Facial Nerve (Cranial Nerve VII)

Facial Nerve (Cranial Nerve VII)

  • Types of Nerve

    • Mixed nerve, containing both sensory (afferent) and motor (efferent) fibers.

  • Entry Point

    • Attaches to the brain at the pons.

    • Fibers separate but join again to exit the skull through the internal acoustic meatus.

  • Pathway and Branches

    • Travels through temporal bone and gives off three branches while in this bone.

  • Chorda Tympani

    • Complex course through the middle ear.

    • Exits the skull at petrotympanic fissure (specific exit name not needed for study).

    • Joins with lingual nerve (branch of the mandibular division of trigeminal nerve).

    • Intermingled fibers appear as one nerve, but the functions differ:

    • Lingual Nerve: All sensory, receives PPTT (Pain, Pressure, Temperature, Touch) sensations from the anterior 2/3 of the tongue.

  • Clinical Considerations

    • Inferior Alveolar Nerve Block

    • Anesthetizes the lingual nerve (intentionally numbing lingual gingiva).

    • Unintentionally numbs PPTT sensations and taste sensations (sweet, sour, salty) from the anterior 2/3 of the tongue.

  • Chorda Tympani Functions

    • Mixed Nerve: Contains both sensory and motor fibers.

    • Sensory fibers receive taste information from the anterior 2/3 of the tongue.

  • Motor Fibers

    • Regulate secretion from submandibular and sublingual glands, branching off before reaching the tongue.

  • Anatomy Overview

    • Major Branches of the facial nerve include:

    1. Temporal Nerve

    2. Zygomatic Nerve

    3. Buccal Nerve

    4. Mandibular Nerve

    5. Cervical Nerve

    6. Posterior Auricular Nerve

  • Branch Functions

    • Digastric Nerve: Motor to the posterior belly of digastric (anterior belly innervated by the mylohyoid nerve, branch of V3).

    • Stylohyoid Nerve: Motor to the stylohyoid muscle.

  • Parotid Gland Entry

    • Enters the parotid gland (does not innervate it) and divides into two divisions:

    • Temporofacial Division

      • Contains branches: Temporal, Zygomatic, Buccal.

      • Innervates zygomaticus major & minor, various levator muscles.

    • Cervicofacial Division

      • Contains Mandibular and Cervical branches.

      • Motor to depressor facial muscles (depressor labii inferioris, depressor anguli oris, mentalis) and platysma.

  • Damage to the Facial Nerve

    • Causes facial paralysis. Common causes include:

    • Stroke (CVA)

    • Cancer of the parotid gland

    • Nerve injuries (e.g., from accidents).

    • Damage is common due to superficial location, and temporary paralysis can result from incorrect block administration.

  • Symptoms of Facial Paralysis

    • Partial or complete paralysis of the affected facial side.

    • Affected facial muscles cannot contract properly, resulting in lack of expression.

    • Drooping of the lateral angle of the eye, inability to close the eye (risk of infection).

    • Drooping of the lateral angle of the mouth (drooling, speech difficulties).

  • Extent of Damage

    • Location of the lesion affects symptoms. Lesions at the stylomastoid foramen cause paralysis of all facial muscles.

    • Lesions within the temporal bone affect chorda tympani and branches for facial muscles, leading to taste loss and impaired secretion from submandibular & sublingual glands on the affected side.

  • Bell’s Palsy

    • Characterized by unilateral facial paralysis with no numbness but pain in the TMJ area and behind the ear.

    • Cause is currently unknown, possibly nerve inflammation within the temporal bone.

    • Abrupt onset; may be temporary or permanent; treatment often includes anti-inflammatory medication.

Glossopharyngeal Nerve (Cranial Nerve IX)

  • Type of Nerve

    • Mixed nerve (both afferent & efferent fibers).

    • Attaches to the brain at the medulla.

    • Exits the skull through the jugular foramen.

  • Branches with Efferent Fibers

    • Lesser Petrosal Nerve: Regulates saliva secretion from the parotid gland.

    • Stylopharyngeal Nerve: Motor to stylopharyngeus muscle, which contracts during swallowing.

  • Branches with Afferent Fibers

    • Lingual Nerve: Receives PPTT sensations and bitter taste from posterior 1/3 of the tongue.

    • Pharyngeal Nerve: Provides PPTT sensation from the pharynx.

    • Carotid Sinus Nerve: Monitors blood pressure via chemoreceptors and pressoreceptors.

  • Lesions to the Glossopharyngeal Nerve

    • Rare but can lead to:

    • Loss of taste & PPTT from the posterior 1/3 of the tongue.

    • Loss of gag reflex (via pharyngeal nerve damage).

    • Loss of cardiovascular reflex (via carotid sinus nerve damage).

  • Carotid Sinus Syndrome

    • Characterized by hyperactive carotid sinus reflex, usually seen in elderly patients.

    • Caused by slight increases in BP or pressure applications under the angle of the mandible.

    • Symptoms include hypotension, bradycardia, dizziness, syncope, and convulsions.

Vagus Nerve (Cranial Nerve X)

  • Type of Nerve

    • Mixed nerve with afferent (sensory) and efferent (motor) fibers.

    • Attaches to the brain at the medulla and exits the skull through the jugular foramen.

    • Descends each side of the neck within the carotid sheath alongside the common carotid artery and jugular vein.

  • Vagus Nerve Branches

    • Pharyngeal Nerve: Sensory for PPTT sensations from the pharynx and motor to all muscles of the pharynx (except stylopharyngeus).

    • Superior Laryngeal Nerve: Sensory fibers receive bitter taste; motor to larynx.

    • Inferior Laryngeal Nerve: Sensory and motor fibers to the larynx.

  • Other Functions

    • Sensory fibers gather information from thorax (heart, lungs, trachea, larynx, and pharynx).

    • Motor fibers control autonomic functions in the abdomen and thorax.

Autonomic Nervous System (ANS)

  • Divisions

    • Sympathetic: Known as the "Fight or Flight" mechanism.

    • Parasympathetic: Referred to as the "Rest and Digest" mechanism.

  • Sympathetic Responses

    • Stimulation leads to adrenaline release, increased heart rate, and redirected blood flow to muscles, resulting in a pale, cold, and clammy appearance.

    • Rapid breathing and dilated pupils for better vision.

    • Dry mouth due to reduced salivation.

  • Parasympathetic Responses

    • Opposite effects of the sympathetic division, promoting glandular secretions and smooth muscle activity during rest and digestion.

  • ANS and Salivary Flow

    • Salivary control: Dependent on the diameter of arteries supply to salivary glands.

    • Sympathetic stimulation constricts arteries leads to reduced saliva secretion.

    • Parasympathetic stimulation dilates arteries, increasing saliva secretion, especially evident with a relaxed patient or during eating.

  • Nerve Supply for the Tongue

    • Palatoglossus (Vagus Nerve CN 10) for motor functions.

    • Hypoglossal Nerve (CN 12) for all other muscle motor functions.

    • Glossopharyngeal Nerve (CN 9): Provides sensory & taste for posterior 1/3 of tongue.

    • Lingual Nerve (CN 5): Sensory for anterior 2/3 of tongue.

    • Chorda Tympani: Provides taste for anterior 2/3.