Which Muscles When Contracted Decrease the Diameter of the Pupil?

Robert Thorne
Robert Thorne
• • 7 min read

The Sphincter Muscle Sphincter Muscle a Sphincter Is a Circular Muscle That Normally Maintains Constriction of a Natural Body Passage or Orifice and Which...

Which Muscles When Contracted Decrease the Diameter of the Pupil?

The sphincter muscle

sphincter muscle
A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and which relaxes as required by normal physiological functioning. ... Sphincters relax at death, often releasing fluids and faeces.
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fibers form a ring at the pupil margin so that when the sphincter contracts, it decreases (constricts) pupil size. The dilator muscle fibers radiate from the pupil aperture so that when the dilator contracts, it increases (dilates) pupil size.

Which muscles decrease the diameter of the pupil?

The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil.

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What muscle changes the size of the pupil?

The iris consists of two sheets of smooth muscle with contrary actions: dilation (expansion) and contraction (constriction). These muscles control the size of the pupil and thus determine how much light reaches the sensory tissue of the retina.

Robert Thorne

Robert Thorne

Automotive & Future Transportation Editor
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Robert Thorne covers electric vehicle innovations, autonomous driving systems, global mobility trends, and automotive engineering developments.