Shelly Lwu Jan. 23, 2009 Spinal Cord Extends from foramen magnum to L1 or L2 vertebra in an adult Level / segments: Cervical 8 Thoracic 12 Lumbar 5 Sacral 5 Coccygeal 1 Each segment specified by the intervertebral foramina thru which the ant & post roots attached to that segment exit the vertebral canal Surface Features Anterolateral sulcus Posterior median sulcus Exit point for anterior roots Posterolateral sulcus Not as distinct as Entry point of dorsal roots posterolateral sulcus Runs full length of cord Anterior median fissure Posterior intermediate sulcus Prominent space dividing ant Found in cervical & upper part of cord into halves thoracic regions Contains delicate strands of Gracile fasciculus – medial pia & sulcal branches of anterior spinal artery Cuneate fasciculus – lateral Spinal Nerve Dorsal root Afferent fibers Cell bodies in dorsal root ganglia Ventral root Efferent fibers Cell bodies in ventral gray horns Dorsal & ventral nerve roots unite at points of exit from vertebral canal to form spinal nerve Spinal Meninges and Spaces Epidural space Dura mater Thecal sac at its caudal end (~S2 vertebra) is anchored to coccyx by filum terminale externum Spinal cord attached to thecal sac by: ○ Dentate ligaments ○ Filum terminale internum – extends caudally from conus medullaris to caudal attenuated portion of the dural sac Arachnoid mater Adheres to inner surface of dura Subarachnoid space Continuous w/ subarachnoid space around brain & filled w/ CSF Pia mater Intimately attached to surface of cord Sections Through Spinal Cord Levels assoc w/ limbs have greater amounts of gray matter White matter increases from caudal to rostral Level-by-level addition of ascending tracts & termination of descending tracts Regional Characteristics: Cervical Cervical Prominent post & ant horns b/c of extensive sensory input & motor outflow to upper & lower extremities Obvious oval shape Regional Characteristics: Thoracic Thoracic Large amount of white matter Both gracile & cuneate fasciculi present at upper thoracic levels (above T6); only gracile fasciculus present at lower thoracic levels (below T6) Posterior thoracic nucleus (dorsal nucleus of Clarke) – prominent cell group in medial parts of lamina VII, contains neurons of dorsal spinocerebellar tract Lateral horn formed by underlying intermediolateral cell column T1~L2,3 – preganglionic sympathetic cell bodies Regional Characteristics: Lumbar Lumbar Prominent post & ant horns Less white matter than at higher levels Cauda equina caudally Regional Characteristics: Sacral Sacral Cord round & small Consists mainly of gray matter w/ white matter forming relatively thin shell Intermediate gray S2~S4 – preganglionic parasympathetic cell bodies (less prominent) Substantia gelatinosa (lamina II) esp obvious White Matter 3 regions composed of tracts or fasciculi Dorsal funiculus: fasciculus cuneatus, fasciculus gracilis Lateral funiculus: lateral corticospinal tract, spinothalamic tract Ventral funiculus: reticulospinal tract, vestibulospinal tract, anterior corticospinal tract, medial longitudinal fasciculus Ascending Tracts Descending Tracts Somatotopic Organization of White Matter Tracts Gray Matter Dorsal horn – laminae I to VI Substantia gelatinosa (lamina I) Ventral horn – laminae VIII & IX Intermediate zone – lamina VII Posterior thoracic nucleus (dorsal nucleus of Clarke) Intermediolateral nucleus / cell column – T1 to L2 Composed of neuron cell bodies, dendrites, & initial part of axon, the axon terminals of fibers synapsing in this area, & glial cells Few myelinated fibers Based on shape, size, & distribution of neurons located in these areas, gray matter is divided into Rexed laminae I to IX, & area X around central canal Somatotopic Organization of the Ventral Horn Autonomic Nervous System Locations of neuronal cell bodies: Sympathetic Preganglionic – within intermediolateral cell column of T1~L2,3 Postganglionic – within sympathetic chain or ganglia Parasympathetic Preganglionic – within brainstem nuclei (CNs III, VII, IX, & X) & intermediolateral cell column of S2~3 Postganglionic – within intramural ganglion of the organ innervated Autonomic Nervous System Paravertebral location of the sympathetic chain Arterial Supply Anterior spinal artery Supplies ant 2/3 Posterior spinal arteries x 2 Supply post 1/3 Branches of vertebral arteries Radicular arteries Branches from aorta “Watershed zone” in midthoracic region Arterial Supply Radicular arteries – dorsal & ventral arteries supply the dorsal & ventral roots of the spinal nerves & their coverings Segmental medullary arteries – largely bypass roots to supplement blood supply to cord; occur irregularly in the place of radicular arteries Artery of Adamkiewicz – usually between T9 & L2 on L side & arises from an inferior intercostal or upper lumbar artery Arterial vasocorona – at each level, terminal branches of segmental medullary arteries join together to form an arterial network on surface of cord Central branches of ASA – tend to alternate serving L & R sides of cord 5 to 9 per segment of cord Arterial Supply Posterior columns & peripheral parts of lateral & anterior funiculi supplied by PSA’s & arterial vasocorona Most of gray matter & adjacent parts of white matter supplied by central branches of ASA Venous Drainage External & internal plexus of veins extend along length of vertebral column, forming a series of venous “rings” w/ extensive anastomoses around each vertebra Venous plexuses drain through intervertebral veins into vertebral, posterior intercostal, subcostal, & lumbar & lateral sacral veins References Felten DL & Jozefowicz RF. Netter’s Atlas of Human Neuroscience Haines DE, ed. Fundamental Neuroscience for Basic and Clinical Applications, 3rd ed. Moore KL & Dalley AF. Clinically Oriented Anatomy, 4th ed. Snell RS. Clinical Neuroanatomy for Medical Students, 5th ed. .