What cranial nerve (CN) corresponds to each facial movement, including frontalis muscle for eyebrow elevation, orbicularis oculi for eye closure, buccinator for cheek puffing, and zygomaticus for teeth baring, in the assessment of a potential stroke patient?

From the Guidelines

When testing facial nerve movements in a potential stroke patient, each facial movement corresponds to specific cranial nerves, with raised eyebrows and forehead wrinkling controlled by the frontal branch of the facial nerve (cranial nerve VII), closing eyes tightly involving the orbital branch of the facial nerve, puffing cheeks and pursing lips controlled by the buccal and marginal mandibular branches of the facial nerve, and showing or baring teeth also involving the facial nerve (cranial nerve VII), while shrugging shoulders is controlled by the accessory nerve (cranial nerve XI), not the facial nerve. The most recent and highest quality study, 1, provides detailed information on the facial nerve and its functions, highlighting the importance of understanding the specific cranial nerves involved in each facial movement. Key points to consider when testing facial nerve movements include:

• Raised eyebrows and forehead wrinkling are controlled by the frontal branch of the facial nerve (cranial nerve VII)
• Closing eyes tightly involves the orbital branch of the facial nerve
• Puffing cheeks and pursing lips are controlled by the buccal and marginal mandibular branches of the facial nerve
• Showing or baring teeth also involves the facial nerve (cranial nerve VII)
• Shrugging shoulders is controlled by the accessory nerve (cranial nerve XI), not the facial nerve These tests are important because in a central facial nerve palsy (typical of stroke), the forehead is often spared due to bilateral cortical innervation, while in peripheral facial nerve palsy, all facial movements on the affected side are impaired, as noted in 1. When conducting these tests, it is essential to observe for facial asymmetry, which is a key indicator of neurological dysfunction, particularly noting if the patient can move both sides of their face equally or if one side appears weaker or immobile, as discussed in 1. The distinction between central and peripheral facial nerve palsy helps differentiate between central causes like stroke and peripheral causes like Bell's palsy, emphasizing the importance of accurate diagnosis and treatment, as highlighted in 1.

From the Research

Facial Nerve Movements

The facial nerve is responsible for controlling various facial movements. When testing facial nerve movements for possible stroke patients, each facial movement corresponds to a specific nerve. The following are some of the facial movements and the corresponding nerves:

• Raised eyebrows:
  • The frontal branch of the facial nerve is responsible for controlling the muscles of the forehead, including the frontalis muscle, which raises the eyebrows 2.
• Close eyes:
  • The orbicularis oculi muscle, which is innervated by the zygomatic branch of the facial nerve, is responsible for closing the eyes 2.
• Puff cheeks:
  • The buccinator muscle, which is innervated by the buccal branch of the facial nerve, is responsible for puffing out the cheeks.
• Shrugging shoulders:
  • This movement is not directly related to the facial nerve, as it is controlled by the accessory nerve (cranial nerve XI) and the muscles of the shoulder region.
• Bare teeth:
  • The muscles of the mouth, including the orbicularis oris, which is innervated by the buccal and marginal mandibular branches of the facial nerve, are responsible for baring the teeth.

Nerve Supply to Facial Muscles

The facial nerve has several branches that supply the muscles of the face. These branches include:

• The temporal branch, which supplies the muscles of the forehead
• The zygomatic branch, which supplies the orbicularis oculi muscle
• The buccal branch, which supplies the muscles of the cheek and mouth
• The marginal mandibular branch, which supplies the muscles of the lower lip and chin

Clinical Implications

In stroke patients, damage to the facial nerve or its branches can result in weakness or paralysis of the facial muscles. The pattern of weakness can help localize the lesion and determine the extent of nerve damage 3. For example, weakness in eyelid closure may be associated with anterior cerebral artery stroke, while weakness in lip opening may be associated with middle cerebral artery stroke 3.