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Iris Dilator Muscle
The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing more light to enter the eye. Structure Innervation It is innervated by the sympathetic system, which acts by releasing noradrenaline, which acts on α1-receptors. page 163 Thus, when presented with a threatening stimulus that activates the fight-or-flight response, this innervation contracts the muscle and dilates the pupil, thus temporarily letting more light reach the retina. The dilator muscle is innervated more specifically by postganglionic sympathetic nerves arising from the superior cervical ganglion as the sympathetic root of cil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iris (anatomy)
In humans and most mammals and birds, the iris (plural: ''irides'' or ''irises'') is a thin, annular structure in the eye, responsible for controlling the diameter and size of the pupil, and thus the amount of light reaching the retina. Eye color is defined by the iris. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm. Structure The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma and, beneath the stroma, pigmented epithelial cells. The stroma is connected to a sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles ( dilator pupillae), which pull the iris radially to enlarge the pupil, pulling it in folds. The sphincter pupillae is the opposing muscle of the dilator pupillae. The pupil's diameter, and thus the inner border of the iris, changes size when constricting or dilating. The outer border of the iris does not change size. The constricti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sympathetic Root Of Ciliary Ganglion
The ciliary ganglion is a parasympathetic ganglion located just behind the eye in the posterior orbit. Three types of axons enter the ciliary ganglion but only the preganglionic parasympathetic axons synapse there. The entering axons are arranged into three roots of the ciliary ganglion, which join enter the posterior surface of the ganglion. Sympathetic root The sympathetic root of ciliary ganglion is one of three roots of the ciliary ganglion. It contains ''postganglionic'' sympathetic fibers whose cell bodies are located in the superior cervical ganglion. Their axons ascend with the internal carotid artery as a plexus of nerves, the internal carotid plexus. Sympathetic fibers supplying the eye separate from the carotid plexus within the cavernous sinus. They run forward through the superior orbital fissure and merge with the long ciliary nerves (branches of the nasociliary nerve) and the short ciliary nerves (from the ciliary ganglion). Sympathetic fibers in the short ciliar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Choroid
The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye, and contains connective tissues, and lies between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The structure of the choroid is generally divided into four layers (classified in order of furthest away from the retina to closest): *Haller's layer - outermost layer of the choroid consisting of larger diameter blood vessels; *Sattler's layer - layer of medium diameter blood vessels; * Choriocapillaris - layer of capillaries; and *Bruch's membrane (synonyms: Lamina basalis, Complexus basalis, Lamina vitra) - innermost layer of the choroid. Blood supply There are two circulations of the eye: the retin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sclera
The sclera, also known as the white of the eye or, in older literature, as the tunica albuginea oculi, is the opaque, fibrous, protective, outer layer of the human eye containing mainly collagen and some crucial elastic fiber. In humans, and some other vertebrates, the whole sclera is white, contrasting with the coloured iris, but in most mammals, the visible part of the sclera matches the colour of the iris, so the white part does not normally show while other vertebrates have distinct colors for both of them. In the development of the embryo, the sclera is derived from the neural crest. In children, it is thinner and shows some of the underlying pigment, appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow. People with dark skin can have naturally darkened sclerae, the result of melanin pigmentation. The human eye is relatively rare for having a pale sclera (relative to the iris). This makes it easier for one individual to ide ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long Ciliary Nerve
The long ciliary nerves are 2-3 nerves that arise from the nasociliary nerve (itself a branch of the ophthalmic branch (CN V1) of the trigeminal nerve (CN V)). They enter the eyeball to provide sensory innervation to parts of the eye, and sympathetic visceral motor innervation to the dilator pupillae muscle. Anatomy Origin The long ciliary nerves branch from the nasociliary nerve as it crosses the optic nerve (CN II). Course Accompanied by the short ciliary nerves, the long ciliary nerves pierce and enter the posterior part of the sclera near where it is entered by the optic nerve, then run anterior-ward between the sclera and the choroid. Function The long ciliary nerves are distributed to the ciliary body, iris, and cornea. Sensory The long ciliary nerves provide sensory innervation to the eyeball, including the cornea. Sympathetic The long ciliary nerves contain post-ganglionic sympathetic fibers from the superior cervical ganglion for the dilator pupillae ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nasociliary Nerve
The nasociliary nerve is a branch of the ophthalmic nerve, itself a branch of the trigeminal nerve (CN V). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve. Structure The nasociliary nerve enters the orbit via the superior orbital fissure, between the two heads of the lateral rectus muscle and between the superior and inferior rami of the oculomotor nerve. It passes across the optic nerve (CN II) and runs obliquely beneath the superior rectus muscle and superior oblique muscle to the medial wall of the orbital cavity. It passes through the anterior ethmoidal opening as the anterior ethmoidal nerve and enters the cranial cavity just below the cribriform plate of the ethmoid bone. It supplies branches to the mucous membrane of the nasal cavity and finally emerges between the inferior border of the nasal bone and the side nasal cartilages as the external nasal branch. Branches * posterior ethmoidal nerve * ante ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superior Orbital Fissure
The superior orbital fissure is a foramen or cleft of the skull between the lesser and greater wings of the sphenoid bone. It gives passage to multiple structures, including the oculomotor nerve, trochlear nerve, ophthalmic nerve, abducens nerve, ophthalmic veins, and sympathetic fibres from the cavernous plexus. Structure The superior orbital fissure is usually 22 mm wide in adults, and is much larger medially. Its boundaries are formed by the (caudal surface of the) lesser wing of the sphenoid bone, and (medial border of the) greater wing of the sphenoid bone. Contents The superior orbital fissure is traversed by the following structures: * (superior and inferior divisions of the) oculomotor nerve (CN III) * trochlear nerve (CN IV) * lacrimal, frontal, and nasociliary branches of ophthalmic nerve (CN V1) * abducens nerve (CN VI) * superior ophthalmic vein and superior division of the inferior ophthalmic vein * sympathetic fibres from the cavernous nerve pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ophthalmic Nerve
The ophthalmic nerve (V1) is a sensory nerve of the face. It is one of three divisions of the trigeminal nerve (CN V). It has three branches that provide sensory innervation to the eye, the skin of the upper face, and the skin of the anterior scalp. Structure The ophthalmic nerve is the first branch of the trigeminal nerve (CN V). It is joined by filaments from the cavernous plexus of the sympathetic, and communicates with the oculomotor, trochlear, and abducent nerves. It gives off a recurrent (meningeal) filament which passes between the layers of the tentorium. Branches The ophthalmic nerve divides into three major branches as it passes through the superior orbital fissure. *The nasociliary nerve gives off several sensory branches to the orbit. It then continues out through the anterior ethmoidal foramen, where it enters the nasal cavity. It provides innervation for much of the anterior nasal mucosa. It also gives off a branch which exits through the nasal bones to form ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optic Canal
The ''optic foramen'' is the opening to the optic canal. The canal is located in the sphenoid bone; it is bounded medially by the body of the sphenoid and laterally by the lesser wing of the sphenoid. The superior surface of the sphenoid bone is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove (optic groove), above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and ophthalmic artery (with accompanying sympathetic nerve fibres) into the orbital cavity. Compared to the optic nerve, the ophthalmic artery is located inferolaterally within the canal. The left and right optic canals are 25mm apart posteriorly and 30mm apart anteriorly. The canals themselves are funnel-shaped (narrowest anteriorly). Additional images File:Orbital_bones.png, The seven bones which articulate to form the orbit. File:Gray145.png, Sphenoid bone. Upper surface. Fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ophthalmic Artery
The ophthalmic artery (OA) is an artery of the head. It is the first branch of the internal carotid artery distal to the cavernous sinus. Branches of the ophthalmic artery supply all the structures in the orbit around the eye, as well as some structures in the nose, face, and meninges. Occlusion of the ophthalmic artery or its branches can produce sight-threatening conditions. Structure The ophthalmic artery emerges from the internal carotid artery. This is usually just after the internal carotid artery emerges from the cavernous sinus. In some cases, the ophthalmic artery branches just before the internal carotid exits the cavernous sinus. The ophthalmic artery emerges along the medial side of the anterior clinoid process. It runs anteriorly, passing through the optic canal inferolaterally to the optic nerve. It can also pass superiorly to the optic nerve in a minority of cases. In the posterior third of the cone of the orbit, the ophthalmic artery turns sharply and medially t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cavernous Sinus
The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica. Structure The cavernous sinus is one of the dural venous sinuses of the head. It is a network of veins that sit in a cavity. It sits on both sides of the sphenoidal bone and pituitary gland, approximately 1 × 2 cm in size in an adult. The carotid siphon of the internal carotid artery, and cranial nerves III, IV, V (branches V1 and V2) and VI all pass through this blood filled space. Both sides of cavernous sinus is connected to each other via intercavernous sinuses. The cavernous sinus lies in between the inner and outer layers of dura mater. Nearby structures * Above: optic tract, optic chiasma, internal carotid artery. * Inferiorly: foramen lacerum, and the junction of the body and greater wing of sphenoid bone. * Medially: pituitary gla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Middle Cranial Fossa
The middle cranial fossa, deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior fossa by the clivus and the petrous crest. It is bounded in front by the posterior margins of the lesser wings of the sphenoid bone, the anterior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; behind, by the superior angles of the petrous portions of the temporal bones and the dorsum sellæ; laterally by the temporal squamæ, sphenoidal angles of the parietals, and greater wings of the sphenoid. It is traversed by the squamosal, sphenoparietal, sphenosquamosal, and sphenopetrosal sutures. It houses the temporal lobes of the brain and the pituitary gland. A middle fossa craniotomy is one means to surgically remove acoustic neuromas (vestibular schwannoma) growing within the internal auditory canal of the temporal bone. Middle part The middle part of the fossa presents, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
