Glabellar reflex (Glabella) is a primitive reflex. It is elicited by repetitive tapping on the forehead. Subjects blink in response to the first several taps. If the blinking persists, this is known as Myerson's sign

Myerson's sign

Myerson's sign is a medical condition where a patient is unable to resist blinking when tapped on the glabella, the area above the nose and between the eyebrows. It is often referred to as the glabellar reflex. It is often an early symptom of Parkinson's disease, but can also be seen in early...

 and is abnormal (ex:Parkinson disease).

The afferent sensory signals are transmitted by the trigeminal nerve

Trigeminal nerve

The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...

, and the efferent signals come back to orbicularis oculi muscle

Orbicularis oculi muscle

The orbicularis oculi is a muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short fibrous band, the medial palpebral ligament.From...

 via the facial nerve

Facial nerve

The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...

, which in turn reflexly contracts causing blinking.

Myerson's sign is often seen in patients with Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

.