Facial muscles

The facial muscles are a group of striated skeletal muscles supplied by the facial nerve that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, although they derive from neural crest cells found in all vertebrates. They are the only muscles that attach to the dermis.

Structure

The facial muscles are just under the skin muscles that control facial expression. They generally originate from the surface of the skull bone, and insert on the skin of the face. When they contract, the skin moves. These muscles also cause wrinkles at right angles to the muscles’ action line.

Nerve supply

The facial muscles are supplied by the facial nerve, with each nerve serving one side of the face. In contrast, the nearby masticatory muscles are supplied by the mandibular nerve, a branch of the trigeminal nerve.

List of muscles

The facial muscles include:

The platysma is supplied by the facial nerve. Although it is mostly in the neck and can be grouped with the neck muscles by location, it can be considered a muscle of facial expression due to its common nerve supply.
The stylohyoid muscle, stapedius and posterior belly of the digastric muscle are also supplied by the facial nerve, but are not considered muscles of facial expression.

Facial muscles by type of movement

Development

The facial muscles are derived from the second branchial/pharyngeal arch. They, like the branchial arches, originally derive from neural crest cells. In humans, they typically begin forming around the eighth week of embryonic development.

Clinical significance

An inability to form facial expressions on one side of the face may be the first sign of damage to the nerve of these muscles. Damage to the facial nerve results in facial paralysis of the muscles of facial expression on the involved side. Paralysis is the loss of voluntary muscle action; the facial nerve has become damaged permanently or temporarily. This damage can occur with a stroke, Bell palsy, or parotid salivary gland cancer because the facial nerve travels through the gland. The parotid gland can also be damaged permanently by surgery or temporarily by trauma. These situations of paralysis not only inhibit facial expression but also seriously impair the patient’s ability to speak, either permanently or temporarily.