PNS Terminology• Ganglia – neuron cell

bodies & dendrites• Nerves – bundles o

myelinated axons• PNS neuroglia

– Satellite cells• Enclose neuron cell bodies in

ganglia

– Schwann cells• Cover peripheral axons

-cranial nerves – 12 pairs-olfactory, optic & acoustic contain only sensory axons = sensory nerves- oculomotor, trochlear, abducens, accessory & hypoglossal carry only motor information = motor nerves-remaining are mixed nerves – both motor and sensory axons“some say my mother bought my brother some bitter beer – my, my”

I - OlfactoryII - OpticIII - OculomotorIV-TrochlearV - TrigeminalVI - AbducensVII - FacialVIII – Acoustic/VestibulocochlearIX - GlossopharyngealX - VagusXI – Accessory/Spinal AccessoryXII - Hypoglossal

VII

VIII

V

VI

IX

X

III

I

II

Optic Chiasma

XI

The Olfactory Nerve (I)• Sensory Nerve• Carries sensory information

– Sense of smell

• Synapse within olfactory bulbs

• Sensory Nerve• The optic nerve (II)

– carries visual information to occipital lobe

The Vestibulocochlear Nerve (VIII)• Sensory Nerve

• also called the Acoustic nerve

• Vestibular nerve– Monitors sense of balance, position and movement

• Cochlear nerve– Monitors hearing

•The abducens nerve (VI)–Innervates lateral rectus muscle of eye

•The oculomotor nerve (III)–Primary source of innervation for extra-ocular muscles

•Move the eyeball

•The trochlear nerve (IV)–Smallest cranial nerve

–Innervates superior oblique eye muscle

Motor Cranial Nerves

• The accessory nerve (XI) – Motor nerve• innervates swallowing muscles & controls

sternocleidomastoid and trapezius muscles and other muscles of pectoral girdle

• two branches: cranial part (internal branch) & spinal part (external branch)

•The hypoglossal nerve (XII) – motor nerve

–voluntary motor control over tongue movements

The Trigeminal Nerve (V)• Largest cranial nerve• Mixed nerve• Ophthalmic branch– sensory – upper eyelid, eyeballlacrimal glands, side of nose, foreheadand scalp

• Maxillary branch– sensory – nose, palate, partof pharynx, upper teeth, upperlip and lower eyelid

• Mandibular branch– sensory – tongue, cheek,lower teeth, skin over mandibleand side of head anterior to ear-motor – muscles of chewing

The Facial Nerve (VII)

– Mixed nerve

– controls muscles of scalp and facial expression

– transmits pressure sensations from face & taste sensations from tongue

– major branches:• Temporal

• Zygomatic

• Buccal

• Mandibular

• Cervical

The Glossopharyngeal Nerve (IX)

• Mixed nerve

• Innervates the tongue & controls swallowing

The Vagus Nerve (NX)

• Mixed nerve• vital to autonomic

control of visceral function

• major nerve of the ANS/parasympathetic system

31 Pairs of Spinal Nerves• Ensheathed by three connective tissue

layers– Outermost epineurium

• dense network of collagen fibers around the peripheral nerve

– Middle perineurium• partitions nerve into fascicles

– Inner endoneurium• delicate connective tissue fibers

surrounding each axon

• under the endoneurium is the myelin sheath

• outer layer of the myelin sheath is called the neurilemma

• neurilemma covers the myelin sheath and Schwann cells

• myelin sheath covers the axon

Spinal Nerves• connected to the spinal cord via roots (bundles of axons)• Posterior root = sensory axons into the posterior gray horn• Anterior root = motor axons from the anterior gray horn

Spinal Nerves• before the posterior root is the dorsal root ganglion = cell bodies

of incoming sensory neurons (axons continue on to form the root)

Spinal Nerve

•spinal nerves emerge from intervertebral foramina as mixed nerves•after passing through intervertebral foramina the spinal nerve branches into three rami•Dorsal ramus•Ventral ramus•Rami communicantes

DorsalRamus

Ventral Ramus

RamiCommunicantes

Dorsal Root

Ventral Root

Dorsal Root Ganglion

Epidural space

Dura andArachnoid maters

•Dorsal ramus-sensory/motor innervation to and from skin and muscles of back

•Ventral ramus- sensory/motor innervation to and from skin and structures of ventral and lateral body wall, muscles of the upper and lower limbs

•rami communicantes -carries nerves of the ANS

Spinal Nerve

Dorsal Root of SN Ventral Root of SN

SPINAL NERVE

DorsalRamus

Ventral Ramus

RamiCommunicantes

Signals to and from the ANS

VISCERA – cardiac andSmooth muscle

Sensory – INMotor – OUT

TRUNKLIMBs

Sensory – INMotor – OUT

SKINBACK MUSCLES

Nerve Plexuses

• Four major plexuses– Cervical plexus– Brachial plexus– Lumbar plexus– Sacral plexus

• nerve networks formed by the ventral rami of spinal nerves

• found in neck, arm, low back & sacral regions

• no plexus in thoracic region– intercostal nerves this region

Cervical Plexus• C1-C4 ventral rami

• Some fibers from C5

• Innervates muscles of the neck and diaphragm– major nerve from plexus =

Phrenic nerve

Brachial Plexus• Ventral rami of C5-T1

• Innervates pectoral girdle and upper limbs

Brachial Plexus• nerves arise from cords & trunks

– Superior, middle and inferior trunks

– Lateral, medial and posterior cords

– musculocutaneous, radial, median and ulnar nerves arise from these cords

• Lateral cord: musculocutaneous, median nerves• Medial cord: ulnar, median nerves• Posterior cord: radial, axillary nerves

Lumbar Plexus• ventral rami of T12–L4

• Innervate pelvic girdle and lower limbs

• femoral nerve gives off many muscular branches

• posterior segment gives off branches to the quads and branches to the knee + large saphenous nerve

Sacral Plexus• ventral rami of L4–S4

• innervates pelvic girdle and lower limbs

• sciatic nerve becomes the tibial nerve, sural nerves & common fibular nerve in the leg