Question

Pupillary light reflex As described in the pre-lab, there are two muscles that control the diameter of the pupil. In response to bright light, we expect the pupils to constrict. In response to low light, we expect the pupils to dilate. Both reflexes are controlled by the autonomic nervous system. In fact, shining a light into a patient's eyes is often done in the emergency room as a quick test of ocular function. Enlarged pupils (or pepils that fail to constrict equally) are considered an abnormal response and are cause for concern-such causes include damage to one or more ocular nerve, severe brain stem damage, or overdose on depressant drugs. Each individual in your group should perform this exercise. 1. Sit in a chair and cover your eyes with your hand. Keep your eyes covered for fitteen seconds. Keep your eyes open, but you should be able to see little or no light.

Answer 1

The pupillary light reflex is controlled by the autonomic nervous system and involves the sensory input of the optic nerve and the parasympathetic motor output of the oculomotor nerve. Shining a light in one eye will cause constriction of both pupils, and different responses can indicate damage to the optic nerve or the oculomotor system.

Step-by-step explanation:

The pupillary light reflex is controlled by the autonomic nervous system and involves the sensory input of the optic nerve and the parasympathetic motor output of the oculomotor nerve. When light hits the retina, it stimulates specialized ganglion cells that send a signal along the optic nerve to the pretectal nucleus in the midbrain. From there, a neuron projects to the Edinger-Westphal nuclei in the oculomotor complex, which give rise to the preganglionic parasympathetic fibers. These fibers project through the oculomotor nerve to the ciliary ganglion, which then sends postganglionic fibers to the iris. The release of acetylcholine onto circular fibers of the iris constricts the pupil to reduce the amount of light hitting the retina.

The sympathetic nervous system is responsible for dilating the pupil when light levels are low.

Shining a light in one eye will cause constriction of both pupils, as the efferent limb of the pupillary light reflex is bilateral. If no changes in pupillary size occur when light is shined in one eye but a normal response is observed when light is shined in the opposite eye, it indicates damage to the optic nerve on the nonresponsive side. If a response is only observed in one eye when light is shined in either eye, it suggests a problem with the oculomotor system.