The Peripheral Nervous System

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• The PeripheralNervous System

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I. The Peripheral Nervous System (PNS)

• A. Nerves allow the CNS to receive information
  and initiate action
• B. The PNS is functionally divided into sensory
  and motor divisions
• C. Sensory (afferent) division
• 1. somatic sensory
• 2. visceral sensory
• 3. special sensory (e.g. eye, ear)
• D. Motor (efferent) division
• 1. somatic motor
• 2. visceral motor (Autonomic Nervous System)
• a. sympathetic division
• b. parasympathetic division

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Peripheral nervous system (PNS)
Central nervous system (CNS)
Sensory (afferent) division
Motor (efferent) division
Somatic sensory
Visceral sensory
Somatic nervoussystem
Autonomic nervoussystem (ANS)
General Touch, pain,pressure,
vibration,temperature, andproprioception in
skin,body wall, and limbs
General Stretch, pain,temperature,
chemical changes, and irritationin viscera
nausea andhunger
Motor innervation of allskeletal muscles
Motor innervation of smooth muscle,
cardiacmuscle, and glands
Special Hearing,equilibrium, vision
Special Taste, smell
Sympatheticdivision
Parasympatheticdivision
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II. General Terms

• A. sensation - awareness of external/internal
  conditions
• B. perception - conscious registration of
  conditions
• C. stimulus - change that can initiate nerve
  impulse
• E. transduction - changing stimulus signal into
  nerve signal
• F. adaptation - decreased sensitivity with repeat
  stimuli
• a. rapidly adapting - pressure, touch, smell
• b. slowly adapting - pain, position, blood
  chemicals
• G. afterimage - sensation even after stimulus is
  gone
• H. modality - distinct property of each sensation

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• I. receptor (sense organ) - converts stimulus to
  impulse
• J. nerve bundle of axons carrying sensory or
  motor information
• a. can be motor only
• b. can be sensory only
• c. can be both sensory and motor (most)
• K. ganglion collection of nerve cell bodies
  located outside the CNS
• a. mostly the autonomic nervous system

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III. General Classification of Receptors

• A. Two main categories of sensory receptors
• 1. Free nerve endings of sensory neurons
• a. monitor general sensory information
• 2. Complete receptor cells
• a. specialized epithelial cells or small neurons
• b. monitor most types of special sensory
  information
• c. special senses vision, hearing, smell,
  taste, balance
•  

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•  B. Receptors Named by Location
•   1. exteroreceptors (outside) respond to
  external environment
• a. located at or near body surfaces
• b. include receptors for touch, pressure, pain,
  and temperature
• 2. enteroreceptors (inside) respond to
  internal environment
• a. located in digestive tube, bladder, and
  lungs
• b. monitor a variety of stimuli
• i. chemical concentration, taste, tissue
  stretching, temperature
• 3. proprioreceptors - respond to body
  position/motion
• a. located in skeletal muscles, tendons,
  joints, and ligaments
• b. monitor degree of stretch
• c. send inputs on body movement to the CNS
•  

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• C. Receptors Named by Type of Stimulus Detected
•   1. mechanoreceptors - any mechanical deviation
•   a. touch, pressure, vibration, proprioception
  etc.
• b. baroreceptors monitor blood pressure
• 2. thermoreceptors - changes in temperature
• 3. nocireceptors - pain physical or chemical
  damage
• 4. photoreceptors - light rods cones of the
  eye
•   5. chemoreceptors - shapes of different
  molecules
•   a. taste, smell, chemicals of blood
•  

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IV. General Sensory Receptors

• A. General sensory receptors (not special
  vision, hearing, etc.)
• 1. widely distributed
• 2. nerve endings of sensory neurons monitor
• a. touch, pressure, stretch, pain, temperature,
  proprioception
• B. Divided into two different groups
• 1. free nerve endings
• 2. encapsulated nerve endings

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• C. Free nerve endings
• 1. abundant in epithelia and underlying
  connective tissue
• 2. respond to pain and temperature
• 3. monitor affective senses (emotional response
  e.g. pain!)
• 4. epithelial tactile complexes (Merkel discs)
• a. tactile epithelial cell innervated by
  sensory nerve ending
• b. slowly adapting receptors for light touch
• 5. hair follicle receptorswrap around hair
  follicles
• a. rapidly adapting receptors

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• D. Encapsulated nerve endings
• 1. consist of one or more end fibers of sensory
  neurons
• 2. enclosed in connective tissue
• 3. mechanoreceptors
• a. tactile (Meissners) corpuscles
• b. lamellar (Pacinian) corpuscles
• c. bulbous corpuscles (Ruffini endings)
• d. proprioceptors

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• 4. Tactile (Meissners) corpuscles
• a. spiraling nerve ending surrounded by Schwann
  cells
• b. occur in the dermal papillae
• c. rapidly adapting receptors for discriminative
  touch
• d. occur in sensitive, hairless areas of the
  skin
• 5. Lamellar corpuscles
• a. nerve ending surrounded by layers of flat
  Schwann cells
• b. occur in the hypodermis
• c. sensitive to deep pressurerapidly adapting
  receptors

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• 6. Bulbous corpuscles
• a. located in the dermis and respond to pressure
• b. monitor continuous pressure on the skin -
  adapt slowly

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• 7. Proprioceptors
• a. monitor stretch in locomotory organs
• Three different types
• i. muscle spindles
• ? measure the changing length of a muscle
• ? embedded in the perimysium between muscle
  fascicles
• ii. intrafusal muscle fibers
• ? modified skeletal muscle fibers located within
  muscle spindles
• iii. anulospiral endings
• ? located around middle of intrafusal fibers
• ? stimulated by rate and degree of stretch

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• c. tendon organs
• ? are located near the muscle-tendon junction
• ? monitor tension within tendons
• d. joint kinesthetic receptors
• ? sensory nerve endings within the joint
  capsules
• i. lamellar corpuscles
• ii. bulbous corpuscles
• iii. free nerve endings
• iv. receptors resembling tendon organs

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Extrafusalmuscle fibers (contact)
Anulo-spiralendings (primarysensory endings)
Musclespindle
Intrafusalmuscle fibers
Capsule
Sensoryfiber
Tendon organ (tension)
Tendon
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V. Cranial Nerves An Overview

• A. Attach to the brain and pass through specific
  foramina of the skull
• B. Numbered from I to XII (roman numerals)
• 1. Cranial nerves I and II attach to the
  forebrain
• 2. All others attach to the brain stem
• C. Primarily serve head and neck structures
• D. vagus nerve (X) is the only cranial nerve that
  extends into the abdomen

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Filaments ofolfactory nerve (I)
Optic nerve (II)
Oculomotornerve (III)
Facial nerve (VII)
Trochlearnerve (IV)
Vestibulocochlearnerve (VIII)
Trigeminalnerve (V)
Abducensnerve (VI)
Glossopharyngealnerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
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Olfactory nerve (I)
Optic nerve (II)
Oculomotornerve (III)
Facial nerve (VII)
Trochlearnerve (IV)
Vestibulocochlearnerve (VIII)
Trigeminalnerve (V)
Abducensnerve (VI)
Glossopharyngealnerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
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The Cranial Nerves
Cranial nerves
Sensory function
Motor function
Cranial nerves
Sensory function
Motor function
Somaticsensory(SS)
Visceralsensory(VS)
Somaticmotor(SM)
Visceral motorparasympathetic(VM)
Somaticsensory(SS)
Visceralsensory(VS)
Somaticmotor(SM)
Visceral motorparasympathetic(VM)
I Olfactory
VII Facial
Smell
VM
SM
General
Generaltaste
II Optic
VIII Vestibulocochlear
Vision
Hearingequilibrium
Some
III Oculomotor
IX Glossopharyngeal
SM
VM
VM
SM
Generaltaste
General
X Vagus
VM
SM
Generaltaste
General
IV Trochlear
SM
V Trigeminal
XI Accessory
General
SM
SM
XII Hypoglossal
SM
SM
VI Abducens
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• Create your own memory device
• O__________________ F_________________
• O__________________ V_________________
• O__________________ G_________________
• T___________________ V_________________
• T___________________ A_________________
• A___________________ H_________________

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• Mikes memory device (not for a mixed audience)
• Oh! Feel
• Oh! Very
• Oh! Good
• To V_________________
• Touch A_________________
• And H_________________

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The Cranial Nerves
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Olfactory Nerves (I)

• A. Special visceral sensory - sense of smell
• B. Olfactory receptor cells located in olfactory
  epithelium of nasal cavity
• C. Olfactory bulbs project fibers into the nasal
  cavity
• C. Pass through the cribriform foramina of the
  ethmoid bone

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Olfactory Nerves (I)
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The Optic Nerves (II)

• A. Special somatic sensory - vision
• B. Originate on the retina of the eye
• C. Pass through the optic canals of the sphenoid
  bone
• D. Criss-cross at the optic chiasma

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Optic Nerves (II)
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The Oculomotor Nerves (III)

• A. Somatic motor - innervate four extrinsic eye
  muscles
• 1. Superior rectus
• 2. medial rectus
• 3. inferior rectus
• 4. inferior oblique
• B. Visceral motor
• ? Constricts pupil
• ? Controls shape of lens
• C. Pass through the superior orbital fissure

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Oculomotor Nerves (III)
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The Trochlear Nerves (IV)

• A. Somatic motor - the superior oblique muscle
• B. Pass ventrally and laterally around midbrain
• C. Pass through superior orbital fissure

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Trochlear Nerves (IV)
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The Trigeminal Nerves (V)

• A. Largest of the cranial nerves
• 1. Ophthalmic division (V1) superior oribital
  fissure
• 2. Maxillary division (V2) foramen rotundum
• 3. Mandibular division (V3) foramen ovale
• B. Cell bodies of sensory neurons located in the
  trigeminal ganglion
• C. Mandibular division motor fibers that
  innervate chewing muscles

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Trigeminal Nerves (V)
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The Abducens Nerves (VI)

• A. Somatic motor - innervates lateral rectus
  muscle
• B. Pass through the superior orbital fissure
• NOTE III (oculomotor) IV (trochlear) and VI
  (abducens)
• innervation of the muscles of the eye

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Abducens Nerves (VI)
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The Facial Nerves (VII)

• A. Special visceral sensory - taste buds on
  anterior two-thirds of tongue
• B. Somatic motor - innervate facial muscles
• C. Visceral motor - innervation of lacrimal
  glands, submandibular and sublingual salivary
  glands
• D. Enter temporal bone through the internal
  acoustic meatus

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Facial Nerves (VII)
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The Vestibulocochlear Nerves (VIII)

• A. Sensory nerve of hearing and equilibrium
• B. From inner ear - pass through the internal
  acoustic meatus
• C. Carries information from vestibular apparatus
  and cochlea

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Vestibulocochlear Nerves (VIII)
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The Glossopharyngeal Nerves (IX)

• A. General visceral sensory
• 1. posterior one-third of tongue
• 2. pharyngeal mucosa
• 3. chemoreceptors in carotid body
• 4. baroreceptors of carotid sinus
• B. Somatic motor - elevate pharynx during
  swallowing
• C. Visceral motor - innervate the parotid
  salivary gland
• D. Fibers pass through the jugular foramen

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Glossopharyngeal Nerves (IX)
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The Vagus Nerves (X)

• A. General visceral sensory - from thoracic and
  abdominal viscera
• B. Special visceral sensory - taste buds on
  epiglottis
• C. Somatic motor - skeletal muscles of the
  pharynx and larynx
• D. Visceral motor - parasympathetic innervation
  to
• 1. Heart, lungs, abdominal organs
• E. Fibers exit through the jugular foramen

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Vagus Nerves (X)
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The Accessory Nerves (XI)

• A. Somatic motor - innervates trapezius and
  sternocleidomastoid
• B. Pass into skull through foramen magnum
• C. Exit skull through the jugular foramen

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Accessory Nerves (XI)
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The Hypoglossal Nerves (XII)

• A. Somatic motor - innervate the tongue muscles
• B. Exit the skull through hypoglossal canal

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Hypoglossal Nerves (XII)
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The Spinal Nerves
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VI. Spinal Nerves

• A. 31 pairs - contain thousands of nerve fibers
• B. Connect to the spinal cord
• C. Named for point of issue from the spinal cord
• 8 pairs of cervical nerves (C1C8) (note C8)
• 12 pairs of thoracic nerves (T1T12)
• 5 pairs of lumbar nerves (L1L5)
• 5 pairs of sacral nerves (S1S5)
• 1 pair of coccygeal nerves (Co1)

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Ventral rami
Spinal nerves
Cervical plexus
CervicalnervesC1 C8
Brachial plexus
Cervicalenlargement
Intercostalnerves
ThoracicnervesT1 T12
Lumbarenlargement
LumbarnervesL1 L5
Lumbar plexus
Sacral plexus
SacralnervesS1 S5
Cauda equina(spinal nerves)
CoccygealnerveCo1
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• D. Connect to the spinal cord by the dorsal root
  and ventral root
• 1. Dorsal rootcontains sensory fibers
• ? cell bodieslocated in the dorsal root ganglion
• 2. Ventral rootcontains motor fibers
• ? arising from anterior gray horn of spinal
  cord
• E. Each branch into dorsal ramus and ventral
  ramus
• ? Dorsal and ventral rami contain sensory and
  motor fibers
• F. Sympathetic chain ganglia from T1 L2

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Sensory axon and cell body
Dorsal rootganglion
Dorsal root
Dorsalramus
Nerves
Spinalnerve
Ventral root
Ventralramus
Axon ofmotorneuron
Sensory receptors inskin (e.g., free
nerveendings of sensoryneuron)
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Gray matter
White matter
Dorsal and ventralrootlets of spinal nerve
Ventral root
Dorsal root
Dorsal rootganglion
Dorsal ramusof spinal nerve
Ventral ramusof spinal nerve
Spinal nerve
Sympathetic chain ganglion
Anterior view showing spinal cord, associated
nerves, and vertebrae. The dorsaland ventral
roots arise medially as rootlets and join
laterally to form the spinal nerve.
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VII. Innervation of the Back

• A. Dorsal rami - innervate back muscles
• 1. follow a neat, segmented pattern
• 2. innervate a horizontal strip of muscle and
  skin
• B. Ventral rami - arranged in simple, segmented
  pattern
• 1. intercostal nerves - supply intercostal
  muscles, skin, and abdominal wall
• 2. each gives off lateral and anterior cutaneous
  branches

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Dorsal ramus
Ventral ramus
Spinal nerve
Intercostal nerve
Sympathetic chainganglion
Branches of intercostal nerve
Sternum
Cross section of thorax showing the main roots
and branches of a spinal nerve
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VIII. Introduction to Nerve Plexuses

• A. Nerve plexus - a network of spinal nerves that
  criss-cross with each other give rise to the
  nerves of the body
• 1. branch and join with one another
• 2. fibers from ventral rami crisscross (except
  T2T12)
• 3. form the four nerve plexuses
• a. cervical plexus
• b. brachial plexus
• c. lumbar plexus
• d. sacral plexus
• 4. primarily serve the limbs

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• B. Cervical plexus
• 1. formed by ventral rami of first four cervical
  nerves (C1C4)
• a. most are cutaneous nerves
• b. some innervate muscles of the anterior neck
• 2. phrenic nerve C3C5
• a. the most important nerve of the cervical
  plexus
• b. innervates the diaphragm
• 3. accessory nerve (XI) C5
• Note a nerve can have nerve fibers from
  different spinal nerves

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Ventral rami
Hypoglossalnerve (XII)
Ventralrami
C1
C2
C3
C4
Accessory nerve (XI) (C3,4,5)
C5
Phrenic nerve (C3,4,5)
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• C. Brachial plexus
• 1. lies in the neck and axilla
• 2. formed by ventral rami of C5T1
• 3. cords give rise to 5 main nerves of the upper
  limb
• a. musculotaneous nerve - biceps brachii and
  brachialis C5C7
• b. axillary nerve - deltoid and teres minor
  C5C6
• c. ulnar nerve - hand muscles and skin of the
  medial hand C8T1
• d. median nerve - anterior forearm muscles and
  lateral palm C5T1
• e. radial nerve - muscles of the posterior
  upper limb C5T1
• 4. Roots gtgtgt Trunks gtgtgt Divisions gtgtgt Cords gtgtgt
  Nerves
• Note a nerve can be composed of fibers from
  different spinal nerves

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The Brachial Plexus
Major terminalbranches(peripheral nerves)
Roots(ventralrami)
Cords
Divisions
Trunks
Anterior
Musculocutaneous
C5
Upper
Lateral
Posterior
Median
C6
Medial
Anterior
C7
Ulnar
Middle
Posterior
C8
Radial
Posterior
Anterior
Axillary
Lower
T1
Posterior
Flowchart summarizing relationships within the
brachial plexus
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The Brachial Plexus
Roots (C5T1)
C5
Upper
C6
Divisions
Middle
Trunks
C7
C8
Lower
Lateral
T1
Cords
Posterior
Medial
Axillary
Musculo-cutaneous
Radial
Median
Ulnar
Anteriordivisions
Posteriordivisions
Trunks
Roots
Roots (rami C5T1), trunks, divisions, and cords
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Axillary nerve
The Brachial Plexus
Musculo-cutaneous nerve
Radial nerve
Median nerve
Ulnar nerve
Digitalbranches
The major nerves of the upper limb
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The Brachial Plexus
Digitalbranches
The major nerves of the upper limb
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• D. Lumbar plexus
• 1. Arises from L1 to L4
• 2. innervate the posterior abdominal wall and
  psoas muscle
• 3. Main branches innervate the anterior thigh
• a. femoral nerve - anterior thigh muscles L2L4
• b. obturator nerve - innervates adductor
  muscles L2L4
• Note a nerve can be composed of fibers from
  different spinal nerves

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Ilioinguinalnerve
Femoral nerve
Lateralfemoralcutaneous
Nerves of the lumbar plexus,anterior view
Obturator
Ventralrami
Anteriorfemoralcutaneous
Ventral rami
Anterior division
L1
Posterior division
Saphenous
L2
Iliohypogastric
Ilioinguinal
L3
Genitofemoral
Lateral femoralcutaneous
L4
Obturator
L5
Femoral
Ventral rami and major branches of thelumbar
plexus
Distribution of the major nerves from thelumbar
plexus to the lower limb
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Nerves of the lumbar plexus,anterior view
Ventralrami
Ventral rami
Anterior division
L1
Posterior division
L2
L3
L4
L5
Ventral rami and major branches of thelumbar
plexus
Distribution of the major nerves from thelumbar
plexus to the lower limb
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• E. Sacral plexus
• 1. Arises from spinal nerves L4S4
• 2. sciatic nerve - the largest nerve of the
  sacral plexus L4S3
• a. actually two nerves in one sheath
• b. tibial nerve - most of the posterior lower
  limb L4S3
• c. common fibular nerve - muscles of
  anterolateral leg L4S2
• 3. superior and inferior gluteal nerves - the
  gluteal muscles L4S2
• 4. pudendal nerve - muscles of the perineum
  S2S4
• Note a nerve can be composed of fibers from
  different spinal nerves
• Note a nerve can be composed of fibers from
  different spinal nerves

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Common fibularnerve
Tibial nerve
Superiorgluteal
Inferiorglutealnerve
Sciatic nerve
Pudendalnerve
Sciatic
Dissection of the gluteal region,posterior view
Posteriorfemoralcutaneousnerve
Ventral rami
Ventralrami
Anterior division
Posterior division
L4
Commonfibular
Superiorgluteal
L5
Tibial
Lumbosacraltrunk
S1
Inferior gluteal
Deep fibular
Commonfibular
S2
Superficialfibular
Tibial
S3
Posteriorfemoralcutaneous
S4
Pudendal
S5
Co1
Sciatic
Ventral rami and major branches of thesacral
plexus, anterior view
Distribution of the major nerves fromthe sacral
plexus to the lower limb, posterior view
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Dissection of the gluteal region,posterior view
Ventral rami
Anterior division
Posterior division
L4
L5
S1
S2
S3
S4
S5
Co1
Ventral rami and major branches of thesacral
plexus, anterior view
Distribution of the major nerves fromthe sacral
plexus to the lower limb, posterior view
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IV. Innervation of the Skin Dermatomes

• A. Dermatome - an area of skin innervated by
  cutaneous branches of a single spinal nerve
• B. Upper limb - supplied by nerves of the
  brachial plexus
• C. Lower limb
• 1. lumbar nerves - anterior surface
• 2. sacral nerves - posterior surface

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C2
Dermatomes of the Anterior
C3
C4
C5
T1
T2
T3
T4
T2
T2
T5
T6
T7
T8
C6
C6
T9
T10
C5
C5
T11
T12
L1
L1
C6
C6
S2
C7
C7
C8
S3
C8
L2
L2
L3
L3
L4
L4
L5
L5
S1
S1
Anterior view
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C2
C3
Dermatomes of the Posterior
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
C6
C6
T11
T12
C7
C7
L1
S1
L2
C8
C8
L3
S2
L5
L4
S3
S4
S4
S2
S2
S1
S1
L1
L2
L5
L5
L3
L4
L4
L4
L5
L5
S1
Posterior view
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IX. Disorders of the PNS

• A. Shingles (herpes zoster)
• 1. viral infection - stems from childhood chicken
  pox
• 2. often brought on by stress
• 3. mostly experienced by people over 50
• 4. extremely painful
• B. Migraine headache
• 1. relates to sensory innervation of cerebral
  arteries
• 2. arteries dilate and compress and irritate
  sensory nerve endings

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• C. Peripheral neuropathy
• 1. pathological condition of peripheral nerves
• 2. symptoms of sensory nerve involvement
• a. paresthesia, pain, burning, loss of sensation
• 3. symptoms of motor nerve involvement
• a. muscle weakness and paralysis
• 4. causes
• a. trauma, repetitive use (e.g. carpal tunnel
  syndrome)
• b. systemic disorders HIV, diabetes, vitamin B
  deficiency