Pupillary light reflex
Pupillary Light Reflex
The Pupillary Light Reflex (pronounced: pyoo-pil-er-ee lahyt ree-fleks) is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the eye. It is an automatic response and is one of the functions of the autonomic nervous system.
Etymology
The term "Pupillary Light Reflex" is derived from three words. "Pupillary" comes from the Latin word "pupilla" which means 'little doll', referring to the tiny reflection of oneself seen in another's pupil. "Light" is from the Old English "leoht", meaning 'radiance, illumination'. "Reflex" is from the Latin "reflexus", meaning 'a bending back', referring to the automatic response of the body to a stimulus.
Function
The Pupillary Light Reflex serves to regulate the amount of light that enters the eye. When an intense light is shone on the retina, the pupillomotor fibers in the oculomotor nerve cause the sphincter muscle of the pupil to contract, reducing the size of the pupil (miosis). This prevents overexposure and potential damage to the retina.
Pathway
The pathway of the Pupillary Light Reflex begins when light hits the retina. The signal is then transmitted to the pretectal nuclei in the midbrain via the optic nerve. From the pretectal nuclei, the signal is sent to the Edinger-Westphal nucleus, which then sends a signal via the oculomotor nerve to the sphincter muscle of the pupil, causing it to contract.
Related Terms
- Miosis: Constriction of the pupil.
- Mydriasis: Dilation of the pupil.
- Photophobia: Sensitivity to light.
- Anisocoria: Unequal pupil sizes.
External links
- Medical encyclopedia article on Pupillary light reflex
- Wikipedia's article - Pupillary light reflex
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