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Chapter 14 Spinal Cord & Spinal Nerves
The Spine
• The spinal cord is a hiway, sensory
impulses going up to the brain and motor
impulses going down from the brain.
• The exceptions are reflexes which are
local.
• The spinal cord begins at the foramen
magnum of this skull and continues down
to L1 or L2
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Functions:
1. Through spinal nerves: involved in sensory and motor innervation of entire body and head.
2. Provides 2 way conduction pathway for signals between body and brain
3. Major center for reflexes.
I. Spinal Cord
A. Anatomy
1. Begins at the foramen magnum of skull  vertebra L1 or L2
2. Conus medullaris: tapered end which tapers into a long filament called the filum
terminale that (becomes coccygeal ligament) attaches to the coccyx,
anchoring the spinal cord in place- prevent upwards movement.
3. Cauda equina: collection of nerve roots at the inferior end of the vertebral column.
The filum terminale and ventral and dorsal spinal cord roots extending distal to the conus
medullaris
the lumbar and sacral nerve roots must descend for some distance before reaching their
corresponding intervertebral foramina or sacral foramina.
4. Cervical & lumbar enlargements- more nerves for limbs
5. Posterior medial sulcus, anterior median fissure
6. Meninges:
a) Denticulate ligament: extensions of the pia mater- connect pia & spinal arachnoid
mater- prevent side to side movem’t.
b) Epidural space: adipose, blood vessels (deliver anesthetics)
7. Gray matter: Mix of neuron cell bodies, short unmyelinated axons, dendrites &
neuroglia. Shaped like the letter H.
gray commissure, central canal, 2 dorsal horns, 2 ventral horns. 2 small
lateral horns present in the thoracic & lumbar regions- contain autonomic NS
neurons.
8. White matter: Contains both myelinated & unmyelated axons. Arranged in columns:
ventral column, lateral column, dorsal column. Tracts are found within columns.
Figure 14.1a
Gross Anatomy of the Spinal Cord
Cervical spinal
nerves
C1
C2
C3
C4
C5
C6
C7
C8
Conus medullaris: the tapered end of the
spinal cord forming a long filament called
the filum terminale which will become the
coccygeal ligamentwhich anchors the
spinal cord in place so to prevent upward
movement
Cervical
enlargement
T1
T2
T3
T4
T5
T6
Cauda equina: a collection of nerve roots
at the inferior and of the vertebral column.
Lumbar and sacral nerve roots must
descend before exiting the proper intervertebral foramen or sacral foramen
T7
Thoracic
spinal
nerves
T8
T9
Posterior
median sulcus
Cervical and lumbar enlargements: nerves
for arms and legs
T10
T11
Lumbosacral
enlargement
T12
L1
Conus
medullaris
L2
Lumbar
spinal
nerves
L3
Inferior
tip of
spinal cord
L4
Cauda equina
L5
Sacral spinal
nerves
S1
S2
S3
S4
S5
Coccygeal
nerve (Co1)
Filum terminale
(in coccygeal ligament)
a Superficial anatomy and orientation of the adult spinal
cord. The numbers to the left identify the spinal nerves and
indicate where the nerve roots leave the vertebral canal.
The spinal cord, however, extends from the brain only to
the level of vertebrae L1–L2.
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Spinal cord
Spinal cords
are about
16”-18” long.
Fiber Types:
Nervous Conduction
Fiber Types:
ascending carry sensory toward brain
descending fibers: motor information to muscles
and glands
commissural fibers: reflex arc fibers within the CNS
Column: (funiculus) dorsal, ventral and lateral
Tract: (fasiculus) separate areas within columns either
motor or sensory
Dorsal Root: sensory only. Impulses enter the dorsal root
and extends to the gray dorsal horn. The cell bodies form
the dorsal root ganglion. (ganglion = a group of cell bodies
in the PNS)
Ventral Root: motor nerves only. Impulses leave the
anterior root and ends in muscles or glands. No ganglion.
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Figure 14.2a The Spinal Cord and Spinal Meninges
Gray matter
White matter
White matter is
composed of axons
while gray matter is
Ventral root
composed of cell
bodies of neurons,
short un myelinated
Dorsal root
axons, dendrites and
neuroglia
Spinal nerve
Meninges
Pia mater
Arachnoid
mater
The meninges are
coverings over the
brain and spinal cord
composed of the
Dura mater which is
most exterior, the
arachnoidid mater,
and the pia mater
which is in close in
proximity to the brain
and spinal cord
Dura mater
a Posterior view of the spinal cord shows the
meningeal layers, superficial landmarks, and
distribution of gray and white matter.
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Dorsal root
ganglion
Figure 14.2b The Spinal Cord and Spinal Meninges
ANTERIOR
Meninges
Dura mater
Ant median fissure
Arachnoid
mater
Vertebral body
Subarachnoid
space
Autonomic
(sympathetic)
ganglion
Pia mater
Ventral
root of
spinal
nerve
Rami
communicantes
Ventral
ramus
Dorsal
ramus
Spinal cord
Adipose tissue
in epidural
space
Post. Medial sulcus
Denticulate Dorsal root
ganglion
ligament
POSTERIOR
b Sectional view through the spinal cord and meninges
shows the peripheral distribution of the spinal nerves.
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Figure 14.2c The Spinal Cord and Spinal Meninges
Spinal cord
Anterior median
fissure
Pia mater
Denticulate
ligaments
Arachnoid mater
(reflected)
Dura mater
(reflected)
Spinal blood
vessel
Dorsal root of
sixth cervical
nerve
Ventral root of
sixth cervical
nerve
c Anterior view of spinal cord shows meninges and spinal
nerves. For this view, the dura and arachnoid membranes
have been cut longitudinally and retracted (pulled aside);
notice the blood vessels that run in the subarachnoid
space bound to the outer surface of the delicate pia mater.
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Clinical Note 14.1 Spinal Taps and Spinal Anesthesia (Part 1 of 2)
Dura mater
Epidural space
Body of third
lumbar vertebra
Interspinous
ligament
Lumbar puncture
needle
Cauda equina in
subarachnoid
space
Filum terminale
The position of the lumbar puncture needle is in the subarachnoid
space, near the nerves of the cauda equina. The needle has been
inserted in the midline between the third and fourth lumbar
vertebral spines, pointing at a superior angle toward the
umbilicus. Once the needle correctly punctures the dura and
enters the subarachnoid space, a sample of CSF may be obtained.
Spinal Cord Structures
Figure 14.4c Sectional Organization of the Spinal Cord
Within columns are
tracts
Leg
Posterior white
column (funiculus)
Hip
Trunk
Arm
Lateral
white
column
(funiculus)
Flexors
Extensors
Hand
Forearm
Arm
Shoulder
Trunk
Anterior white
column (funiculus)
Anterior white
commissure
The left half of this sectional view shows the major columns of white matter. The right half
indicates the anatomical organization of sensory tracts in the posterior white column for
comparison with the organization of motor nuclei in the anterior gray horn. Note that both
sensory and motor components of the spinal cord have a definite regional organization.
C. Reflex Arcs
1. Monosynaptic Arc *fastest
a) Sensory neurons with receptor sense stimulus & bring
message to spinal cord &
synapse with…
b) motor neurons that send a message to an effector.
Eg) knee jerk
2. Polysynaptic reflex arcs * slower
1) Sensory neuron with receptors…
2) Interneurons, integration. One to 100’s of interneurons
3) Motor neuron & effector
Eg) Pull foot away from pain, but also activates
other muscles so you don’t fall.
Figure 14.6b Peripheral Distribution of Spinal Nerves
Sensory Information
From interoceptors
of back
From exteroceptors,
proprioceptors of back
Dorsal
root
Somatic
sensory
Visceral
sensory
Dorsal ramus
Ventral ramus
From exteroceptors,
proprioceptors of
body wall, limbs
Dorsal
root
ganglion
From interoceptors
of body wall, limbs
Rami
communicantes
KEY
Ventral
root
Somatic
sensations
Visceral
sensations
From interoceptors
of visceral organs
b A comparable view detailing the distribution of sensory neurons and sensory fibers
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Figure 14.6a Peripheral Distribution of Spinal Nerves
Motor Commands
Postganglionic fibers
to smooth muscles,
glands, etc., of back
To skeletal
muscles of back
Dorsal root
ganglion
Dorsal
root
Visceral
motor
Somatic
motor
Dorsal ramus
Ventral ramus
To skeletal
muscles of body
wall, limbs
Ventral
root
Postganglionic fibers to
smooth muscles, glands,
etc., of body wall, limbs
Spinal nerve
Sympathetic ganglion
White ramus
(preganglionic)
Rami
communicantes
Gray ramus
(postganglionic)
Sympathetic nerve
Postganglionic fibers
to smooth muscles,
glands, visceral organs
in thoracic cavity
KEY
Somatic motor
commands
Visceral motor
commands
a The distribution of motor neurons in the spinal cord and
motor fibers within the spinal nerve and its branches
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Preganglionic fibers to
sympathetic ganglia
innervating aboominopelvic viscera
Figure 14.16
Neural Organization and Simple Reflexes
Sensory
receptor
Ganglion
CENTRAL
NERVOUS
SYSTEM
Sensory
neuron
CENTRAL
NERVOUS
SYSTEM
Ganglion
Sensory
neuron
Interneurons
Circuit 2
Motor
neuron
Motor
neurons
Circuit 1
Sensory
receptor
(muscle
spindle)
Skeletal muscle 1
Skeletal muscle
A monosynaptic reflex circuit involves a peripheral
sensory neuron and a central motor neuron. In this
example, stimulation of the receptor will lead to a
reflexive contraction in a skeletal muscle.
Skeletal muscle 2
A polysynaptic reflex circuit involves a sensory neuron,
interneurons, and motor neurons. In this example, the
stimulation of the receptor leads to the coordinated
contractions of two different skeletal muscles.
Figure 14.16 Stretch Reflexes
Receptor (muscle spindle)
Stretch
1
Stimulus
Stimulus.
Stretching
of muscle
stimulates
muscle
spindles
2
Spinal cord
REFLEX
ARC
Activation of a
sensory neuron
Effector
3
4
5
Contraction
Information
processing at
motor neuron
Activation of
motor neuron
Response.
Contraction
of muscle
a Steps 1- 5 are common to all stretch reflexes.
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Sensory neuron
(stimulated)
Motor neuron
(stimulated)
b The patellar reflex is controlled by
Response
muscle spindles in the quadriceps
muscle group.The stimulus is a
reflex hammer striking the muscle
tendon, stretching the spindle fibers.
This results in a sudden increase in
the activity of the sensory neurons,
which synapse on spinal motor
neurons.The response occurs upon
the activation of motor units in the
quadriceps group, which produces
an immediate increase in muscle
tone and a reflexive kick.
Figure 14.13 A Reflex Arc
1
2
Arrival of
stimulus and
activation
of receptor
Dorsal
root
Activation of a
sensory neuron
Sensation
relayed to
the brain by
collateral
REFLEX
ARC
Receptor
Stimulus
Effector
5
Response
by effector
Ventral
root
4
Activation of a
motor neuron
3
Information processing
in CNS
KEY
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
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1. Destruction of ventral horn cells of spinal
cord result in a loss of :
a) association areas
b) all sensation
c) pain
d) motor control
Paired structures that contain cell bodies of sensory
neurons are:
a) Dorsal rami
b) ventral rami
c) dorsal root ganglion
d) ventral root ganglion
Spinal nerves are mixed nerves because:
a) They contain sensory and motor fibers
b) They exit at intervertebral foramina
c) Associate with dorsal root ganglia
d) Associated with ventral and dorsal roots
II. Spinal Nerves
II. Spinal Nerves
A. Anatomy
1. Spinal nerve: mixed. As it approaches the spinal cord, motor & sensory fibers separate forming
roots. (ventral root: motor fibers only; dorsal root; sensory fibers only) * mentioned
above
2. Arrangement of spinal nerve:
a) endoneurium: covers nerve fiber (axon)
b) perineurium: arranges nerve fibers into fascicles
c) epineurium: covers the entire peripheral nerve
3. Dorsal & ventral ramus: branching of spinal nerve. Delivers both sensory & motor to dorsal
& ventral compartments of the body.
4. Ramus communicans (Rami communicantes pl)leading to the sympathetic trunk gangliafor sympathetic fibers (ANS) to travel to the sympathetic ganglion.
5. 31 pairs of spinal nerves- all attached to spinal cord
Each nerve contains thousands of nerve fibers!
8 pairs cervical nerves (one nerve is above C1, one below C7, 6 in between = 8 pairs)
12 pairs of thoracic nerves
5 pairs lumbar
5 pairs of sacral nerves
1 coccygeal nerve
- Spinal nerves leave spinal cord via intervertebral foramen & sacral foramen
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Roots (either sensory or motor) Rami (mixed, spinal nerve split)
Spinal Nerves can be motor, sensory or mixed (both)
On the next slide, be able to identify the endoneurium, perineurium and epineurium
We have 8 pair of cervical nerves exiting through intervertebral foramina and are
named C1-C8
12 pair of thoracic nerves
5 pair of lumbar nerves
5 pair sacral nerves
1 coccygeal nerve
Plexus: A network of nerves – Cervical, brachial, lumbar and Sacral plexuses
Connections to head, arms, legs, addominal wall, pelvis
Figure 14.5a Anatomy of a Peripheral Nerve
Blood vessels
Connective Tissue
Layers
Epineurium covering
peripheral nerve
Perineurium (around
one fascicle)
Endoneurium
Schwann
cell
Fascicle
a A typical peripheral nerve and its
connective tissue wrappings
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Myelinated
axon
Figure 14.5b Anatomy of a Peripheral Nerve
Blood vessels
Connective Tissue
Layers
Epineurium covering
peripheral nerve
Perineurium (around
one fascicle)
Endoneurium
b A scanning electron micrograph showing
the various layers in great detail
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Define:
• Neuron
• Nerve fiber
• Nerve:
Spinal Nerves
B. Nerve plexus is a network of nerves. The ventral rami of all spinal nerves (except T2T12) branch & join each other lateral to the vertebral column.
Why?
1. So each branch of the plexus contains fibers from several different spinal
nerves.
2. Fibers from each spinal nerve travel to the body’s limbs in several different
ways.
*Damage of one spinal nerve cannot completely paralyze a particular
muscle
1. Cervical Plexus:
Spinal nerves C1-C4 (some fibers from C5)form this plexus which
innervates head,neck & diaphragm. Sensation of neck, ear, cheek,
shoulder, clavicular region motor to neck muscles (infrahyoid
muscles, scalenes, trapezius, levator scapulae)
a) Phrenic nerve: fibers from C3-C5 for motor & sensory
innervation to diaphragm. If both phrenic nerves are cut, or if
there is damage superior to C3-C5 respiratory failure will
occur.
Also responsible for hiccups! Reflexive response commonly
originates from sensory irritation to diaphragm or stomach.
Figure 14.9
The Cervical Plexus
C1
C2
Nerve roots of
cervical plexus
C3
C4
C5
Supraclavicular
nerves
Clavicle
Geniohyoid muscle
Thyrohyoid muscle
Phrenic nerve
Sternohyoid muscle
Sternothyroid muscle
2. Brachial Plexus:
C5-T1. innervate shoulder, thorax & upper extremity.
a) Axillary nerve: muscle of upper arm eg) deltoid, teres minor
b) Musculocutaneous nerve: innervates muscles of anterior arm eg) biceps
brachii, coracobrachialis, brachialis.
c) Median nerve: flexor/pronator of anterior forearm & hand, motor supply to
thumb (most of thenar muscles)
d) Ulnar nerve: to muscles & skin on ulnar side of forearm, hand & hypothenar
muscles. Because the ulnar nerve is exposed as it passes by the elbow, hitting
it will produce tingling sensation of little finger. “funny bone”
Ulnar nerve is also commonly damaged in the carpal tunnel region b/c its
superficially located there too- People with damage to this nerve cannot
adduct/abduct fingers nor form a tight grip b/c hypothenar muscles not working.
e) Radial nerve: muscles & skin on posterior arm & forearm & moves digits 2-5
* pressure palsy= limbs fall asleep.
Radial nerve palsy: “wrist drop”
Fibular palsy: leg falls asleep when they are crossed.
Figure 14.10b
The Brachial Plexus
C4
C5
C6
C7
C8
Superior trunk
Middle trunk
BRACHIAL
PLEXUS Inferior trunk
T1
Musculocutaneous
nerve
Median nerve
Ulnar nerve
Radial
nerve
Deep radial nerve
Superficial branch
of radial nerve
Ulnar nerve
Median nerve
Radial nerve
Deep branch of ulnar nerve
Superficial branch of ulnar nerve
Ulnar nerve
Palmar digital nerves
Median nerve
Anterior view of the brachial plexus and upper limb
showing the peripheral distribution of major nerves
Anterior
Distribution of
cutaneous nerves
Figure 14.10c The Brachial Plexus (Part 1 of 2)
Musculocutaneous
nerve
Axillary nerve
Branches of
axillary nerve
Radial nerve
Ulnar nerve
Median nerve
Posterior view of the brachial plexus and
the innervation of the upper limb
Figure 14.10b The Brachial Plexus
b This posterior view of the brachial
plexus shows the location and
distribution of the nerves.
Musculocutaneous
nerve
Axillary nerve
Branches of
axillary nerve
Radial nerve
Ulnar nerve
Median nerve
Posterior antebrachial
cutaneous nerve
Deep branch of
radial nerve
Radial
nerve
Superficial branch
of radial nerve
Ulnar
nerve
Dorsal digital nerves
Median
nerve
Posterior
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Radial Nerve Palsy
• Wrist drop, Saturday night palsy
• Pressure on back of the arm interrupts function of
radial nerve.
Figure 14.11 The Cervical and Brachial Plexuses
Clavicle, cut
and removed
Deltoid muscle
Musculocutaneous
nerve
Right axillary artery
over axillary nerve
Median nerve
Radial nerve
Biceps brachii,
long and short heads
Cervical
plexus
Right common
carotid artery
Brachial plexus
(C5–T1)
Sternocleidomastoid muscle,
sternal head
Sternocleidomastoid muscle,
clavicular head
Right subclavian
artery
Ulnar nerve
Coracobrachialis
muscle
Skin
Right brachial
artery
Median
nerve
Retractor holding
pectoralis major
muscle (cut and
reflected)
Nerves to thorax & abdomen:
don’t form a plexus
• T2-T12 innervate intercostal & abdominal muscles, as well
as sensory for skin on thorax & abdomen.
3. Lumbar plexus (L1-L4) . Lies within the psoas major muscle. Innervates muscles of
abdominal wall, psoas major itself, anterior thigh.
a) Femoral nerve: largest branch, descends vertically through center of the femoral
triangle. It then divides into several large branches. Innervates muscles & skin of
anterior thigh (quadriceps)
The largest branch of the femoral nerve becomes the saphenous after it passes
the knee. Saphenous nerve serves medial leg.
b) Obturator nerve: innervates adductors & skin on medial thigh. Passes through the
obturator foramen of pelvis & enters medial compartment of thigh
4. Sacral Plexus
L4-S4 (Lumbar & sacral plexus also called lumbosacral plexus)
These innervate the perineum, gluteal area & lower extremity.
a) Sciatic nerve: largest branch, longest & thickest in the body! Innervates posterior thigh
Actually, sciatic is 2 nerves in oneYou will see the split of these just before the back of the knee.
i. Tibial nerve: innervates muscles of calf & sole of foot
ii. Common fibular nerve: innervates superficial & deep muscles of
anterior & lateral leg
b) pudendal nerve: muscles of the perineum, urogenital diaphragm, external anal
sphincter, external urethral sphincter, skin of external genitalia &
bulbospongiosis, ischiocavnerosis ( muscles around the genitals)
5. Coccygeal nerve S4-S5 innervates skin & ligaments of coccyx
Figure 14.12a The Lumbar and Sacral Plexuses, Part I
T12
T12 subcostal nerve
L1
Iliohypogastric nerve
L2
LUMBAR
PLEXUS
Ilioinguinal nerve
Genitofemoral nerve
Lateral femoral
cutaneous nerve
Branches of
Femoral branch
genitofemoral
nerve Genital branch
Femoral nerve
Obturator nerve
L3
L4
L5
Lumbosacral
trunk
The lumbar plexus, anterior view
Figure 14.12a Peripheral Nerves Originating from the Lumbar and Sacral Plexuses
Nerves Originating
from the Lumbar
Plexus
Subcostal nerve
Iliohypogastric nerve
Illioinguinal nerve
Genitofemoral nerve
Lateral femoral
cutaneous nerve
Femoral nerve
Obturator nerve
Saphenous nerve
Common Fibular
Nerve and
Its Branches
Common fibular
nerve
Superficial fibular
nerve
Deep fibular nerve
a The lumbar and sacral
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plexuses, anterior view
Nerves Originating
from the Sacral Plexus
Superior gluteal nerve
Inferior gluteal nerve
Posterior femoral
cutaneous nerve
Pudendal nerve
Sciatic nerve
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Figure 14.12b Peripheral Nerves Originating from the Lumbar and Sacral Plexuses
Nerves Originating
from the Sacral Plexus
Superior gluteal nerve
Inferior gluteal nerve
Posterior femoral
cutaneous nerve
Pudendal nerve
Sciatic nerve
Branches of
the Sciatic
Nerve
Tibial nerve
Common fibular
nerve
Medial sural
cutaneous nerve
Lateral sural
cutaneous nerve
Sural nerve
Medial plantar nerve
Lateral plantar nerve
b The sacral plexus,
posterior view
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Figure 14.13c The Lumbar and Sacral Plexuses, Part II
Gluteus maximus
(cut)
Inferior gluteal
nerve
Pudendal nerve
Perineal branch
Hemorrhoidal
branch
Gluteus medius
(cut)
Gluteus minimus
Superior gluteal
nerve
Piriformis
Posterior femoral
cutaneous nerve
Perineal branches
Sciatic
nerve
Descending
cutaneous
branch
Semitendinosus
Biceps femoris
(cut)
Tibial nerve
Popliteal artery
and vein
Medial sural
cutaneous
nerve
Common fibular
nerve
Lateral sural
cutaneous
nerve
Gastrocnemius
Small saphenous
vein
Sural nerve
Calcaneal tendon
Tibial nerve
(medial calcaneal
branch)
A diagrammatic posterior view of the
right hip and lower limb detailing the
distribution of peripheral nerves
Figure 14.12d Peripheral Nerves Originating from the Lumbar and Sacral Plexuses
Gluteus
maximus (cut)
Superior gluteal
artery and nerve
Internal
pudendal
artery
Gluteus medius
Inferior gluteal nerve
Piriformis
Pudendal
nerve
Nerve to
gemellus
and
obturator
internus
Sciatic nerve
Posterior femoral
cutaneous nerve
Gluteus
maximus
d A dissection of the right gluteal region
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C. Dermatomes - Area of skin that is
mainly supplied by a single spinal nervesensory information.
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Dermatomes:
is an area of skin
that is mainly
supplied by a
sensory neurons
of one spinal nerve.
C2–C3
Figure 14.7 Dermatomes
NV
C2–C3
C2
C3
T2
C6
L1
Loss of sensation
to a particular
area tells you
there may be damage
to that spinal nerve.
L2
C8
C7
T1
L3
L4
L5
C3
C4
C5
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L4 L 3
L5
C4
C5
T2
C6
T1
C7
SS
S2
4 3
L1
S5
C8
S1 L5
L2 S2
L3
S1
L4
ANTERIOR
POSTERIOR