Unilateral, peripheral facial paresis or paralysis that has an abrupt onset and no detectable cause is called Bell's palsy .It is one of the most common neurologic disorders affecting the cranial nerves. This was first described in 1821, by the Scottish anatomist and surgeon Sir Charles Bell. Weakness and/or paralysis from involvement of the facial nerve affects the entire face (upper and lower) on the affected side. Focus attention on the voluntary movement of the upper part of the face on the affected side: in supranuclear lesions (upper motor neuron; above the facial nucleus in the pons), the upper third of the face is spared while the lower two thirds are paralyzed. The orbicularis, frontalis, and corrugator muscles are innervated bilaterally, which explains the pattern of facial paralysis in these cases. Eye closure on the affected side may be partially or completely impaired. On attempting to close the eye, the patient may demonstrate the Bell phenomenon: the eye on the affected side rolls upward and inward.