2.10.9 The Human Eye Flashcards
What is the human eye
The eye is a highly specialised sense organ containing receptor cells that allow us to detect the stimulus of light
The retina of the eye contains two types of receptor cells, what are they?
Receptor cells that are sensitive to light, known as rods, and receptor cells that can detect colour, known as cones
Name the 10 parts of the eye
Cornea Iris Pupil Lens Ciliary Muscle Suspensory Ligment Sclera Retina Fovea Optic Nerve
What is the function of the cornea
Transparent lens that refracts light as it enters the eye
What is the function of the Iris
Controls how much light enters the pupil
What is the function of the lens
Transparent disc that can change shape to focus light onto the retina
What is the function of the retina
Contains light receptor cells - Rods (detect light intensity) and cones (detect colour)
What is the role of the optic nerve
Sensory neurone that carries impulses between the eye and the brain
What is the function of the pupil
Hole that allows light to enter the eye
What is the function of the Ciliary muscle
A ring of muscle that contracts and relaxes to change the shape of the lens
What is the function of the suspensory ligaments
ligaments that connect the ciliary muscle to the lens
What is the function of the sclera
the strong outer wall of the eyeball that helps to keep the eye in shape and provides a place of attachment for the muscles that move the eye
What is the function of the fovea
a region of the retina with the highest density of cones (colour detecting cells) where the eye sees particularly good detail
What is the function of the aqueous humour
the watery liquid between the cornea and the lens
What is the role of the vitreous humour
the jelly-like liquid filling the eyeball
What is the function of the choroid
a pigmented layer of tissue lining the inside of the sclera that prevents the reflection of light rays inside the eyeball
What is the function of the blind spot
the point at which the optic nerve leaves the eye, where there are no receptor cells
The way the lens brings about fine focusing is called, what?
accommodation
The lens is elastic and its shape can be changed when, what?
the suspensory ligaments attached to it become tight or loose
The changes are brought about by
by the contraction or relaxation of the ciliary muscles
When an object is close up, what happens
1. The ciliary muscles contract (the ring of muscle decreases in diameter)
When an object is far away, what happens
1. The ciliary muscles relax (the ring of muscle increases in diameter)
What is the pupil reflex
a reflex action carried out to protect the retina from damage
In dim light, what happens to the pupil
the pupil dilates (widens) in order to allow as much light into the eye as possible to improve vision
In bright light, what happens to the pupil
the pupil constricts (narrows) in order to prevent too much light from entering the eye and damaging the retina
Exam Tip
The focusing of the eye on distant and near objects is complex and it can be hard to remember what is happening. This is something you can work out in an exam if you have forgotten – staring at your hand right in front of your eye will make your eyes feel tight and tired after a few seconds. This is because the ciliary muscles are contracted. Staring at an object far away feels relaxing and comfortable because the ciliary muscles are relaxed.
