QS Study

The facial nerve is the seventh cranial nerve which conies both motor and sensory fibers. It is composed of approximately 10,000 neurons, 7,000 of which are myelinated and innervate the nerves of facial expression. It is the seventh paired cranial nerve.

Origin: The nuclei of the facial nerves are situated in the lower pons. It is the only cranial nerve that may show normal post-contrast enhancement, although this applies only to the labyrinthine segment up to the stylomastoid foramen. These are –

  • Motor nucleus.
  • Superior salivatory nucleus.
  • Lacrimatory nucleus.
  • The nucleus of tractus solitarius.

Facial Nerve 1

Fig: Facial Nerve

Course:

At the brainstem, the facial nerve has two distinct roots, motor and sensory. The motor root passes dorsomedially, winds around the abducent nuclei beneath the facial calculus from medial to the lateral side and then emerges at the cerebellopontine angle.

At the base of the brain, the two roots are attached to the pons just medial to the 8th cranial nerve. Then they run laterally and forward with the 8th cranial nerve to reach the internal acoustic meatus.

In the meatus, the motor root with the sensory root form a single branch and enter the facial canal accompanying with the 8th cranial nerve.

In the petrous part of the temporal bone, the nerve runs in the bony facial canal. It is divided into three parts. The nerve leaves the skull by passing out through the stylomastoid foramen.

In its extracranial courses, it enters into the parotid gland and divides into its five terminal branches for the face which emerge along the anterior border of the parotid gland.

Branches

(A) Within the facial canal:

  • The greater petrosal nerve.
  • The nerve to stapedius.
  • Chorda tympani.

(B) At the exit from the stylomastoid foramen:

  • Posterior auricular branch.
  • Digastric branch.
  • Stylohyoid brunch.

(C) Terminal branches emerging from the parotid gland:

  • Temporal branch.
  • Zygomatic branch.
  • Buccal branch.
  • Mandibular branch.
  • Cervical branch.

 Functional components:

  • General visceral efferent.
  • Special visceral efferent.
  • General somatic afferent.
  • Special somatic afferent.

Clinical importance:

According to the difference in the site of the lesion of the facial nerve, upper or lower motor type of facial palsy can occur which is manifested by both motor and sensory loss in the face.

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