Flashcards in TBL2 - Vertebral Column Deck (22):
What does the axial skeleton include?
The skull, vertebral column (aka spine), ribs and sternum
What accounts for the height of the presacral vertebral column?
1) Vertebral bodies account for 75% of the height of the presacral vertebral column
2) Intervertebral (IV) discs occupy the remaining 25%
Describe 6 important positional descriptions of anatomy
1) Superior (cranial) - closer to the head
2) Inferior (caudal) - closer to the feet
3) Medial - Nearer to the median plane
4) Lateral - Farther from median plane
5) Posterior (dorsal) - Nearer to back
6) Anterior (ventral) - Nearer to the front
What is the structure of the vertebral column?
1) The vertebral arch is posterior to the vertebral body and consists of two (right and left) pedicles and laminae. The pedicles are short, stout cylindrical processes that project posteriorly from the vertebral body to meet two broad, flat plates of bone, called laminae, which unite in the midline (they help protect the spinal cord)
2) 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)
3) The canal contains the spinal cord and the roots of the spinal nerves, along with the membranes (meninges), fat, and vessels that surround and serve them
What are seven processes that arise from the vertebral arch of a typical vertebra?
1) One median spinous process projects posteriorly (and usually inferiorly, typically overlapping the vertebra below) from the vertebral arch at the junction of the laminae
2) Two transverse processes project posterolaterally from the junctions of the pedicles and laminae
3) 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)
What is the function of vertebral processes?
1) 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 vertebrae
2) The articular processes (superior & inferior) also assist in keeping adjacent vertebrae aligned, particularly preventing one vertebra from slipping anteriorly on the vertebra below
What is spondylolysis?
When spondylolysis—fracture of the column of bones connecting the superior and inferior articular processes (the pars interarticularis, or interarticular part)—occurs, the interlocking mechanism is broken
What is spondylolisthesis?
1) Failure or fracture of the interarticular parts of the vertebral laminae of L5 (spondylolysis of L5) especially may result in spondylolisthesis of the L5 vertebral body relative to the sacrum (S1 vertebra) due to the downward tilt of the L5/S1 IV joint
2) Spondylolisthesis at the L5–S1 IV joint may (but does not necessarily) result in pressure on the spinal nerves of the cauda equina as they pass into the superior part of the sacrum, causing lower back and lower limb pain
What are IV discs?
1) The articulating surfaces of adjacent vertebrae are connected by IV discs and ligaments
2) 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. Their resilient deformability provides shock absorbers for the spine as well
3) Each IV disc consists of an anulus fibrosus, an outer fibrous part, composed of concentric lamellae of fibrocartilage (Type 1 collagen fibers), and a gelatinous central mass, the nucleus pulposus
How do IV discs serve as a boundary for intervertebral foramina?
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 projections of the body anteriorly. The superior and inferior vertebral notches of adjacent vertebrae and the IV discs connecting them form intervertebral foramina (positioned on left and right sides of vertebral column) through which the spinal nerves emerge from the vertebral column. Also, the spinal (posterior root) ganglia are located in these foramina
Which clinical conditions might require a laminectomy and how is a laminectomy surgically performed?
1) The surgical excision of one or more spinous processes and the adjacent supporting vertebral laminae in a particular region of the vertebral column is called a laminectomy
2) The term is also commonly used to denote removal of most of the vertebral arch by transecting the pedicles
3) Laminectomies are performed surgically (or anatomically in the dissection laboratory) to gain access to the vertebral canal, providing posterior exposure of the spinal cord (if performed above the L2 level) and/or the roots of specific spinal nerves
4) Surgical laminectomy is often performed to relieve pressure on the spinal cord or nerve roots caused by a tumor, herniated IV disc, or bony hypertrophy (excess growth)
How does stenosis affect the lumbar portion of the vertebral canal and the lumbar spinal nerves?
1) Lumbar spinal stenosis describes a stenotic (narrow) vertebral foramen in one or more lumbar vertebrae. This condition may be a hereditary anomaly that can make a person more vulnerable to age-related degenerative changes such as IV disc bulging
2) Lumbar spinal nerves increase in size as the vertebral column descends, but paradoxically, the IV foramina decrease in size. Narrowing is usually maximal at the level of the IV discs. However, stenosis of a lumbar vertebral foramen alone may cause compression of one or more spinal nerve roots occupying the inferior vertebral canal
3) Surgical treatment of lumbar stenosis may consist of decompressive laminectomy
4) When IV disc protrusion occurs in a patient with spinal stenosis, it further compromises a vertebral canal that is already limited, as does arthritic proliferation and ligamentous degeneration
What is the function of the ligamenta flavum?
1) The flaval ligaments bind the lamina of the adjoining vertebrae together, forming alternating sections of the posterior wall of the vertebral canal
2) The ligamenta flava are long, thin, and broad in the cervical region, thicker in the thoracic region, and thickest in the lumbar region. These ligaments resist separation of the vertebral lamina by limiting abrupt flexion of the vertebral column, and thereby prevent injury to the IV discs
3) The strong, elastic yellow ligaments help preserve the normal curvatures of the vertebral column and assist with straightening of the column after flexing
What is the anterior longitudinal ligament?
1) The anterior longitudinal ligament is a ligament that runs down the anterior surface of the spine. It traverses all of the vertebral bodies and intervertebral discs.
2) The ligament is thick and slightly more narrow over the vertebral bodies and thinner but slightly wider over the intervertebral discs which is much less pronounced than that seen in the posterior longitudinal ligament
3) This ligament prevents hyperextension of the vertebral column, maintaining stability of the joints between the vertebral bodies. The anterior longitudinal ligament is the only ligament that limits extension; all other IV ligaments limit forms of flexion
What is the posterior longitudinal ligament?
1) The posterior longitudinal ligament is situated within the vertebral canal, and extends along the posterior surfaces of the bodies of the vertebrae, from the body of the axis, where it is continuous with the membrana tectoria, to the sacrum
2) It is broader above than below, and thicker in the thoracic than in the cervical and lumbar regions. The ligament is more narrow at the vertebral bodies and wider at the intervertebral disc space which is more pronounced than the anterior longitudinal ligament
3) It functions to prevent hyperflexion of the vertebral column
Describe the primary and secondary curvatures of the spine
1) The vertebral column in adults has four curvatures that occur in the cervical, thoracic, lumbar, and sacral regions. The thoracic and sacral kyphoses are concave anteriorly, whereas the cervical and lumbar lordoses are concave posteriorly
2) The thoracic and sacral kyphoses are primary curvatures that develop during the fetal period in relationship to the (flexed) fetal position
3) 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 (once an infant can lift his head and begins to walk). Secondary curvatures are maintained primarily by differences in thickness between the anterior and the posterior parts of the IV discs
Why do herniations of the nucleus pulposus usually protrude posterolaterally?
1) Herniations of the nucleus pulposus usually extend posterolaterally, where the anulus fibrosus is relatively thin, and does not receive support from either the posterior or the anterior longitudinal ligaments.
2) A posterolateral herniated IV disc is more likely to be symptomatic because of the proximity of the spinal nerve roots
What are primary causes of excessive kyphosis and lordosis? How does scoliosis differ in appearance from excessive kyphosis?
1) Abnormal curvatures in some people result from developmental anomalies; in others, the curvatures result from pathological processes. The most prevalent metabolic disease of bone occurring in the elderly, especially in women, is osteoporosis (atrophy of skeletal tissue)
2) Scoliosis (G., crookedness or curved back) is characterized by an abnormal lateral curvature that is accompanied by rotation of the vertebrae. The spinous processes turn toward the cavity of the abnormal curvature, and when the individual bends over, the ribs rotate posteriorly (protrude) on the side of the increased convexity
3) Excessive thoracic kyphosis (clinically shortened to kyphosis, although this term actually applies to the normal curvature, and colloquially known as humpback or hunchback) is characterized by an abnormal increase in the thoracic curvature; the vertebral column curves posteriorly. This abnormality can result from erosion (due to osteoporosis) of the anterior part of one or more vertebrae
What induces formation of the axial skeleton and neural tube? What does the notochord develop into?
1) Migrating mesodermal cells that initially invade the developing endoderm detach and form the notochord, a rigid rod of supporting mesoderm that induces formation of the axial skeleton and neural tube
2) The notochord (immediately below the neural tube) ultimately forms the nucleus pulposus of the IV discs
What does par-axial mesoderm form?
1) Paraxial mesoderm forms block-like somites adjacent to the notochord and neural tube
2) Mesenchymal cells of the somites differentiate into fibroblasts that form the annulus fibrosis of the IV discs and the dermis mainly associated with the vertebral column and thoracic wall (recall the epidermis is ectoderm derived)
3) Mesenchymal cell-derived myoblasts form skeletal muscles associated with the spine and thoracic wall
4) Mesenchymal cells also generate chondroblasts and osteoblasts that produce cartilage and bone, respectively. Chondroblasts and osteoblasts of the cervical, thoracic, lumbar, sacral, and coccygeal somites form the vertebrae of the respective segments of the vertebral column
What causes spina bifida occulta, the most common congenital anomaly of the vertebral column?
1) A common birth defect of the vertebral column is spina bifida occulta, in which the neural arches of L5 and/or S1 fail to develop normally and fuse posterior to the vertebral canal
2) Severe forms of spina bifida result from neural tube defects, such as the defective closure of the neural tube during the 4th week of embryonic development