Peripheral Nervous System

Nerves

Bundles of axons enclosed in connective tissue wrappings.

Cranial nerves

Twelve pairs of nerves that carry information in and out of the brain.

Spinal nerves

Thirty-one pairs of nerves that carry information in and out of the spinal cord.

Nerve plexus

An interlacing nerve network formed by several spinal nerves that join and then branch again.

dermatome

A region of the skin monitored by a nerve.

epineurium

A layer of dense irregular connective tissue that covers the surface of the nerve.

perineurium

A thin connective tissue membrane that surrounds bundles of axons called nerve fascicles.

endoneurium

Loose areolar connective tissue that surrounds individual axons within a nerve fascicle.

Olfactory nerve (CNI)

Carries the sense of smell.

pathway of the Optic nerve (CNII)

Contains axons of retinal ganglion cells that travel through optic chiasm to the lateral geniculate nucleus.

Vestibulocochlear nerve (CNVIII)

Carries the sense of hearing (audition).

muscles affected by Oculomotor nerve (CNIII)

Excites most extraocular muscles, including the medial rectus, superior rectus, inferior rectus, and inferior oblique.

Trochlear nerve (CNIV)

Excites the superior oblique extraocular muscle leading to inferior and lateral rotation of the eye.

Abducens nerve (CNVI)

Motor control of the lateral rectus extraocular muscles.

Spinal Accessory nerve (CNXI)

Excites the trapezius and sternocleidomastoid muscles.

Hypoglossal nerve (CNXII)

Excites muscles that move the tongue.

Trigeminal nerve (CNV)

Carries the sense of touch from the face and excites the muscles of mastication.

Ophthalmic branch of the Trigeminal nerve

A somatosensory nerve from the superior facial region including ocular regions.

Maxillary branch of the Trigeminal nerve

Somatosensory from the middle face including the superior oral region.

Mandibular branch of the Trigeminal nerve

Motor to masseter and temporalis and somatosensory from the inferior facial region.

Facial nerve (CNVII)

Carries taste from the anterior 2/3 of the tongue and excites muscles of facial expression.

Glossopharyngeal nerve (CN IX)

Carries taste from the posterior 1/3 of the tongue and controls pharynx muscles important for swallowing.

Vagus nerve (CNX)

Carries sensory information from visceral organs and regulates visceral organs.

Cervical plexus

Forms from C1 – C5 and innervates skin and muscles of the neck and shoulder.

Phrenic nerve

Excites the diaphragm and forms from ventral rami of C3-C5.

Brachial plexus

Ininnervates the pectoral girdles and upper limbs.

Lateral cord of the Brachial plexus

Formed from anterior divisions of superior & middle trunks.

Medial cord of the Brachial plexus

Formed by anterior division of inferior trunk.

Posterior cord of the Brachial plexus

Formed by union of all 3 posterior divisions.

Ulnar nerve

Innervates flexors of the medial forearm and hand.

Median nerve

Innervates flexors of the lateral forearm and hand.

Musculocutaneous nerve

Flexor arm muscles like biceps brachii & brachialis.

Radial nerve

Innervates arm and forearm extensor muscles.

Axillary nerve

Innervates the deltoid and teres minor muscles.

Femoral nerve

Innervates quadriceps femoris in the anterior thigh.

Obturator nerve

Innervates adductor magnus and adductor longus.

Sciatic nerve

Largest nerve in the body, excites hamstrings.

Muscle spindles

Sensory receptors in quadriceps femoris that detect stretching.

Efferent pathway in the patellar tendon stretch reflex

Efferent fibers carry action potentials out through spinal nerve roots L2-L4 and the femoral nerve.

Effector in the patellar tendon stretch reflex

Quadriceps femoris muscle group is the effector that contracts to extend the leg at the knee joint.