SummaryofFunctionofCranial Nerves

Cranial Nerve I: Olfactory
Arises from the olfactory epithelium
Passes through the cribriform plate of the ethmoid bone
Fibers run through the olfactory bulb and terminate in the primary olfactory cortex
Functions solely by carrying afferent impulses for the sense of smell

Cranial Nerve I: Olfactory
Figure I from Table 13.2

Cranial Nerve II: Optic
Arises from the retina of the eye
Optic nerves pass through the optic canals and converge at the optic chiasm
They continue to the thalamus where they synapse
From there, the optic radiation fibers run to the visual cortex
Functions solely by carrying afferent impulses for vision

Cranial Nerve II: Optic
Figure II Table 13.2

Cranial Nerve III: Oculomotor
Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape
The latter 2 functions are parasympathetically controlled
Parasympathetic cell bodies are in the ciliary ganglia

Cranial Nerve III: Oculomotor
Figure III from Table 13.2

Cranial Nerve IV: Trochlear
Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball

Cranial Nerve IV: Trochlear
Figure IV from Table 13.2

Cranial Nerve V: Trigeminal
Composed of three divisions
Ophthalmic (V1)
Maxillary (V2)
Mandibular (V3)
Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3)
Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication
Tic douloureux or trigeminal neuralgia
- Most excruciating pain known (?)
- Caused by inflammation of nerve
- In severe cases, nerve is cut; relieves agony but results in loss of sensation on that side of the face

Cranial Nerve V: Trigeminal

Cranial Nerve VI: Abducens
Fibers leave the inferior pons and enter the orbit via the superior orbital fissure
Primarily a motor nerve innervating the lateral rectus muscle (abducts the eye; thus the name abducens)

Cranial Nerve VII: Facial
Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face
Motor functions include;
Facial expression
Transmittal of parasympathetic impulses to lacrimal and salivary glands (submandibular and sublingual glands)
Sensory function is taste from taste buds of anterior two-thirds of the tongue

Cranial Nerve VII: Facial
Figure VII from Table 13.2

Facial Nerve (CN VII)
Bell’s palsy: paralysis of facial muscles on affected side and loss of taste sensation
Caused by herpes simplex I virus
Lower eyelid droops
Corner of mouth sags
Tears drip continuously and eye cannot be completely closed (dry eye may occur)
Condition my disappear spontaneously without treatment

Cranial Nerve VIII: Vestibulocochlear
Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border
Two divisions – cochlear (hearing) and vestibular (balance)
Functions are solely sensory – equilibrium and hearing

Cranial Nerve VIII: Vestibulocochlear
Figure VIII from Table 13.2

Cranial Nerve IX: Glossopharyngeal
Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat
Nerve IX is a mixed nerve with motor and sensory functions
Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland
Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx

Cranial Nerve IX: Glossopharyngeal
Figure IX from Table 13.2

Cranial Nerve X: Vagus
The only cranial nerve that extends beyond the head and neck
Fibers emerge from the medulla via the jugular foramen
The vagus is a mixed nerve
Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs
Its sensory function is in taste
Paralysis leads to hoarseness
Total destruction incompatible with life

Cranial Nerve X: Vagus

Cranial Nerve XI: Accessory
Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord
The spinal root passes upward into the cranium via the foramen magnum
The accessory nerve leaves the cranium via the jugular foramen
Primarily a motor nerve
Supplies fibers to the larynx, pharynx, and soft palate
Innervates the trapezius and sternocleidomastoid, which move the head and neck

Cranial Nerve XI: Accessory
Figure XI from Table 13.2

Cranial Nerve XII: Hypoglossal
Fibers arise from the medulla and exit the skull via the hypoglossal canal
Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech
If damaged, difficulties in speech and swallowing; inability to protrude tongue