The Facial Muscles
By Belinda Kirkland
The Facial Muscles
The muscles of facial expression are located just below the skin. They originate from bone or fascia (connective tissue), and insert onto the skin. When contracting, the muscles pull on the skin and exert their effects. The facial muscles are the only group of muscles that insert onto the skin. All of the muscles of facial expression are innervated by the facial nerve which is Cranial Nerve 7. The facial muscles can be split into 3 groups: orbital, nasal and oral.
The orbital group of facial muscles acts to affect the eye area. This group includes the Orbicularis Oculi and the Corrugator Supercilii. The Orbicularis Oculi muscle surrounds the eye socket and extends into the eyelid. The action of this muscle is to gently close the eye, assist with drainage of tears, and to tightly close the eyelid. Behind the orbicularis oculi, is the Corrugator Supercilii which inserts into the skin of the eyebrow and acts to draw the eyebrows together.
The next group of facial muscles is the nasal group. This group is associated with movements of the nose and the skin around it. These muscles serve little importance in humans. The nasalis muscle is the largest in humans. The nasalis has two functions: to compress and open the nostrils. The procerus muscle pulls the eyebrows downward to produce wrinkles across the nose in a horizontal fashion. The last muscle of the nasal group, depressor septi nasi which pulls the nose down opening the nostrils.
The last group of facial muscles is the oral group. This group is the most important group of muscles in the face. This group consists of the orbicularis oris, buccinator and other oral mucles which form an upper and lower group. The orbicularis oris purses the lips. The buccinators pulls the cheek inwards against the teeth preventing accumulation of food in that area. The lower group of other oral muscles contains the depressor anguli oris, depressor labi inferioris and the mentalis. The upper group contains the risorius, zygomaticus major and minor, levator labii superioris, levator labii superioris alaeque nasi and levator anguli oris.
If one notices difficulty or an inability to form facial expressions on one side of the face this may be the first sign of nerve damage. Damage to the facial nerve results in facial paralysis of the muscles of facial expression on the involved side. The damage can occur with a stroke, Bell’s Palsy or parotid salivary gland cancer because the facial nerve travels through the gland. The parotid gland can also be damaged by surgery or temporarily by trauma. These situations of paralysis not only inhibit facial expression but also impair the patient’s ability to speak.
In peripheral facial lesions, the facial muscles are completely paralyzed on the affected side. When trying to close the lids, the eye rotates upwards exposing the outer membrane of the eye called the sclera. In central facial lesions, one can wrinkle the forehead on both sides. The reason for this is that the motor branches of the forehead muscles derive from both sides of the facial nuclei. In both types of facial nerve paralysis speech, chewing and facial expression are severely impaired. Depending on the location of the lesion, the affected patients suffer from additional disturbances of tear and saliva secretion, hearing or taste.
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Written by: Belinda Kirkland