Spinal Cord - Internal Structure - AN5203 PDF

Spinal Cord – Internal Structure AN5203 Internal structure of the spinal cord Central gray matter and peripheral white matter Gray matter -Butterfly or H-shaped; contains central canal -Divided into three horns (or cell columns) on each side -Divided into cytoarchitectural areas – Rexed laminae Id...

Spinal Cord – Internal Structure AN5203 Internal structure of the spinal cord Central gray matter and peripheral white matter Gray matter -Butterfly or H-shaped; contains central canal -Divided into three horns (or cell columns) on each side -Divided into cytoarchitectural areas – Rexed laminae Identified in the middle 1950s by Swedish neuroscientist Bror Rexed -Contains nuclei White matter -Consists of bundles of myelinated fibers organized into ascending and descending tracts 2 INTERNAL ORGANIZATION • • White matter • Funiculi: dorsal, ventral, lateral • Ventral white commissure Decussation of spinothalamic tract Gray matter • Dorsal, ventral, lateral horns; intermediate gray; gray commissure; central canal • Mainly cell bodies, • glial cells, vessels, projections Neuron Types Each neuron cell body is one of 4 types 1. Motor - to skeletal, smooth, cardiac muscle and glands – Lateral horn preganglionic – Ventral horn - alpha, gamma 2. Interneuron - form circuits 3. Tract - axons project to higher centers 4. Propriospinal - axons ascend/descend to other cord segments, only a few levels so hug gray matter General Structure Gray Matter Lamination – 10 layers • I - VI Dorsal horn • I, II (substantia gelatinosa) Process nociception pain and tempurature • III, IV (nucleus proprius); innocuous input (everything but pain and temp) • V, VI nociceptive, visceral input • Interneurons synapse in many laminae and on many different neurons; contribute to general responsiveness of cord to afferent and efferent stimuli • Can go ant-post, superior-inf, medial-lateral • These are not “sensory” neurons Lamination – 10 layers Lamina VII • In intermediate gray and ventral horn • Clarke’s nucleus • IML cell column • Sacral autonomic nucleus Lamina IX clusters of nuclei • Alpha and gamma motor neurons • Lateral group - innervates the extremities, not in Thoracic cord • Medial group - innervates the axial muscles • Central - phrenic and accessory nuclei, only in cervical cord Lamina X - visceral input; nociceptive surrounds central canal Nuclei of the Spinal Cord (sensory) • Substantia gelatinosa, I, II nociception, spinothalamic relay • Nucleus Proprius- III, IV proprioception, touch, dorsal column relay • Dorsal Nucleus of Clarke-VII relay for spinocerebellar tract Nuclei-Lamina visceral/somatic sensory gray Nucleus proprius Substantia gelatinosa Clarke column / dorsal nucleus • C1 - 3 dorsal horn: site of convergence of trigeminal and cord afferents; basis for pain referral from the neck to trigeminal territory and vice versa [pp. 353-354] Phrenic nucleus (rexed lamina IX) • Extends from C3 to C5 • Innervation of diaphragm – “C3-C5 keep diaphragm alive” Spinal accessory nucleus (Rexed lamina IX) • From C1 to C6 • Gives rise to the spinal root of the spinal accessory nerve (CN XI) • Innervates the sternocleidomastoid and trapezius muscle Nuclei of the Spinal Cord (motor) • • Motor (GVE) VII Intermediolateral Cell Column-VII Preganglionic sympathetic neurons T1-L2 sympathetic (S2,3,4 parasympathetic is a nucleus, not lateral gray horn) Motor (GSE)- IX medial axial lateral extremities Cervical -Phrenic Nucleus C3-C5 -Spinal Accessory Nucleus C1-C5 Nuclei-Lamina Somatic motor gray (=ventral horn) Visceral motor grey (IML column) / intermedioMotor neurons of the lateral anterior horn nucleus Intermediolateral column T1-L2 White matter contains nerve fibers (ascending and descending) • divided into 3 myelinated funiculi (=columns) – dorsal – lateral – ventral • Regional characteristics – Cervical - oval; large ventral horn; large amount of white; dorsal intermediate sulcus present – Thoracic - small amount of gray; lateral horn; dorsal intermediate sulcus in upper thoracic segments – Lumbar - round shape; large horns – Sacral - mostly gray matter Vasculature • Spinal arteries • Anterior (unpaired) • In ventral median fissure • Posterior • Descend as 2 longitudinal channels on dorsolateral sulci • Reinforced by branches of segmental arteries (branches of arteries located distal to the IVF) Blood Supply Segmental Arteries (give rise to radiculomedullary arteries) • Although these arterial channels (anterior and posterior spinal arteries) may run the length of the spinal cord, they are not sufficient to supply the entire cord - Reinforced at intervals by segmental arteries arising from intercostal or lumbar arteries that follow the nerve roots (radicular arteries) to the spinal cord. Radiculomedullary Arteries reinforce spinal arteries Vasculature • Radiculomedullary – Anterior (5-10) • Reinforces anterior spinal artery • Great radicular/Artery of Adamkiewicz (artery of the lumbar enlargement) - Source of blood to lower 2/3 or 1/2 of the cord; enters from left, usually from posterior intercostal or lumbar artery, within the range of T8 -L3 roots • *Important to visualize before thoracic or abdominal surgery – Posterior (10 - 23) • Reinforces posterior spinal artery VASCULAR DISTRIBUTION • Anterior spinal ventral 2/3 • Ventral horns, spinothalamic tracts, corticospinal tracts • Posterior spinal dorsal 1/3 • Dorsal column and dorsal horns • Anterior spinal artery syndrome • Weakness, pain and temperature loss Venous Drainage (entire system is devoid of valves) • Anterior (3) and Posterior (3) veins • Receive blood from neural tissue • Drain into anterior and posterior radiculomedullary veins • Empty into epidural venous plexus Epidural Venous Plexus • Epidural (internal vertebral) plexus – Communicates superiorly with vertebral veins, dural venous sinuses, and venous channels – Drains into intervertebral veins and into the external vertebral venous plexus – Intervertebral veins drain into segmental veins – Route for infection spread or metastasis Route for infection spread or metastasis