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Cranial and Spinal Nerves

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Cranial Nerves emerge from the brain emerge through holes in the cranium

- cranial foramina 12 pairs of cranial nerves Contains:

- sensory fibers (afferent)

- motor fibers (efferent)

- both sensory and motor fibers

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Cranial Nerves (cont.)

I Olfactory

II Optic

III Oculomotor

IV Trochlear

V Trigeminal

VI Abducens

VII Facial

VIII Vestibulocochlear

IX Glossopharyngeal

X Vagus

XI Accessory

XII Hypoglosseal

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I Olfactory

sensory nerve Function:

- smell (olfactory bulbs)

anosmia - loss of sense of smell

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II Optic

sensory nerve Function:

- vision (retina)

anopsia - defective vision

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III Oculomotor

mixed nerve (primarily motor) Functions:

- eyeball movement (4 eyeball muscles and 1 eyelid muscle)

- lens accommodation

- pupil constriction

- muscle proprioception

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III Oculomotor (cont.)

Injury or lesion may cause:

- strabismus - squinting

- ptosis - drooping of upper eye lid

- diplopia - loss of accommodation for near vision and double vision

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IV Trochlear

mixed nerve (primarily motor) Functions:

- eyeball movement (superior oblique muscles)

- muscle proprioception

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V Trigeminal

mixed nerve Functions:

- sensations ( face, scalp, teeth, lips, eyeballs, nose and throat lining)

- general sensations from the tongue

- proprioception (face and scalp)

- chewing (muscles of mastication)

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VI Abducens

mixed nerve (primarily motor) Functions:

- eyeball movement (lateral rectus muscle)

- muscle proprioception

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VII Facial

mixed nerve Functions:

- taste (anterior 2/3 of tongue)

- proprioception (face and scalp)

- facial expression (muscles of the face) Injury:

Bell’s palsy - loss of taste, inability to close eyes

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VIII Vestibulocochlear sensory nerve Functions:

- balance (vestibular apparatus of the internal ear)

- hearing (cochlea of internal ear)

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VIII Vestibulocochlear (cont.)

Injury may cause:

- tinnitus - ringing of the ear or deafness

- vertigo - feeling of rotation, dizziness

- ataxia and nystagmus - involuntary rapid movement of the eyeball

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IX Glossopharyngeal

mixed nerve Functions:

- taste (posterior 1/3 of the tongue)

- proprioception for swallowing (throat muscles)

- blood pressure receptors (carotid sinuses)

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X Vagus mixed nerve Functions:

- chemoreceptors (blood oxygen concentration, aortic bodies)

- pain receptors (respiratory and digestive tracts)

- sensations (external ear, larynx, and pharynx)

- taste (tongue)

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X Vagus (cont.)

Functions:

- heart rate and stroke volume (pacemaker and ventricular muscles)

- peristalsis (smooth muscles of the digestive tract)

- airflow (smooth muscles in bronchial tubes)

- speech and swallowing (muscles of larynx and pharynx)

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XI Accessory

mixed nerve (primarily motor) Function:

- head rotation (trapezius and sternocleidomastoid muscles

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XII Hypoglosseal

mixed nerve (primarily motor) Functions:

- speech and swallowing (tongue and throat muscles)

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Classification of Spinal Nerves all emerge from spinal cord emerge through holes formed by notches

on adjoining vertebrae 31 pairs all mixed nerves (containing both sensory

and motor) named and numbered according to region

and level of spinal cord from which they emerge

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Classification of Spinal Nerves (cont.)

8 pairs of cervical nerves

- first cervical pair emerges between atlas (first cervical vertebra) and occipital bone

- first 7 emerge above vertebra of the same number

- 8th emerges between 7th cervical vertebra and 1st thoracic vertebra

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Classification of Spinal Nerves (cont.)

12 pairs of thoracic nerves 5 pairs of lumbar nerves 5 pairs of sacral nerves 1 pair of coccygeal nerves

- all emerge below vertebra of the same number

- emerge through intervertebral foramina

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Plexuses (plexus = braid)

network of adjacent nerves

cervical plexus: C1 - C5 brachial plexus: C5 - T1 lumbar plexus: L1 - L4 sacral plexus: L4 - S4

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Brachial Plexus

C 4C 5C 6C 7C 8T 1

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Lumbo-Sacral Plexus

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Dermatomes

specific segment of skin which each spinal nerve innervates

knowledge can help physician determine which segment of the spinal cord or which spinal nerve is affected