Cranial Nerves Overview

Cranial Nerves Overview

• Cranial nerves are 12 paired nerves arising directly from the brain.
• The first two (olfactory and optic) originate from the cerebrum.
• The remaining ten emanate from the brainstem.
• Cranial nerve names relate to their function and are identified using Roman numerals (I-XII).

Learning Outcomes

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

GDC Learning Outcomes

• Describe relevant and appropriate dental, oral, craniofacial, and general anatomy.
• Explain the application of this anatomy to patient management.

Intended Learning Outcomes

• List the 12 paired cranial nerves.
• Describe the functions of each nerve.
• Outline the anatomical regions they supply.
• Explain the relevance of each nerve to dentistry, as applicable.

Resources

• Anatomy.tv
• Acland's Video Atlas of Human Anatomy
• YouTube videos
• Netter's Head and Neck Anatomy for Dentistry (3rd Edition)

Lecture Outline

• Overview of cranial nerves
• Function and clinical relevance
• Summary and quiz

What are the Cranial Nerves?

• 12 paired nerves that originate directly from the brain.
• The first two (olfactory & optic) emanate from the cerebrum.
• The remaining ten emerge from the brainstem.
• The names and numeric identification (I-XII) are linked to their associated functions.

Cranial Nerve I - Olfactory

• Sensory nerve
• Sensory receptors are located in the olfactory epithelium of the nasal cavity.
• Nerve fibers pass through the cribriform plate of the ethmoid bone.
• They enter the olfactory bulb.
• Function: Smell

Damage to Olfactory Nerve

• Total or impaired loss of smell
• Abnormal taste perception
• Trauma or tumor are possible causes.

Cranial Nerve II - Optic

• Sensory nerve
• Optic nerve fibers originate in the retina of the eye.
• The two optic nerves merge at the optic chiasm.
• Function: Vision

Damage to Optic Nerve

• Loss of vision, ranging from complete blindness in one eye to loss of half the visual field in both eyes.
• The location of damage dictates the nature and severity of the vision loss.

Cranial Nerve III - Oculomotor

• Motor nerve
• Contains parasympathetic fibers to the ciliary ganglion.
• It enters the orbit via the superior orbital fissure.
• Supplies four of the six extraocular muscles of the eye and the levator palpebrae superioris muscle.
• Parasympathetic fibers control the pupil and lens.

Damage to Oculomotor Nerve

• Eyelid drooping (ptosis)
• Impaired eye movements (up, down, and medial)
• Dilated pupil

Cranial Nerve IV - Trochlear

• Motor nerve
• Originates near the midbrain and pons.
• Enters the orbit through the superior orbital fissure.
• Supplies the superior oblique muscle.

Damage to Trochlear Nerve

• Eyeball deviation upwards
• Double vision
• Compensation head tilt

Cranial Nerve V - Trigeminal

• Mixed nerve, covered in a separate lecture.

Cranial Nerve VI - Abducens

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

Damage to Abducens Nerve

• Affected eye deviates medially.
• Lateral gaze issues.
• Double vision.

Cranial Nerve VII - Facial

• Mixed nerve, covered in a separate lecture.

Cranial Nerve VIII - Vestibulocochlear

• Sensory nerve, also known as the auditory nerve.
• Two divisions (vestibular and cochlear).
• Passes through the internal auditory meatus to the medulla oblongata.
• Function: Hearing and balance.

Damage to Vestibulocochlear Nerve

• Vertigo (spinning sensation).
• Nystagmus (eye movements).
• Loss of equilibrium.
• Nausea and vomiting

Cranial Nerve IX - Glossopharyngeal

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

Damage to Glossopharyngeal Nerve

• Sharp, stabbing, or shooting pain in the throat, tongue, and tonsils.
• Loss of taste (sometimes incomplete).
• Difficulty swallowing.

Cranial Nerve X - Vagus

• Mixed nerve
• Motor and sensory fibers arise from the medulla.
• Leaves the skull through the jugular foramen.
• Innervates smooth muscles, certain organs.

Damage to Vagus Nerve

• Uvula deviation
• Hoarse voice
• Difficulty swallowing or drinking
• Abnormal blood pressure
• Nausea, vomiting
• Abdominal pain & bloating

Cranial Nerve XI - Accessory

• Spinal and cranial components
• Comes from segments 5–6 of the cranial spinal cord.
• Enters the cranial cavity through the foramen magnum.
• Motor nerve to trapezius and sternocleidomastoid muscles.

Damage to Accessory Nerve

• Shoulder pain and weakness; restricted upper arm movement; asymmetrical shoulders.

Cranial Nerve XII - Hypoglossal

• Motor nerve
• Originates in the medulla oblongata.
• Leaves the skull via the hypoglossal canal.
• Supplies muscles of the tongue.

Damage to Hypoglossal Nerve

• Wasting of the tongue on the affected side.
• Tongue deviation to the affected side.
• Difficulties with eating, speaking, and swallowing.

Summary of Cranial Nerves

• 12 pairs of cranial nerves are listed.
• Their origin, function, and clinical significance are discussed.
• Facial and trigeminal nerves are highlighted as being primarily relevant to dentistry