All vertebrae have a common structural pattern (Fig. 6-1), although variations exist between them. The thick, anterior, weight-bearing portion of a vertebra is the body or centrum The posterior, curved portion is the vertebral arch Together, the body and vertebral arch surround a central opening, the vertebral foramen When the vertebrae are stacked together, the vertebral foramina make a vertebral canal, which contains and protects the spinal cord. The vertebral arch is formed by the transverse processes, the spinous process, the pedicles, the laminae, and the superior and inferior articular processes. Transverse processes project laterally from the vertebral arch, and the spinous process is in the posterior midline. These processes are places for muscle attachment. The spinous processes can be felt as bony projections along the midline of the back. The portion of the vertebral arch adjacent to the body, between the body and the transverse process, is the pedicle A concave surface on the upper and lower margins of the pedicles is called the vertebral notch When the superior and inferior vertebral notches of adjacent vertebrae meet, they form intervertebral foramina, which transmit spinal nerves and blood vessels. The portion between the transverse process and the spinous process is the lamina Superior and inferior articular processes project superiorly and inferiorly, respectively, from the vertebral arch. The superior articular process of one vertebra articulates with the inferior articular process of the preceding vertebra in the column. Fig. 6-2 is a radiograph of cervical vertebrae that demonstrates some of these features.

Cervical Vertebrae

The seven cervical vertebrae are designated C1 through C7. In general, the cervical vertebrae (Figs. 6-3 and 6-4) can be distinguished from other vertebrae because the cervicals have transverse foramina in the transverse processes. The foramina allow passage of the vertebral arteries as they ascend through the neck to the brain. Also, the spinous processes of cervical vertebrae are forked, or bifid. The exception to this is the seventh cervical vertebra (C7), which has a long spinous process that typically is not bifid. The C7 spinous process is easily palpable at the base of the neck.

The first two cervical vertebrae are modified and have no disc between them. The atlas (C1), shown in Figs. 6-5 and 6-6, has no body and no spinous process, and it has short transverse processes. It is a ring that consists of an anterior arch, a posterior arch, and two large lateral masses that have large articular facets. The superior facets articulate with the occipital condyles on the occipital bone, and the inferior facets articulate with the vertebra below. The axis (C2), shown in Figs. 6-7 to 6-9, has a dens, or odontoid process, that projects upward from the vertebral body like a tooth. The odontoid process acts as a pivot for rotation of the atlas.

Thoracic Vertebrae

The 12 thoracic vertebrae are designated T1 through T12. These can be distinguished from other vertebrae by the costal facets, located on the bodies and transverse processes, for articulation with the ribs. The head of the rib articulates with the vertebral body, and the tubercle of the rib articulates with the transverse process. They also have long, pointed spinous processes. These features are illustrated in Fig. 6-10. The axial CT image in Fig. 6-11 shows the articulations of a thoracic vertebra with ribs. The sagittal CT image in Fig. 6-12 shows the long, pointed spinous processes that are typical of thoracic vertebrae.

Lumbar Vertebrae

The five lumbar vertebrae, designated L1 through L5, make up the part of the vertebral column in the small of the back. The lumbar vertebrae (Figs. 6-13 and 6-14) have large, heavy bodies because they support most of the body weight and have many back muscles attached to them. They also have short, blunt spinous processes. The sagittal MR image in Fig. 6-15 shows the thick, heavy bodies of the lumbar vertebrae and the intervertebral discs between the vertebrae.

Sacrum and Coccyx

The sacral region of the vertebral column (Fig. 6-16) consists of five vertebrae that fuse to form the sacrum The transverse processes of the vertebrae fuse to form the lateral masses (alae) which articulate with the pelvic girdle laterally at the sacroiliac joints Within the lateral masses, sacral foramina allow for passage of nerves. The first sacral segment has a prominent ridge, called the sacral promontory, on the visceral surface. The region inferior to this landmark is the true pelvic cavity. The spinous process of the S5 segment is absent, leaving an opening called the sacral hiatus The coronal CT image in Fig. 6-17 shows these features.

The coccyx, or tailbone, is the most inferior region of the vertebral column. The child has four separate small bones (the number can vary from three to five), which fuse to form a single bone in the adult. Several muscles have some point of attachment on the coccyx. The CT reconstruction in Fig. 6-18 shows features of the sacrum and coccyx.

QUICK CHECK

6.3. What feature distinguishes cervical vertebrae from all other types of vertebrae?

6.4. What is the primary distinguishing feature of thoracic vertebrae?

6.5. Where do the fused transverse processes of the sacral vertebrae articulate with the appendicular skeleton?

Intervertebral Discs

The intervertebral discs, located between the vertebral bodies, are fibrocartilaginous pads classified as symphysis joints; they are designed for strength. In addition to the discs, the vertebral bodies are joined by ligaments. Each disc consists of a soft central core, called the nucleus pulposus, and a firm outer ring, called the anulus fibrosus Fig. 6-19 illustrates an intervertebral disc. The sagittal MR image in Fig. 6-20 shows lumbar vertebrae with intervertebral discs. The nucleus pulposus acts as a shock absorber and as a ball bearing during flexion, extension, and lateral bending of the vertebral column. The anulus fibrosus is composed of rings of fibrocartilage that run obliquely from one vertebra to another to form strong bonds between the vertebrae. The intervertebral discs are thickest in the cervical and lumbar regions, which provides greater flexibility in these regions. As people get older, the nucleus pulposus may become thinner. This accounts for some of the loss of height that occurs as a result of aging. Changes also may occur in the anulus fibrosus that permit the nucleus pulposus to protrude through the outer ring; this is called a herniated disc (Fig. 6-21). The protrusion may compress an adjacent spinal nerve and cause pain in the lower back and/or leg.

Curvatures of the Vertebral Column

Normally, when viewed from the side (Fig. 6-22), the vertebral column has four curvatures. These curvatures increase the strength, resilience, and flexibility of the vertebral column. The thoracic curvature and the sacral curvature are concave anteriorly (convex posteriorly) and are present at birth. The cervical and lumbar curvatures are convex anteriorly (concave posteriorly). The cervical curvature develops when the baby holds its head erect, and the lumbar curvature develops when the child begins to stand. Fig. 6-23 is a radiograph of the lumbar spine that shows the anteriorly convex curvature. Several types of abnormal variations occur in the curvatures of the vertebral column. Some of these are congenital, whereas others may be due to poor posture, disease, or unequal muscle pull on the column. Scoliosis is an abnormal lateral curvature that most commonly occurs in the thoracic region. If left untreated, it may become severe and result in breathing difficulties. Kyphosis is an exaggerated dorsal curvature in the thoracic region. It is frequently seen in older individuals as a result of osteoporosis. It also may be due to a bone deformity known as rickets. Lordosis is an exaggerated lumbar curvature. This may occur temporarily in pregnant women when they throw back their shoulders and accentuate the lumbar curvature in an attempt to maintain their center of gravity. Fig. 6-24 illustrates abnormal spinal curvatures.

Ligaments of the Vertebral Column

The vertebral column is held in place by straplike ligaments. The major supporting ligaments are the anterior and posterior longitudinal ligaments The anterior longitudinal ligament begins at C1 and extends downward along the entire anterior surface of the vertebral bodies to the sacrum. It is strongly attached to the bony vertebral bodies and to the discs to maintain stability of the joints and to prevent hyperextension (bending too far backward). The posterior longitudinal ligament is a narrow ligamentous band that runs inside the vertebral canal, along the posterior surface of the vertebral bodies, for the entire length of the vertebral column. It is somewhat weaker than the anterior longitudinal ligament. The ligament is attached to the intervertebral discs and the posterior edges of the vertebral bodies. The posterior longitudinal ligament tends to prevent hyperflexion (bending too far forward) of the vertebral column. Ligamenta flava are short bands of yellow elastic fibers on each side of the spinous process. These ligaments connect the laminae of adjacent vertebrae and help to maintain the normal curvature of the vertebral column. The margins of adjacent spinous processes from C7 to the sacrum are joined by interspinous ligaments. Supraspinous ligaments join the tips of the spinous processes in the same region. From C7 upward to the occipital bone, the interspinous and supraspinous ligaments are represented by the ligamentum nuchae Intertransverse ligaments connect adjacent transverse processes. These consist of a few scattered ligamentous fibers, except in the lumbar region, where they are membranous. The ligaments associated with the vertebral column are summarized in Table 6-1. Fig. 6-25 illustrates some of the ligaments.

Muscles Associated With the Vertebral Column

The muscles associated with the back are arranged in three layers. The superficial and intermediate layers are extrinsic muscles and are concerned with respiration and movement of the limbs. These muscles, described in other portions of this book, include the trapezius, the latissimus dorsi, the levator scapulae, the rhomboids, and the serratus posterior. The deep muscle layer includes the true back muscles; these are the intrinsic muscles, which are concerned with the maintenance of posture and movements of the vertebral column. The intrinsic muscles are summarized in Table 6-2.

TABLE 6-2

Intrinsic Muscles Associated With the Vertebral Column

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1. Introduction to Sectional Anatomy
2. The Thorax
3. The Abdomen
4. The Pelvis

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Tags: The Sectional Anatomy Learning System Concepts and Applications

Jun 16, 2016 | Posted by admin in ANATOMY | Comments Off on The Vertebral Column, Spinal Cord, and Neck

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Muscle	Origin	Insertion	Function	Description
Superficial Layer
Splenius capitis	Ligamentum nuchae and spinous processes of C7 to T6	Mastoid process of temporal bone and adjacent occipital bone	Extend the head; rotate neck if one side contracts	Superficial intrinsic muscle in the neck
Splenius cervicis	Ligamentum nuchae and spinous processes of C7 to T6	Transverse processes of C2 to C4	Extend the head; rotate neck if one side contracts	Superficial intrinsic muscle in the neck
Intermediate Layer
Iliocostalis	Iliac crests and ribs	Angles of ribs and transverse processes of C4 to C6	Extend vertebral column to maintain posture; if one side contracts, column bends to that side	Most lateral column of the erector spinae muscle group
Longissimus	Transverse processes of lumbar through cervical vertebrae	Transverse processes of thoracic and cervical vertebrae, ribs superior to origin, and mastoid process of temporal bone	Extend vertebral column; if one side contracts, column bends to that side	Intermediate column of erector spinae muscle group
Spinalis	Spinous processes of upper lumbar and lower thoracic vertebrae	Spinous processes of upper thoracic and cervical vertebrae	Extend vertebral column	Most medial column of erector spinae muscle group
Deep Layer
Semispinalis	Transverse processes of C7 to T12	Occipital bone, spinous processes of cervical and thoracic vertebrae	Extend vertebral column	Composite muscle of deep layer; extends from thoracic region to head; part of the transversospinal group
Multifidus	Transverse processes of vertebrae	Spinous processes of preceding vertebrae	Stabilize vertebral column and rotate to opposite side	Short muscle bundles that pass superiorly over two to five vertebrae and then insert; part of the transversospinal group
Rotatores	Transverse processes of vertebrae	Spinous process of vertebra immediately superior to origin