Quiz #4 - CNS - The Spinal Cord (A&P)

1. Basic functions
a. Spinal nerves are involved in sensory and motor innervation of the entire body inferior to the
head.
b. Provides a two-way conduction pathways between the brain and the body.
c. Major reflex integrating center in the body.
2. Basic Anatomy
a. The spinal cord is a long 45cm long cylinder from the foramen magnum to somewhere
between L1 and L2 in the vertebral canal.
b. The spinal cord tapers off to a point called the conus medullaris between L1 and L2.
c. A long connective tissue filament called the filum terminale connects the conus medullaris to
the coccyx to hold the spinal cord in place.
d. The spinal cord has two prominent surface folds:
i. Anterior/ventral median fissure
ii. Posterior/dorsal median sulcus
e. The spinal cord contains 31spinal cord segments from which spinal nerve roots and spinal
nerves originate.
i. 8 cervical spinal cord segments with 8 cervical spinal nerve pairs attached named C1-C8.
ii. 12 thoracic spinal cord segments with 12 thoracic spinal nerve pairs attached named T-
T12.
iii. 5 lumbar spinal cord segments with 5 lumbar spinal nerve pairs attached named L1-L5.
iv. 5 sacral spinal cord segments with 5 sacral spinal nerve pairs attached named S1-S5.
v. 1 coccygeal spinal cord segments with 1 coccygeal spinal nerve pair named Co1.
vi. Spinal cord segments L1-Co1 are very small and are all in the conus medullaris.
f. Spinal nerve roots extend to the intervertebral foramen where spinal nerves exit the
vertebral canal. Cervical spinal nerves exit above the cervical vertebrae they are named for,
all others exit inferior to the vertebrae they are named for. Spinal roots for lumbar and
sacral spinal nerves must extend further than all others and create a structure that looks like
a horse’s tail called the cauda equina below vertebrae L1.
g. Spinal cord enlargements
i. There are enlarged regions of the spinal cord in the cervical and lumbar regions. The
cervical enlargement is to accommodate extra neurons that control the upper limbs. The
lumbar enlargement is to accommodate extra neurons that control the lower limbs.
3. Sectional anatomy
a. A cross section through the spinal cord reveals arrangements of many spinal cord structures:
b. Central canal
i. In the center of the spinal cord is a small tube called the central canal that carries CSF
down the center of the spinal cord from the fourth ventricle in the brain to an opening in
the conus medullaris where the CSF drains into the subarachnoid space around the spinal
cord.
c. Gray matter vs. White matter

i. The inner layer of the spinal cord is a butterfly-shaped region of gray matter. In the center
of the spinal cord a small section of gray matter surrounds the central canal. This layer is
surrounded by a layer of white matter that gives the spinal cord a cylinder shape.
ii. Gray matter regions
1. The gray matter in the center of the spinal cord is divided into sections due to
differences in the types of neurons found in them:
2. Posterior/dorsal horn
a. The posterior/dorsal pointed region of gray matter.
b. The posterior region of dorsal horns contains portions of somatic sensory
neurons.
c. The anterior sections of the dorsal horn contains portions of visceral sensory
neurons.
3. Lateral horn
a. Bump on the lateral side of the gray matter.
b. Contains the cell bodies of visceral motor neurons only.
4. Anterior/ventral horn
a. Blunt, anterior region of the gray matter.
b. Contains the cell bodies of somatic motor neurons only.
5. Gray commissure
a. Thin region of gray matter surrounding the central canal.
b. Contains short axons that allow information in the CNS to cross over from the L
side to the R side and vice versa.
iii. White matter regions
1. The outer white matter regions are divided into sections called white columns or
funiculi:
2. Posterior/dorsal funiculus/white column
a. Posterior region of white matter
b. Between the posterior horn and posterior median sulcus
c. Contains axons of sensory and motor pathways
3. Lateral funiculus/white column
a. Lateral region of white matter.
b. Between the posterior horn and tip of anterior horn
c. Contains axons of sensory and motor pathways
4. Anterior/ventral funiculus/white column
a. Anterior region of white matter
b. Between the tip of the anterior horn and anterior median fissure
c. Contains axons of sensory and motor pathways
iv. Spinal cord roots and spinal nerves
1. Lots of small branches called rootlets carry axons between the spinal cord segments
and the roots branching off the spinal cord segment.
2. Dorsal root
a. Nerve-like arch between the dorsal surface of the spinal cord and the spinal
nerve.

b. Contains the axons of sensory neurons only. Carries sensory information into
the spinal cord from the spinal nerve.
c. The dorsal root contains an enlarged section near the spinal nerve called the
dorsal root ganglion.
3. Ventral root
a. Nerve-like arch between the ventral surface of the spinal cord and the spinal
nerve.
b. Contains the axons of motor neurons only. Carries motor information from the
spinal cord into the spinal nerve.
4. Spinal nerves
a. Mixed nerves= contain sensory and motor axons. Carry both sensory and motor
information.
b. Very short, extend through the interventricular foramen and then immediately
split into branches called spinal rami.