Chapter 2
Spinal Cord and Spinal Nerves
12-1
Spinal Cord
• Extends from foramen magnum to
second lumbar vertebra
• Segmented
– Cervical
– Thoracic
– Lumbar
– Sacral
• Connected to 31 pairs of spinal nerves
– All are mixed nerves; I.e., contain both
sensory and motor fibers
• Not uniform in diameter throughout
length
– Cervical enlargement: supplies
upper limbs
– Lumbar enlargement: supplies
lower limbs
• Conus medullaris: tapered inferior end.
• Cauda equina: origins of spinal nerves
extending inferiorly from lumbosacral
enlargement and conus medullaris. 12-2
Spinal Meninges
– Dura mater: outermost layer;
continuous with epineurium of the
spinal nerves
• No firm connections to vertebrae
• Epidural space: external to the
dura; anesthesia injected here in sc.
Contains blood vessels, areolar
connective tissue and fat.
– Arachnoid mater: delicate network of collagen and elastic fibers
• Subarachnoid space: between pia
and arachnoid
• CSF and blood vessels within web-like
strands of arachnoid tissue
• Fluid functions as a shock absorber
– Pia mater: thin layer of elastic and
collagen fibers bound tightly to
surface of brain and spinal cord
• Denticulate ligaments extend from pia
through arachnoid to dura; prevent
lateral movement
• Forms the filum terminale, which
anchors spinal cord to coccyx and the
denticulate ligaments that attach the
12-3
spinal cord to the dura mater
Cross Section of Spinal Cord
12-4
Cross
Section of
Spinal Cord
• Anterior median fissure and
posterior median sulcus: deep
clefts partially separating left
and right halves
• Gray matter: contains neuron
cell bodies, dendrites, axons
– Divided into:
• Posterior (dorsal) horns
• Anterior (ventral) horns
• Lateral horns (found only
in thoracic and lumbar
regions
• White matter
– Myelinated axons
– Three columns (funiculi):
ventral, dorsal, lateral
• Each of these divided into
sensory or motor tracts
12-5
Organization of Gray Matter
1. Posterior gray horns - contain somatic and visceral sensory
cells bodies (SS and VS in diagram)
2. Anterior horns - contain somatic motor cell bodies (SM)
3. Lateral horns - located ONLY in thoracic and lumbar regions
contain visceral motor cell bodies
12-6
Organization of White Matter
• Divided into three funiculi (columns) – posterior, lateral, and anterior
• Each column contains several fiber tracts (bundles of axons)
– All axons with a tract relay the same information in the same direction
• Ascending tracts - carry sensory information toward the brain
• Descending tracts - carry motor commands to spinal cord
– Fiber tract names reveal their origin and destination
12-7
Cross section of Spinal Cord,
cont.
• Commissures: connections
between left and right halves
– Gray with central canal in
the center
– White
• Roots: spinal nerves arise as
rootlets then combine to form
roots
– Dorsal (posterior) root has a
ganglion
– Ventral (anterior)-no
ganglion
– Two roots merge laterally
and form the spinal nerve
12-8
Organization of
Neurons in
Spinal Cord and
Spinal Nerves
• Dorsal root ganglion:
collections of cell bodies of
unipolar sensory neurons
forming dorsal roots.
• Motor neuron cell bodies are
in anterior and lateral horns
of spinal cord gray matter.
– No ganglion formed
– Multipolar somatic
motor neurons in
anterior (motor) horn
– Autonomic neurons in
lateral horn
• Axons of motor neurons
form ventral roots and pass
into spinal nerves
12-9
Spinal Nerves
• Thirty-one pairs of spinal
nerves
• First pair exit vertebral
column between skull and
atlas (C1)
• Last four pair exit via the
sacral foramina
• Others exit through
intervertebral foramina
• Eight pair cervical, twelve pair
thoracic, five pair lumbar, five
pair sacral, one pair coccygeal
12-10
Dermatomal Map
• Spinal nerves indicated by capital letter and number
• Dermatomal map: skin area supplied with sensory
innervation by spinal nerves
12-11
Spinal Nerves
• Medially, give rise to the roots
that attach the nerve to the s.c.
• Laterally, give rise to the rami
that innervate the dorsal and
ventral regions of the body
– Dorsal ramus
• Contains both sensory and
motor neurons that
innervate the dorsal
regions of the body
– Ventral ramus
• Contains both sensory and
motor neurons that
innervate the ventral
regions of the body
• Braid together to form
plexuses (plexi)
12-12