1Chapter 12bSpinal CordOverview•Spinal cord gross anatomy•Spinal meninges•Sectional anatomy•Sensory pathways•Motor pathways•Spinal cord pathologiesThe Adult Spinal Cord•About 18 inches (45 cm) long•1/2 inch (14 mm) wide•CNS tissue ends between vertebrae L1and L2– At birth, cord and vertebrae are about the same size but cord stops elongating at around age 4•31 segments (31 pairs of spinal nerves)•Each pair of nerves exits the vertebral column at the level it initially lined up with at birthFigure 13-2Gross Anatomy of the SpinalCord Distal End• Conus medullaris: – thin, conical end of the spinal cord• Cauda equina:– nerve roots extending below conus medullaris• Filum terminale:– thin thread of fibrous tissue at end of conus medullaris– attaches to coccygeal ligamentSize of cord segments•The more superior, the more white matter. Why do you think this is?•Grey matter larger in cervical and lumbar regions. Why is this?
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231 Spinal Cord Segments•C8, T12, L5, S5, Co1•Based on vertebrae where spinal nerves originate •Positions of spinal segment and vertebrae change with age•Spinal nerves originally line up with their exit point from the cord.•Even after the vertebral column grows much longer, each pair of spinal nerves still exits at its original location, now several segments awayRoots•2 branches of spinal nerves:– ventral root:•contains axons of motor neurons– dorsal root:•contains axons of sensory neurons•Dorsal root ganglia:– contain cell bodies of sensory neurons– Pseudounipolar neurons - weirdDorsal Root GangliaDendritesSpinal Meninges•Specialized membranes isolate spinal cord from surroundings•Spinal meninges:– protect spinal cord– carry blood supply – continuous with cranial meningesFigure 13–3Spinal MeningesDura mater:outer layerArachnoidmater:middle layer Pia mater:inner layerThe Spinal Dura Mater•Are tough and fibrous • Cranially:– fuses with periosteum of occipital bone– continuous with cranial dura mater • Caudally:– tapers to dense cord of collagen fibers– joins filum terminalein coccygeal ligament (for longitudinal stability)