The Eye Flashcards
Definition of Iris
A coloured ring of circular and radial muscle that controls the size of the pupil and so controls the amount of light entering the eye
Definition of Cornea
A transparent, curved layer at the front of the eye that refracts the light entering and helps to focus it
Definition of Lens
A transparent, convex, flexible, jelly-like structure that refracts light to focus it onto the retina and to produce an image. This final adjustment is called accommodation.
Definition of Retina
A light-sensitive layer at the back of the eye made up of rods, which detect light of low-intensity, and cones, which detect different colours.
Definition of Optic Nerve
Transmits electrical impulses from the retina to the brain
Definition of Conjunctiva
Thin layer covering the front of the eye which protects the cornea
Definition of Eye Muscles
Allow the eyeball to move from side to side and up down
Definition of Sclera
Tough non-elastic coat, that is white in colour and protects the eyeball
Definition of Ciliary Muscles and Suspensory Ligaments
Cause the lense to change shape and so allow fine focusing onto the retina
Definition of Choroid
Layer of blood vessels inside the sclera which supplies food and oxygen to the eye
How does they eye respond to bright light?
Circular muscles of iris contract to reduce diameter of pupil.
Less light can enter and the retina is protected from bleaching.
How does they eye respond to dim light?
Radial muscles of iris contract to make the diameter of the pupil larger, allowing a larger amount of light to reach and stimulate the light-sensitive cells in the retina.
What is the job of the aqueos / vitreous humour?
They create outward pressure on the sclera, which keeps the spherical shape of the eyeball.
What does the ciliary body produce?
Aqueos humour
What is the blind spot?
Part of the retina on top of the optic nerve which doesn’t contain any light-sensitive cells.
How do our eyes detect light
STAGE 1
Light from a source travels towards the eye
STAGE 2
Light passes through the cornea and enters the eye. The cornea refracts the light rays.
STAGE 3
Light passes through the lens, which changes shape to refract the light even more. This is how the eye focuses light.
STAGE 4
Light rays hit the back of the retina. The light receptors detect the light and a nerve impulse is sent along the optic nerve to the brain.
What type of organ is the eye?
A sense organ
What type of receptors does it contain?
Light receptors
What are rod cells sensitive to?
They’re sensitive to light at LOW INTENSITIES.
Rod cells are more sensitive to light than cone cells.
They do NOT detect colour.
What are cone cells sensitive to?
They’re sensitive to COLOUR and light at HIGH INTENSITIES.
Humans have 3 different types of cone cells, each sensitive to a different range of colours (ones which respond to red, green or blue)
Definition of suspensory ligaments
Attachment between the lens and the ciliary muscles which keeps the lens in place and allows its shape to be changed by the ciliary muscles.
Definition of cillary muscles
Small muscles attached to suspensory ligaments which alter the shape of the lens
How does the eye focus on distant objects?
- Ciliary muscles relax, eyeball becomes more spherical
- Suspensory ligaments tighten, pulling lens thin
To focus distant objects, the lens must be thin so light rays are only slightly refracted
How does the eye focus on close objects?
- Ciliary muscles contract, pull eyeball inwards (bulges forward)
- Suspensory ligaments loosen, causing the lens to thicken
To focus on close objects, the lens needs to be thick to refract the light rays greatly
