He is noted for discovering the difference between sensory nerves and motor nerves in the spinal cord.
A number of discoveries received his name:
Bell's (external respiratory) nerve: The long thoracic nerve.
Bell's palsy: a unilateral idiopathic paralysis of facial muscles due to a lesion of the facial nerve.
Bell's phenomenon: A normal defense mechanism—upward and outward movement of the eye which occurs when an individual closes their eyes forcibly. It can be appreciated clinically in a patient with paralysis of the orbicularis oculi (e.g. Guillain–Barré syndrome or Bell's palsy), as the eyelid remains elevated when the patient tries to close the eye.
Bell's spasm: Involuntary twitching of the facial muscles.
Bell-Magendie law or Bell's Law: States that the anterior branch of spinal nerve roots contain only motor fibers and the posterior roots contain only sensory fibers.