When the facial nerve does not work, dogs have an inability to blink, their lips droop, and there is decreased tear production on the affected side.
Twelve pairs of nerves, one on each side of the head, originate at the base of the brain and are responsible for certain neurological functions of the head and face. These paired nerves are called the cranial nerves and they are numbered 1 through 12. The 7th cranial nerve is the facial nerve, and it controls the muscles involved in facial expression, blinking and tear production. The cause of this condition is unknown. Although some cases of facial nerve paralysis have an identifiable origin, such as diseases of the ear, tumors and metabolic disorders, usually the cause of this disease is not well-defined.
Typically, a sudden weakness or paralysis occurs on one side of the face. If nerves on both sides of the head are affected, weakness is seen on both sides of the face. This weakness causes the ears and lips to droop. Animals may drop food or drool from the affected side of their mouth. Sensation, or feeling, of the face is normal. Because the facial nerve causes the eyelids to blink and controls the tear glands, affected animals may be unable to blink and may develop “dry eye” from a lack of tears on the affected side of the face. “Dry eye” may be associated with conjunctivitis, yellow-green discharge, and ulceration of the cornea. Vision remains normal.
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