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The Spinal Cord Decussation – crossing over Ipsilateral – same side Contralateral – opposite side Bilateral – both sides FEATURES Same 3 protective surround layers i.e. dura, arachnoid and pia Denticulate ligaments – extension of pia matter that anchor the spinal cord within dura mater Cauda equina – loose bundle of nerve rootlets (passed L2/L3) Conus medullaris – narrow tapered end of spinal cord Filum terminale – thin extension from conus medullaris o Connective tissue o Attaches to coccyx Agenesis or severing causes dysfunction of nerve rootlets in the cauda equina Anterior surface = MOTOR – VENTRAL MEDIAN FISSURE, helps to identify what side Posterior surface = SOMATOSENSORY – DORSAL SULCUS Enlargements – result from large number of lower motor neurons present in ventral horn o CERVICAL – innervates upper limbs, also large volume of myelinated axons descending from higher cortical areas o LUMBOSACRAL – innervates lower limbs (comparatively smaller) Spinal Nerves o Arise lateral to the midline of spinal cord LHS and RHS o Dorsal + ventral root = SPINAL NERVE o Ventral root = bodies in ventral & lateral horn Motor EFFERENT fibres Voluntary – bodies in ventral horn Autonomic (visceral) – bodies in lateral horn (T1-L2) MOTOR axons = lower motor neurons o Dorsal root = bodies in dorsal root ganglia (DRG) Sensory AFFERENT fibres Myelinated Unmyelinated SENSORY axons from periphery Pseudo-unipolar neurons i.e. single axon, NO dendrite Dermatome – surface map of skin regions innervated by a single DRG White matter divided into FUNICULI o Dorsal o Ventral o Lateral More white matter in ROSTRAL levels – greater myelinated axon travel More grey matter at SPINAL ENLAREMENTS – greater lower motor neuron innervation of limbs T1-L2 = lateral horn present, region of SYMPATHETIC flow (autonomic) CNS TRACTS 1) Descending Carry MOTOR information Target lower motor neurons Corticospinal tract o Cell bodies in cortex o Decussate in caudal medulla o Synapse on lower motor neurons in ventral horn Rubrospinal tract o cell bodies in red nucleus (midbrain) o synapse on lower motor neurons in ventral horn 2) Ascending Carry SOMATOSENSORY information Dorsal column tract – 2 divisions o Fine touch and proprioception o Gracile fasciculus – information from LOWER body o Cuneate fasciculus – information from UPPER body o Synapse FIRST - in medulla o Decussate in SENSORY DECUSSATION Spinothalamic tract o Pain and temperature o Synapse in superficial dorsal horn FIRST o Decussate VENTRAL COMMISURE o Ascend to cortex If descending information doesn’t reach lower motor neurons = FLACCID PARALYSIS, loss of motor control o DOES NOT affect reflex arc (autonomic function) Lesioning a tract will affect information everywhere AT and BELOW level of lesion Damage to spinal nerve causes loss of function AT level of lesion Damage of DECUSSATION itself result in BILATERAL damaged effect at level of lesion (approx.)