Peripheral Distribution of Cranial Nerves VII to XII CAM

Cranial Nerves VII to XII: Overview

• Internal acoustic meatus: Passage for CN VII (Facial) and CN VIII (Vestibulocochlear)

• Jugular Foramen: Passage for CN IX (Glossopharyngeal), CN X (Vagus), CN XI (Accessory) along with the internal jugular vein/sigmoid sinus

• Hypoglossal Canal: Passage for CN XII (Hypoglossal)

• Stylomastoid Foramen: Exit for CN VII (Facial)

Facial Nerve (CN VII)

• Emerges from the pons and enters the internal acoustic meatus.

• Courses through the petrous part of the temporal bone and exits the skull through the stylomastoid foramen.

• Functions:

  • Motor: Muscles of facial expression

  • Intermediate Nerve: Comprises special sensory fibers (taste) and parasympathetic fibers.

    • Special Sensory: Taste from anterior 2/3 of tongue via chord tympani

    • Parasympathetic:

      • Lacrimal gland innervation via greater petrosal nerve

      • Salivary glands (Sublingual & submandibular) via chord tympani.

• Pathways:

  • Greater Petrosal Nerve: Splits off within the temporal bone to innervate lacrimal gland with parasympathetic fibers.

  • Chorda Tympani: Splits off within the temporal bone, travels through the infratemporal fossa with V3 (Lingual nerve) to provide taste and parasympathetic fibers to respective glands.

• Motor Roots:

  • Emerges from the stylomastoid foramen.

  • Enters the parotid gland (does not supply it).

  • Supplies muscles of facial expression (including: temporal, zygomatic, buccal, marginal mandibular, cervical, posterior auricular) along with the post-belly of digastric, stylohyoid, and stapedius muscles.

Facial Muscles Innervated by VII

• Expression Muscles

  • Orbicularis Oris

  • Orbicularis Oculi

  • Buccinator

  • Frontalis

  • Occipitalis

  • Nasalis

  • Levator Labii Superioris

  • Zygomaticus Major and Minor

  • Mentalis

  • Depressor Anguli Oris

  • Platysma

  • Auricularis (Superior, Anterior, Posterior)

Facial Nerve Palsy (Bell’s Palsy)

• Definition: Paralysis of facial muscles due to lower motor neuron lesion.

• Causes: Commonly of unknown origin, often associated with swelling in the facial canal.

• Symptoms:

  • Dry cornea

  • Dry mouth

  • Impaired taste

• Risks: Peripheral branches vulnerable during parotid and submandibular surgeries.

Clinical Tests for Bell’s Palsy

1. Patient is asked to smile and raise eyebrows.

2. Patient is asked to close eyes.

• Management: Conservative treatment includes corticosteroids, eye care (drops, taping eyes at night).

Vestibulocochlear Nerve (CN VIII)

• Emerges from the pons.

• Enters the internal acoustic meatus with CN VII.

• Contains special sensory fibers for hearing (cochlear) and balance (vestibular) functions.

Glossopharyngeal Nerve (CN IX)

• Emerges from the medulla and exits via the jugular foramen.

• Functions:

  • Motor fibers for swallowing and pharynx control

  • Sensory fibers for taste posterior 1/3 of the tongue

  • General visceral afferent fibers from carotid body and sinus for blood pressure and oxygen level regulation.

Vagus Nerve (CN X)

• Motor Functions: Swallowing, phonation, controls muscles of palate, pharynx, larynx, and esophagus.

• Sensory Functions: Supplies larynx and lower pharynx along with aortic body sensory input.

• Visceral Motor: Supplies thoracic and abdominal viscera with parasympathetic fibers.

• Tests: "Say Ah" to assess the elevation of arches and voice quality.

Accessory Nerve (CN XI)

• Emerges from the first 5-6 cervical segments.

• Runs through the foramen magnum and exits via the jugular foramen.

• Motor Function: Controls sternocleidomastoid and trapezius muscles.

Hypoglossal Nerve (CN XII)

• Emerges from the anterior medulla and exits via the hypoglossal canal.

• Contains motor fibers to control tongue movements.

Sympathetic Supply to the Head

• Sympathetic Trunks: Three cervical sympathetic ganglia supplying the head.

  • Horner’s Syndrome:

    • Ptosis due to loss of sympathetic innervation to the upper eyelid.

    • Miosis (constricted pupil) indicating lack of dilatory control.

Summary of Cranial Nerves and Their Parasympathetic Functions