Download Nervous System

Chapter 2
The Nervous System
Overview

The human nervous system is an
extremely complex entity that
performs a multitude of functions, in
much the same way as a dynamic
network of interconnected computers
ANATOMY
Nervous system

The nervous system can be divided
into two anatomical divisions, each
with their own subdivisions:
– Central nervous system (CNS)
Brain
 Spinal cord

– Peripheral nervous system (PNS)
Cranial nerves
 Spinal nerves

Nerve


The nerve cell, or neuron, is the
functional unit of the nervous system
There are four functional parts to each
nerve:
– Dendrite
– Axon
– Cell body
– Axon terminal
Central Nervous System


Spinal cord - participates directly with
the control of body movements, the
processing and transmission of
sensory information from the trunk
and limbs, and the regulation of
visceral functions
Brain – central processor
Meninges

Three membranes, or meninges, envelop
the structures of the CNS:
– The dura. The outermost and strongest of the
layers
– The arachnoid. A thin and delicate avascular
layer
– The pia. Conveys the blood vessels that supply
the spinal cord, and has a series of lateral
specializations, the denticulate (dentate)
ligaments
Peripheral Nervous
System

Somatic Nerves
– Consists of the cranial nerves and the
spinal nerves
Cranial Nerves


The cranial nerves (CN) are typically
described as comprising 12 pairs,
which are referred to by the Roman
numerals I through XII
CN I (olfactory) and II (optic) are not
true nerves but are fiber tracts of the
brain
Cranial nerves


CN I – Olfactory. The olfactory nerve
is responsible for the sense of smell
CN II – Optic. The optic nerve is
responsible for vision
Cranial nerves

CN III – Oculomotor
– The somatic portion supplies the levator
palpabrae superioris muscle, the superior,
medial and inferior rectus muscles, and the
inferior oblique muscles. These muscles are
responsible for some eye movements.
– The visceral efferent portion of this nerve
innervates two smooth intraocular muscles: the
ciliary and the constrictor pupillae. These
muscles are responsible for papillary
constriction.
Cranial nerves


CN IV – Trochlear. Supplies the
superior oblique muscle
CN VI – Abducens. Supplies the lateral
rectus muscle
Cranial nerves

CN V – Trigeminal. Maxillary, ophthalmic
and mandibular branches. Ophthalmic and
maxillary are exclusively sensory, the latter
supplying the soft and hard palate, maxillary
sinuses, upper teeth and upper lip and the
mucous membrane of the pharynx. The
mandibular branch carries sensory
information but also represents the motor
component of the nerve, supplying the
muscles of mastication, both pterygoids, the
anterior belly of digastric, tensor tympani,
tensor veli palatini and mylohyoid.
Cranial nerves

CN VII – Facial. Comprised of a
sensory (intermediate) root, which
conveys taste, and a motor root, the
facial nerve proper, which supplies the
muscles of facial expression, the
platysma muscle, and the stapedius
muscle of the inner ear
Cranial nerves


CN VIII – Vestibulocochlear. Subserves
two different senses – balance and
hearing
CN IX – Glossopharyngeal. Contains
somatic motor, visceral efferent,
visceral sensory, and somatic sensory
fibers
Cranial nerves



CN X – Vagus. Contains somatic
motor, visceral efferent, visceral
sensory, and somatic sensory fibers
CN XI – Accessory. Cranial and spinal
component
CN XII – Hypoglossal. The motor
nerve of the tongue
The Spinal Nerves

A total of 31 symmetrically arranged pairs
– Divided topographically into 8 cervical pairs (C 18), 12 thoracic pairs (T 1-12), 5 lumbar pairs (L
1-5), 5 sacral pairs (S 1-5), and a coccygeal pair

Peripheral nerves are enclosed in three
layers of tissue of differing character. From
the inside outward, these are the
endoneurium, perineurium, and epineurium
Cervical Nerves

The 8 pairs of cervical nerves are
derived from cord segments between
the level of the foramen magnum and
the middle of the seventh cervical
vertebra
– Divide into a larger ventral ramus, and a
smaller dorsal ramus
Cervical Plexus

Sensory branches
– The small occipital nerve (C 2, 3)
– The great auricular nerve (C 2, 3)
– The cervical cutaneous nerve (cutaneous coli) (C
2, 3)
– Supraclavicular branches (C 3, 4)

Communication branches
– Ansa cervicalis

Muscular branches
Brachial Plexus

Arises from the anterior primary
divisions of the fifth cervical through
the first thoracic nerve roots, with
occasional contributions from the
fourth cervical and second thoracic
roots
Plexus Roots


The roots of the plexus, which consist
of C 5 and C 6, join to form the upper
trunk, C 7 becomes the middle trunk,
and C 8 and T 1 join to form the lower
trunks
Each of the trunks divides into anterior
and posterior divisions, which then
form cords
Plexus Branches

The branches give rise to the
peripheral nerves:
– Musculocutaneous (lateral cord)
– Axillary
– Radial (posterior cord)
– Ulnar (medial cord)
– Median (medial and lateral cords)
Nerves from the Roots

The dorsal scapular nerve (C 5)
– Supplies the rhomboids and levator
scapulae muscles

The long thoracic nerve (C 5-7)
– Supplies the serratus anterior muscle
Nerves from the Trunks


Subclavius
Suprascapular nerve. Motor supply to
the supraspinatus and infraspinatus
muscles, and sensory innervation to
the shoulder joint
Nerves from the Cords

The medial and lateral pectoral nerves.
– Supply the pectoralis major and pectoralis minor
muscles

Subscapular nerve
– Supplies the subscapularis muscle

Thoracodorsal nerve
– Supplies the latissimus dorsi muscle


Medial antebrachial cutaneous nerve
Medial brachial cutaneous nerve
The Musculocutaneous
Nerve (C 5-6)


Motor - supplies the coracobrachialis,
biceps brachii and brachialis muscles
Sensory - lateral antebrachial
cutaneous nerve
Axillary Nerve (C5–6)


Motor - Teres minor, deltoid muscle
Sensory - Superior lateral brachial
cutaneous nerve
The Radial Nerve (C 6-8, T 1)

Motor
– In the arm - supplies the triceps, anconeus, and
the upper portion of the extensor-supinator
group of forearm muscles
– In the forearm, the posterior interosseous nerve
innervates all of the muscles of the six extensor
compartments of the wrist, with the exception of
the extensor carpi radialis brevis (ECRB) and
extensor carpi radialis longus (ECRL)
The Radial Nerve (C 6-8, T 1)

Sensory
– The posterior brachial cutaneous nerve:
the dorsal aspect of the arm
– The posterior antebrachial cutaneous
nerve: the dorsal surface of the forearm
– The superficial radial nerve: the dorsal
aspect of the radial half of the hand
The Median Nerve (C 5-T 1)

Motor (anterior interosseous nerve)
– Innervation to flexor pollicis longus (FPL), and to
the pronator quadratus (PQ)
– May supply all or none of the flexor digitorum
profundus and part of the flexor digitorum
superficialis

Sensory - supplies the skin of the palmar
aspect of the thumb and the lateral 2 ½
fingers, and the distal ends of the same
fingers
The Ulnar Nerve (C 8, T 1)


Motor – supplies the flexor carpi ulnaris, the
ulnar head of the flexor digitorum
profundus, and all of the small muscles
deep and medial to the long flexor tendon
of the thumb, except the first 2 lumbricales
Sensory - supplies the ulnar side of the
dorsum of the hand, the dorsal aspect of
the fifth finger and the ulnar half of the
forefinger
The Thoracic Nerves


Dorsal rami
Ventral rami
The Lumbar Plexus

Formed from the ventral nerve roots
of the second, third, and fourth
lumbar nerves (in approximately 50%
of cases, the plexus also receives a
contribution from the last thoracic
nerve)
Branches

L 1, L 2, and L 4 divide into upper and
lower branches.
– The upper branch of L 1 forms the
iliohypogastric and ilioinguinal nerves
– The lower branch of L 1 joins the upper
branch of L 2 to form the genitofemoral
nerve
– The lower branch of L 4 joins L 5 to form
the lumbosacral trunk
Femoral Nerve (L2-4)

The motor component supplies the
iliopsoas muscle, while in the thigh it
supplies the sartorius, pectineus, and
quadriceps femoris muscles
Femoral Nerve (L2-4)

The sensory distribution of the femoral
nerve includes the anterior and medial
surfaces of the thigh via the anterior
femoral cutaneous nerve, and the
medial aspect of the knee, the
proximal leg and articular branches to
the knee, via the saphenous nerve
Obturator Nerve (L2-4)


The anterior division - supplies
muscular branches to the adductors
longus, brevis and the gracilis, and
rarely to the pectineus
The posterior division - supplies the
obturator externus, and the adductors
magnus and brevis
Lateral Cutaneous Nerve
(LCN) of the Thigh


A purely sensory nerve that is derived
primarily from the second and third
lumbar nerve roots, with occasional
contributions from the first lumbar
nerve root
Associated with meralgia paresthetica
The Sacral Plexus


The sacral plexus is formed by the ventral
rami of the L4-5 and the S1-4 nerves
The upper 3 nerves of the plexus divide into
2 sets of branches; the medial branches,
which are distributed to the multifidi
muscles, and the lateral branches, which
become the medial cluneal nerves
Superior Gluteal Nerve


The roots of the superior gluteal nerve
(L4, L5, S1) arise within the pelvis
from the sacral plexus
Supplies the gluteus medius and
gluteus minimus
Inferior Gluteal Nerve

Supplies the gluteus maximus
Sciatic Nerve



The largest nerve in the body
Arises from the L 4, L 5 and S 1-3
nerve roots as a continuation of the
lumbosacral plexus
Composed of the independent tibial
(medial) and common peroneal
(lateral) divisions
Common Fibular
(Peroneal) Nerve


Formed by the upper 4 posterior
divisions (L 4, 5 and S 1, 2) of the
sacral plexus
Three terminal rami: the recurrent
articular, the superficial peroneal, and
deep peroneal
The Superficial Fibular
(Peroneal)


Motor supply to the peroneus longus
and brevis muscles
Sensory distribution to the lower front
of the leg, to the dorsum of the foot,
part of the big toe, and adjacent sides
of the second to fifth toes up to the
second phalanges
The Deep Fibular
(Peroneal)


Supplies the tibialis anterior, extensor
digitorum longus, extensor hallucis
longus, and peroneus tertius muscles
Divides into a medial and lateral
branches
The Pudendal Plexus

Supplies the coccygeus, levator ani,
and sphincter ani externus muscles
Coccygeal Plexus

Small sensory anococcygeal nerves
derived from the last three segments
(S 4, 5, C)
The Tibial Nerve



Formed from all 5 anterior divisions (L 4, 5
and S 1, 2, 3)
Supplies the gastrocnemius, plantaris,
soleus, popliteus, tibialis posterior, flexor
digitorum longus pedis, and flexor hallucis
longus muscles
The portion of the tibial trunk below the
popliteal space is often called the posterior
tibial nerve
Sural nerve


A sensory branch of the tibial nerve
Formed by the lateral sural cutaneous
nerve from the common peroneal
nerve and the medial calcaneal nerve
from the tibial nerve
Proprioception

A specialized variation of the sensory
modality of touch, which plays an important
role in coordinating muscle activity, involves
the integration of sensory input concerning
static joint position (joint position
sensibility), joint movement (kinesthetic
sensibility), velocity of movement, and force
of muscular contraction, from the skin,
muscles, and joints
Mechanoreceptors

Four different types:
– Type I. Small Ruffini endings. Slowadapting, low threshold
– Type II. Pacinian corpuscles. Rapidly
adapting, low threshold
– Type III. Large Ruffini. Slowly adapting,
high threshold
– Type IV. Slowly adapting, high threshold
Balance


Balance is the process by which the body’s
center of mass is controlled with respect to
the base of support, whether that base of
support is stationary or moving
Three components of balance
– Vision
– Inner ear
– Vestibular system
Pain transmission

Common free nerve endings have two
distinct pathways into the central
nervous system, which correspond to
the two different types of pain:
– Fast conducting - A-delta fibers
– Slow conducting - C-fibers
Pain Control


Gate theory
The peri-aquaductal grey (PAG)
system
EXAMINATION
Upper Motor Neuron
Lesion

Characterized by spastic paralysis or
paresis, little or no muscle atrophy,
hyperreflexive deep tendon reflexes in
a non-segmental distribution, and the
presence of pathological signs and
reflexes
UMN Signs and Symptoms
– Periodic loss of consciousness
– Dysphasia
– Diplopia
– Hemianopia
– Ataxia
– Hyperreflexia
– Babinski response
UMN Signs and Symptoms
– Positive Hoffman or Oppenheim test
– Flexor withdrawal
– Nystagmus
– Quadrilateral paresthesia
– Bilateral upper limb paresthesia
– Peri-oral anesthesia
– Drop attacks
– Wallenberg syndrome
Lower Motor Neuron
Lesion

Characteristics of a LMN include
muscle atrophy and hypotonus, a
diminished or absent deep tendon
reflex (DTR) of the areas served by a
spinal nerve root, or a peripheral
nerve and an absence of pathological
signs or reflexes
Deep Tendon Reflex


A reflex is a subconscious programmed unit
of behavior in which a certain type of
stimulus from a receptor automatically leads
to the response of an effector
The spinal reflexes are the simplest (e.g.,
stretch reflex, withdrawal reflex) and are
entirely contained in the spinal cord
Pathological Reflexes

Pathological reflexes are normally
integrated by individuals as they
develop, unless an injury or disease
process results in a loss of this normal
suppression by the cerebrum on the
segmental level of the brainstem or
spinal cord, resulting in a release of
the primitive reflex
Pathological reflexes




Babinski
Oppenheim
Clonus
Hoffmann’s Sign
Supraspinal reflexes



The supraspinal reflexes produce
movement patterns that can be
modulated by descending pathways
and the cortex
Integrate vision with balance
Include the cervico-ocular reflexes
(COR) and vestibulo-ocular reflexes
(VOR)
Sensory testing


The dorsal roots of the spinal nerves
are represented by restricted
peripheral sensory regions called
dermatomes
The peripheral sensory nerves are
represented by more distinct and
circumscribed areas
Specific sensory tests

Pain
– Origin: Lateral spinothalamic tract
– Test: Pin-prick

Temperature
– Origin: Lateral spinothalamic tract
– Test: Using two test tubes, filled with hot
and cold water, the clinician touches the
skin and asks the patient to identify “hot”
or “cold.”
Specific sensory tests

Pressure
– Origin: Spinothalamic tract
– Test: Firm pressure is applied to the
patient’s muscle belly

Vibration
– Origin: Dorsal column/medial lemniscal
tract
– Test: Low-pitched tuning fork applied
over a bony process
Specific sensory tests

Position sense (Proprioception)
– Origin: Dorsal column/medial lemniscal tract
– Test: Ability to perceive passive movements of
the extremities

Movement sense (Kinesthesia)
– Origin: Dorsal column/medial lemniscal tract
– Test: Indicate verbally the direction of
movement while the extremity is in motion
Specific sensory tests

Stereognosis
– Origin: Dorsal column/medial lemniscal tract
– Test: Ability to recognize, through touch alone, a
variety of small objects such as comb, coins,
pencils, safety pins that are placed in the hand

Graphesthesia
– Origin: Dorsal column/medial lemniscal tract
– Test: Ability to recognize letters, numbers or
designs traced on the skin
Specific sensory tests

Two point discrimination
– Origin: Dorsal column/medial lemniscal
tract
– Test: A measure is taken of the smallest
distance between two stimuli that can still
be perceived by the patient as two
distinct stimuli
Tonal Abnormality


Spasticity
Rigidity
Cranial Nerve
Examination

CN I – The Olfactory Nerve
– The sense of smell is tested by having the
patient identify familiar odors

CN II – The Optic Nerve
– The optic nerve is tested by examining
visual acuity, and confrontation
Visual acuity - Snellen eye chart
 Confrontation - Test of peripheral vision

Cranial Nerve
Examination

CN III - Oculomotor; CN IV Trochlear; CN VI - Abducens (tested
together)
– Observation for pupil size, and ptosis of
the upper eyelids
– Consensual pupillary response to light
– Ability of the eyes to track movement in
the six fields of gaze
Cranial Nerve
Examination

CN V - Trigeminal
– Motor: The patient is asked to clench the
teeth, and the clinician palpates the
temporal and masseter muscles.
– Sensory: The three sensory branches of
the trigeminal nerve are tested, with pinprick, close to the mid-line of the face
– The jaw tendon reflex is assessed for the
presence of hyperreflexia
Cranial Nerve
Examination

CN VII – Facial
– The patient is asked to smile. If there is
asymmetry, the patient is asked to frown,
or wrinkle the forehead

CN VIII – Vestibulocochlear
– Balance testing
– Caloric stimulation or the ability of the
eyes to follow a moving object
– Hearing
Cranial Nerve
Examination

CN IX - Glossopharyngeal
– The gag reflex is used to test this nerve,
but is only reserved for the severely
affected patients

CN X - Vagus
– Voice quality
– Ability to say “aah”
Cranial Nerve
Examination

CN XI - Spinal Accessory
– Resisted shoulder shrug
– Resisted head rotation

CN XII - Hypoglossal
– The patient is asked to stick out the
tongue