This condition is termed heterochromia. Fovea The fovea is a small depression in the retina near the optic disc. Nightblindness is treated by supplementing the diet with vitamin A. Muscles responsible for moving the eyeball are attached to the eyeball at the sclera. Also in the fovea centralis, the overlying layers of the retina and the retinal blood vessels are displaced to the sides, more fully exposing photoreceptors to incoming light. Six extrinsic muscles move the eye in different directions Figure 5. It provides attachment surfaces for eye muscles Choroid Has a network of blood vessels to supply nutrients to the cells and remove waste products.
When the muscle contracts, the choroid coat is pulled forward and the ciliary body shortens. Impulses from the sympathetic nerve cause pupil dilation and impulses from the parasympathetic nerve causes pupil constriction. You are expected to know the roles of the cornea, lens, ciliary body, suspensory ligaments in the process. Other problems: If the lens becomes cloudy, the result is called a cataract. This may be corrected by removal of the lens.
The drug atropine inhibits the parasympathetic nerve, causing the pupil to dilate. Cloudiness of the cornea may be dealt with by a corneal transplant - a fairly simple operation. Ciliary body Has suspensory ligaments that hold the lens in place. Many rods usually connected to one bipolar cell, so poor acuity i. If the eyeball or lens is not symmetrical, then astigmatism is the result, and special lenses are needed.
Four of these muscles are straight and two are oblique. Conjunctiva: It is a transparent mucous membrane, which covers the internal palpebral surfaces, and folds on to the anterior sclera and comea where it is continuous with the comeal epithelium. Most of the fibers, however, enter the thalamus and synapse in its posterior portion lateral geniculate body. Coloured light will stimulate these three cells differently, so by comparing the nerve impulses from the three kinds of cone, the brain can detect any colour. It is just reverse to the monocular vision, as in many animals like rabbit, in which each eye focuses its own object and both the eyes cannot focus on one object. It is attached to the lens by suspensory ligaments. The ciliary processes secrete aqueous humour.
This explains why you are initially blind when you walk from sunlight to a dark room: in the light almost all your retinal was in the trans form, and it takes some time to form enough cis retinal to respond to the light indoors. Central Artery and Vein The central artery and vein runs through the center of the optic nerve. Summary of actions of each extrinsic eye muscle: Lateral rectus- moves eye laterally Medial rectus- moves eye medially Superior rectus- Eleva … tes eye and turns it medially Inferior rectus- Depresses the eye and turns it medially Inferior oblique- Elevates eye and turns it laterally Superior oblique- Depresses eye and turns it laterally. The choroid coat, in the posterior five-sixths of the globe of the eye, is loosely joined to the sclera and is honeycombed with blood vessels, which nourish surrounding tissues. The space bounded by the lens, ciliary body, and retina is the largest compartment of the eye and is called the posterior cavity.
It is transparent because it contains few cells and no blood vessels, and the cells and collagenous fibers form unusually regular patterns. Accommodation Accommodation refers to the ability of the eye to alter its focus so that clear images of both close and distant objects can be formed on the retina. The cytoplasm of these cells is the transparent substance of the lens. It contains two types of smooth muscles, circular muscles sphincters and radial muscles dilators , of ectodermal origin. Light rays from the outside world first pass through the cornea before reaching the lens.
Extrinsic Eye Muscles and their Nerve Supply: There are six extrinsic muscles attached to the eyeball. The Latin verb differe can mean, to carry different ways, to spread abroad, to scatter, but also to delay. Cats' eyes are exceptions, as they have a layer to reflect light and so maximise their sensitivity to dim light. It serves as a soft, shockproof pad. The Lacrimal Apparatus: The lacrimal apparatus of each eye consists of a lacrimal gland and its numerous ducts, the superior and inferior canaliculi, a lacrimal sac and a nasolacrimal duct. Thus, when presented with a threatening stimuli that activates the response, this innervation contracts the muscle and dilates the , thus temporarily letting more light reach the.
They are called the superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique and inferior oblique. It is the light sensitive part of the eye. Retinal is the light-sensitive part, and it can exists in 2 forms: a cis form and a trans form: In the dark retinal is in the cis form, but when it absorbs a photon of light it quickly switches to the trans form. From the anterior chamber the aqueous humour, which is continuously produced, is drained off into the canal of Schlemm and then into the blood. Optic nerve The optic nerve is located at the back of the eyeball.
Versammlung in Basel angenommenen Namen. Many other anatomical models and charts available by following. To do this the ciliary muscles relax, making a wider ring and allowing the suspensory ligaments which are under tension from the pressure of the vitreous humour to pull the lens out, making it thinner. The oculomotor 3rd cranial nerve innervates the median rectus, superior rectus, inferior rectus and inferior oblique. Structure of the human eye Outer Layer of the Eye Light is often described as moving in straight lines called rays of light. Contraction of the ciliary muscles slackens the zonules so they don't pull so much on the lenses.