 2. List the functions of the vertebral column. 4.0 3. Differentiate between the primary and secondary curvatures of the spine. 3.0 4. Describe the osteol...

Vertebral Column and Spinal Cord DPM Program Learning Objectives: 1. Identify the major surface features and anatomical landmarks of the back. 4.0 2. List the functions of the vertebral column. 4.0 3. Differentiate between the primary and secondary curvatures of the spine. 3.0 4. Describe the osteological features of vertebrae. 4.0 5. Describe the osteological features of the atlas and axis. 3.0 6. Describe the osteological features of the sacrum and coccyx 4.0 7. Explain the structure and function of an intervertebral disc. 4.0 8. Describe the attachments and locations of the ligaments of the vertebral column. 4.0 9. Describe the intervertebral joints. 4.0 10. Explain the structure and function of the facet (zygapophyseal) joints and compare them in the cervical, thoracic, and lumbar regions. 3.0 11. Describe the boundaries of the intervertebral foramen and its contents. 4.0 12. Describe the atlanto-occipital and atlanto-axial joints with emphasis on their movements. 3.0 13. Describe the features of the vertebral column that control its mobility. 4.0 14. Contrast the movements found in the cervical, thoracic, and lumbar regions of the spine. 3.0 15. Describe the relationship between the vertebral levels and spinal cord levels in the adult and child. 4.0 16. Describe the major features of the spinal cord and meninges. 4.0 17. Diagram a transverse section through the vertebral canal demonstrating the meninges and the meningeal spaces. 4.0 18. Draw the structure of a typical spinal nerve. 4.0 19. Identify the spinal nerves in relation to the adjacent vertebrae above and below. 4.0 20. Describe the vascular supply and venous and lymphatic drainage of the back, vertebral column, and spinal cord. 3.0 Function of the Vertebral Column The vertebral column forms a highly mobile part of the axial skeleton (i.e., the skull, the vertebral column, the ribs, and the sternum) that extends from the base of the skull through the neck, thorax, abdomen, and pelvis to end at the sacroiliac region (i.e., the tip of the coccyx). As you already know the vertebral column consists of a series of vertebrae united by intervertebral articulations. FUNCTIONS 1. To protect the spinal cord and the roots of the spinal nerves. 2. To support the weight of the trunk and transmit it to the pelvis and the lower limbs (i.e., via the sacroiliac joints). 3. To maintain the posture of the trunk. 4. To assist in locomotion. 5. To provide attachment sites for numerous muscles. The Vertebral Column A series of bones arranged vertically separated by intervertebral discs forming the central axis of the axial skeleton. The vertebral column is composed of 33 bones in total -24 unfused vertebrae separated by the intervertebral discs and 5 fused vertebrae in the sacrum and variably 4 fused coccygeal vertebrae. 7 cervical vertebrae (CI-CVII) (T3) 12 thoracic vertebrae (TI-TXII) (L4) 5 lumbar vertebrae (LI-LV) (S2) Sacrum 5 fused sacral vertebra (I-V) Coccyx 3-4 fused coccygeal vertebra (I-IV) There are a number of clinical procedures that 3 require knowledge of the surface anatomy of the back. Curvature of the Vertebral Column The curvatures of the vertebrae can be clearly seen as two S-shaped curvatures across the spine from the lateral view. Early embryo Somites Concave primary curvature of back Secondary curvatures (lordoses) develop as a result of anteroposterior variations in IV disk thickness that occur with the developmental stages of raising the head and beginning to walk Primary Curvature: Thoracic Kyphosis & Sacral Kyphosis (exist during fetal life) Secondary Curvature: Cervical Lordosis & Lumbar Lordosis (develop after birth) 4 Definitions of the General Characteristics of Typical Vertebrae Body: (anteriorly located, weight bearing portion of the vertebra) Pedicles (2): arise posterolaterally from the vertebral body and form the “foot” processes of the vertebral arch Laminae (2): extend posteromedially from the pedicles and fuse in the midline to complete the vertebral arch and form the spinous process Superior articular processes (2): located on the superior surface of the pedicles Inferior articular processes (2): arise from the inferior surface of the pedicles Transverse processes (2): arise on each side of the vertebral arch where the pedicles and laminae fuse Spinous process (1): arise from the vertebral arch where the laminae fuse Vertebral foramen: the opening bounded by the body, pedicles, and laminae Vertebral canal: canal formed by the vertebral foramina (contains the spinal cord, meningeal coverings, and associated vessels) Superior Vertebral Notch: a shallow notch in the superior surface of the each pedicle Inferior Vertebral Notch: a deep notch in the inferior surface of each pedicle Intervertebral foramen: opening formed by the superior and inferior vertebral notches of adjacent vertebrae when the vertebrae are articulated (dorsal root ganglia of spinal nerves lies in in intervertebral foramina, the spinal nerves transmit through these foramina) General Characteristics of Typical Vertebrae Vertebrae of the vertebral column share similar characteristics. Unique characteristics of specific vertebrae will be discussed in the slides to follow. Superior view Superolateral oblique view 6 Cervical, Thoracic & Lumbar Vertebrae Cervical (C3-C7) Body: small, wide side to side Spinous process: short, bifid, projects directly posteriorly Vertebral foramen: triangular Transverse processes: contain foramina Articulating processes: transverse plane Movements allowed: flexion and extension; lateral flexion, rotation Allows for the greatest range of motion Thoracic (T1-T12) Body: larger than cervical; heart shaped; bears two costal facets Spinous process: long; sharp; projects inferiorly Vertebral foramen: circular Transverse processes: Bear facets for ribs (except T11 & T12) Articulating processes: coronal plane Movements allowed: rotation; flexion & extension Lumbar (L1-L5) Body: massive; kidney shaped Spinous process: short; blunt; projects directly posteriorly Vertebral foramen: triangular Transverse processes: thin & tapered Articulating processes: mid-sagittal plane Movements allowed: flexion & extension; lateral flexion; rotation prevented 7 Atlas (C1) and Axis (C2) ATLAS: The skull rests upon C1 which is named after Atlas, who, according to Greek mythology supported the heavens upon his shoulders. -Widest of the cervical vertebrae. -Lacks a body and spinous process. -The anterior arch possesses a prominent tubercle (i.e., anterior tubercle) for the attachment of the anterior longitudinal ligament and the Longus colli. - On the posterior surface of the anterior arch is an articular facet for the dens of the axis (C2). AXIS: Called the axis because it forms a pivot around which the atlas turns -Similar to the typical cervical vertebrae except that it has a superior projection from the body called the DENS (ODONTOID PROCESS). It articulates anteriorly with the anterior arch of the atlas. -It possesses a pair of large superior articular surfaces, or facets, for articulating with the atlas. -Spinous process is broad, heavy, and bifurcated. -Transverse processes are short and angled inferiorly. Unique Vertebrae: C1 & C2 and Joints Anterior tubercle Atlas (C1): Atlanto-occipital joint -between superior articular facets of atlas and occipital condyles of the cranial base Atlas (C1 vertebra) Transverse ligament of atlas Anterior arch Facet for dens Lateral mass Transverse process -Condyloid type of synovial joint allowing primarily for flexion/extension (with some lateral bending and rotation) -Reinforced by anterior and posterior atlanto-occipital membranes as well as the tectorial membrane (the superior continuation of the posterior longitudinal ligament) Foramen transversarium Facet for occipital condyle Posterior arch Posterior tubercle **permits flexion and extension (nodding) and tilting of the head sideways Superior view Superior view Apical ligament of dens Axis (C2):Atlanto-axial joint -Three joints that allow for rotation of skull and atlas on C2 (around dens) Dens Axis (CII vertebra) -Reinforced by alar ligaments, the cruciate ligament (composed of the transverse ligament of the atlas and the superior & inferior longitudinal bands) & the tectorial membrane Right & Left Lateral atlanto-axial joints: -between inferior facets of C1 and superior facets of C2 -Biconvex synovial joint Median atlanto-axial joint: -Between anterior arch of C1 and dens of C2 -Pivot type of synovial joint **permits the skull and atlas to be rotated (side to side as shaking your head no) as a unit on the axis Alar ligaments Transverse ligament of atlas Inferior longitudinal band of cruciform ligament Dens Superior view Posterior view Posterosuperior view 9 Joints of the Vertebral Column Symphyseal Joints-Intervertebral Discs SYMPHYSES (secondary cartilaginous joints): -intervertebral joints between vertebral bodies and containing intervertebral discs (IV discs). The discs are thickest in the lumbar regions. -NOTE: There is no IV disc between C1 &C2 - each IV disk is composed of: -Nucleus pulposus: -fills the center of the IV disc -gelatinous -absorbs the compression forces between vertebrae -Anulus fibrosus: -concentric layers of densely fibrous connective tissue that restrain the spread of the nucleus pulposus when the disc is enduring compressive forces -limits rotation between vertebrae -Connective tissue structure that allows for intervertebral motion and can sustain compressive loads. Functions: -binds the vertebral bodies together and provides stability -it allows motion between vertebral bodies -prevents excessive movement -acts as a shock absorbing mechanism 10 Joints of the Vertebral Column Synovial Joints SYNOVIAL JOINTS (diarthroses): - zygapophyseal joints (a.k.a. posterior IV joints/ facet joints) (plane synovial joints) -between superior articular facets of one vertebra and the inferior facets of the preceding vertebra Cervical “Sloped from anterior to posterior” Zygapophysial joint Lateral view Thoracic “Vertical” -Shape and disposition of facets determines direction of movement (and may limit movement) -In the cervical region, the column of these posterior intervertebral joints, on each side, is called an articular pillar -Uncovertebral joints (a.k.a. Lushka’s joints) -between uncinate processes of C3-C6 (C7) and the inferolateral surfaces of the vertebral bodies superior to them. -Some consider them to be degenerative spaces (rather than synovial joints) that occur when the IV disc has flattened and the vertebral bodies appose each other. Zygapophysial joint Lateral view Lumbar “Wrapped” Lateral view Zygapophysial joint -Common site of bone spur formation Superior view 11 Ligaments of the Vertebral Column Anterior Longitudinal Ligament -passes along the anterior surface of the vertebral bodies -Functions: -limit extension of the vertebral column -prevents hyperextension of the vertebral column (vulnerable to tearing i.e., whiplash) Posterior Longitudinal Ligament -attaches to the posterior borders of the vertebral bodies and IV discs Functions: -limit flexion of vertebral column -prevents hyperflexion of the vertebral column Ligamentum Flavum “yellow ligament” -strongest and most important of the posteriorly placed ligaments -connect to laminae Functions: -assist in the maintenance of the upright position -resume the upright position after flexion of the vertebral column Supraspinous Ligament -interconnect the tips of the spinous processes -Functions to limit the flexion of the vertebral column Interspinous Ligament -unite adjacent spinous processes, best developed in the lumbar region -functions to limit flexion of the vertebral column Primary Ligaments of the Vertebral Column The anterior longitudinal ligament is taut in extension of the vertebral column, all other listed ligaments are taut in flexion. 13 Sacrum and Coccyx Anterior View Dorsolateral View Posterior View Anatomy of the Spinal Cord The spinal cord extends from the foramen magnum to the level of the disc between vertebrae L1 and LII in adults. In neonates the spinal cord extends approximately to vertebra LIII. The apex of the spinal cord is the termination and is referred to as conus medullaris. Cervical enlargement Pedicles of vertebrae The dorsal and ventral roots below L1 and L2 continue to descend as a group of nerve fibers termed cauda equina. Cervical (C5-T1) and lumbosacral (L1-S3) enlargements are increases in the circumference of the spinal cord where regions of spinal nerves are going to supply the upper and lower limbs. Filum terminale consists of neuroglia and a prolongation of pia mater from the conus. The filum extends with the cauda equina to the level of S2, the point at which the subarachnoid space ends. It is at this level that the filum joins with dura and arachnoid mater. Conus medullaris Lumbosacral enlargement End of cord L1-L2 Pial part Filum terminale Dural part End of subarachnoid space S4 15 Relationship between Vertebral Levels in Adult and Child The spinal cord is housed in the vertebral canal. Up to about the third month of fetal life the spinal cord is the same length as the vertebral canal and the spinal nerves exit from the intervertebral foramina at the same level as their origin. Due to the fact that the vertebral column grows more rapidly than does the spinal cord, this relationship changes such that by the time of birth the end of the cord lies at the lower border of L3, and slightly higher in the adult (i.e., L1 – L2) As a result of the disparity between the length of the spinal cord and the vertebral column in the adult, the spinal segments do not necessarily lie at the level of the vertebra for which they and their nerves are numbered. This is especially evident for the roots of the spinal nerves of the lower levels. As an example, the roots for spinal nerve L5 come off the cord adjacent to vertebra T12 (or T11), but exits from the vertebral canal below L5. Consequently, the roots of the spinal nerves become increasingly longer as one goes inferiorly. Spinal Nerves There are 31 pairs of spinal nerves divided regionally: CERVICAL - 8 pairs (C1 – C8) THORACIC - 12 pairs (T1 – T12) LUMBAR - 5 pairs (L1 – L5) SACRAL - 5 pairs (S1 – S5) COCCYGEAL - 1 pair (Co1) For the most part the spinal nerves emerge through the intervertebral foramen below the vertebrae corresponding to them in number. The cervical region is an exception to the rule, however, for its eight nerves are associated with only seven cervical vertebrae, and the first cervical nerve emerges between the skull and the first vertebra. As a result, the cervical nerves correspond in number to the vertebrae below them, whereas all more caudal nerves are numbered with the vertebrae above them. Typical Spinal Nerve (transverse section) All spinal nerves have the following roots and branches (rami): -Dorsal root (consists of afferent fibers only) -Ventral root (for our purposes, efferent fibers only) -Posterior (Dorsal) primary ramus (branch) (mixed) -Anterior (Ventral) primary ramus (branch) (mixed) -Gray ramus (visceral efferent fibers) -Recurrent (meningeal) ramus (mixed) Typical Spinal Nerve (transverse section) Practice labeling and drawing Meninges Epidural space: -Contains fat, loose connective tissue, and the vertebral venous plexus, which is an important collateral channel connecting branches of the inferior vena cava and the dural venous sinuses Dura Mater: -A tough, tubular sheath or sac that lies free within the vertebral canal -Continuous with the meningeal layer of the cranial dura mater -Blends with the periosteal lining of each intervertebral foramen -Ends by blending with the epineurium of the spinal nerves -Narrows at the level of SII and forms an investing sheath for the pial part of the filum terminale; referred to as the dural part of the filum terminale Subarachnoid space: -Contains cerebrospinal fluid (CSF) -Continuous superiorly with the subarachnoid space surrounding the brain -Enlarges inferiorly after the spinal cord ends as the lumbar cistern vertebrae LII and SII; contains cauda equina and part of filum terminale Pia mater: -A vascular membrane that adheres to the surface of the spinal cord -Continuous with the denticulate ligaments (longitudinally oriented sheet that extends laterally from the cord to the arachnoid and dura) -Extends inferiorly to the conus medullaris and continues from the apex of the conus as the pial part of the filum terminale Arachnoid Mater: -A thin, delicate, avascular lining -Lies against but does not adhere to the deep surface of the dura mater -Covers the nerve roots and spinal ganglia and blends with the sheaths of the spinal nerves -Terminates at the level of SII -Connected to the pia by delicate strands of tissue called arachnoid trabeculae 20 The Spinal Meninges Subarachnoid space Posterior spinal artery Anterior spinal artery -Dura mater “hard mother” outermost tough layer -Arachnoid mater thin and “spiderweb” like held tight against the dura by pressure of CSF -Pia mater delicate layer lining the surface of the spinal cord 21 Arteries of the Vertebral Column The arterial supply to the vertebral column is derived from a number of arteries along its length. The major arteries and their respective branches may be summarized as follows: External Carotid Artery: -Occipital Artery (anastomoses with branches of deep cervical a.) -Ascending Pharyngeal Artery Subclavian Artery: -Vertebral Artery (anatomoses with branches of ascending cervical a.) -Inferior Thyroid Artery (Thyrocervical Trunk) -Transverse Cervical Artery (Thyrocervical Trunk) -Superior Intercostal Artery (Costocervical Trunk) -Deep Cervical Artery (Costocervical Trunk) Thoracic Aorta: -Posterior Intercostal Arteries (numbers 3 – 11) -Subcostal Artery Abdominal Aorta: -Lumbar Arteries (4 pairs) (4th lumbar a. anastomoses with branches of iliolumbar a.) -Median Sacral Artery (gives off the 5th pair of Lumbar Arteries) (anastomoses with branches of lateral sacral artery/internal iliac a.) Internal Iliac Artery: -Iliolumbar Artery -Lateral Sacral Artery Veins of the Vertebral Column a, b, c, & d identify the spinous & transverse processes and the body of the vertebra & the vertebral canal 1 is the anterior external vertebral venous plexus 2, the posterior external vertebral 2’, connections between the posterior internal vertebral, 4, and the posterior external vertebral 3, the anterior internal vertebral plexus 5, the major drainage of the vertebral body (basivertebral vein) 6, intervertebral veins and their tributaries Arteries of the Spinal Cord The spinal cord receives blood supply from 3 longitudinal vessels: -1 anterior spinal artery -formed by branches from vertebral aa. -passes inferiorly in the anterior median fissure of the spinal cord -supplies the gray matter of the anterior 2/3 of the cord -2 posterior spinal arteries -arise from either the vertebral or posterior inferior cerebellar arteries -supply the posterior 1/3 of the cord * these are not large vessels, they are segmentally supplemented by blood from arteries along the length of the spinal cord which are called radiular arteries Radicular arteries -run the entire length of the spinal cord because of small diameter they only supply blood to the superior cervical segments of the cord -enter the vertebral canal through the intervertebral foramina -the remainder of the cord receives its vascular supply from radicular aa. which arise from a number of vessels including the spinal branches of: -vertebral a, deep cervical a., ascending cervical a., posterior intercostal aa., lumbar aa., lateral sacral a. VENOUS DRAINAGE OF THE SPINAL CORD The venous drainage of the spinal cord consists of six longitudinally arranged veins—three ANTERIOR EXTERNAL SPINAL VEINS and three POSTERIOR EXTERNAL SPINAL VEINS—which are situated deep to the arachnoid mater and drain into the internal vertebral venous plexus. Anterior radicular artery Segmental spinal artery Posterior radicular artery Posterior spinal arteries Posterior radicular artery Anterior radicular artery Segmental medullary artery Segmental spinal artery Posterior branch of right posterior intercostal artery Segmental medullary artery Posterior branch of left posterior intercostal artery Anterior spinal artery Segmental spinal artery Left posterior intercostal artery Aorta Lymphatic Drainage of the Spinal Cord Deep Cervical Nodes -located along the IJV -revieve lymph directly from the cervical regions -deep cervical nodes form the jugular trunk that empties into the thoracic duct Axillary Nodes (subscapular group) -within the axilla -receives lymph from the skin and superficial mm. of the back of the neck and trunk -transported to subclavian vein Intercostal Nodes -lie near the heads of the ribs in each intercostal space -receive lymph from thoracic portion of the deep back -drain directly into cisterna chyli or thoracic duct Lateral Aortic Nodes -both sides of the abdominal aorta -receive lymph from posterolateral abdominal wall -drain into lumbar trunks which join cisterna chyli Internal Iliac and Sacral Nodes -surround internal iliac vessels -receive lymph from pelvic visceral and posterior pelvic wall -drain into common iliac nodes and lateral aortic nodes