Cranial Nerves

Cranial Nerves

• 12 paired nerves originate directly from the brain
• The first two (olfactory and optic) arise from the cerebrum
• The remaining ten originate from the brainstem
• Cranial nerve names relate to their function and are numerically identified (I-XII)
• A range of resources are available for studying cranial nerves, including anatomy.tv, Acland's Video Atlas of Human Anatomy, and the resources available

Intended Learning Outcomes

• Students should be able to list the 12 paired cranial nerves
• Students should be able to describe the functions of each nerve
• Students should be able to outline anatomical regions each nerve supplies
• Students should be able to explain the relevance of each nerve to dentistry, when applicable.

Overview of Cranial Nerves

• Includes an overview of the 12 cranial nerves
• Details of function and clinical relevance
• Separate summary and quiz

Cranial Nerve I - Olfactory

• Sensory nerve
• Receptors located in the nasal cavity olfactory epithelium
• Nerve fibers pass through the cribriform plate of the ethmoid bone
• Information passed into the olfactory bulb
• Function: Sense of smell

Damage to Olfactory Nerve

• Total loss of smell
• Impaired or distorted smell
• Abnormal taste perception
• Possible causes are trauma and tumors

Cranial Nerve II - Optic

• Sensory nerve
• Fibers originate in the retinae of the eye
• Optic nerves join at the optic chiasma
• Function: Vision

Damage to Optic Nerve

• Loss of vision depending on the area of damage
• Possible presentation of blindness in one eye or loss of lateral vision, or half of the visual field

Cranial Nerve III - Oculomotor

• Motor nerve
• Travels with parasympathetic fibers to the ciliary ganglion
• Divides into superior and inferior branches
• Enters the orbit through the superior orbital fissure of sphenoid
• Supplies four of the six extraocular muscles of the eye
• Supplies levator palpebrae superioris muscle
• Parasympathetic fibers aid pupil constriction and lens adjustment

Damage to Oculomotor Nerve

• Drooping eyelid (ptosis)
• Impaired eye movement
• Pupil dilation

Cranial Nerve IV - Trochlear

• Motor nerve
• Originates near the midbrain, near the junction of the midbrain and pons
• Passes through the superior orbital fissure
• Supplies superior oblique muscle

Damage to Trochlear Nerve

• Not as noticeable as other cranial nerve damage
• Eyeball deviation upward
• Double vision
• Head tilt to compensate

Cranial Nerve V - Trigeminal

• Sensory and motor nerve
• Further discussion to be provided in a separate lecture

Cranial Nerve VI - Abducens

• Motor nerve
• Originates from the abducens nucleus in the pons
• Enters the orbit through the superior orbital fissure
• Supplies the lateral rectus muscle

Damage to Abducens Nerve

• Affected eye moves medially
• Lateral gaze deficit
• Double vision

Cranial Nerve VII - Facial

• Further discussion to be provided in a separate lecture

Cranial Nerve VIII - Vestibulocochlear

• Sensory nerve
• Also known as the auditory nerve
• Two divisions
• Cochlear nerves for hearing
• Vestibular nerves for balance

Damage to Vestibulocochlear Nerve

• Various symptoms
• Vertigo: a false sensation that the surroundings are spinning or moving
• Nystagmus: a repetitive, involuntary eye movement

Cranial Nerve IX - Glossopharyngeal

• Motor and sensory nerve
• Motor fibers originate in the medulla oblongata
• Leaves the skull through the jugular foramen
• Sensory and motor branches present

Damage to Glossopharyngeal Nerve

• Sharp, stabbing pain in the throat, tonsils, and middle ear
• Reduced taste
• Loss of gag reflex
• Dry mouth

Cranial Nerve X - Vagus

• Sensory and motor nerve
• Originates in the medulla
• Exits skull through the jugular foramen
• Innervates various structures

Damage to Vagus Nerve

• Symptoms may include deviation of the uvula away from the damaged side
• Hoarse voice
• Difficulty drinking or loss of gag reflex
• Pain in the ear
• Abnormal blood pressure

Cranial Nerve XI - Accessory

• Spinal and cranial components
• Arises from the spinal cord, entering the cranial cavity through the foramen magnum
• Motor nerve, affecting the trapezius muscle, and sternocleidomastoid muscle, and some soft palate muscles
• Cranial portion joins the vagus nerve

Damage to Accessory Nerve

• Shoulder pain and weakness
• Limitied upper arm movement
• Asymmetrical shoulder

Cranial Nerve XII - Hypoglossal

• Motor nerve
• Originates in the medulla oblongata
• Leaves skull through the hypoglossal canal
• Supplies intrinsic and extrinsic muscles of the tongue

Damage to Hypoglossal Nerve

• Wasting of tongue on affected side
• Deviation of tongue to affected side
• Difficulty in eating, speaking, and swallowing

Summary

• 12 pairs of cranial nerves
• Origin, function, and relevance outlined
• Facial and trigeminal nerves are the most relevant to dentistry