Peripheral Nervous System Nerves outside the brain

Peripheral Nervous SystemPeripheral Nervous System

Nerves outside the brainNerves outside the brain

Peripheral Nervous SystemPeripheral Nervous System StructuresStructures

Sensory receptorsSensory receptors– Mechanoreceptors (touch, pressure, vibration, and stretch)Mechanoreceptors (touch, pressure, vibration, and stretch)– Thermoreceptors (temperature changes)Thermoreceptors (temperature changes)– Photoreceptors (light energy)Photoreceptors (light energy)– Chemoreceptors (chemicals in solution)Chemoreceptors (chemicals in solution)

Nerves (cranial and spinal)Nerves (cranial and spinal)– Cordlike organ that is part of the PNSCordlike organ that is part of the PNS– Consists of parallel bundles of peripheral axons enclosed by Consists of parallel bundles of peripheral axons enclosed by

connective tissue wrappingsconnective tissue wrappings

GangliaGanglia– Collections of neuron cell bodies associated with nerves in the PNSCollections of neuron cell bodies associated with nerves in the PNS

Efferent motor endingsEfferent motor endings

Peripheral Nervous System

12 cranial nerves– Associated with the brain– We need to learn their:

Names Locations Functions

31 spinal nerves– Associated with the spinal cord– We need to learn their:

Plexus Functions

Cranial NervesCranial Nerves

10 of 12 cranial nerves attach to the brain stem 10 of 12 cranial nerves attach to the brain stem Their name reflects their function or the major Their name reflects their function or the major

structures they controlstructures they control Numbered (Roman numerals) in order from Numbered (Roman numerals) in order from

anterior to posterioranterior to posterior Described by name, Roman numeral, and functionDescribed by name, Roman numeral, and function Function can be purely sensory, motor, or bothFunction can be purely sensory, motor, or both

Cranial NervesCranial Nerves I Olfactory nerve (sensory)

smell

II Optic nerve (sensory)

vision

III Oculomotor nerve (motor)

eye muscles

IV Trochlear (motor)

eye muscles

V Trigeminal nerve (sensory/motor)

sensory for face

motor for chewing

VI Abducens nerve (motor)

eye muscles

Cranial NervesCranial Nerves VII Facial nerve (sensory/motor)

sensory for taste

Motor for facial expression

VIII Vestibulococchlear nerve (sensory)

balance and hearing

IX Glossopharyngeal nerve (sensory/motor)

sensory for taste

motor for pharynx

X Vagus nerves (sensory/motor)

pharynx, larynx, and viscera

XI Accessory nerve (motor)

neck and upper back

XII Hypoglossal nerve (motor)

tongue

Here are mnemonic devices for the 12 cranial nerves:– On occasion our trusty truck

acts funny – very good vehicle anyhow

– On old Olympus' towering tops, a fin and German viewed some hops.

– Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulococchlear, glossopharyngeal, vagus, hypoglossal


Cranial nerves can have sensory only, motor only, or mixed functions

Sensory only– Olfactory and optic are sensory only

Motor only– Oculomotor– Trochlear– Abducens– Accessory– Hypoglossal

Mixed (sensory and motor)– Trigeminal– Facial– Vestibulococchlear– Glossopharyngeal– Vagus

Mnemonic device to help: – Some say marry money but my brother says

big butts matter more.– Some Scientists Make Money But My Brother Some Scientists Make Money But My Brother

Says Beautiful Blonds Make More Says Beautiful Blonds Make More


Olfactory (I)Sensory

SmellImbalance: fracture of ethmoid bone or lesions

may result in partial or total loss of smell

Optic (II)SensoryVision

Imbalance: damage to optic nerve results in blindness in eye served by nerve; damage beyond optic chiasm

results in partial vision loss

Oculomotor (III)Motor

Eye and pupil movementImbalance: eye cannot move up, down or inward; at rest

eye rotates laterally and trouble focusing on close objects

Trochlear (IV)Motor

Eye and peripheral visionImbalance: Trauma or paralysis results in double vision

and reduced ability to rotate eye inferolaterally

Trigeminal (V)Both (sensory and motor)

Ophthalmic division (s)Maxillary division (s)

Mandibular division (s & m)Largest of the cranial nerves

Imbalance: trigeminal neuralgia – caused by inflammation of the nerve, stabbing pain that lasts for a few seconds to a

minute, provoked by a sensory stimulus

Abducens (VI)Motor

Abduction of eyeImbalance: eye cannot be moved laterally; at rest, affected

eyeball rotates medially

Facial Nerves (VII)Both (sensory and motor)

Muscles of facial expression: temporal, zygomatic, buccal, mandibular, cervical (m)

Taste buds (anterior) (s)Imbalance: Bell’s Palsy – paralysis of facial muscles on

affected side and partial loss of taste sensation; Lower eyelid droops, corner of mouth sags, tears drip continuously from eye

and eye cannot be completely closed

Vestibulocochlear (VIII)

SensoryHearing (cochlear)

Equilibrium (vestibular)Imbalance: lesions of cochlear nerve result in nerve deafness; damage to vestibular produces dizziness, rapid involuntary eye

movement, loss of balance, nausea and vomiting

Glossopharyngeal (IX)Both (sensory and motor)

Pharynx (throat)(m)Taste buds and throat (posterior) (s)

Imbalance: injury impairs swallowing and taste

Vagus (X)Only cranial nerve to extend beyond

head and neckBoth (sensory and motor)

Pharynx, larynx, heart, lungs, and abdominal organs (m)

Thoracic and abdominal organs (s)Imbalance: Injury can lead to hoarseness or loss of voice, difficulty swallowing and impaired digestive

system motilityTotal destruction of nerves is incompatible with life

because they are needed to maintain normal activity

Accessory (XI)Motor

Trapezius and sternocleidomastoid

Hypoglossal (XII)Motor

Glossal = tongueMuscles of the tongue

Imbalance: difficulty in speech and swallowing

Spinal nerves are named for the region from which they arise

A pair of spinal nerves at each vertebrae for a total of 31 pairs– 8 pairs of cervical

(1 extra)

– 12 pairs of thoracic

– 5 pairs of lumbar

– 5 pairs of sacral

– 1 pair of coccyx

Spinal NervesSpinal Nerves

All are mixed nerves (sensory and motor) Each nerve connects to the spinal cord by a dorsal and ventral root

– Ventral root – motor

– Dorsal root – sensory


The spinal nerve is actually short (1-2 cm)

Immediately it divides into its ramus (branch)– Dorsal rami – serve the skin and

muscles of the posterior trunk

– Ventral rami – forms a complex of networks for the anterior and limbs called plexuses


PlexusesPlexuses All ventral rami (except

thoracic) branch and join one another lateral to the vertebral column that form a complex network called a plexus

Nerve plexuses occur in cervical, brachial, lumbar and sacral regions to serve the motor and sensory needs of the limbs

The fibers diverge again from the plexuses to form the peripheral nerves

Examples of Nerve DistributionExamples of Nerve Distribution

Figure 7.23

Spinal Nerve PlexusesSpinal Nerve PlexusesPLEXUSPLEXUS SPINAL ROOTS SPINAL ROOTS

(ORIGIN)(ORIGIN)BODY AREA SERVEDBODY AREA SERVED IMBALANCEIMBALANCE

CervicalCervical CC11-C-C55 Skin of neck, shoulder Skin of neck, shoulder and clavicle regionand clavicle region

Diaphragm (phrenic Diaphragm (phrenic nerve) and muscles of nerve) and muscles of shoulder and neckshoulder and neck

Irritation of the phrenic Irritation of the phrenic nerve causes spasms of nerve causes spasms of the diaphragm - hiccupsthe diaphragm - hiccups

BrachialBrachial CC55– C– C88 and T and T11 All nerves that innervate All nerves that innervate upper limbupper limb

Arm muscles – deltoid, Arm muscles – deltoid, triceps, biceps, flexor, triceps, biceps, flexor, extensor, wrist and handsextensor, wrist and hands

Cutaneous sensation of Cutaneous sensation of the upper limbthe upper limb

Weakness or paralysis of Weakness or paralysis of entire upper limbentire upper limb

Carpal tunnel syndrome Carpal tunnel syndrome the median nerve is the median nerve is compressedcompressed

““The funny bone” results The funny bone” results from an injury to the from an injury to the ulnar nerveulnar nerve

Spinal Nerve PlexusesSpinal Nerve Plexuses

PLEXUSPLEXUS SPINAL SPINAL ROOTS ROOTS (ORIGIN)(ORIGIN)

BODY AREA SERVEDBODY AREA SERVED IMBALANCEIMBALANCE

LumbarLumbar LL11– L– L44 Innervation of lower limb and Innervation of lower limb and abdomenabdomen

Muscles of the thigh, leg and footMuscles of the thigh, leg and foot

Cutaneous sensation of thigh, leg, Cutaneous sensation of thigh, leg, foot, external genitalia and lower foot, external genitalia and lower abdomenabdomen

Compression of the Compression of the spinal roots of the spinal roots of the lumbar plexus results lumbar plexus results in walking problemsin walking problems

SacralSacral LL44 – S – S44 Innervation of the buttock, pelvic Innervation of the buttock, pelvic structures and lower limbstructures and lower limb

Sciatic nerve is the thickest and Sciatic nerve is the thickest and longest nerve in the body –entire longest nerve in the body –entire lower limblower limb

Muscles of the posterior surface of Muscles of the posterior surface of buttock, thigh, leg and foot,buttock, thigh, leg and foot,

Cutaneous sensation of posterior Cutaneous sensation of posterior surface of buttock, thigh, leg and foot, surface of buttock, thigh, leg and foot,

Sciatica – stabbing Sciatica – stabbing pain over the course pain over the course of the nerve from of the nerve from injury to sciatic nerve injury to sciatic nerve such as disc such as disc herniation or herniation or improper injection in improper injection in the buttockthe buttock

ReflexesReflexes

The ReflexThe Reflex Anyone who has had a routine physical examination

is familiar with the reflex tests done to assess neural function.

A tap with a reflex hammer stretches your quadriceps tendon and your anterior thigh muscles contract, which results in the knee-jerk response

This response shows that the spinal cord and upper brain centers are functioning normally

Abnormal reflex test responses may indicate such serious disorders as intracranial hemorrhage, multiple sclerosis, or hydrocephalus

Reflex ArcReflex Arc Reflex

– Rapid, predictable, involuntary motor response to stimuli– Inborn or acquired reflexes– Occur over neural pathways called reflex arcs

Reflex arc – Receptor sensory neuron integration center

(monosynaptic or polysynaptic) motor neuron effector

ReflexesReflexes Receptor

– Site of the stimulus

Sensory neuron – Transmits afferent impulses to the CNS

Integration center – Single synapse (monosynaptic)– Multiple synapses (polysynaptic) btw the afferent

Motor neuron – Conducts efferent impulses from the integration center to an

effector organ

Effector– Muscle fiber or gland cell that responds to the impulses

Reflex ArcsReflex Arcs Monosynaptic reflex arc – knee-jerk reflex Polysynaptic reflex arc – most reflexes

Types of ReflexesTypes of Reflexes

Somatic reflexes– Any reflex in which the skeletal muscles are the effectors– Stretch reflexes

Maintain posture, balance and locomotion Produced by tapping a tendon, which stretches the attached

muscle Knee-jerk (patellar) reflex

– Superficial reflexes Gentle cutaneous stimulation Plantar reflex tests the integrity of lower spinal cord Corneal reflex Gag reflex

Autonomic reflexes– Smooth muscle

regulation– Heart and blood

pressure regulation– Digestive system

regulation (saliva)– Elimination (excretion)– Change size of eye pupil – Sweating



Documents

Peripheral Nervous System Nerves outside the brain