What is the function of the sphincter Pupillae muscles of the iris?
What is the function of the sphincter Pupillae muscles of the iris?
The sphincter muscle fibers are located near the pupillary margin and are slightly anterior to the pigmented epithelium of the iris. It encircles the pupil of the iris and functions to constrict the pupil in bright light via the pupillary light reflex or during accommodation.
What muscle dilates the iris?
iris dilator muscle
The iris dilator muscle has fibers arranged radially from the sphincter to the ciliary border, receives sympathetic innervation, and functions to cause dilation of the pupil (mydriasis).
What muscle of the eye constricts and dilates the pupil?
The sphincter muscle 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.
What is the sphincter Pupillae innervated by?
parasympathetic nerve fibres
This muscle is innervated by parasympathetic nerve fibres derived from the oculomotor nerve (postganglionic fibres from the ciliary ganglion travel via the short ciliary nerves) although sympathetics also terminate in this muscle.
What type of muscle is sphincter Pupillae?
circular muscle
Origin and insertion. Sphincter pupillae is a circular muscle, about 1 millimeter wide. It is located in the pupillary zone of stromal layer of the iris, attaching to and encircling the pupillary margin of iris.
What is the muscle that encircles the eye known?
Iris sphincter muscle
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….
| Iris sphincter muscle | |
|---|---|
| Origin | encircles iris |
| Insertion | encircles iris |
| Artery | long posterior ciliary arteries |
| Nerve | short ciliary nerves |
Where is the dilator Pupillae?
iris
In humans, the dilator muscle of the iris contains fibres that extend radially through the iris of the eye and involuntarily contract as available light decreases, thus dilating the pupil. Pupillary dilation is controlled primarily by the sympathetic nervous system.
What is the muscle that encircles the eye known as?
Beneath this layer is a donut-shaped muscle that encircles the eye called orbicularis oculi, which is innervated by the 7th cranial nerve, and is in charge of closing the eyelids.
What is the muscles that encircles the eye known as?
What does the iris consist of?
From back to front, the iris is composed of a two-cell layer, heavily pigmented epithelium (iris pigment epithelium, IPE); the dilator and sphincter muscles; a stroma of highly vascularized connective tissue containing melanocytes, melanin granules and chromatophores, and an anterior cellular border layer of irregular.
