Lab 11: Peripheral Nervous System Overview

Cranial Nerves

12 pairs of nerves that primarily originate in the brainstem, except Olfactory and Optic.

Olfactory Nerve (I)

Sensory nerve responsible for the sense of smell; exits from the olfactory fossa in the cribriform plate.

Optic Nerve (II)

Sensory nerve responsible for vision and visual field; exits from the optic foramen.

Oculomotor Nerve (III)

Motor nerve that controls eye muscles and pupil; exits from the superior orbital fissure.

Trochlear Nerve (IV)

Motor nerve responsible for one eye muscle (superior oblique); exits from the superior orbital fissure.

Trigeminal Nerve (V)

Sensory and motor nerve; the largest cranial nerve.

Ophthalmic Branch (V1)

Sensory branch of the Trigeminal nerve responsible for sensation in the forehead, around the eyes, and cornea; exits from the superior orbital fissure.

Maxillary Branch (V2)

Sensory branch of the Trigeminal nerve responsible for sensation in teeth, gums, and skin over the maxilla; exits from the foramen rotundum.

Mandibular Branch (V3)

Sensory and motor branch of the Trigeminal nerve responsible for sensation in the teeth of the lower jaw and tongue, and mastication; exits from the foramen ovale.

Abducens Nerve (VI)

Motor nerve responsible for eye muscle (lateral rectus); exits from the superior orbital fissure.

Facial Nerve (VII)

Sensory and motor nerve; responsible for taste in the anterior part of the tongue and facial expression; exits from the internal auditory meatus and stylomastoid foramen.

Vestibulocochlear Nerve (VIII)

Sensory nerve responsible for hearing and balance; exits from the internal auditory meatus.

Glossopharyngeal Nerve (IX)

Sensory and motor nerve responsible for taste in the posterior part of the tongue and pharyngeal muscles; exits from the jugular foramen.

Vagus Nerve (X)

Sensory and motor nerve responsible for thoracic and abdominal viscera; provides parasympathetic innervation to abdominal organs; exits from the jugular foramen.

Spinal Accessory Nerve (XI)

Motor nerve responsible for sternocleidomastoid and trapezius muscles; exits from the jugular foramen.

Hypoglossal Nerve (XII)

Motor nerve responsible for tongue and throat muscles; exits from the hypoglossal canal.

Spinal Nerves

31 pairs of nerves that arise from rootlets sprouting from the spinal cord, with both sensory and motor functions.

Dorsal Roots

Roots of spinal nerves that carry sensory information.

Ventral Roots

Roots of spinal nerves that carry motor information.

Dorsal Rami

Branches of spinal nerves that innervate deep muscles of the dorsal trunk and skin near the midline of the back.

Ventral Rami

Branches of spinal nerves that form intercostal nerves in the thoracic region and nerve plexuses elsewhere.

Cervical Plexus

Formed from C1-C4; most nerves are sensory to the neck region, with the phrenic nerve innervating the diaphragm.

Brachial Plexus

Formed from C5-T1; consists of three major trunks, six divisions, and three cords.

Axillary Nerve

Motor - deltoid and teres minor muscles; Sensory - skin around deltoid and upper arm.

Radial Nerve

Motor - extensors of arm and forearm; Sensory - dorsum of hand, forearm; Common clinical - wrist drop due to crutches.

Musculocutaneous Nerve

Motor - anterior arm muscles; Sensory - lateral forearm.

Ulnar Nerve

Motor - 2 forearm flexors, many intrinsic hand muscles; Sensory - ulnar side of arm and hand; Commonly referred to as the funny bone.

Median Nerve

Motor - innervates all but 2 of the flexors of the forearm and muscles near the thumb; Sensory - skin on radial side of palm; Clinical - carpal tunnel syndrome.

Thoracic Nerves (2-12)

No plexus; Motor to intercostal muscles; Sensory - skin of overlying area; Nerves run from spinal cord out through costal grooves in ribs.

Lumbar Plexus

L1-L5; Branches mainly go to the anterior of the lower limb.

Sacral Plexus

L5-S4; Branches mainly go to the posterior of the lower limb.

Obturator Nerve

Motor - supplies the muscles that adduct the thigh; Sensory - Skin of medial thigh.

Femoral Nerve

Motor - iliopsoas, quads, sartorius; Sensory - anterior of upper leg and to the top of the foot as the saphenous nerve.

Sciatic Nerve

Tibial and common peroneal nerves bound together (L5 - S4); Runs down back of leg and splits just above the popliteal fossa into the Tibial and Fibular nerves.

Tibial Portion of Sciatic Nerve

Motor - posterior thigh (hamstrings) and lower leg (plantarflexors) muscles; Sensory - much of the posterior thigh and lower leg and sole of foot as the Sural nerve.

Peroneal/Fibular Portion of Sciatic Nerve

Motor - runs laterally around head of fibula and innervates the fibularis muscles and dorsiflexors of the lower leg; Sensory - lateral lower leg and dorsum of foot mainly as the superficial fibular nerve.

Reflex Arc

Most reflex arcs involve 3 neurons; some only require 2 and function without an association neuron.

Hypoflexia

Malnutrition, neuronal lesions, aging.

Hyperflexia

Usually seen with increased muscle tone due to damage to the motor cortex.

Scaling Reflex Responses

++++: Very brisk, hyperactive; +++: More brisk than average; ++: Normal response; +: Somewhat diminished; 0: No response, usually pathological.

Stretch Reflexes

Involves muscle groups and specific spinal nerves.

Plantar Reflex

Normal response is toe curling in adults; Damage can lead to Babinski's sign, which is dorsiflexion of the toes.

Babinski's Sign

Normal in babies; indicates damage in adults when there is dorsiflexion of the toes

Pupillary Reflex

Controlled by cranial nerve; pupil constricts when light is shone on it.

On

Occassion

Our

Trusty

Truck

Acts

Funny

Very

Good

Vehicle

Any

How

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

Facial

Vestibulocochlear

Glossopharyngeal

Vagus

Accessory

Hypoglossal