Lecture - Spinal Cord

The Spinal Cord The spinal cord is a cylindrical greyish-white structure. It follows a relatively simple anatomical path: The spinal cord is born from the medulla oblongata (part of the brainstem). It then travels inferiorly within the vertebral canal, surrounded by spinal meninges that contain cerebrospinal fluid. The conus medullaris develops when the spinal cord tapers off at the L2 vertebral level. Because the spinal cord terminates at L2, it occupies approximately two-thirds of the vertebral canal. The spinal nerves that emerge from the end of the spinal cord form the cauda equina. There are two points of enlargement along the path of the spinal cord. The enlargement of the cervical spine is near the C4-T1 level. It represents the origin of the brachial plexus. The location of the spinal cord is indicated by two depressions on its surface. The anterior median fissure is a deep groove that runs along the anterior surface of the spinal cord. The posterior median sulcus is a shallower depression on the backside. The three membranes that surround the spinal cord are the dura mater, arachnoid mater, and pia mater. They contain cerebrospinal fluid, which supports and protects the spinal cord. The meninges form a strand of fibrous tissue known as the filum terminale, which connects to the vertebral bodies of the coccyx. It safeguards the spinal cord and meninges. The spinal dura mater is the most external of the meninges. The epidural space separates it from the vertebral canal walls as it runs from the foramen magnum to the filum terminale. As they exit the vertebral canal, the spinal nerves pierce the dura mater and briefly pass through the epidural space. As a result, the dura mater surrounds and fuses with the epineurium, the outer connective tissue covering of the nerve. The spinal arachnoid mater is a thin membrane that connects the dura and pia maters. It is separated from the latter by the subarachnoid space, which contains cerebrospinal fluid. Lumbar cisterns form when the subarachnoid space expands distal to the conus medullaris. This area is accessed during a lumbar puncture (to obtain CSF fluid) and spinal anaesthesia. The spinal pia mater is the innermost layer of the meninges. It is a thin membrane that shields the spinal cord, nerve roots, and blood vessels from damage. Inferiorly, the spinal pia mater fuses with the filum terminale. Denticulate ligaments form when the pia mater between the nerve roots thickens. These ligaments connect to the dura mater, which keeps the spinal cord in the vertebral canal. The spinal nerves are a collection of mixed nerves that branch out from the spinal cord to form the peripheral nervous system. Each spinal nerve has two roots: anterior (motor) and posterior (sensorimotor) (sensory). At the intervertebral foramina, these roots emerge from the spinal cord and join to form a single spinal nerve. The spinal nerve then exits the vertebral canal through intervertebral foramina and divides into two branches: The posterior rami sends nerve fibres to the synovial joints, deep back muscles, and skin of the vertebral column. The anterior rami provide nerve fibres to the majority of the remaining areas of the body, both motor and sensory. The cauda equina, or nerve bundle, is formed by the L2-S5 nerve roots emerging from the distal end of the spinal cord. The anterior spinal artery and the paired posterior spinal arteries supply blood to the spinal cord via three longitudinal arteries. The anterior spinal artery is a branch of the vertebral artery. They pass through the anterior median fissure. The posterior spinal arteries are formed by the vertebral or posteroinferior cerebellar arteries. In the pia mater, they anastamose with one another. The anterior and posterior segmental medullary arteries, which are small vessels that enter through the nerve roots, provide additional arterial supply. The Adamkiewicz artery is the largest anterior segmental medullary artery. The inferior intercostal or upper lumbar arteries form it, and it supplies the lower two-thirds of the spinal cord. Three anterior and three posterior spinal veins drain venous blood. These veins are valveless and form an anastamosing network along the spinal cord's surface. The radicular veins also supply them with venous blood. The spinal veins empty into the internal and external vertebral plexuses, which drain into the systemic segmental veins. Superiorly, the internal vertebral plexus drains into the dural venous sinuses.