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Lecture 4,5,6:Spinal Cord
Structure & Function
Dr. Amjad El-Shanti
MD,MPH, PhD
Assistant professor of Public Health- Epidemiology
2014-2015
Grouping of Neural Tissue
• White matter: Aggregations of myelin
axons from many neurons supported by
neuroglia.
• The lipid of substance myelin have a
whitish color that gives white matter its
name
• Gray matter: contains either nerve cell
bodies, and dendrites or bundles of
unmyelinated axons , and neuroglia.
• The absence of myelin in these areas
accounts for their gray color.
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• Nerve: A bundle of fibers located outside
the central nervous system
• The dendrites of somatic afferent neurons
and axons of somatic efferent neurons of
peripheral nervous system are myelinated,
so most nerves are white matter.
• Ganglia: A group of nerve cell bodies with
other group of cell bodies outside the
central nervous system.
• Ganglia are masses of gray matter since
they are made up of a nerve cell bodies
• Tract: A bundle of fibers in the central nervous system.
• Tracts may run long distances up and down the spinal
cord.
• Tracts also exit in the brain and connect parts of the
brain with each other and with the spinal cord.
• Ascending Tracts: Tracts that conduct impulses up the
cord and concerned with sensory impulses.
• Descending Tracts: Tracts that carry impulses down the
cord and carry motor commands.
• The major tracts consist of myelinated fibers and are
therefore white matter
• Nucleus: A mass of nerve cell bodies and dendrites in
the central nervous system.
• The nucleus forms gray matter.
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• Horns (Columns) are the chief areas of
gray matter in the spinal cord.
• Horn describes the (Two- Dimensional
appearance) of the organization of gray
matter in the spinal cord (cross-section).
• Column describes the (Three-Dimensional
appearance) of gray matter in the spinal
cord (Longitudinal columns).
• The gray matter will be described as
arranged in horns, because the white
matter also arranged incolumns.
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General Features of Spinal Cord
• Shape: Cylindrical structure (slightly
flattened anteriorly & posteriorly.
• Location: Extends from the foramen
magnum of the occipital bone as a
continuation of the medulla oblongata
(inferior part of the brain stem) to the level
of the second lumbar vertebra.
• Length: 42- 45 cm (adult spinal cord)
• Diameter: about 2.54 cm at midthoracic,
but larger in the lower cervical & midlumbar region
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•
Enlargments: There are two conspicuous
enlargements.
1. Cervical enlargement: The superior
enlargement extends from the C4 to T1
vertebra. (Nerves that supply the upper
extremities arise from the cervical
enlargement).
2. Lumbar enlargement: The inferior
enlargement extends from T9 to T12
vertebra. (Nerves that supply the lower
extremities arise from the lumbar
enlargement).
• Conus medularis: Ending of spinal cord below the lumbar
enlargement as a conical portion at the level of intervertebral disc between the first and second lumbar vertebra
• Filum terminale: Anon-nervous fibrous tissue of the spinal
cord that extends inferiorly to attach to the coccyx. (consists
mostly of pia matter: inner most of three membranes that
cover and protect the spinal cord and brain)
• Cauda equina: (Horse’s tail) Some nerves that arise from
lower portion of the cord do not leave the vertebral column
immediately but angle inferiorly in the vertebral canal like
wips of coarse hair flowing from the end of the cord.
• Spinal segment: A region of spinal cord from which a pair of
spinal nerves arises.
• Spinal cord is a series of 31 segments, each giving rise to a
pair of spinal nerves.
• Anterior median fissure: Deep wide groove on the anterior
(ventral) surface of spinal cord.
• Posterior median sulcus: shallower narrow groove on the
posterior (dorsal) surface of spinal cord.
• The spinal cord is divided into right & left sides by the above
two grooves
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Protection of Spinal Cord
The spinal cord is protected by different
structures:
A.
B.
C.
D.
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Vertebral column
Meninges
Ligaments
Cerebrospinal fluid (CSF)
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A. Vertebral Canal
• The spinal cord is located in the vertebral
column.
• The canal is formed by the vertebral
foramina of all vertebrae arranged on top
of each other.
• The cord is well protected, because the
wall of vertebral canal is essentially a ring
of bone surrounding the spinal cord.
B. Spinal Meninges
•
Meninges: Are coverings that run
continuously around the spinal cord &
brain.
• There are three layers of membranes
that cover the spinal cord arranged from
outside to inside respectively as
following:
1. Dura matter (Outermost layer).
2. Arachnoid layer (Middle layer).
3. Pia matter (Innermost layer).
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•
•
•
•
•
Dura matter
The outer spinal meninx. (Tough mother).
It forms a tube from the level of S2 vertebra,
where it is fused with the filum terminale, to the
foramen magnum, where it is continuous with
the dura matter of brain.
It is composed of dense fibrous connective
tissue.
Epidural Space: Space between the dura
matter and the wall of vertebral canal.
Epidural space is filled with:
1. Fat
2. Connective tissue
3. Blood vessels
•
•
Epidural space serves as a padding around
the cord.
Epidural space inferior to L2 vertebra is the
site for the injection of anesthetics.
Arachnoid Layer
• The middle spinal meninx . (Spider layer).
• It is a delicate connective tissue membrane
that forms a tube inside the dura matter.
• It is continuous with arachnoid of the brain.
• Subdural Space: Space between the dura
matter and the arachnoid contains serous
fluid.
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•
•
•
•
Pia matter
The inner meninx. (Delicate mother).
It is transparent fibrous membrane that
forms a tube around and adheres to the
surface of the spinal cord & brain.
It contains numerous blood vessels.
Subarachnoid space: Space between the
arachnoid and the pia matter, where the
cerebrospinal fluid (CSF) circulates.
• All three spinal Meninges cover the spinal
nerves up to the point of exit from the spinal
column through the intervertebral foramina.
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C. Ligaments
•
Denticulate Ligaments: Are extensions of pia
matter attached laterally to the dura matter
along the length of the cord between the
ventral and dorsal roots of spinal nerves on
either side
• Denticulate Ligaments protect spinal cord
against shock & sudden displacement.
•
Summary:
Spinal cord is fixed in its position in the vertebral
canal by:
1. Filum Terminale which anchored to the coccyx
inferiorly.
2. Denticulate Ligaments laterally to the dura matter
3. Superiorly to the brain
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Structure of spinal cord in cross section
• The spinal cord consists of both gray and white matter.
• Gray matter consists primarily of nerve cell bodies and
unmyelinated axons and dendrites of association and
motor neurons.
• White matter consists of bundles of myelinated axons of
motor and sensory neurons.
• Gray matter forms H- shaped area within the white
matter.
• Gray commissure The cross bar of h shaped area.
• Central canal small space in the central of gray
commissure runs the length of spinal cord with
continuation with the fourth ventricle of fourth brain.
• Anterior (Ventral) white Commissure Bar connects the
white matter of left & right side of spinal cord.
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1
Spinal Nerve
5
Central Canal
2
Dorsal Root Ganglion
6
Grey Matter
3
Dorsal Root (Sensory)
7
White Matter
4
Ventral Root (Motor)
Gray Matter of Spinal Cord
• Anterior (Ventral) gray horns: The motor part of
gray matter closer to the front of the cord
• Posterior (Dorsal) gray horns: The sensory part
of gray matter closer to the back of the cord.
• Lateral (Intermediate) gray horns: The region
between the anterior & posterior gray horns
• The gray matter contains several nuclei that
serve as relay stations for impulses and origins
for certain nerves.
• Nuclei: are clusters of nerve cell bodies and
dendrites in the spinal cord and brain.
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White Matter of spinal cord
•
The white matter like the gray matter is organized into
regions divided by anterior & posterior gray horns into
3 broad areas:
1.
2.
3.
•
•
•
•
•
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Anterior white Columns
Posterior white Columns
Lateral white Columns
Column (Funiculus) consists of bundles of myelinated
fibers run the length of the cord.
Tracts (Fasiculi): Bundles of fibers
Ascending tracts: Sensory axons that conduct
impulses that enter the spinal cord upward to the brain.
(Sensory Tracts)
Descending Tracts: Motor axons that conduct impulses
from the brain downward into the spinal cord which
synapse with other neurons whose axons pass out to
muscles and glands. (Motor Tracts)
Short Tracts: Ascending and Descending axons that
convey impulses from one level of the cord to other.
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Function of Spinal Cord
1. Convey sensory impulses from the
periphery to the brain, and conduct motor
impulses from the brain to the periphery.
2. Provide means of integrating reflexes.
Spinal Tracts
•
•
•

1.
2.
3.
4.

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Vital function of spinal tracts is to convey sensory
& motor information to & from the brain.
These informations are carried by Ascending &
descending tracts of spinal cord.
Names of Spinal Tracts:
indicates the followings:
White column (Funiculus) in which the tract
travels.
Where the cell bodies of the tract originate
Where the axons of the tract terminate
The direction of impulse conduction
E.g. Anterior Spinothalamic Tract
Origin :
Spinal cord, Termination: Thalamus, Direction :
Ascending
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Ascending & Descending Tracts
Ascending Tracts
Location
(White Column)
Origin
Termination
Function
Anterior
Spinothalamic
Anterior column
Posterior gray horn, crossed to
opposite side of brain
Thalamus, Impulses
eventually conveyed to
cerebral cortex
Touch , pressure sensations
from one side of body to
opposite side of thalamus.
Eventually reach cerebral
cortex.
Lateral
spinothalamic
Lateral column
Posterior gray horn, crossed to
opposite side brain
Thalamus, Impulses
eventually conveyed to
cerebral cortex
Pain, temperature
sensations from one side of
body to opposite side of
thalamus. Eventually reach
cerebral cortex.
Posterior
column
Axons of afferent neurons from
periphery that enter posterior
column on one side of cord and
rise to same side of brain
Nucleus gracilis &
nucleus cuneatus of
medulla, impulses
conveyed to cerebral
cortex eventually
1-Two-point discrimination
2-proprioception
3- stereognosis
4-weight discrimination
5- vibration
From one side To same side
of medulla . Eventually
reach cerebral cortex.
Fasciculus
gracilis &
Fasciculus
cuneatus
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Posterior
spinocerebellar
Posterior
portion of lateral
column
Posterior gray horn, rises to same
side of brain
cerebellum
Sensations from one side of
body to same side of
cerebellum for subconscious
proprioception.
Anterior
spinocerebellar
Anterior portion
of lateral
column
Posterior gray horn, contains both
crossed & uncrossed fibers
cerebellum
Sensations from both sides
of body to cerebellum for
subconscious
proprioception.
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• Two-point discrimination: Ability to
distinguish that two points on skin are
touched even though close together.
• Proprioception: Awareness of precise
position of body parts and their direction of
movement.
• Stereognosis: ability to recognize size,
shape and texture of object.
• Weight discrimination: Ability to assess
weight of an object
Lateral Spinothalamic Tract
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Fasciculus gracilis & Fasciculus Cuneatus
Spinocerebellar Tracts
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Descending
Tracts
Location
(White Column)
Origin
Termination
Function
Lateral
Corticospinal
Lateral column
Cerebral cortex on one side of
brain but crosses in base of
medulla to opposite side of cord
Anterior gray horn
Motor impulses from one side of
cortex to anterior gray horn of
opposite side. Eventually reach
skeletal muscle on opposite
side of body that coordinate
precise discrete movements.
Anterior
Corticospinal
Anterior Column
Cerebral cortex on one side,
uncrosses in medulla, but
crosses to opposite side of
cord
Anterior gray horn
Motor impulses from one side of
cortex to anterior gray horn of
same side. But cross to
opposite side in spinal cord and
reach skeletal muscles that
coordinate discrete movement.
Rubrospinal
Lateral Column
Midbrain (Red nucleus) on one
side of brain, but crosses to
opposite side of cord.
Anterior gray horn
Motor impulses from one side of
midbrain to skeletal muscles on
opposite side of body that are
concerned with muscle tone and
posture.
Tectospinal
Anterior Column
Midbrain (Red nucleus) on one
side of brain, but crosses to
opposite side of cord.
Anterior gray horn
Motor impulses from one side of
midbrain to skeletal muscles on
opposite side of body that
control movements of head in
response to auditory, visual, and
cutaneous stimulation
Vestibulospinal
Anterior Column
Medulla on one side of brain
and descends to same side of
cord
Anterior gray horn
Motor impulses from one side of
medulla to skeletal muscles on
same side of body that regulate
body in tone in response to
movements of head
(equilibrium).
Descending Tracts
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Reflex Center
• The second principal function of spinal cord is to serve
as center for reflex action.
• Spinal nerves are the paths of communication between
the spinal cord tracts and the periphery.
• Dorsal Root (sensory): contains sensory nerve fibers
only and conducts impulses from the periphery to the
spinal cord. Fibers extend into the posterior gray horn
• Dorsal Root Ganglion: swelling contains the cell bodies
of the sensory neurons from the periphery.
• Ventral Root (Motor): contains motor nerve fibers only
and conduct impulses from the spinal cord to the
periphery.
• Cell bodies of the motor neurons are located in the gray
matter of the cord.
• If motor impulses supplies a skeletal muscle, the cell
bodies located in anterior gray horn.
• If motor impulses supplies a smooth muscle, cardiac
muscle & a gland, the cell bodies located in lateral gray
horn. (Autonomic Nervous System).
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1
Spinal Nerve
5
Central Canal
2
Dorsal Root
Ganglion
6
Grey Matter
3
Dorsal Root
(Sensory)
7
White Matter
4
Ventral Root (Motor)
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•
•
•
Reflex Arc &Homeostasis
Conduction pathway : The path an
impulse follows from its origin in the
dendrites or cell body of a neuron in one
part of the body. (Circuits of neurons).
Reflex Arc: Functional unit of the
nervous system contains two or more
neurons over which impulses are
conducted from a receptor to the brain or
spinal cord and then to the effector. ( one
pathway).
Function of Reflex Arc: Responding to a
change in the internal or external
environment. Responding to preserve
homeostasis.
• Components of Reflex Arc :
1. Receptor: The distal end of a dendrite or a
sensory structure with the distal end of a
dendrite.
2. Sensory Neuron: Passes the impulse from
receptor to its axonal terminal in CNS.
3. Center: A region in the central nervous system
where an incoming sensory impulse generates
an outgoing motor impulse.
4. Motor Neuron: Transmit the impulse generated
by the sensory or association neuron in the
center to the organ of body that will respond.
5. Effector : The organ of body (muscle, gland) that
responds to the motor impulse.
• Responding= Reflex
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• In the center, the impulse may be inhibited
or transmitted or rerouted.
• In the center of :
some reflex arcs, the sensory neuron
directly generates the impulse in the motor
neuron.
The center may contain association
neuron between the sensory neuron and
motor neuron.
Reflex Arc components
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Reflexes Features & Types
• Reflexes are fast responses to changes in the internal or
external environment that allow the body maintain
homeostasis.
• Reflexes are associated not only with skeletal muscle
contraction but also with body functions ( heart rate,
respiration, digestion, urination, & deification).
• Spinal reflexes: Reflexes carried out by spinal cord alone
• Spinal reflexes are either somatic reflexes or Visceral
Reflexes.
• Somatic reflexes: Reflexes that result in contraction of
skeletal muscles.
• Visceral (Autonomic ) reflexes: reflexes cause the
contraction of smooth or cardiac muscle or secretion by
glands.
Somatic Spinal Reflexes
1.
2.
3.
4.
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Stretch Reflex
Tendon Reflex
Flexor (Withdrawal) Reflex
Crossed Extensor Reflex
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Characters
Stretch Reflex
Tendon Reflex
Flexor Reflex
Crossed Extensor
Synapse
Monosynaptic (at
anterior gray horn)
polysynaptic
Polysynaptic
polysynaptic
stimulus
Rapid Stretching of
muscle (Change in the
length of muscle):
degree, rate
Change in muscle
tension caused by
passive stretch or
muscular contraction
Painful (Noxious)
stimulus (nail, Tack)
Painful (Noxious)
stimulus (nail, Tack)
Receptor
Muscle Spindle
Golgi tendon organ
Cutaneous (skin) and pain
receptors
Cutaneous (skin) and
pain receptors
pathway
Ipsilateral
Ipsilateral
Ipsilateral &
intersegmental
(Ascending &
Descending branches)
Contralateral
Response
Contraction of
stretched muscle
Relaxation of muscle
which its tendon
stretched
Several motor
responses
Opposite to action of
muscles affected bt
flexor reflex
Function
1- essential for
maintaining of muscle
tone
2-Important for muscle
function during exercise
3- prevent injury from
over stretching
Protection of tendon
& their muscles from
damage that might be
brought by excessive
tension
(Protective reflex)
Withdrawing of
affected extremity to
avoid pain
Cross extension aids in
maintaining posture
when leg is lifted
Reciprocal
innervation
Yes: inhibition of
antagonistic muscles
Yes: excitation of
antagonistic muscles
Yes: Inhibition of
antagonistic muscles
Yes: excitation of
antagonistic muscles
e.g.
Patellar reflex (Tapping
Quadriceps femoris
muscle)
Large force on tendon
(pull on muscle when
resisted)
Sharp, painful stimulus (as
in stepping on nail)
Sharp, painful stimulus
(as in stepping on nail)
•
•
•
•
•
•
•
•
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Monosynaptic reflex Arc: There is only one synapse in the pathway (only
two neurons are involved).
Polysynaptic reflex arc: More than two neurons are involved, there is more
than one synapse.
Ipsilateral reflex: The sensory impulse enters the spinal cord on the same
side that the motor impulse leaves the spinal cord.
Contralateral reflex: The sensory impulse enters one side of the spinal
cord & exits on the opposite side.
Reciprocal Innervation: Phenomenon by which impulses stimulate
contraction of muscle and simultaneously inhibit contraction of
antagonistic muscles.
Reciprocal innervation is important to avoid conflict between prime movers
and antagonists, an is vital in coordinating body movements.
Inhibition of antagonistic muscles: inhibition of contraction of antagonistic
muscles (Extension of antagonistic muscles).
Excitation of antagonistic muscles: excitation of contraction of antagonistic
muscles (flexion of antagonistic muscles).
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Stretch & tendon Reflexes
Flexor & Crossed Extensor
Reflexes
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Reflexes and Diagnosis
•
•
•
•
•
Reflexes are often used for diagnosis disorders of the
nervous system and locating the injured tissue.
If a reflex cease to function or if functions abnormally,
the specialist may suspect that the damage lies
somewhere along a particular conduction pathway.
Visceral reflexes are usually not practical tools for
diagnosis, since they are deep in the body.
Somatic reflexes can be tested simply by tapping or
stroking the body.
The reflexes of clinical significance are:
1. Patellar reflex.
2. Achilles reflex.
3. Babinski sign.
4. Abdominal reflex.
Spinal Nerves
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Names of Spinal Nerves
•
•
•
•
The 31 pairs of spinal nerves are named &
numbered according to the region and level of
spinal cord from which they emerge.
The first cervical pair emerges between the atlas
& the occipital bone.
All other spinal nerves leave the vertebral column
from the intervertebral foramina between
adjoining vertebrae.
There are:
1.
2.
3.
4.
5.
8 pairs of cervical nerves
12 pairs of thoracic nerves
5pairs of lumbar nerves
5 pairs of sacral nerves
1 pair of coccygeal nerves
Composition & Coverings of Spinal Nerves
• A spinal nerve has two points of attachments (posterior root
&anterior root).
• The posterior &anterior roots unite to form a spinal nerve at the
intervertebral foramen.
• The spinal nerve is a mixed nerve since the posterior root
contains sensory fibers, and the anterior root contains motor
fibers.
• The individual fibers, whether myelinated or unmyelinated are
wrapped in a connective tissue called the Endoneurium.
• Groups of fibers with their endoneurium in bundles called
Fascicles.
• Each fascicle is wrapped in connective tissue called
Perineurium.
• The outermost covering around entire nerve is the Epineurium.
• The spinal meninges fuse with the epineurium as the nerve
exits from the vertebral canal.
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Coverings of spinal nerves
Distribution of Spinal nerves
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Branches of spinal nerve
•
After a spinal nerve leaves its intervertebral
foramen, it divides into several branches
(Rami):
1. Dorsal ramus: innervates the deep muscles and
skin of dorsal surface of the back.
2. Ventral ramus: innervates the superficial back
muscles and all the structures of the extremities and
the lateral and ventral trunk.
3. Meningeal branch: reenters the spinal canal through
the intervertebral foramen and supplies the
vertebrae, vertebral ligaments, blood vessels of the
spinal cord and the meninges.
4. Rami communicants: components of autonomic
nervous system.
Cross-Section of Spinal Cord
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Plexuses
•
•
Plexus: Networks of ventral rami of spinal nerves
with adjacent nerves on either side of the body
(except for thoracic nerves T2-T11).
The principal plexus are:
1.
2.
3.
4.
•
•
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Emerging from the plexuses are nerves bearing
names that are often descriptive of the general
regions that supply.
Each nerve have several branches named for the
specific structures they innervate.
plexuses
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Cervical plexus
• Deep in the side of the neck, just even with the initial 4 cervical
vertebrate, there lies the cervical plexus.
• The anterior rami of the initial 4 cervical nerves with
combination of C5 designate the nerve fibers which create this
particular plexus
• The cervical plexus creates numerous branches and then
innervate the various related structures, such as the skin and
muscles of the neck and the appropriate surrounding skin and
muscles of the shoulders and head.
• A few muscles belonging to the neck and pharynx receive a
few extra nerve fibers, derived from the cervical plexus and a
combination of the accessory and hypoglossal cranial nerves
that all mesh into one in order to serve this area.
• The phrenic nerve is created by the unification of the third,
fourth, and fifth cervical nerve.
• The phrenic nerve is responsible for innervating the
diaphragm.
• The diaphragm contracts, which expels air into the lungs, due
to the commands of the motor impulses relayed by the phrenic
nerve.
Branches of
•
The cervical plexus has two types of branches:
cutaneous and muscular.
A. Cutaneous (4 branches):
A. Lesser occipital nerve - innervates lateral part of occipital region
(C2,C3)
B. Greater auricular nerve - innervates skin near concha auricle
and external acoustic meatus (C2&C3)
C. Transverse cervical nerve - innervates anterior region of neck
(C2&C3)
D. Supraclavicular nerves - innervate region of suprascapularis,
shoulder, and upper thoracic region (C3,C4)
B. Muscular
A. Ansa cervicalis (loop formed from C1-C3), etc. (geniohyoid (C1
only), thyrohyoid (C1 only), sternothyroid, sternohyoid,
omohyoid)
B. Phrenic Nerve (C3-C5) :Diaphragm
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Brachial plexus
• The brachial plexus is an arrangement of nerve fibres,
running from the spine, specifically from above the fifth
cervical vertebra to underneath the first thoracic vertebra
(C5-T1).
• It proceeds through the neck, the axilla (armpit region)
and into the arm.
• The brachial plexus is responsible for cutaneous and
muscular innervation of the entire upper limb, with two
exceptions: the trapezius muscle innervated by the
spinal accessory nerve and an area of skin near the
axilla innervated by the intercostobrachialis nerve.
• This function may be impaired by tumor growth of the
Apical region of either Lung.
• Therefore, brachial plexus lesions can lead to severe
functional impairment.
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Path of Brachial Plexus
•
•
•
One can remember the order of brachial plexus elements by way of the
mnemonic, "Read The Damn Cadaver Book" (Or, alternatively, Randy
Travis Drinks Cold Beer") - Roots, Trunks, Divisions, Cords, Branches or Roots, Trunks, Divisions, Cords, Collateral/Pre-terminal Branches, and
(Terminal) Branches.
The five roots are the five anterior rami of the spinal nerves, after they have
given off their segmental supply to the muscles of the neck.
These roots merge to form three trunks:
– "superior"or "upper" (C5-C6)
– "middle" (C7)
– "inferior"or "lower" (C8-T1)
•
Each trunk then splits in two, to form six divisions:
– anterior division of the superior, middle and inferior trunks
– posterior division of the superior, middle, and inferior trunks
•
These six divisions will regroup to become the three cords. The cords are
named by their position in respect to the axillary artery.
– The posterior cord is formed from the three posterior divisions of the trunks (C5T1)
– The lateral cord is the anterior divisions from the upper and middle trunks (C5C7)
– The medial cord is simply a continuation of the lower trunk (C8-T1)
•
The branches are listed below. Most branch from the cords, but a few
branch directly from earlier structures.
•
Three important nerves arising from
brachial plexus:
1. Radial nerve: supplies the muscles on the
posterior aspect of the arm and the forearm.
(Posterior cord: C5-T1)
2. Median nerve: supplies most of the muscles
of the anterior forearm and some of the
muscles in the palm. (union of Lateral &
Medial cords: C5-T1)
3. Ulnar nerve: supplies the anteromedial
muscles of the forearm an most of the
muscles of the palm. (Medial cord: C8-T1)
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Nerves & Distributions of Brachial Plexus
From
Nerve
Roots
Muscles
Cutaneous
roots
dorsal scapular nerve
C5
rhomboid muscles and levator scapulae
-
roots
long thoracic nerve
C5, C6,
C
7
serratus anterior
-
superior
trunk
nerve to the subclavius
C5, C6
subclavius muscle
-
superior
trunk
suprascapular nerve
C5, C6
supraspinatus and infraspinatus
-
lateral cord
lateral pectoral nerve
C5, C6,
C
7
pectoralis major (by communicating with the medial
pectoral nerve)
-
lateral cord
musculocutaneous nerve
C5, C6,
C
7
coracobrachialis, brachialis and biceps brachii
becomes the lateral cutaneous nerve of the
forearm
lateral cord
lateral root of the median nerve
C5, C6,
C
7
fibres to the median nerve
-
posterior
cord
upper subscapular nerve
C5, C6
subscapularis (upper part)
-
posterior
cord
thoracodorsal nerve (middle
subscapular nerve)
C6, C7,
C
8
latissimus dorsi
-
posterior
cord
lower subscapular nerve
C5, C6
subscapularis (lower part ) and teres major
-
posterior
cord
axillary nerve
C5, C6
anterior branch: deltoid and a small area of
overlying skin
posterior branch: teres minor and deltoid
posterior branch becomes upper lateral
cutaneous nerve of the arm
muscles
33
posterio
r cord
radial nerve
C5, C6,
C7, C8,
T1
triceps brachii, supinator, anconeus, the
extensor muscles of the forearm, and
brachioradialis
skin of the posterior arm as the posterior cutaneous nerve of the arm
medial
cord
medial pectoral
nerve
C8, T1
pectoralis major and pectoralis minor
-
medial
cord
medial root of
the median
nerve
C8, T1
fibres to the median nerve
portions of hand not served by ulnar or radial
medial
cord
medial
cutaneous nerve
of the arm
C8, T1
-
front and medial skin of the arm
medial
cord
medial
cutaneous nerve
of the forearm
C8, T1
-
medial skin of the forearm
medial
cord
ulnar nerve
C8, T1
flexor carpi ulnaris, the medial 2 bellies of
flexor digitorum profundus, most of the small
muscles of the hand
the skin of the medial side of the hand and medial one and a half
fingers on the palmar side and medial two and a half fingers on the
dorsal side
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Brachial Plexus
Lumbar Plexus
• The lumbar plexus is a nervous plexus in
the lumbar region of the body.
• It is formed by the loops of communication
between the anterior divisions of the first
three and the greater part of the fourth
lumbar nerves; the first lumbar often
receives a branch from the last thoracic
nerve.
• It is situated in the posterior part of the
Psoas major, in front of the transverse
processes of the lumbar vertebræ
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Branches of Lumbar plexus
• The lumbar plexus differs from the brachial plexus in not
forming an intricate interlacement, but the several nerves of
distribution arise from one or more of the spinal nerves, in the
following manner:
• The first lumbar nerve, frequently supplemented by a twig
from the last thoracic, splits into an upper and lower branch;
the upper and larger branch divides into the iliohypogastric
and ilioinguinal nerves; the lower and smaller branch unites
with a branch of the second lumbar to form the genitofemoral
nerve.
• The remainder of the second lumbar nerve, and the third and
fourth lumbar nerves, divide into ventral and dorsal divisions.
• The ventral division of the second lumbar nerve unites with
the ventral divisions of the third and fourth lumbar nerves to
form the obturator nerve.
• The dorsal divisions of the second and third nerves divide into
two branches, a smaller branch from each uniting to form the
lateral femoral cutaneous nerve, and a larger branch from
each joining with the dorsal division of the fourth nerve to form
the femoral nerve (The largest nerve arising from the lumbar plexus).
• The accessory obturator, when it exists, is formed by the
union of two small branches given off from the third and fourth
nerves.
Nerves & Distributions of Lumbar plexus
35
Division
Name
Source
Target
Main
Iliohypogastric nerve
1 L.
Skin over the lateral gluteal region and above the pubis
Main
Ilioinguinal nerve
1 L.
Skin over the root of the penis and upper part of the scrotum (male), skin
covering the mons pubis and labium majus (female)
Main
Genitofemoral nerve
1, 2 L.
Genital Branch: Cremaster muscle, skin of scrotum/labia majora Femoral
Branch: Skin on anterior thigh
Dorsal
Lateral femoral cutaneous
2, 3 L.
Skin on the lateral part of the thigh
Ventral
Obturator nerve (and Accessory
obturator nerve, when
present)
2, 3, 4 L.
Medial compartment of thigh
Dorsal
Femoral nerve
2, 3, 4 L.
Anterior compartment of thigh
Ventral
Lumbosacral trunk
4, 5L., 1,
2, 3,
4 S.
Sacral plexus
[1]
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Lumbar Plexus
Sacral Plexus
• In human anatomy, the sacral plexus is a nerve plexus
emerging from the sacral vertebrae (S1-S4), and which
provides nerves for the pelvis and lower limbs.
• The sacral plexus lies on the back of the pelvis between
the piriformis muscle and the pelvic fascia.
• In front of it are the internal iliac artery, internal iliac
vein, the ureter, and the sigmoid colon.
• The superior gluteal artery and vein run between the
lumbosacral trunk and the first sacral nerve, and the
inferior gluteal artery and vein between the second and
third sacral nerves.
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Branches of Sacral plexus
•
1.
2.
3.
•
•
•
•
•
The sacral plexus is formed by:
the lumbosacral trunk
the anterior division of the first sacral nerve
portions of the anterior divisions of the second, third and fourth
sacral nerves
The nerves forming the sacral plexus converge toward the lower
part of the greater sciatic foramen, and unite to form a flattened
band, from the anterior and posterior surfaces of which several
branches arise.
The band itself is continued as the sciatic nerve, which splits on the
back of the thigh into the tibial nerve and common fibular nerve;
these two nerves sometimes arise separately from the plexus, and
in all cases their independence can be shown by dissection.
The largest nerve in the body is the sciatic nerve.
The Sciatic nerve supplies the entire musculature of leg and foot.
Often, the sacral plexus and the lumbar plexus are considered to be
one large nerve plexus, the lumbosacral plexus. The lumbosacral
trunk connects the two plexuses.
Nerves & Distributions of Sacral Plexus
37
Nerve
Segmen
ts
Muscles
Nerve to
quadratus
femoris
L4-S1
gemellus inferior,
quadratus femoris
Superior
gluteal nerve
L4-S1
gluteus medius,
gluteus minimus,
tensor fasciae latae
Sciatic nerve
L4-S3
* Tibial
nerve
L4-S3
posterior
compartment
posterolateral leg and foot - medial sural cutaneous nerve
* Common
fibular
(Peroneal)
nerve
L4-S3
anterior compartment
and lateral
compartment
anterolateral leg and foot - Lateral sural cutaneous nerve, medial
dorsal cutaneous nerve, intermediate dorsal cutaneous nerve
Nerve to
obturator
internus
L5-S2
gemellus superior,
obturator internus
Inferior
gluteal nerve
L5-S2
gluteus maximus
Nerve to
piriformis
S1-S2
piriformis
Cutaneous
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Posterior cutaneous
nerve of thigh
S1-S3
-
Thigh
&
Buttock
Perforating
cutaneous nerve
S2-S3
-
Buttock
Pudendal nerve
S2-S4
bulbospongiosus, deep transverse perineal, ischiocavernosus,
sphincter urethrae, superficial transverse perineal
clitoris,
penis
Coccygeal nerve
S4-Co1
-
perineu
m
Sacral Plexus
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Thoracic (Intercostal ) Nerves
• Spinal nerves T2-T11 do not enter into the formation of
plexuses.
• Nerves T2-T11 are known as Intercostal (Thoracic)
nerves.
• They are distributed directly to the structures they supply
in the intercostal spaces.
• After leaving its intervertebral foramen, the ventral ramus
of nerve T2 supplies the intercostal muscles of the skin
and the skin of the axilla and posteromedial aspect of the
arm.
• Nerves T3-T6 pass in the costal grooves of the ribs and
are distributed to the intercostal muscles and skin of the
anterior and lateral chest wall.
• Nerves T7-T11 supply the intercostal muscles and the
abdominal muscles and overlying skin.
• The dorsal rami of the intercostal nerves supply the deep
back muscles and skin of the dorsal aspect of the thorax.
Dermatomes
• Dermatome is a Greek word which literally means
"skin cutting".
• A dermatome: is an area of the skin supplied by
nerve fibers originating from a single dorsal nerve
root.
• The dermatomes are named according to the
spinal nerve which supplies them.
• The dermatomes form into bands around the
trunk but in the limbs their organisation is more
complex as a result of the dermatomes being
"pulled out" as the limb buds form and develop
into the limbs during embryological development.
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• In diagrams or maps, the boundaries of
dermatomes are usually sharply defined.
• However, in life there is considerable
overlap of innervation between adjacent
dermatomes. Thus, if there is a loss of
afferent nerve function by one spinal nerve
sensation from the region of skin which it
supplies is not usually completely lost as
overlap from adjacent spinal nerves
occurs: however, there will be a reduction
in sensitivity.
Dermatome Map of the Body
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Spinal cord injury
•
1.
2.
3.
4.
5.
6.
7.
Causes:
Tumors
Blood Clots
Degenerative disorders
Demylination disorders
Fracture of the vertebrae
Dislocation of the vertebrae
Penetrating wounds by projectile metal
fragments.
8. Traumatic events (Automobile
Accidents).
Plegia: Paralysis
• The paralysis which caused due to spinal cord
injury depends on the location and extent of
the injury:
• Monoplegia: paralysis of one extremity only.
• Diplegia: paralysis of both upper extremities or
both lower extremities.
• Paraplegia: paralysis of both lower extremities.
• Hemiplegia: paralysis of the upper extremity,
trunk, and lower extremity of one side of the
body.
• Quadriplegia: paralysis of the two upper and
two lower extremities.
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21/04/36
•
Complete Transection of the spinal cord: The cord is
cut transversely and severed from one side to the
other side. The following results:
1.
2.
Loss of all sensations below the level of transection
Loss of all voluntary movement blow the level of transection
A.
B.
•
If the upper cervical cord is transected: quadriplegia results.
If the Transection is between the cervical & lumbar enlargements:
paraplegia results.
Partial Transection (Hemisection): below the
hemisection, the following results:
1.
2.
3.
A.
B.
Loss of proprioception, tactile discrimination, and feeling of
vibration on the same side of injury.
Paralysis on the same side.
Loss of feelings of pain and temperature on the opposite side.
If the hemisection is of the upper cervical cord , Hemiplegia
results.
If the hemisection of the thoracic cord , paralysis of one lower
extremity results (Monoplegia).
• Spinal Shock: An initial period following
transection lasts from a few days to
several weeks characterized by areflexia
condition.
• During this period, all reflex activity is
abolished (Areflexia).
• After this period, there is return of reflex
activity.
• The first reflex to return is the knee jerk. Its
appearance may take several days.
• Next, the flexion reflexes return over a
period of up to several months.
• Then the crossed extensor reflexes return.
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Delayed Nerve Grafting
•
•
•
•
Severe damage resulting from transection was
thought to be irreversible.
Technique for regenerating severed spinal
cords in animals is developed recently.
This technique is called Delayed Nerve
Grafting .
Delayed Nerve Grafting:
1. Cutting the crushed or injured section of the spinal
cord
2. Bridging the gap with nerve segments from the arm
or the leg.
3. The original served axons in the cord can grow
through the bridge.
43