The spinal cord provides a vital link between the brain and the rest of the body, and yet it exhibits some functional independence from the brain.

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The spinal cord provides a vital link between the
brain and the rest of the body, and yet it
exhibits some functional independence from the
brain.
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The adult spinal cord travels from the foramen
magnum and terminates within the vertebral
foramen of the first lumbar vertebra (L1) in
adults.
3
The spinal cord can be subdivided into five
regions cervical region, thoracic region, lumbar
region, sacral region, and coccygeal region
(which has only one pair of nerves).
Dont be confused and think that the sacral
region of the spinal cord is surrounded by
sacral vertebrae. It is NOT!
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The diameter of the spinal cord is the largest in
the cervical region and there is a larger
proportion of white matter compared to gray
matter.
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The diameter of the sacral region of the spinal
cord (which is surrounded by the T12/L1
vertebrae) is the smallest and the proportion of
gray matter is largest in the spinal cord.
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The cervical enlargement contains the neurons
that innervate the upper limbs
The lumbar enlargement contains the neurons that
innervate the lower limbs.
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The tapering end of the spinal cord is called the
conus medullaris.
The conus medullaris is surrounded by L1 in and
adult and L2 in a child.
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The adult spinal cord terminates at the level of
the first lumbar vertebra (L1)
In a developing child, the spinal cord can extend
to the level of the second lumbar vertebra (L2)
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The cauda equina (horses tail) is composed of
nerves that arise from the conus medullaris and
extend inferiorly.
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The filum terminale, which is composed of pia
mater, extends from the conus medullaris to the
coccyx. Note the subarachnoid space also
continues for some distance.
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There are 31 pairs of spinal nerves that serve
defined segments of the human body.
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There are 8 pairs of cervical spinal nerves.
This is possible because the first pair (C1
spinal nerves) exits the spinal column between
the occipital bone and the atlas (C1). The
remaining 7 pairs (C2-C8 spinal nerves) exit
below each of the 7 cervical vertebrae via the
intervertebral foramina. All the spinal nerves
are mixed nerves.
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The spinal cord is surrounded by the dura,
arachnoid, and pia maters (the meninges)
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WHAT IS THE NAME OF THE NERVE THAT EXITS VIA THE
INTERVERTEBRAL FORAMEN BETWEEN THE ATLAS AND THE
AXIS? A VAGUS NERVE B FIRST CERVICAL SPINAL
NERVE C ACCESSORY NERVE D LONG THORACIC
NERVE E SPINAL NERVE C2
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The epidural space is between the vertebra and
the dura mater
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Epidural anesthesia
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Epidural anesthesia
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Effect of epidural anesthesia
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A person who needs an epidural!
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The dura mater extends along the entire length of
the vertebral canal and surrounds the spinal
cord. It also extends along the initial portion
of the radiating spinal nerves
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The subarachnoid space is a real space filled
with CSF
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In this midsagittal picture 3 is the dura mater,
5 is the spinal cord, 4 is the epidural space,
and 6 is the subarachnoid space where CSF is
located (1 is an intervertebral disc and 2 is
the body of a vertebrae).
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Needle for spinal tap
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Spinal taps are done between the third and fourth
lumbar vertebrae because there is no spinal cord
at that location
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The tip of the needle is inserted into the
subarachnoid space outside the cauda equina and
spinal fluid is removed for testing.
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The entering pressure can be determined when the
needle is inserted into the subarachnoid space
during a spinal tap.
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Spinal fluid is normally crystal clear like
water. Cloudy spinal fluid, like the specimen
shown, is a sign of white blood cells (pus). The
most common cause for white blood cells in the
spinal fluid is viral or bacterial meningitis.
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The pia mater directly adheres to the spinal cord
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WHICH OF THE FOLLOWING IS TYPICALLY PENETRATED
DURING A ROUTINE SPINAL TAP? A PIA
MATER B NUCLEUS PULPOSUS C ANULUS
FIBROSUS D SPINAL CORD E NONE OF THE ABOVE
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The cross-sectional view shows that the gray
matter is central and the white matter is
peripheral
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The peripheral white matter contains ascending
and descending tracts of nerves traveling to and
from the brain. The central gray matter serves
as a center for spinal reflexes.
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The central canal runs the entire length of the
spinal cord, is contiguous with the brain and
contains cerebrospinal fluid (CSF)
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The spinal cord develops as 31 segments, each of
which gives rise to a pair of spinal nerves that
emerge from the cord through the intervertebral
foraminae
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Nerves can be sensory, motor, or mixed (sensory
and motor)
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Mixed nerves carry both types of information and
some axons are transmitting impulses in one
direction, while other axons are transmitting
impulses in the opposite direction. All spinal
nerves are mixed nerves.
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There are 8 pairs of cervical spinal nerves.
This is possible because the first pair (C1
spinal nerves) exits the spinal column between
the occipital bone and the atlas (C1). The
remaining 7 pairs (C2-C8 spinal nerves) exit
below each of the 7 cervical vertebrae via the
intervertebral foramina. All the spinal nerves
are mixed nerves.
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Most of the spinal nerves are associated with
specific dermatomes (an area of skin innervated
by all the cutaneous neurons of a certain spinal
or cranial nerve).
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trigeminal
Dermatome map. Note the trigeminal nerve has
dermatomes on the face.
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Dermatomes of the trigeminal nerve (cranial nerve
V) are seen on the face
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Note that the trigeminal nerve has dermatomes on
the face (see white area) and that the first pair
of cervical spinal nerves (C1 spinal nerves) are
not represented on the surface at all.
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Chickenpox (varicella) virus is acquired by the
respiratory route and causes a head-to-toe rash
in children.
The chickenpox virus can invade the ganglia along
the spinal cord and remain latent until
adulthood. It can then be activated by
suppression of the immune system. It will then
travel through sensory axons of a single
dermatome and erupt onto the skin in a single
dermatome on one side of the body (unilateral
eruption)
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Shingles is a reactivation of latent chickenpox
from childhood that travels to the surface via a
single nerve on one side of the body.
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Shingles involving the first (ophthalmic)
division of the trigeminal nerve (cranial nerve
V) on face.
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Explanation of referred pain. Numerous cutaneous
and visceral sensory neurons share the same
ascending tracts.
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Body diagram of where referred pain may be felt.
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WHICH OF THE FOLLOWING IS CORRECT ABOUT
SHINGLES? A ADULTS WITH THIS CONDITION CAN CAUSE
A HEAD-TO-TOE RASH IN CHILDREN B IT TYPICALLY
OCCURS BILATERALLY C IT IS TRIGGERED BY ETHYL
ALCOHOL AND PROLONGED NERVE COMPRESSION D IT IS
MOST COMMON IN PERSONS UNDER 50 E ALL OF THE
ABOVE
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The majority of the spinal nerves combine and
then split again as networks of nerves referred
to as plexuses. The exceptions are T2-T12 and
S5-Co1, which do NOT form plexuses
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The cervical plexus is formed primarily by spinal
nerves C1-C4 (C5 is not considered part of this
plexus, even though it contributes some axons)
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The cervical plexus, and particularly spinal
nerves C3, C4, and part of C5, give rise to the
phrenic nerve which innervates the diaphragm.
Injury above C3 would lead to death by
suffocation.
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The brachial plexus is formed primarily by spinal
nerves C5-C8, and T1. This plexus gives rise to
five nerves that serve the arm or hand.
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There are five nerves that arise from the
brachial plexus
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The axillary nerve innervates the teres minor
muscle and the deltoid muscle.
It receives sensory information from the
superolateral part of the arm and skin.
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The median nerve innervates muscles in the
antebrachium and manus.
It receives sensory information from the palmar
side of fingers 1, 2, 3, and the lateral
one-half of finger 4 and from the dorsal tips of
these same fingers.
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Median nerve dermatome
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(Flexor retinaculum)
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Note adduction of thumb
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Note adducted thumbs
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When draping my arm around my daughters neck for
prolonged periods I would develop anesthesia of
fingers 1-4 only from pressure on my median
nerve.
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It receives sensory input from the lateral
surface of the forearm.
The musculocutaneous nerve innervates the biceps
brachii muscle and several other muscles.
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The radial nerve innervates the triceps brachii
and numerous muscles of the antebrachium.
It receives sensory input from the posterior arm
and forearm surface and the dorsolateral side of
the hand.
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The radial nerve receives sensory input from the
posterior arm and forearm surface and the
dorsolateral surface of the hand.
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The ulnar nerve, which passes near the medial
epicondyle of the humerus, is the funny bone.
It innervates muscles in the antebrachium and
manus.
It receives sensory input from the skin of the
dorsal and palmar aspects of fingers 5, and the
medial half of finger 4.
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The ulnar nerve receives sensations from the skin
of the dorsal and palmar surfaces of fingers 5
and medial half of fingers 4.
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Atrophy of the arm muscles caused by a brachial
plexus injury in adulthood.
Read about brachial plexus injuries in the
clinical view in your text.
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A PATIENT HAS SUFFERED A FRACTURE OF THE SURGICAL
NECK OF THE FEMUR THAT IS SUCCESSFULLY REPAIRED
WITH A MEDULLARY ROD THAT BRIDGES THE FRACTURE
LINE. HOWEVER, AS THE WEEKS PASS, THE PATIENT IS
UNABLE TO ABDUCT THE ARM AND SUFFERS FROM
ANESTHESIA ALONG THE SUPEROLATERAL SKIN OF THE
ARM. WHAT HAS BEEN DAMAGED? A MEDIAN
NERVE B MUSCULOCUTANEOUS NERVE C AXILLARY
NERVE D ULNAR NERVE E RADIAL NERVE
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The lumbar plexus is formed by spinal nerves
L1-L4. It gives rise to two major nerves the
femoral nerve and the obturator nerve
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Note the two major nerves that arise from the
lumbar plexus
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The femoral nerve innervates the quadriceps
femoris muscles on the anterior of the thigh to
help extend the knee. It also innervates the
sartorius muscle and several other muscles.
It receives sensory input from the anterior and
inferomedial thigh as well as the medial aspect
of the leg.
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The obturator nerve innervates the gracilis and
several other muscles.
It receives sensory information from the
superomedial skin of the thigh
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The sacral plexus is formed by spinal nerves from
L4, L5, and S1-S4. It gives rise to the sciatic
nerve, which is actually composed of two nerves
the tibial nerve and the common fibular (common
peroneal) nerve.
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The sacral plexus gives rise to two principal
nerves the tibial nerve and the common fibular
(peroneal) nerve. The sciatic nerve is composed
of these two nerves wrapped in a common
connective sheath. These two nerves separate
just above the popliteal fossa.
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The sciatic nerve splits into its separate
components tibial nerve and common fibular
(peroneal) nerve just superior to the popliteal
fossa.
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A tight piriformis muscle can compress the
sciatic nerve
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Dont stick needles in the sciatic nerve!
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The tibial nerve innervates the hamstrings, the
gastrocnemius, the soleus, and several other
muscles.
It receives sensory input from the skin on the
plantar surface of the foot.
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The common fibular nerve (common peroneal nerve)
innervates the peroneus (fibularis) longus, the
tibialis anterior, and several other muscles of
the leg and foot. This is the branch of the
sciatic nerve that caused me problems!
It receives sensory input from the anterolateral
part of the leg, the toes, and dorsum of the foot.
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Read about sacral plexus injuries and sciatica in
the clinical view in your text.
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Reflexes are rapid, automatic, involuntary
reactions of muscles or glands to a stimulus
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An example occurs when you accidentally touch a
hot object. You remove your hand even before you
are completely aware of the heat. A reflex can
precede sensation (a reflex does not need to
involve the brain)
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A typical reflex arc
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Generally, there are five steps involved in a
neural reflex stimulus, transmission via a
sensory neuron, processing in CNS, transmission
via a motor neuron, and an effector (muscle or
gland) responds.
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Read in your text about different types of
reflexes for your own information if you desire.
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Neural tube
The cranial (superior) portion of the neural tube
expands and develops into the brain, while the
caudal (inferior) part of the neural tube forms
the spinal cord. The hollow neural canal
develops into the central canal of the spinal
cord.
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The bony vertebral column (dark line shown) grows
faster than the spinal cord. A newborns spinal
cord extends to about the level of L3. A childs
spinal cord may extend to the level of L2. An
adults spinal cord typically terminates at the
level of L1.
Bony vertebral column
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The inner delicate spinal cord terminates in an
adult, as the conus medullaris, at the level of
the L1vertebra.
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Damage to the spinal cord can lead to paralysis
or death
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Severing the spinal cord above C3 typically leads
to death by asphyxiation because the victim
cannot use the spinal nerves to contract the
intercostal muscles and cannot utilize the
phrenic nerve to contract the diaphragm.
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Christopher Reeve as Superman
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In his fall, he crushed both the atlas (C1) and
the axis (C2). He would have died by
asphyxiation, but his accident was witnessed and
rescue breathing was done. He became a very
famous respirator-dependent quadriplegic.
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Christopher Reeve after his fall.
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Christopher Reeeve shortly before his death from
an infected bed sore (decubitus ulcer). He did a
great deal to advance research on spinal trauma.
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Damage below C3 also results in quadriplegia, but
the person can still utilize their diaphragm for
breathing via their intact phrenic nerves.
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WHICH OF THE FOLLOWING IS CORRECT? A FOOT DROP
IS TYPICALLY CAUSED BY DAMAGE TO THE COMMON
PERONEAL NERVE B THE OBTURATOR NERVE STIMULATES
ADDUCTION OF THE THIGH C THE EMBRYONIC NEURAL
CANAL BECOMES THE CENTRAL CANAL OF THE SPINAL
CORD D THE PHRENIC NERVE IS FUNCTIONAL
FOLLOWING TRANSECTIONS OF THE SPINAL CORD AT
C5/C6 E ALL OF THE ABOVE