SPINAL CORD STRUCTURE
SPINAL and CRANIAL NERVES
I. Spinal Cord
part of the CNS continuous with brain
housed within the vertebral canal of spinal
column
A. Exterior Features
1. posterior median fissure: deep
median fissure in midline of
posterior aspect of spinal cord
2. anterior mediam fissure: deep
median fissure in midline of
anterior aspect of spinal cord
3. conus medullaris: tapering inferior
end of spinal cord
4. cauda equina: bundle of spinal
nerves arising from lumbosacral
enlargement and conus medullaris;
runs inferiorly through vertebral
column below first lumbar vertebra
5. enlargements
areas where diameter of spinal cord
increases; found as the cervical enlargement and the lumbar enlargement
B. Internal Features
1. central canal: space in middle of
spinal cord continuous with brain’s
ventricular system filled with
cerebrospinal fluid
2. gray matter: found surrounding
central canal, generally described
as having a butterfly-like shape;
divided into posterior, anterior,
and lateral horns
3. white matter: found on outside of
spinal cord; divided into posterior,
anterior, and lateral columns
II. Spinal Nerves
arise from the spinal cord
formed by the merging of the dorsal and
ventral roots
A. Dorsal (or Posterior or Sensory) Root
exclusively composed of portions of
sensory neurons
carry information into spinal cord
cell bodies of sensory neurons are found
in dorsal root ganglia of each
dorsal root
B. Ventral (or Anterior or Motor) Root
exclusively composed of portions of
motor neurons
carry information away from spinal
cord
Because the dorsal and ventral roots merge
to form the spinal nerve, a spinal nerve
carries both sensory and motor information
III. Nerve Plexuses
as spinal nerves exit intervertebral foramina
they branch and interconnect with other
branches
this network of nerves is a nerve plexus
four plexuses send specific nerves to particular locations in the body
A. Cervical Plexus
arises from spinal nerves C1 through C4
or C5
1. phrenic nerve
motor to diaphragm
B. Brachial Plexus
arises from spinal nerves C5 through C8
or T1
1. axillary nerve
motor to deltoid and teres major
sensory from skin of shoulder
2. musculocutaneous nerve
motor to flexor muscles of arm
sensory from skin of forearm
3. radial nerve
motor to extensor muscles
sensory from some skin of upper
extremity
4. median nerve
motor to most flexor muscles of
the forearm and hand
sensory from some skin of hand
5. ulnar nerve
motor to some flexor muscles of
forearm and hand
sensory from some skin of hand
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C. Lumbar Plexus
1. femoral nerve
motor to quadriceps femoris,
sartorius and psoas major
sensory from skin of anterior and
medial aspects of lower
extremity
2. obturator
motor to adductor muscles of thigh
D. Sacral Plexus
1. sciatic nerve
motor to hamstring
sensory from skin of posterior thigh
two major branches
a. tibial nerve
motor to flexor muscles of leg
and extensor muscles of
foot
sensory from skin of leg
b. (common) peroneal nerve
motor to biceps femoris,
peroneus longus and
extensor digitorum
sensory from skin of anterior
leg and dorsum of foot
2. pudendal nerve
motor to muscles of the urogenital
diaphragm
sensory from penis and scrotum in
males or clitoris, labia and
vagina in females
IV. Cranial Nerves
arise directly from brain
mainly sensory, mainly motor or mixed
identified by a proper name or a Roman
numeral
A. Olfactory Nerve (CN I)
sensory from nasal cavity (sense of
smell)
B. Optic Nerver (CN II)
sensory from retina of eye (sense of
sight)
C. Oculomotor (CN III)
motor to four of the extrinsic eye
muscles (superior, inferior and
medial rectus and inferior oblique)
D. Trochlear (CN IV)
motor to superior oblique muscle
E. Trigeminal (CN V)
motor to muscles of mastication
sensory from skin of face, oral and
nasal cavities and paranasal sinuses
F. Abducens (CN VI)
motor to lateral rectus muscle
G. Facial (CN VII)
motor to facial and scalp muscles
sensory from anterior two-thirds of
tongue
H. Auditory or Vestibulocochlear (VIII)
sensory from inner ear (sense of hearing
and equilibrium)
J. Glossopharyngeal (CN IX)
motor to pharyngeal muscles
sensory from posterior two-thirds of
tongue
K. Vagus (CN X)
motor to larynx (speech) and esophagus (swallowing) and to gut,
bronchial tree and heart
sensory from pharynx, larynx, gut,
bronchial tree and heart
L. (Spinal) Accessory (CN XI)
motor to trapezius and sternocleidomastoid
M. Hypoglossal (CN XII)
motor to intrinsic and extrinsic
tongue muscles
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