Anatomy of the spinal cord
The spinal cord is the part of the central nervous system running inside the spinal column from which spinal nerves branch out.
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Our nervous system is divided into the central nervous system and the peripheral nervous system. The main components of the central nervous system are the brain and the spinal cord. The peripheral nervous system is composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves.
In the cervical region 8 pairs of nerves emerge from the spinal cord. There are 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and 1 pair of coccygeal nerves. The spinal cord ends in the lumbar region of the spinal column. The cauda equina or horse's tail is a bundle of spinal nerves. Spinal nerves are responsible for carrying information between the central nervous system and other parts of the body. The spinal cord is the center of many reflexes, such as the patellar reflex, and contains nerve fibers ascending to and descending from the brain.
The spinal cord is protected by the vertebrae. Nerves emerge above the transverse processes of the vertebrae. The elasticity of the intervertebral disks provide flexibility for the spinal cord.
The spinal cord - and the brain - are also protected by three layers of membranes, called meninges: the external dura mater, the arachnoid mater and the internal pia mater. The arachnoid mater is a thin membrane with a spiderweb-like structure, it is composed of fibrous tissue and contains cerebrospinal fluid. This fluid protects the central nervous system, providing a mechanical protection and decreasing the net weight of the brain.
The spinal cord consists of an external white substance and a gray, butterfly-shaped central region made up of nerve cell bodies. Nerve fibers make up pathways in the white matter. Ascending pathways contain sensory fibers that originate in the body, while descending pathways contain motor fibers that originate in the brain.
The color of the white matter is due to the myelin sheath that covers nerve fibers. The anterior horn of the gray matter contains the cell bodies of motoneurons. The axons of motoneurons, called motor fibers, emerge from the spinal cord through the anterior root. The sensory fibers enter the posterior horn of the gray matter through the posterior root. The central canal is filled with cerebrospinal fluid, it is continuous with the ventricular system of the brain.
Intervertebral disks consist of two main parts: the annulus fibrosus or fibrous ring and the nucleus pulposus or pulpy nucleus. As we age, the fibrous ring loses its flexibility and becomes vulnerable, increasing the risk of spinal disk herniation. A herniated disk may apply pressure to the spinal nerve or the spinal cord itself, which can cause pain, numbness, paresthesia, reflex disorders and paralysis, as well as problems with vegetative functions (such as urinary or fecal incontinence). Spinal disk herniation can be treated by exercise, by wearing a back brace, or with surgery.
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