The Spinal Cord - p67-75

The Spinal Cord - p67-75

1. External Features of Spinal Cord

   • Topographical Anatomy
     • CERICAL ENLARGEMENT C4-T1 provides innervations for the upper limp via BRACHIAL PLEXUS
     • LUMBAR ENLARGEMENT is made up of L1-S3 and innervates the lower limb via LUMBOSACRAL PLEXUS
       • Caudal to Lx enlargement the cord tapers abruptly to form
         • CONUS MEDULLARIS
           • From the tip a strand of connective tissue is attached to the dorsal surface of the 1st coccygeal vertebra
             • FILUM TERMINALE
     • In adult life the cord terminates between IVD L1 and L2
   • Spinal Nerves
     • 31 bilat paired spinal nerves
       • attach to spinal cord as dorsal and ventral roots, carrying afferent and efferent nerve fibres respectively
         • Cell bodies of AFFERENT neurons are located in DORSAL ROOT GANGLION
         • Cell bodies of EFFERENT neurons are in spinal GREY MATTER
       • Exit vertebral canal via intervertebral foramina
     • Below termination of cord, spinal nerve roots descend as
       • CAUDA EQUINA
     • Cord and nerve roots are susceptible to traumatic injury
       • cord is invested by 3 meninges
         • subarachnoid space contains CSF
           • CSF can be removed by a lumbar puncture at L2-3 or L3-4

2. Internal Structure of Spinal Cord

   • Spinal cord is divided into 2 halves
     • DORSAL MEDIAN SULCUS
     • VENTRAL MEDIAN FISSURE
   • In the centre of the cord is CENTRAL CANAL
     • Surrounding it is GREY MATTER
       • (consists of nerve cell bodies, their dendrites and synaptic contacts)
     • Outer part of cord consists of WHITE MATTER
       • (contains ascending and descending nerve fibres)
   • Grey Matter
     • H-shaped, with 4 protrusions
       • DORSAL HORN (posterior)
         • Attach zones of dorsal and ventral root fascicles
         • Many efferent nerve fibres entering dorsal roots terminate in dorsal horn
         • Afferent fibres entering dorsal horn divide into
           • ASCENDING AND DESCENDING BRANCHES
         • At the tip, close to Rexed lamina I-III is the
           • SUBSTANTIA GELATINOSA
             • Receives group A delta and C afferents associated with nociception
             • involved in GATE CONTROL THERORY of pain
         • Deeper is lamina VII contains no of important cell groups
           • At C8-L3 is
             • CLARKE'S COLUMN
               • Origin of ASCENDING FIBERS OF DORSAL SPINOCEREBELLAR TRACT
               • The cells receive afferent input from muscle spindles, Golgi tendon organs, tactile and pressure receptors
           • At Tx and upper Lx levels lat part contains
             • PREGANGLIONIC SYMPATHETIC NEURONS
               • (S2-4 contains preganglionic parasympathetic neurons)
       • VENRAL HORN (anterior)
         • contains cell bodies of motor neurons exiting through ventral nerve roots and innervate skeletal muscles
         • Lamina IX corresponds to groups of motor neurons innervating skeletal muscle
           • 2 types
             • ALPHA MOTOR NEURONS
               • Innervate EXTRAFUSAL muscle fibres
             • GAMMA MOTOR NEURONS
               • innervate INTRAFUSAL muscle fibres (within muscle spindles)
               • LOWER MOTOR NEURONS
         • Particularly well developed in Cx and Lx enlargements
       • Thoracic and upper lumbar have a small
         • LATERAL HORN (intermediolateral)
           • Contains cell bodies of PREGANGLIONIC SYMPATHETIC NEURONS
     • Divided into 10 zones
       • REXED'S LAMINAE
         • Cutaneous afferents tend to terminate in superficial (dorsal) laminae
           • Proprioceptive and muscle afferents project mostly to deeper laminae