Download The Spinal Cord

The Spinal Cord
 Decussation – crossing over
 Ipsilateral – same side
 Contralateral – opposite side
 Bilateral – both sides
FEATURES
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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
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Anterior surface = MOTOR – VENTRAL MEDIAN FISSURE, helps to identify what side
Posterior surface = SOMATOSENSORY – DORSAL SULCUS
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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
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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
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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.)