What triggers the pupil reflex?

What triggers the pupil reflex?

The pupillary light reflex (PLR) is the constriction of the pupil that is elicited by an increase in illumination of the retina. The direct PLR, present in virtually all vertebrates, is the constriction of the pupil in the same eye as that stimulated with light.

What causes abnormal pupillary light reflex?

Pupillary light reflex is used to assess the brain stem function. Abnormal pupillary light reflex can be found in optic nerve injury, oculomotor nerve damage, brain stem lesions, such as tumors, and medications like barbiturates.

What is the main stimulus for the pupillary light reflex?

…the best-known reflex is the pupillary light reflex. If a light is flashed near one eye, the pupils of both eyes contract. Light is the stimulus; impulses reach the brain via the optic nerve; and the response is conveyed to the pupillary musculature by autonomic nerves that supply the eye.…

What does it mean when pupils react to light?

Reaction to light Introducing the light into one pupil should cause a similar, simultaneous contraction in the other pupil. When the light is withdrawn from one eye, the opposite pupil should dilate simultaneously. This response is called the consensual light reflex.

What causes pupils to not react?

Some neurologic conditions, such as stroke, tumor, or brain injury, can also cause changes in pupil size in one or both eyes. Pupils that do not respond to light or other stimuli are called fixed pupils. Often, fixed pupils are also dilated pupils.

Is the pupillary light reflex somatic or autonomic?

Autonomic Reflexes- The autonomic reflexes include the pupillary reflexes as well as many others.

What causes pupil constriction and dilation?

Stimulation of the autonomic nervous system’s sympathetic branch, known for triggering “fight or flight” responses when the body is under stress, induces pupil dilation. Whereas stimulation of the parasympathetic system, known for “rest and digest” functions, causes constriction.

What causes slow pupil dilation?

Adie syndrome, or Holmes-Adie syndrome, is a rare neurological disorder affecting the pupil of the eye. In most patients the pupil is larger than normal (dilated) and slow to react in response to direct light. Absent or poor tendon reflexes are also associated with this disorder.

What are the five basic components of the pupillary light reflex pathway?

retina, optic nerve, optic chiasm, and the optic tract fibers that join the ; brachium of the superior colliculus, which terminate in the ; pretectal area of the midbrain, which sends most of its axons bilaterally in the posterior commissure to terminate in the The cause might be that different components of the …

Is pupillary light reflex somatic or autonomic?

What is the normal response of the pupils when exposed to bright light?

The normal pupil size in adults varies from 2 to 4 mm in diameter in bright light to 4 to 8 mm in the dark. The pupils are generally equal in size. They constrict to direct illumination (direct response) and to illumination of the opposite eye (consensual response). The pupil dilates in the dark.

Is pupil dilation a reflex?

Pupillary reflex is synonymous with pupillary response, which may be pupillary constriction or dilation. Right pupillary reflex means reaction of the right pupil, whether light is shone into the left eye, right eye, or both eyes.

What can cause an abnormal pupillary light reflex?

Abnormal pupillary light reflex can be found in optic nerve injury, oculomotor nerve damage, brain stem lesions, such as tumors, and medications like barbiturates.

Where does the pupillary reflex take place in the eye?

Pupillary reflexes involve the autonomic (Edinger-Westphal) component of the oculomotor nucleus. In the light reflex, the pupils constrict when light is shone on the retina. If one eye only is stimulated, both pupils constrict, the so-called consensual reflex.

How does the pupil constrict in response to light?

Eyes allow for visualization of the world by receiving and processing light stimuli. The pupillary light reflex constricts the pupil in response to light, and pupillary constriction is achieved through the innervation of the iris sphincter muscle.

What causes constriction of the pupils in the retina?

Illumination of one eye causes reflexive constriction of both pupils: via the direct and indirect pupillary light reflexes. This is mediated by projections from the retina to the pretectal nucleus of the midbrain, just rostral to the superior colliculus.