THE PERIPHERAL NERVOUS SYSTEM

FUNCTION OF PNS

• CARRIES MESSAGES AWAY FROM CNS

• CARRIES MESSAGES TOWARD CNS

STRUCTURAL COMPONENTS OF PNS

• 12 CRANIAL NERVES• 31 SPINAL NERVES

FUNCTIONAL COMPONENTS OF PNS

• AFFERENT/SENSORY DIVISION• EFFERENT/MOTOR DIVISION

– SOMATIC NERVOUS SYSTEM– AUTONOMIC NERVOUS SYSTEM

CRANIAL NERVES

• ORIGINATE FROM FOREBRAIN AND BRAIN STEM

• MOST ARE MIXED NERVES• A FEW ARE SENSORY ONLY

CRANIAL NERVE GANGLIA

• SENSORY CELL BODIES OUTSIDE CNS

• CELL BODIES OF MOTOR NEURONS ARE LOCATED IN NUCLEI IN CNS

CRANIAL NERVE NUCLEI

• NUCLEI IN CNS– SOMATIC MOTOR NEURONS– VOLUNTARY CONTROL

• VISCERAL MOTOR NEURONS– PART OF PARASYMPATHETIC DIVISION OF

AUTONOMIC NERVOUS SYSTEM– ALL BUT VAGUS SERVE ONLY STRUCTURES IN

NECK AND HEAD• NUMBERED I – XII

CRANIAL NERVE I• OLFACTORY NERVES• ARISE FROM RECEPTOR CELLS IN EPITHELIA OF NASAL

MUCOSA• PASS THROUGH CRIBIFORM PLATE• ENTER OLFACTORY BULBS• PASS BACK THROUGH OLFACTORY TRACT• TERMINATE IN RHINENCEPHALON • MEDIAL SIDES OF TEMPORAL LOBE• ENTIRELY SENSORY• SENSE OF SMELL

CRANIAL NERVE II

• OPTIC NERVE• ACTUALLY BRAIN TRACTS

– OUTGROWTHS OF EMBRYONIC DIENCEPHALON• ORIGINATE IN RETINA OF EYES• ENTERS BRAIN THROUGH OPTIC FORAMEN OF

SPHENOID• TWO NERVES MEET IN OPTIC CHIASMA• SENSORY ONLY• VISION

DECUSSATION AT OPTIC CHIASMA

• TWO OPTIC NERVES MEET AT CHIASMA• NERVE FIBERS FROM MEDIAL HALF OF

EACH RETINA CROSS OVER TO OTHER SIDE• NERVE FIBERS FROM LATERAL HALF OF

EACH RETINA REMAIN ON SAME SIDE• OPTIC TRACT CONTINUES ON FROM OPTIC

CHIASMA• EACH OPTIC TRACT CONSISTS OF FIBERS

FROM RETINA OF BOTH EYES

OPTIC TRACTS• SOME OPTIC TRACT FIBERS TERMINATE IN SUPERIOR

COLLICULI – SUBCONSCIOUS VISUAL REFLEXES

• MOST OF FIBERS TRAVEL TO LATERAL GENICULATE BODIES OF THALAMUS– SYNAPSE WITH NEURONS THAT FORM OPTIC RADIATIONS

• OPTIC RADIATIONS ARE THIRD ORDER NEURONS– PASS THROUGH INTERNAL CAPSULE

• TERMINATES IN VISUAL CORTEX OF THE OCCIPITAL LOBE

CRANIAL NERVE III

• OCULOMOTOR NERVE• EMERGE FROM THE MIDBRAIN• JUST SUPERIOR TO PONS• ENTER ORBITS THROUGH SUPERIOR

ORBITAL FISSURES• SOMATIC MOTOR NEURONS• PROPRIOCEPTIVE SENORY NEURONS• FOUR OF SIX EXTRINSIC MUSLCE HTAT

MOVE EYEBALL

EYE MUSCLES INNERVATED BY CRANIAL NERVE III

• SUPERIOR RECTUS• MEDIAL RECTUS• INFERIOR RECTUS• INFERIOR OBLIQUE MUSCLE• LEVATOR PALPEBRAE• INTINSIC MUSCLE OF EYE

– SHAPE OF LENS– SIZE OF PUPIL

PARASYMPATHETIC COMPONENTS

• PREGANGLIONIC (PRESYNAPTIC) NEURON

• POST GANGLIONIC (POSTSYNAPTIC) NEURON

• CILIARY GANGLIA

CRANIAL NERVE IV

• TROCHLEAR NERVE• ARISE BELOW INFERIOR COLLICULI• DORSAL SURFACE OF MIDBRAIN• ONLY CRANIAL NERVES TO EXIT FORM

DORSAL SURFACE• ENTER ORBITS THROUGH SUPERIOR

ORBITAL FISSURES• SOMATIC MOTOR NEURONS• PROPRIOCEPTIVE SENSORY NEURONS

EYE MUSCLES INNERVATED BY CRANIAL NERVE IV

• SUPERIOR OBLIQUE MUSCLES

CRANIAL NERVE V• TRIGEMINAL NERVES• EMERGE FROM LATERAL SIDES OF PONS• THREE DIVISIONS• OPTHALMIC

– SUPERIOR ORBITAL FISSURE• MAXILLARY

– FORAMEN ROTUNDUM• MANDIBULAR

– FORAMEN OVALE• MAJOR SENSORY NERVES OF FACE

GANGLIA OF CRANIAL NERVE V

• TRIGEMINAL/SEMILUNAR GANGLIA– LOCATED AT THE POINTS WHERE DIVISIONS

JOIN BEFORE ENTERING BRAIN

SOMATIC MOTOR NEURONS

• IN MANDIBULAR NERVE• INNERVATES MUSCLE OF

MSTIDCATION– MEDIAL AND LATERAL PTERYGOID– MASSETER– TEMPORALIS– ANTERIOR BELLY OF DIGASTRIC

CRANIAL NERVE VI

• ABDUCENS• ARISES IN METENCEPHALON• EXIT BELOW BRAIN STEM• ENTER ORBITS THROUGH SUPERIOR

ORBITAL FISSURES• SOMATIC MOTOR NEURONS• PROPRIOCEPTIVE SENSORY

NEURONS

EYE MUSCLES INNERVATED BY CRANIAL NERVE VI

• LATERAL RECTUS MUSCLES

COORDINATION OF EYE MOVEMENTS

• REQUIRES COORDINATION OF CRANIAL NERVES III, IV AND VI.

CRANIAL NERVE VII

• FACIAL NERVE• ARISE AT LOWER BORDER OF PONS• LATERAL TO ABDUCENS• LEAVE THROUGH THE INTERNAL

AUDITORY MEATUS TO THE STYLOMASTOID FORAMINA.

• PASS FORWARD ACROSS CHEEK• PIERCES PAROTID SALIVARY GLAND

DIVISIONS OF FACIAL NERVES

• MOTOR• SENSORY• PARASYMPATHETIC

MOTOR

• MUSCLES OF FACIAL EXPRESSION

SENSORY

• PROPRIOCEPTION• TASTE BUDS ON NATERIOR TWO

THIRDS OF TONGUE• CELL BODEIS ARE GOUND IN

GENICULATE GANGLIA IN PETROUS PORTION OF TEMPORAL BONE

PARASYMPATHETIC

• LACRIMAL GLAND• MUCOUS GLANDS OF NASAL CAVITY• SUBLINGUAL AND SUBMANDIBULAR

SALIVAR GLANDS• PTERYGOPLATINE GANGLIA• SUBMANDIBULAR GANGLIA

CRANIAL NERVE VIII

• VESTIBULOCOCHLEAR NERVE– VESTIBULAR– COCHLEAR

• ARISE FROM INNER EAR RECPTORS• PERTROUS PORTIONS OF TEMPORAL BONE• EXITS THROUGH INTERAL AUDITORY

MEATUS• ENTERS BRAIN STEM JUST BELOW PONS

COCHLEAR DIVISION

• ORIGINATES IN SPIRAL ORGAN– COCHLEA OF EAR

• SPIRAL GANGLIA• HEARING

VESTIBULAR DIVISION

• ORIGINATES IN AMPULLAE OF SEMICIRCULAR DUCTS, SACCULE AND UTRICLE

• VESTIBULAR GANGLIA• EQUILIBRIUM

CRANIAL NERVE IX

• GLOSSOPHARYNGEAL NERVE• MIXED NERVE• EMERGES FROM MEDULLA • EXITS THROUGH JUGULAR

FORAMEN

SENSORY COMPONENTS

• FROM TASTE BUDS OF POSTERIOR THIRD OF TONGUE

• FROM MUCOUS MEMBRANES OF PHARYNX, TONISL AND MIDDLE EAR CAVITIES

• FROM RECEPTORS THAT MONITOR BLOOD LEVELS OF OXYGEN AND CARBON DIOXIDE– CAROTID BODIES

• BLOOD PRESSURE– CAROTID SINUS

• SUPERIOR AND INFERIOR GANGLIA

SOMATIC MOTOR COMPONENTS

• STYLOPHARYNGEUS MUSCLES• JOIN WITH CRANIAL NERVES X AND

XI TO INNERVATE OTHER PHARYNGEAL STRUCTURES

PARASYMPATHETIC COMPONENTS

• SYNAPSE IN OTIC GANGLIA• INNERVATES PAROTID SALIVARY

GLANDS

CRANIAL NERVE X

• VAGUS NERVE• ONLY CRANIAL NERVE NOT

RESTRICTED TO HEAD AND NECK• ARISE FROM SIDES OF MEDULLA• EXITS THROUGH JUGULAR

FORAMEN• ENTERS THORAX AND ABDOMEN

SOMATIC MOTOR COMPONENT

• VOLUNTARY MUSCLE OF PHARYNX, AND LARYNX

SENSORY

• FROM TASTE RECEPTORS IN BASE OF TONGUE

• SENSORY INPUT FROM VISERA– PROVIDE INPUT FOR REGULATION OF

HEART RATE, RESPIRATION, BLOOD PRESSURE, DIGESTION, ETC.

– NAUSEA AND DISTENSION

CRANIAL NERVE XI• ACCESSORY NERVE• TWO NERVES

– ONE RISES FROM MEDULLA– ONE RISES FROJM CERVICAL REGION

• SPINAL COMPONENT ENTERS THROUGH FORAMEN MAGNUM

• JOINS CRANIAL COMPONENT AND LEAVES THROUGH JUGULAR FORAMEN

• SUPPLIES MUSCLE SOF LARYNX AND PHARYNX• TRAPEZIUS AND STERNOCLEIDOMASTOID

CRANIAL NERVE XII

• HYPOGLOSSAL NERVES• ARISE FROM ANTERIOR MEDULLA• EXIT THROUGH HYPOGLASSAL CANALS• LOCATED BELOW TONGUE• CLOSE RELATIONSHIP TO FIRST CERVICAL

SPINAL NERVE• SOMATIC MOTOR NEURONS• PROPRIOCEPTIVE SENSORY NEURONS

ANSA CERVICALIS

• FIRST THREE CERVICAL NERVES• SO CLOSELY ASSOCIATED WITH

HYPOGLOSSAL THAT THEY APPEAR TO ARISE FROM THE CRANIAL NERVE

SPINAL NERVES• 31 PAIRS• LEAVE VETERBRAL

CANAL BY APSSING THOUGH INTERVERTEBRAL FORAMINA

• FIRST PAIR EXIT BETWEEN OCCIPTIAL BONE AND ATLAS

• SECOND –SEVENTH CERVICAL EMERGE ABOVE VERTEBRAE

• REST PASS BELOW VERTEBRAE

FORMATION OF SPINAL NERVES

• UNION OF VENTRAL AND DORSAL ROOTS

• VENTRAL ROOTS CONTAIN MOTOR NEURONS

• DORSAL ROOTS CONTAIN SENSORY NEURONS

• ALL SPINAL NERVES ARE MIXED NERVES

BRANCHES OF SPINAL NERVES• DORSAL RAMUS

– INNERVATES SKIN AND MUSCLES OF BACK• VENTRAL RAMUS

– VARIES ACCORDING TO BODY REGION– T2 – T 12 PASS THOUGH INTERCOSTAL SPACES TO

SUPPLY SKIN AND MUSCLES OF LATERAL AND ANTERIOR BODY WALLS

– CERVICAL, LUMBAR AND SACRAL REGIONS FORM PLEXUSES TO INNERVATE SKIN, MUSCLES AND JOINTS OF UPPER AND LOWER LIMBS

DERMATOMES

• SYSTEMATIC DISTRIBUTION OF SPINAL NERVE RAMI

• AREA OF SKIN SUPPLIED BY A SINGLE SPINAL NERVE

• ESPECIALLY REGULAR IN BACK REGION

• VARIES SOMEWHAT IN OTHERS

PLEXUSES

• INTERMINGLING OF VENTRAL RAMI• CERVICAL• BRACHIAL• LUMBOSACRAL

– LUMBAR– SACRAL

• DO NOT DUPLICATE CUTANEOUS DISTRIBUTION

CERVICAL PLEXUS

• VENTRAL RAMI OF FIRST FOUR CERVICAL NERVES

• INNERVATES MUSCLES AND SKIN OF NECK, SHOULDER AND CHEST

• CONNECT WITH CRANIAL NERVES X, XI AND XII

• PHRENIC NERVE

BRACHIAL PLEXUS• VENTRAL RAMI OF LAST FOUR CERVICAL

NERVES • FIRST THORACIC NERVE• IINERVATES BACK AND UPPER LIMBS• MAJOR NERVES

– AXILLARY – RADIAL– MUSCULOCUTANEOUS– ULNAR– MEDIAN

LUMBOSACRAL PLEXUS

• INNERVATE SKIN AND MUSCLES OF BUTTOCKS, PELVIS, LOWER ABDOMEN, LOWER LIMBS

• LUMBAR PLEXUS• SACRAL PLEXUS

LUMBAR PLEXUS

• VENTRAL RAMI OF TWELTH THORACIC – SOME FIBERS

• VENTRAL RAMI OF FIRST FOUR LUMBAR

SACRAL PLEXUS

• VENTRAL RAMI OF LAST TWO LUMBAR

• VENTRAL RAMI OF FIRST FOUR SACRAL

• LUMBAR NEURONS REACH PLEXUS BY WAY OF LUMBOSACRAL PLEXUS

• SUPPLY LOWER BACK, PELVIS, LATERAL SURFACE OF THIGH AND LEG, AND DORSAL AND VENTRAL SURFACE OF FOOT

REPAIR OF DAMAGED NEURONS

CLINICAL CONDITIONS

NEURITIS

• INFLAMMATION OF NERVE • OFTEN TIMES MORE DEGENERATIVE THAN

INFLAMMATORY• CHARACTERIZED BY

– SHARP, STABBING PAINS• CAUSES

– MECHANICAL DAMAGE– PROLONGED PRESSURE– VASCULAR DISORDERS– PATHOGENIC ORGANISMS

BELL’S PALSY

• PERIPHERAL INFLAMMATION OF CRANIAL NERVE VII

• MUSCLES OF FACIAL EXPRESSION• CAUSES DIFFICULTY IN SPEAKING

AND EATING• FACE SAGS ON AFFECTED SIDE

SHINGLES

• INFECTION OF DORSAL ROOT GANGLION

• HERPES ZOESTER• CAUSES PAIN AND FLUID FILLED

VESCILES • ALONG PATH OF PERIPHERAL

SENSORY NERVES