Reflexes are not limited to the spinal cord. Responses involving the musculature of the face and neck can also be reflexive in nature. For example, a puff of air that strikes the cornea of the human eye elicits a brisk, short-latency eyelid closure. Like the polysynaptic spinal reflexes, this eyeblink reflex appears to involve three elements: a sensory nerve, called the trigeminal nerve, that carries information from receptors in the cornea of the eye to the trigeminal nucleus (a cranial nerve nucleus); interneurons that connect the trigeminal nucleus with several other brain-stem neurons; and a motor nerve that originates from brain-stem motor neurons and contracts the muscles surrounding the eye to produce the eyeblink. This reflex is defensive in nature because it ensures that the eyeball is protected from further stimulation if a stimulus strikes the cornea.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.