The Eye Flashcards
what are the photoreceptors in the eye sensitive to?
-light
how is the eye given the correct intensity of light?
-through the structures in the eye that ensure the correct intensities of light are received by receptors in the retina
look at diagram of the eye in book page 69 be able to draw it out
what is the conjunctiva and what is its function?
-thin epithelial layer which moistens and lubricates the eye
what is the sclera and what is its job?
-tough connective tissue covering the eye
-protects against damage
what is the cornea and what is its job?
-transparent part of the sclera
-refracts light
what is the aqueous humour and what is its job?
-watery fluid between the cornea and lens
-maintains shape of the front of the eye
what is the iris and what is its job?
-muscular layer which contains both circular and radical muscle also contains a pigment that absorbs light
-adjusts size of pupil to control amount of light entering
what is the pupil and what is its job?
-gap within the iris
-the area where light reaches the lens and enters the center of the eye
what is the ciliary body and what is its job?
-contains a muscular ring and suspensory ligaments which holds the lens in place
-adjusts shape of the lens to focus light rays
what are suspensory ligaments and what is its job?
-connects biliary body to the lens
-transfers tension so that the light can focus on distant objects
what is the lens and what is its job?
-transparent and biconvex
-refracts light and focuses light rays
what is the viteous humour and what is its job?
-jelly like material between the lens and the back of the eye
-maintains shape of the eye
what is the retina and what is its job?
-inner layer of the eyeball which contains cones and rods
-initiate impulses associated with neurones
what is the foeva and what is its job?
-region in the center of the retina which is rich in cones
-give clear daylight and colour vision
what is the choroid and what is its job?
-layer of pigmented cells between retina and sclera
-contains blood vessels and prevents reflection at the back of the eye
what is the optic nerve and what is its job?
-bundle of sensory nerve fibers
-transmits impulses from the retina to the brain
what is the blind spot and what is its job?
-part of retina that is not sensitive to light
what are the two functions of the eye?
-obtaining a focused image
-controlling the amount of light that enters the retina
where does most refraction of light occur? where does some occur initially?
-most happens in the cornea however some refraction can occur when light initially hits the eye
how is light focused on the retina?
-by adjusting the thickness of the lens
how do the light rays arrive when the eyes are focusing on a distant object? what is the thickness of the lens like?
-light rays arrive parallel at the eye
- the lens is thin as little additional refraction has to occur for the light to focus on the retina
how do the light rays arrive when the eyes are focusing on a close up object? what is the thickness of the lens like?
-light rays diverge from a close up object
-lens is thicker as further refraction must occur to focus light on the retina
what is the ciliary muscle?
-a ring of muscle in the ciliary body which runs around the inside of the eyeball
what do suspensory ligaments resemble?
-thin small pieces of nylon thread
what happens if the ciliary body relaxes? what happens to the lens?
-tension on the walls of the eyeball is transferred to suspensory ligaments
-meaning the ciliary body has a larger diameter and so the suspensory ligaments are pulled taut
-this makes the lens thinner and so the eye has less refractive power
what happens when if the ciliary body contracts and what happens to the lens?
-to make the lens fatter when a greater degree of refraction is required
-ciliary muscle contracts
-forms a tighter circle with a smaller diameter
-suspensory ligaments are not pulled taut
-less pressure on the lens so the lens is at its thicker normal shape
what is the definition of accommodation?
-the adjustment of lens thickness to ensure that light rays are focused on the retina
-irrespective of the angle of light reaching the eye
look at diagram on page 72
what are the two things that prevents an image being formed? (types of light intensites)
-too little or too much light prevents an image being formed
what also can happen due to too high a light intensity?
-damage the sensitive light receptors
what size is the pupil in low light intensities? why?
-large
-allow as much light as possible to enter the eye to ensure there is enough light for an image to be formed
-to stimulate the photoreceptors
what size is the pupil in bright light and why?
-pupil is reduced to a smaller size to restrict the amount of light entering
how is the pupils size changed?
-due to the iris contracting or relaxing
what are the two types of muscle that the iris contains?
-circular and radical
what happens to the muscles in the iris in low light intensities?
-the radical muscles contract and the circular muscles relax which makes the pupil larger
what happens to the muscles in the iris in bright light?
-the circular muscles contract and the radical muscles relax which makes the pupil smaller
