ANATOMY OF THE BACK

1. ANATOMY OF THE BACK BY DR. AHMAD K. SHAHWAN PH.D. GENERAL SURGERY

2. The Back The back, which extends from the skull to the tip of the coccyx, can be defined as the posterior surface of the trunk. Superimposed on the upper part of the posterior surface of the thorax are the scapulae and the muscles that connect the scapulae to the trunk

4. The Vertebral Column The vertebral column is the central bony pillar of the body. It supports the skull, pectoral girdle, upper limbs, and thoracic cage and, by way of the pelvic girdle, transmits body weight to the lower limbs. Within its cavity lie the spinal cord, the roots of the spinal nerves, and the covering meninges, to which the vertebral column gives great protection

5. The Vertebral Column It is composed of 33 vertebraea{7cervical, 12 thoracic, 5 lumbar, 5sacral (fused to form the sacrum), and 4 coccygeal (the lower 3 are commonly fused)}. Because it is segmented and made up of vertebrae, joints, and pads of fibrocartilage called intervertebraldiscs,It is a flexible structure. The intervertebral discs form about one fourth the length of the column.

7. General Characteristics of a Vertebra A typical vertebra consists of a rounded body anteriorly and a vertebral arch posteriorly. These enclose a space called the vertebral foramen, through which run the spinal cord and its coverings. The vertebral arch consists of a pair of cylindrical pedicles, which form the sides of the arch, and a pair of flattened laminae, which complete the arch posteriorly. The spinousprocess, or spine, is directed posteriorly from the junction of the two laminae. The transverseprocesses are directed laterally from the junction of the laminae and the pedicles. Both the spinous and transverse processes serve as levers and receive attachments of muscles and ligaments .

8. General Characteristics of a Vertebra Thearticular processesare vertically arranged and consist of two superior and two inferior processes. They arise from the junction of the laminae and the pedicles, and their articular surfaces are covered with hyaline cartilage. The two superior articular processes of one vertebral arch articulate with the two inferior articular processes of the arch above, forming two synovial joints The 1st cervical vert. called atlas while the 2nd cervical vert. called axis .

13. Sacrum The sacrumconsists of five rudimentary vertebrae fused together to form a wedge-shaped bone, which is concave anteriorly. The upper border, or base, of the bone articulates with the fifth lumbar vertebra. The narrow inferior border articulates with the coccyx. Laterally, the sacrum articulates with the two iliac bones to form the sacroiliac joints .The anterior and upper margin of the first sacral vertebra bulges forward as the posterior margin of the pelvic inlet and is known as thesacral promontory. . Coccyx The coccyx consists of four vertebrae fused together to form a single, small triangular bone that articulates at its base with the lower end of the sacrum . The first coccygeal vertebra is usually not fused or is incompletely fused with the second vertebra.

16. Curves of the Vertebral Column In the fetus, the vertebral column has one continuous anterior concavity(primarycurve ). As development proceeds, the lumbosacral angle appears. After birth, when the child becomes able to raise his or her head and keep it poised on the vertebral column, the cervical part of the vertebral column becomes concave posteriorly,towards the end of the first year, when the child begins to stand upright, the lumbar part of the vertebral column becomes concave posteriorly. The development of these secondarycurves is largely caused by modification in the shape of the intervertebral discs.

19. Movements of the Vertebral Column • The following movements are possible: flexion, extension, lateral flexion, rotation, and circumduction. • Flexionis a forward movement, andextensionis a backward movement. Both are extensive in the cervical and lumbar regions but restricted in the thoracic region. • Lateral flexionis the bending of the body to one or the other side. It is extensive in the cervical and lumbar regions but restricted in the thoracic region. • Rotationis a twisting of the vertebral column. This is least extensive in the lumbar region. • Circumductionis a combination of all these movements.

20. Spinal Cord The spinal cord is a cylindrical, grayish white structure that begins above at the foramen magnum, where it is continuous with the medullaoblongata of the brain. It terminates below in the adult at the level of the lower border of the first lumbar vertebra . Inferiorly, the spinal cord tapers off into theconus medullaris, from the apex of which a prolongation of the pia mater, thefilum terminale, descends to be attached to the back of the coccyx. Along the whole length of the spinal cord are attached 31pairs of spinal nerves by the anterior, or motor, roots and the posterior, or sensory, roots The spinal nerve roots pass laterally from each spinal cord segment to the level of their respective intervertebral foramina, where they unite to form a spinal nerve.

22. Because of the disproportionate growth in length of the vertebral column during development compared to that of the spinal cord, the length of the roots increases progressively from above downwardIn the upper cervical region the spinal nerve roots are short and run almost horizontally, but the roots of the lumbar and sacral nerves below the level of the termination of the cord (lower border of the first lumbar vertebra in the adult) form a vertical leash of nerves around the filum terminale. The lower nerve roots together are called thecauda equina

23. Meninges of the Spinal Cord The spinal cord, like the brain, is surrounded by three meninges: the dura mater, the arachnoid mater, and the pia mater. Dura Mater The dura mater is the most external membrane and is a dense, strong, fibrous sheet that encloses the spinal cord . It is continuous above through the foramen magnum with the meningeal layer of dura covering the brain. Inferiorly, it ends on the filum terminale at the level of the lower border of the second sacral vertebra

24. Arachnoid Mater The arachnoid mater is a delicate impermeable membrane covering the spinal cord and lying between the pia mater internally and the dura mater externally,It is separated from the dura by the subdural space that contains a thin film of tissue fluid. The arachnoid is separated from the pia mater by a wide space, thesubarachnoid space, which is filled withcerebrospinal fluid;The arachnoid is continuous above through the foramen magnum with the arachnoid covering the brain. Inferiorly, it ends on the filum terminale at the level of the lower border of the second sacral vertebra

25. Pia Mater The pia mater is a vascular membrane that closely covers the spinal cord. It is continuous above through the foramen magnum with the pia covering the brain; below it fuses with the filum terminale

29. Cerebrospinal Fluid The cerebrospinal fluid is a clear, colorless fluid formed mainly by thechoroid plexuses, within the lateral, third, and fourth ventricles of the brain. The fluid circulates through the ventricular system and enters the subarachnoid space through the three foramina in the roof of the fourth ventricle. It circulates both upward over the surface of the cerebral hemispheres and downward around the spinal cord. The spinal part of the subarachnoid space extends down as far as the lower border of the second sacral vertebra, where the arachnoid fuses with the filum terminale. Eventually, the fluid enters the bloodstream by passing through thearachnoid villiinto the dural venous sinuses,