Peripheral Nervous Peripheral Nervous SystemSystem

Ch. 13Ch. 13

Sensory receptors:Sensory receptors: Classified according to location and Classified according to location and

type of stimulationtype of stimulation

Location: Location: Exteroceptors - stimulation arising outside of Exteroceptors - stimulation arising outside of

the body (touch, pain, and temperature) the body (touch, pain, and temperature)

Interoceptors - stimulation arising inside the Interoceptors - stimulation arising inside the body (chemical messengers, stretching of body (chemical messengers, stretching of tissue, and internal temperature) tissue, and internal temperature)

Proprioceptors - respond to internal Proprioceptors - respond to internal stimuli, but located only in skeletal stimuli, but located only in skeletal muscle, tendons, joints, and ligaments muscle, tendons, joints, and ligaments and C.T. covering bones and muscles. and C.T. covering bones and muscles.

Stimulus detected: Stimulus detected: -- Mechanoreceptors (touch, pressure, Mechanoreceptors (touch, pressure,

vibrations) vibrations) -- Thermoreceptors (temperature) Thermoreceptors (temperature) -- Photoreceptors (light) Photoreceptors (light) -- Chemoreceptors (smell, taste, blood Chemoreceptors (smell, taste, blood

chemistry) chemistry) -- Nociceptors (pain) Nociceptors (pain)

Nerves:Nerves:

Nerve consists of parallel bundles of Nerve consists of parallel bundles of peripheral axons enclosed by peripheral axons enclosed by connective tissue coverings: connective tissue coverings:

-- Epineurium Epineurium

-- Perineurium (surrounds fascicle) Perineurium (surrounds fascicle)

-- Endoneurium (surrounds axon) Endoneurium (surrounds axon)

Direction of transmission: Direction of transmission:

-- Mixed nerves - contain both sensory and Mixed nerves - contain both sensory and motor fibers and transmit to and away motor fibers and transmit to and away from CNS from CNS

-- Sensory nerves - contain sensory fibers Sensory nerves - contain sensory fibers carrying impulses toward the CNS carrying impulses toward the CNS

-- Motor nerves - contain sensory fibers Motor nerves - contain sensory fibers carrying impulses away from the CNScarrying impulses away from the CNS

PNS nerves classified as cranial or spinal PNS nerves classified as cranial or spinal

Regeneration of a severed nerve:Regeneration of a severed nerve:

1- Separated ends seal off and swell 1- Separated ends seal off and swell

2- Axon and myelin sheath (of injured 2- Axon and myelin sheath (of injured site) disintegrates site) disintegrates

3- Schwann cells and macrophages 3- Schwann cells and macrophages migrate to site to phagocytize migrate to site to phagocytize debris debris

4- Neurilemma remains intact and 4- Neurilemma remains intact and schwann cells proliferate schwann cells proliferate

5- Axon "sprouts", guided by schwann 5- Axon "sprouts", guided by schwann cells, gap to original contact cells, gap to original contact

Cranial nerves:Cranial nerves:- 12 pairs12 pairs- Classified as sensory, motor or mixedClassified as sensory, motor or mixed- First two pairs attach to the forebrainFirst two pairs attach to the forebrain- Remaining ten pairs attach to the Remaining ten pairs attach to the

brainstembrainstem

Olfactory nerve (I)Olfactory nerve (I)- SensorySensory- Sense of smellSense of smell- Olfactory bulbs that terminate into Olfactory bulbs that terminate into

filaments piercing the cribriform filaments piercing the cribriform plate of the ethmoid bone.plate of the ethmoid bone.

- Clinical: person is asked to identify Clinical: person is asked to identify an odoran odor

- Anosmia: lack of smellAnosmia: lack of smell

Optic nerve (II)Optic nerve (II)- SensorySensory- VisionVision- Not a true nerve but an extension of Not a true nerve but an extension of

the brainthe brain- Begins at the retina, converges at the Begins at the retina, converges at the

optic chiasma, partial crossing over of optic chiasma, partial crossing over of the fibers to enter the thalamus. Optic the fibers to enter the thalamus. Optic radiations take impulse to the visual radiations take impulse to the visual cortex in the occipital lobe.cortex in the occipital lobe.

http://www.occipital.net/main.php

Oculomotor Nerve (III)Oculomotor Nerve (III)- MotorMotor- Motor fibers to the 4 of the six eye Motor fibers to the 4 of the six eye

musclesmuscles- Eyeball movementEyeball movement- Pupil constrictionPupil constriction

Trochlea Nerve (IV)Trochlea Nerve (IV)- MotorMotor- Movement of one eye muscle: Movement of one eye muscle:

superior oblique musclesuperior oblique muscle- Downward and lateral movement of Downward and lateral movement of

the eyeball.the eyeball.

Trigeminal nerve (V)Trigeminal nerve (V)- MixedMixed- Largest cranial nerveLargest cranial nerve- Sensory to the face, controls muscles of Sensory to the face, controls muscles of

mastication (temporalis and masseter)mastication (temporalis and masseter)- Three divisions: VThree divisions: V11- Ophthalmic division- Ophthalmic division

VV22- Maxillary division- Maxillary division

VV33- Mandibular division- Mandibular division- Nucleus located in the ponsNucleus located in the pons

Abducens (VI)Abducens (VI)- MotorMotor- Innervates the lateral rectus muscle Innervates the lateral rectus muscle

of the eyeof the eye- Moves eyeball laterally Moves eyeball laterally

Facial Nerve (VII)Facial Nerve (VII)- MixedMixed- Exits at the stylomastoid foramenExits at the stylomastoid foramen- Controls muscles of facial expressionControls muscles of facial expression- Controls lacrimal and salivary glandsControls lacrimal and salivary glands- Taste of anterior 2/3 of tongueTaste of anterior 2/3 of tongue- Bell’s palsy; unilateral facial paralysisBell’s palsy; unilateral facial paralysis

Vestibulocochlear Nerve Vestibulocochlear Nerve (VIII)(VIII)

- SensorySensory- Vestibulo branch: equilibriumVestibulo branch: equilibrium- Cochlear branch: hearingCochlear branch: hearing- Travels through the internal acoustic Travels through the internal acoustic

meatusmeatus

Glossopharyngeal Nerve (IX)Glossopharyngeal Nerve (IX)- MixedMixed- Fibers emerge from medulla and exit Fibers emerge from medulla and exit

the jugular foramen.the jugular foramen.- Innervates part of the tongue and Innervates part of the tongue and

pharynxpharynx- Taste for bitter on the posterior 1/3 Taste for bitter on the posterior 1/3

of the tongue (Bitter Back 9)of the tongue (Bitter Back 9)- Swallowing and gag reflexSwallowing and gag reflex

Vagus (X)Vagus (X)- MixedMixed- Only cranial nerve to extend below the Only cranial nerve to extend below the

head and neck into thorax and head and neck into thorax and abdomenabdomen

- Heart rate, breathing and digestive Heart rate, breathing and digestive function.function.

- Sensory from the visceraSensory from the viscera- Recurrent laryngeal nerve branches Recurrent laryngeal nerve branches

innervate larynx (voice box)innervate larynx (voice box)

Spinal Accessory Nerve (XI)Spinal Accessory Nerve (XI)- MotorMotor- Innervates trapezius and Innervates trapezius and

sternocleidomastoid musclesternocleidomastoid muscle- Clinical: ask patient to shrug Clinical: ask patient to shrug

shoulders against resistanceshoulders against resistance

Hypoglossal Nerve (XII)Hypoglossal Nerve (XII)- MotorMotor- Tongue movements: swallowing and Tongue movements: swallowing and

speech.speech.

OOh, h, ooh, h, ooh, h, tto o ttouch ouch aand nd ffeel eel vvery ery

ggreen reen vvegetables- egetables- AHAH

OrOr

OOn n ooccasion ccasion oour ur ttrusty rusty ttruck ruck aacts cts ffunny- unny- vvery ery ggood ood vvehicle ehicle aanynyhhowow

Spinal nervesSpinal nerves 31 pairs of spinal nerves31 pairs of spinal nerves- Mixed nervesMixed nerves- (8) Cervical - cervical and brachial - (8) Cervical - cervical and brachial

plexus plexus - (12) Thoracic - intercostal nerves and - (12) Thoracic - intercostal nerves and

cervical and lumbosacral enlargement cervical and lumbosacral enlargement - (5) Lumbar - lumbar plexus - (5) Lumbar - lumbar plexus - (5) Sacral - sacral plexus - (5) Sacral - sacral plexus - (1) Coccygeal - (1) Coccygeal

Branches (one passing through Branches (one passing through intervertebral foramen): intervertebral foramen):

- dorsal ramus: deep muscles and skin dorsal ramus: deep muscles and skin of the dorsal surface of the trunkof the dorsal surface of the trunk

- ventral ramus: muscles and ventral ramus: muscles and structures of the upper and lower structures of the upper and lower limbs and the lateral and ventral limbs and the lateral and ventral trunk trunk

Formation of Spinal NervesFormation of Spinal Nerves

Formation of Spinal NervesFormation of Spinal Nerves

Brachial plexusBrachial plexus Arises from spinal nerves C4-T1Arises from spinal nerves C4-T1Serves the arm and shoulderServes the arm and shoulder

Median nerve: Flexor muscles of the Median nerve: Flexor muscles of the anterior forearm and small muscle in anterior forearm and small muscle in hand (thenar eminence).hand (thenar eminence).

Radial nerve: extensor muscle of Radial nerve: extensor muscle of posterior forearm and triceps brachiiposterior forearm and triceps brachii

Musculocutaneous nerve: biceps Musculocutaneous nerve: biceps brachiibrachii

Axillary nerve: deltoidAxillary nerve: deltoid

Lumbosacral plexusLumbosacral plexusLumbar plexus: Arises from spinal Lumbar plexus: Arises from spinal

nerves L1- L4nerves L1- L4

Sacral plexus: L4-S4Sacral plexus: L4-S4- Innervates lower limb, buttocks and Innervates lower limb, buttocks and

pelvic musclespelvic muscles

- Femoral nerve: Quadriceps and Femoral nerve: Quadriceps and sartoriussartorius

- Obturator nerve: Adductor musclesObturator nerve: Adductor muscles

- Sciatic nerve: 2 nervesSciatic nerve: 2 nerves

- tibial nerve- tibial nerve

- common fibular - common fibular nervenerve

Tibial: hamstringsTibial: hamstrings

Common fibular: anterior tibialisCommon fibular: anterior tibialis

Sacral PlexusSacral Plexus