Nervous System and Spinal Neurons

General organization of the nervous system

Somatic nervous system - neurons controlling non-visceral body

Autonomic nervous system - neurons controlling visceral body

Afferent division - neurons responsible for sensory signalling

Efferent division - neurons responsible for motor signalling

Central nervous system - neurons within the brain and spinal cord

Peripheral nervous system - neurons outside of brain and spinal cord


General structure of neurons

perikaryon (cell body)

axon hillock - site for generation of action potential

axon - carry signals away from cell body

synaptic knobs (boutons, axon terminals)

dendrites - carry signals toward cell body


Major anatomical shapes of neurons

Unipolar neurons - commonly function as afferent (sensory) neurons

Multipolar neurons - commonly function as efferent (motor) neurons


Afferent (sensory) portion of spinal cord

dorsal root ganglia - contain cell bodies of sensory neurons

dorsal root - contain axons of sensory neurons

dorsal horns - entry point for sensory neurons


Efferent (motor) portion of spinal cord


ventral root - axons of somatic motor neurons

ventral horns - contain cell bodies of somatic motor neurons


lateral horns - contain cell bodies of autonomic motor neurons

ventral root - axons of sympathetic preganglonic neurons


Major cells associated with neurons (neuroglia)

Schwann cells - provide a myelin sheath for many PNS axons / dendrites

nodes of Ranvier - separation between Schwann cells

Oligodendrocytes - provide a myelin sheath for many CNS neurons


Peripheral neurons

Peripheral nerves - neural processes outside of CNS

epineurium - surrounds nerve

perineurium - surrounds nerve fascicles

endoneurium - surrounds individual neural processes

Ganglia - groups of cell bodies outside of the CNS


Gross Anatomy of the Spinal Cord

cervical enlargement

thoracic region

lumbar enlargement

sacral region

conus medullaris - end of spinal cord

filum terminale - continuation of pia mater toward coccyx

cauda equina - dorsal and ventral roots within spinal column


Nerve plexi

cervical plexus

phrenic nerve

brachial plexus

lumbar plexus

femoral nerve

sacral plexus

sciatic nerve


Spinal Meninges

dura mater

epidural space

subdural space

pia mater

denticulate ligaments


David G. Ward, Ph.D.  Last modified by wardd 23 May, 2006