Week 4: Cranial Nerves*

Introduction to Cranial Nerves

  • The cranial nerves are 12 pairs of nerves originating from the brain.

  • They primarily innervate structures of the head and neck.

  • Key roles include various sensory and motor functions, facilitating communication between the brain and different parts of the body.

  • Each cranial nerve is labeled with a Roman numeral (I-XII) based on location and function.

  • Important for healthcare professionals to understand their anatomy and functions.

Overview of Cranial Nerves

  • A total of 12 pairs of cranial nerves exist, categorized by function:

    • Sensory Neurons: Carry sensory information.

    • Motor Neurons: Carry motor information.

    • Mixed Nerves: Contain both sensory and motor fibers.

  • Mnemonic to remember the nerves: Only One Of The Two Athletes Felt Very Good, Victorious, And Healthy.

List of Cranial Nerves

  1. Olfactory Nerve (CN I): Sense of smell.

  2. Optic Nerve (CN II): Vision.

  3. Oculomotor Nerve (CN III): Eye movements, pupil constriction.

  4. Trochlear Nerve (CN IV): Controls superior oblique muscle of the eye.

  5. Trigeminal Nerve (CN V): Largest cranial nerve with sensory and motor functions affecting the face and mastication.

  6. Abducens Nerve (CN VI): Controls lateral rectus muscle for outward eye movement.

  7. Facial Nerve (CN VII): Facial expressions, taste, and secretion of saliva and tears.

  8. Vestibulocochlear Nerve (CN VIII): Hearing and balance.

  9. Glossopharyngeal Nerve (CN IX): Taste from the back of the tongue, swallowing, and baroreception.

  10. Vagus Nerve (CN X): Controls heart rate and digestive tract.

  11. Accessory Nerve (CN XI): Controls neck and shoulder muscles.

  12. Hypoglossal Nerve (CN XII): Tongue movement.

Individual Cranial Nerves

Olfactory Nerve (CN I)

  • Origin: Olfactory epithelium of the nasal cavity.

  • Function: Sense of smell.

  • Examination: Assess by having the patient identify odors with eyes closed.

Optic Nerve (CN II)

  • Origin: Retina via ganglion cell axons.

  • Function: Vision.

  • Examination: Use a direct ophthalmoscope and test for pupil reaction to light and visual fields.

Oculomotor Nerve (CN III)

  • Origin: Oculomotor nucleus in the midbrain.

  • Function: Controls most extraocular movements and pupil constriction.

  • Examination: Check eye movement and pupil responses.

Trochlear Nerve (CN IV)

  • Origin: Trochlear nucleus in the midbrain.

  • Function: Movement of superior oblique muscle.

  • Examination: Assess eye movement in conjunction with CN III and VI.

Trigeminal Nerve (CN V)

  • Branches: Ophthalmic (V1), Maxillary (V2), Mandibular (V3).

  • Function: Facial sensation, mastication.

  • Examination: Test sensation across the areas of the face and strength of mastication by palpating the masseter muscle.

Abducens Nerve (CN VI)

  • Origin: Abducens nucleus in the pons.

  • Function: Controls the lateral rectus muscle for eye abduction.

  • Examination: Similar to other eye movement tests.

Facial Nerve (CN VII)

  • Origin: Pons, via motor and sensory roots.

  • Function: Controls facial expressions and taste from the anterior two-thirds of the tongue.

  • Examination: Inspect facial symmetry and test taste sensations with sweet substances.

Vestibulocochlear Nerve (CN VIII)

  • Origin: Vestibular and cochlear nuclei in the brainstem.

  • Function: Hearing and balance.

  • Examination: Test hearing acuity and balance, using tuning fork tests.

Glossopharyngeal Nerve (CN IX)

  • Origin: Medulla oblongata.

  • Function: Taste and autonomic functions including salivation.

  • Examination: Test gag reflex and taste sensation on the posterior tongue.

Vagus Nerve (CN X)

  • Origin: Medulla.

  • Function: Controls heart rate and digestion; sensory functions from thoracic and abdominal viscera.

  • Examination: Check for rise of the soft palate and monitor heart rate/blood pressure responses.

Accessory Nerve (CN XI)

  • Origin: Spinal roots (C1-C5).

  • Function: Motor function to sternocleidomastoid and trapezius muscles.

  • Examination: Test shoulder shrug and head rotation against resistance.

Hypoglossal Nerve (CN XII)

  • Origin: Hypoglossal nucleus in the medulla.

  • Function: Tongue movements for speech and eating.

  • Examination: Observe tongue movement and strength of protrusion.