Exercise 15:
Spinal Cord and Spinal Nerves
1. Spinal Cord
• Extends from the foramen
magnum of the skull to the
first or second lumbar vertebra
(L1& L2)
• 31 pairs of spinal nerves arise
from the spinal cord
• Cauda equina is a collection of
spinal nerves at the inferior end
The cord does not extend the entire length of the
vertebral column – so a group of nerves leaves the
inferior spinal cord and extends downward. It
resembles a horses tail and is called the cauda equina
2. Spinal Cord Anatomy
Figure 7.21
2. Another spinal cord picture
Dorsal ramus
of spinal nerve
Ventral ramus of spinal nerve
The Spinal Nerves-
immediately after being formed the spinal
nerves split into dorsal and ventral rami.
Figure 7.25b
3. Gross Anatomy of
Spinal Cord
• Thicker at the neck
and end of the cord
(cervical and lumbar
enlargements)
• Reason: large group of
nerves leave the cord
to serve the arms and
legs .
Spinal Cord Anatomy
• Meninges cover the spinal cord
• Spinal nerves leave at the level of each
vertebrae
– Dorsal root
• Associated with the dorsal root ganglia—collections
of cell bodies outside the central nervous system
– Ventral root
• Contains axons
Spinal Cord Anatomy
• Internal gray matter is
mostly cell bodies
– Dorsal (posterior) horns
– Anterior (ventral) horns
– Gray matter surrounds the
central canal
• Central canal is filled with
cerebrospinal fluid
• Exterior white mater—
conduction tracts
– Dorsal, lateral, ventral
columns
Up close view of cervical enlargement
Spinal Cord Anatomy
Figure 7.20 (1 of 2)
Up close view of lumbar enlargement
Spinal Cord Anatomy
Figure 7.20 (2 of 2)
Spinal Nerves and Nerve Plexuses
4. Spinal Nerves
• 31 nerves connecting
the spinal cord and
various body regions.
• 8 paired cervical nerves
• 12 paired thoracic
nerves
• 5 paired lumbar nerves
• 5 paired sacral nerves
• 1 pair of coccygeal
nerves
Spinal Nerves
• There is a pair of spinal
nerves at the level of each
vertebrae for a total of 31
pairs
• Formed by the combination
of the ventral and dorsal
roots of the spinal cord
• Named for the region from
which they arise
Figure 7.25a
5.Anatomy of Spinal Nerves
• Spinal nerves divide soon after leaving the
spinal cord
– Dorsal rami—serve the skin and muscles of the
posterior trunk
– Ventral rami—form a complex of networks (plexus)
for the anterior
5.& 7. Plexuses
Plexus- ventral rami C1-T1 and T12-S4 branch
extensively and join one another lateral to the
vertebral column forming complicated nerve
plexuses that serve motor and sensory needs
***Except for T2 to T12,
Ventral Rami from C1- T1 form Cervical & Brachial
plexuses
Ventral rami from L1-S4 form Lumbar and Sacral
plexuses
6. Serve motor and sensory needs of the limbs
Ventral rami from T2-T12 do not form
plexuses..they serve the muscles of intercostal
spaces and the skin and muscles of the
anterior and lateral trunk
Sacral Plexus
This diagram shows the
nerves leaving from the
vertebral canal
Note: There are 7 cervical
vertebrae but 8 pairs of
cervical nerves.
C1 – C7 emerge above the
vertebrae for which they are
named.
C8 emerges between C7 and
T1.
The remaining spinal nerve
pairs emerge below the
same numbered vertebra.
PNS: The Spinal Nerves
Look how the dorsal and
ventral roots merge to
form the spinal nerve
then split again to form
the ventral and dorsal
rami
Figure 7.25b
Table 7.2 (1 of 2)
Table 7.2 (2 of 2)
6. Spinal Nerves
• Each connects to the spinal
cord by 2 roots – dorsal
and ventral.
• Ventral roots are motor
while dorsal roots are
sensory.
6.
Dorsal root – sensory function
Ventral root – motor function
Dorsal Root
Figure 7.22
Ventral root
Dorsal root – sensory function
Ventral root – motor function
Important nerve= phrenic nerve which
serves the diaphragm and muscles of
shoulder and neck
Major Peripheral Nerves
of the Upper Limbs
The brachial plexus
branches into 5 major
peripheral nerves of the
upper limbs :
• Axillary
• Radial
• Median
• Musculocutaneous
• Ulnar
Figure 7.26a
Major Peripheral
Nerves of the Lower Limbs
The nerves from the lumbar
plexus serve the abdominal
region and the anteromedial
thigh.
Important nerves:
• Femoral
• Obturator
Figure 7.26b
Major Peripheral
Nerves Lower Limbs
Sacral plexus – supply buttock,
posterior thigh, and almost all
leg and foot.
Important Nerves:
• The sciatic nerve – largest
nerve in the body; divides
into common fibular nerve
and tibial nerve.
• Superior and Inferior Gluteal
Figure 7.26c
8.
Table 7.2 (2 of 2)
Extra/ More information on the brain
Spinal Cord
• Functions to transmit messages to
and from the brain (white matter)
and to serve as a reflex center (gray
matter).
• extends about 17”
• diameter of your thumb
• Thicker at the neck and end of the
cord (cervical and lumbar
enlargements) b/c of the large group
of nerves connecting these regions
of the cord w/ the arms and legs.
Spinal Cord
• The cord does not extend the
entire length of the vertebral
column – so a group of nerves
leaves the inferior spinal cord and
extends downward. It resembles a
horses tail and is called the cauda
equina.
Spinal Cord
• Notice the gross features of
the spinal cord on the right.
• 31 pairs of spinal nerves
attach to the cord by paired
roots and exit from the
vertebral canal via the
intervertebral foramina.
Cross Sectional Anatomy of the Spinal Cord
• Flattened from front to back.
• Anterior median fissure and posterior median sulcus
partially divide it into left and right halves.
• Gray matter is in the core of the cord and surrounded by
white matter.
• Resembles a butterfly.
• 2 lateral gray masses connected by the gray
commissure.
• Posterior projections are the posterior or dorsal horns.
• Anterior projections are the anterior or ventral horns.
• In the thoracic and lumbar cord, there also exist lateral horns.
Gray Matter
• Posterior horns contain
interneurons.
• Anterior horns contain some
• interneurons as well as the cell
bodies of motor neurons.
– These cell bodies project their axons via the
ventral roots of the spinal cord to the skeletal
muscles.
– The amount of ventral gray matter at a given level
of the spinal cord is proportional to the amount of
skeletal muscle innervated.
Gray Matter
• Lateral horn neurons are
sympathetic motor neurons
serving visceral organs.
– Their axons also exit via the
ventral root.
• Afferent sensory fibers carrying
info from peripheral receptors
form the dorsal roots of the
spinal cord. The somata of these
sensory fibers are found in an
enlargement known as a dorsal
root ganglion.
• The dorsal and ventral roots fuse
to form spinal nerves.
White Matter
• Myelinated nerve fibers.
• Allows for communication btwn the brain and spinal cord or btwn
different regions of the spinal cord.
• White matter on each side of the cord is divided into columns or
funiculi.
– Typically, they are ascending or descending.
• What does that mean?
Spinal Nerves
• The 2 roots join to
form a spinal nerve
prior to exiting the
vertebral column.
• Roots are short and
horizontal in the
cervical and thoracic
regions while they
are longer and more
horizontal in the
sacral and lumbar
regions.
• Almost immediately after emerging from its intervertebral foramen,
a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a
meningeal branch that reenters and innervates the meninges and
associated blood vessels.
• Each ramus is mixed.
• Joined to the base of the ventral rami of spinal nerves in the thoracic
region are the rami communicantes.
• Dorsal rami supply the posterior body trunk whereas the thicker
ventral rami supply the rest of the body trunk and the limbs.