Neuroanatomy 3 ASYNCHRONOUS Spinal Cord (External Internal Features).pdf

Spinal Cord (External & Internal Features) (E-Learning Module) Presented By: Dr. M. Doroudi; [email protected] Link to this module recording Boucher Campus: https://ccnm.ca.panopto.com/Panopto/Pages/Viewer.aspx?id=7eb888a 5-d940-4dc0-802f-af54006f4570&instance=Moodle Toronto Campus: https://ccnm.ca....

Spinal Cord (External & Internal Features) (E-Learning Module) Presented By: Dr. M. Doroudi; [email protected] Link to this module recording Boucher Campus: https://ccnm.ca.panopto.com/Panopto/Pages/Viewer.aspx?id=7eb888a 5-d940-4dc0-802f-af54006f4570&instance=Moodle Toronto Campus: https://ccnm.ca.panopto.com/Panopto/Pages/Viewer.aspx?id=cfba4dca -2342-41eb-9e8d-af54006f51e8&instance=Moodle Spinal Cord The spinal cord is the terminal cord-like part of the CNS located in the vertebral canal. Its length is about 43 to 45 cm, occupying the vertebral canal's upper two-thirds. The spinal cord starts from the medulla oblongata at the level of the foramen magnum and ends at the level of the L1/L2 intervertebral disc. However, it extends as low as the level of the L3 vertebra in newborn infants. This difference is because elongation of the spinal cord stops at the age of 4 – 5, but the growth of the vertebral column continues. External Features of the Spinal Cord The spinal cord, when viewed externally, looks like a cylinder with two enlargements in its cervical and lumbar regions. The cervical enlargement gives rise to the nerves innervating the upper limbs, whereas the nerves arising from the lumbar (lumbosacral) enlargement supply the lower limbs. The spinal cord tapers down inferior to the lumbar enlargement forming the conus medullaris. External Features of the Spinal Cord On the surface of the spinal cord, two main longitudinal grooves – the ventral (anterior) median fissure and dorsal (posterior) median sulcus – can be identified. On either side of the ventral median fissure, the ventral (motor) rootlets of the spinal nerves emerge. On either side of the dorsal median sulcus, the dorsal (sensory) rootlets of the spinal nerves emerge. The ventral rootlets join to form the ventral (motor) root of the spinal nerves. In the same way, the dorsal rootlets merge to form the dorsal (sensory) root of the spinal nerves. Each dorsal root of the spinal nerve is associated with a ganglion, the dorsal root ganglion, housing the cell bodies of the sensory neurons. Each spinal nerve is formed by the union of the ventral and dorsal roots. The section of the spinal cord that gives rise to a pair of spinal nerves is known as a spinal cord segment; thus, there are 31 spinal cord segments, including: v v v v v 8 cervical segments, C1-C8 12 thoracic segments, T1-T12 5 lumbar segments, L1-L5 5 sacral segments, S1-S5 1 coccygeal segment, Co External Features of the Spinal Cord Spinal Cord Segments & Nerves vSince the spinal cord ends at the level of vertebra LI-LII, the ventral and dorsal roots of the lumbar, sacral, and coccygeal spinal nerves descend to the respective foramina before emerging from the vertebral canal. This bundle of roots is known as cauda equina (horse’s tail). Somatic Nerve Plexuses Internal Features of the Spinal Cord Like the other parts of the CNS, the spinal cord consists of gray matter and white matter. The gray matter of the spinal cord is shaped like the letter “H” with a ventral (anterior) horn and a dorsal (posterior) horn on each side. The right and left halves of the gray matter are connected by a narrow strip, gray commissure, containing the central canal. In some segments of the spinal cord – T1 to L2 and S2 to S4 – there is a third horn between the ventral and dorsal horns known as the lateral horn. The lateral horns of T1 to L2 segments carry the cell bodies of the sympathetic neurons, whereas the lateral horns of S2 to S4 segments house the cell bodies of the parasympathetic neurons. The ventral horns contain the cell bodies of the motor neurons whose axons form the motor (ventral) roots of the spinal nerves. The dorsal horns contain the cell bodies of the sensory neurons. These neurons receive information from the sensory neurons residing in the dorsal root ganglia, whose axons form the dorsal root of the spinal nerves. Internal Features of the Spinal Cord The white matter of the spinal cord surrounds the gray matter and is organized as ventral, lateral, and dorsal columns (funiculi) on each half of the spinal cord. These three columns contain bundles of myelinated nerve fibres (tracts) that travel along the length of the spinal cord. There are two main groups of tracts in the white matter of the spinal cord: 1.The ascending (sensory) tracts convey the messages from the periphery to the upper centers of the nervous system, e.g. dorsal (posterior) spinocerebellar tract, dorsal column (medial lemniscus) tract, and lateral spinothalamic tract. 2.The descending (motor) tracts convey messages from the upper centers of the nervous system to the periphery, e.g. lateral and ventral corticospinal tracts.