Download spinal nerves

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.
The adult
spinal cord
travels from
the foramen
magnum
and
terminates
within the
vertebral
foramen of
the first
lumbar
vertebra
(L1) in
adults.
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).
Don’t be confused and think
that the sacral “region” of the
spinal cord is surrounded by
sacral vertebrae. It is NOT!
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.
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.
The cervical enlargement
contains the neurons that
innervate the upper limbs
The lumbar
enlargement contains
the neurons that
innervate the lower
limbs.
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.
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)
The cauda
equina
(horse’s tail)
is composed
of nerves that
arise from
the conus
medullaris
and extend
inferiorly.
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.
There are 31
pairs of spinal
nerves that
serve defined
segments of the
human body.
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 (C2C8 spinal nerves) exit
below each of the 7
cervical vertebrae via
the intervertebral
foramina. All the
spinal nerves are mixed
nerves.
The spinal cord
is surrounded by
the dura,
arachnoid, and
pia maters (the
meninges)
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
The epidural space is between the vertebra and the dura mater
Epidural
anesthesia
Epidural
anesthesia
Effect of epidural
anesthesia
A person who needs an epidural!
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
The subarachnoid
space is a real
space filled with
CSF
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).
Needle for
spinal tap
Spinal taps are done
between the third and
fourth lumbar
vertebrae because
there is no spinal cord
at that location
The tip of the
needle is
inserted into the
subarachnoid
space outside the
cauda equina and
spinal fluid is
removed for
testing.
The entering
pressure can
be
determined
when the
needle is
inserted into
the
subarachnoid
space during
a spinal tap.
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.
The pia mater
directly adheres to
the spinal cord
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
The cross-sectional view
shows that the gray
matter is central and
the white matter is
peripheral
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.
The central canal runs the entire length of the spinal cord, is
contiguous with the brain and contains cerebrospinal fluid (CSF)
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
Nerves can be sensory, motor, or mixed (sensory and motor)
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.
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 (C2C8 spinal nerves) exit
below each of the 7
cervical vertebrae via
the intervertebral
foramina. All the
spinal nerves are mixed
nerves.
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).
trigeminal
Dermatome
map. Note
the trigeminal
nerve has
dermatomes
on the face.
Dermatomes of the trigeminal nerve (cranial nerve V) are seen
on the face
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.
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)
Shingles is a reactivation of latent chickenpox from childhood that
travels to the surface via a single nerve on one side of the body.
Shingles involving the first (ophthalmic) division of the trigeminal
nerve (cranial nerve V) on face.
Explanation of
referred pain.
Numerous cutaneous
and visceral sensory
neurons share the same
ascending tracts.
Body diagram of where referred pain may be felt.
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
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
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)
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.
The brachial plexus is formed
primarily by spinal nerves C5C8, and T1. This plexus gives
rise to five nerves that serve the
arm or hand.
There are five nerves that arise from the brachial plexus
It receives
sensory
information
from the
superolateral
part of the
arm and
skin.
The axillary nerve
innervates the teres
minor muscle and
the deltoid muscle.
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.
Median nerve dermatome
(Flexor retinaculum)
Note adduction
of thumb
Note adducted thumbs
When draping my arm around my daughter’s neck for prolonged
periods I would develop anesthesia of fingers #1-#4 only from
pressure on my median nerve.
The
musculocutaneous
nerve innervates the
biceps brachii
muscle and several
other muscles.
It receives
sensory input
from the lateral
surface of the
forearm.
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.
The radial nerve receives sensory input from the posterior arm
and forearm surface and the dorsolateral surface of the hand.
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.
The ulnar nerve receives sensations from the skin of the dorsal and
palmar surfaces of fingers #5 and medial half of fingers #4.
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.
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
The lumbar plexus is formed by spinal nerves L1-L4. It gives rise
to two major nerves: the femoral nerve and the obturator nerve
Note the two major
nerves that arise
from the lumbar
plexus
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.
The obturator nerve
innervates the
gracilis and several
other muscles.
It receives sensory
information from the
superomedial skin of the
thigh
The sacral plexus is formed by spinal nerves from L4, L5, and S1S4. It gives rise to the sciatic nerve, which is actually composed of
two nerves: the tibial nerve and the common fibular (common
peroneal) nerve.
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.
The sciatic nerve
splits into its separate
components [tibial
nerve and common
fibular (peroneal)
nerve] just superior
to the popliteal fossa.
A tight piriformis muscle can compress the sciatic nerve
Don’t stick
needles in the
sciatic nerve!
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.
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.
Read about sacral plexus injuries
and sciatica in the clinical view in
your text.
Reflexes are
rapid,
automatic,
involuntary
reactions of
muscles or
glands to a
stimulus
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)
A typical
reflex arc
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.
Read in your text
about different types
of reflexes for your
own information if
you desire.
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.
The bony vertebral column
(dark line shown) grows
faster than the spinal cord.
A newborn’s spinal cord
extends to about the level of
L3. A child’s spinal cord
may extend to the level of
L2. An adult’s spinal cord
typically terminates at the
level of L1.
Bony vertebral column
The inner delicate
spinal cord terminates
in an adult, as the
conus medullaris, at
the level of the
L1vertebra.
Damage to the spinal cord
can lead to paralysis or death
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.
Christopher
Reeve as
Superman
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
respiratordependent
quadriplegic.
Christopher
Reeve after his
fall.
Christopher
Reeeve shortly
before his death
from an infected
bed sore
(decubitus ulcer).
He did a great
deal to advance
research on spinal
trauma.
Damage below
C3 also results in
quadriplegia,
but the person
can still utilize
their diaphragm
for breathing via
their intact
phrenic nerves.
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