eye Flashcards
sense organ
a group of receptor cells that are able to respond to a specific stimulus
What keeps the eyes shape?
Fluid.
What keeps the eye moist and where is it made?
Fluid on the surface of the eye made in tear glands.
What does the fluid contain and what does it do? How? What do the other structures do?
The fluid contains an enzyme called lysozyme which can kill bacteria. Washed over the eyes by the eyelids when you blink. Eyelids, eyebrows and eyelashes prevent dirt from landing on the surface of the eye
What is the retina?
a tissue at the back of the eye that contains receptor cells that are sensitive to light.
How is the image formed in the brain?
When light falls on a receptor cell in the retina, the cell sends an electrical impulse along the optic nerve to the brain. The brain uses the impulse from each to build up an image.
Where is there no receptor cells and what do you call this part?
Blind spot (it is apart of the retina)
What do you call the part of the retina that is mostly closely packed with receptor cells? It is also the part where light is focused if you look directly at an object.
Fovea.
What are the two kinds of receptor cells?
Rods are sensitive to dim light but do not respond to color. Cones distinguish the different colors of light but only function when its bright.
What are the three different kinds of cones?
Ones sensitive to red, green and blue light
What does the fovea contain?
Almost entirely cones packed tightly together to form a clear, sharp image. Rods are found further out on the retina and are less tightly packed– less detailed image produced.
define iris
the coloured part of the eye; it contains muscles that can alter the size of the pupil
define pupil
a circular gap in the middle of the iris, through which light can pass
What do you call: an automatic response to a change in light intensity; the receptors are in the retina and the effector is the muscle in the iris?
Iris reflex or pupil reflex
Light rays must be refracted so that they focus exactly onto the retina. Done by?
Mostly by the cornea. Lens makes fine adjustments.
cornea definition
a transparent layer near the front of the eye, which refracts light rays entering the eye
lens definition
a transparent structure in the eye, which changes shape to focus light rays onto the retina
How does the brain interpret an image?
The image is formed onderstebo on the retina. The brain interprets this so that you see it the right way up.
Light rays from an object far away are
slightly diverging. They do not need much bending.
accommodation definition
changing the shape of the lens to focus on objects at different distances from the eye
suspensory ligaments
strong, inelastic fibres that hold the lens in position; they pull the lens into a thinner shape when they are under tension.
ciliary muscles
a circle of muscle surrounding the lens and joined to it by the suspensory ligaments; when it contracts, it slackens the ligaments so that the lens becomes fatter
What is the function of the optic nerve?
carries impulses to the brain
What is the function of the lens?
focus light onto the back of the eye
