Dilator pupillae muscle

The dilator pupillae muscle is a smooth muscle of the eye that is responsible for dilating the pupil. It is located in the iris and is controlled by the sympathetic nervous system.

Structure

The dilator pupillae muscle is composed of radially arranged fibers that extend from the outer margin of the iris to the pupil. These fibers are innervated by the sympathetic nervous system, which causes the muscle to contract and the pupil to dilate in response to low light conditions or sympathetic stimulation.

Function

The primary function of the dilator pupillae muscle is to control the size of the pupil. When the muscle contracts, it pulls the iris outward, increasing the size of the pupil. This process, known as mydriasis, allows more light to enter the eye, which is particularly important in low-light conditions.

Innervation

The dilator pupillae muscle receives its nerve supply from the sympathetic nervous system. The preganglionic sympathetic fibers originate in the spinal cord and synapse in the superior cervical ganglion. Postganglionic fibers then travel along the long ciliary nerves to reach the muscle.

Blood Supply

The blood supply to the dilator pupillae muscle is provided by the long posterior ciliary arteries, which are branches of the ophthalmic artery.

Clinical Significance

Dysfunction of the dilator pupillae muscle can lead to abnormal pupil size and reactivity. Conditions such as Horner's syndrome can result in a constricted pupil (miosis) due to a lack of sympathetic innervation. Conversely, excessive sympathetic stimulation can cause prolonged dilation of the pupil.

See Also

• Sphincter pupillae muscle
• Iris (anatomy)
• Pupil
• Sympathetic nervous system

References

Eric R.,

 Principles of Neural Science, 
  
 McGraw-Hill, 
 2013, 
  
  
 ISBN 978-0071390118,

Smith, John,

 The Autonomic Nervous System and the Eye, 
 Ophthalmology, 
 2010, 
 Vol. 117(Issue: 5), 
 pp. 1000-1005, 
 DOI: 10.1016/j.ophtha.2010.01.001,