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The iris sphincter muscle (pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor of the pupil. The ciliary muscle, pupillary sphincter muscle and pupillary dilator muscle sometimes ...
Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. A constriction response (miosis), [1] is the narrowing of the pupil, which may be caused by scleral buckles or drugs such as opiates / opioids or anti-hypertension medications. Constriction of the pupil occurs when the ...
The central outermost transparent colorless part of the eye (through which we can see the iris and pupil) is the cornea. Cross-section of the human eye, showing the position of the pupil. The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. [ 1 ] It appears black because light rays entering ...
The ciliary ganglion is a parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. [1] The ganglion contains postganglionic parasympathetic neurons. These neurons supply the pupillary sphincter muscle, which constricts the pupil, and the ciliary ...
Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in controlling hemorrhage and reducing acute blood loss.
The iris dilator and sphincter muscles are contained in the iris and contract in order to dilate or constrict the pupils. The ciliary muscles change the shape of the lens to focus on objects in accommodation. In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature and fear.
Pilocarpine is a drug that acts as a muscarinic receptor agonist. It acts on a subtype of muscarinic receptor (M 3) found on the iris sphincter muscle, causing the muscle to contract - resulting in pupil constriction (miosis). Pilocarpine also acts on the ciliary muscle and causes it to contract. When the ciliary muscle contracts, it opens the ...
Vasodilation, also known as vasorelaxation, is the widening of blood vessels. [1] It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. [2] Blood vessel walls are composed of endothelial tissue and a basal membrane lining the lumen of the vessel ...