Spinal Cord and Spinal
Nerves
Major association,reflex and
communication center
Conduction route to and from the
brain
Structure of the Spinal Cord
 About 18 inches long
 Extends from the foramen magnum to
the level of the 1st-2nd lumbar
vertebrae
 Very well protected by the vertebral
column, meninges, CSF, vertebral
ligaments
 Gives rise to 31 pairs of spinal nerves
MENINGES
 Pia mater
 sub-arachnoid space
 Arachnoid
 sub-dural space
 Dura mater
 Meningitis
External Anatomy
 Cervical enlargement
 Lumbar enlargement
 Conus medullaris
 Filum terminale - extension of pia
mater that anchors to coccyx
 Cauda equina
Internal Anatomy
 Central canal containing CSF
 Anterior median fissure
 Posterior median sulcus
 Gray matter
 inner portion in the shape of a butterfly
 Anterior, posterior, and lateral gray horns
 White matter - 6 columns that
contain ascending and descending
fiber tracts
 These white tracts are paired and
decussate
 Ascending tracts - Sensory tracts
 Descending tracts - Motor tracts
Spinal Nerves
 Numbered and named according to the
region of cord from which they emerge
 Designated by LETTER and NUMBER
 Coverings - endoneurium, perineurium,
epineurium
 All are mixed nerves
 Arise from 2 roots
Roots
 Dorsal root - is a sensory root
 contains sensory nerve fibers carrying
impulses toward the CNS into the cord
 sensory cell bodies are located in the
dorsal root ganglion
 Ventral root - is a motor root
 contains motor axons carrying impulses
AWAY from the cord to the periphery
 motor neuron cell bodies are located in
the gray matter of the cord
Spinal Plexuses
 Cervical plexus - phrenic nerve
 Brachial plexus - axillary, radial, ulnar
 Lumbar plexus - femoral nerve
 Sacral plexus - sciatic nerve
 tibial nerve and common peroneal
Reflexes
Rapid, involuntary, automatic
responses to stimuli
Reflex Arc
 Receptor - distal end of a sensory
neuron dendrite
 Afferent sensory neuron
 Integrating center - an association
neuron or the spinal cord itself
 Effector neuron
 Effector - muscle or a gland
Types of Reflexes
 Stretch reflex – patellar reflex
 Tendon reflex – produces relaxation in
antagonist muscles
 Withdrawal reflex – touch hot object
 Crossed extensor - causes opposite
motion on other side of body