Structure and Function of the Eye Flashcards
The Eye
______________________are receptors in the eye that detect light.
Light enters the eye through the ____and the amount of light that enters is controlled by the ____. Light rays are focused by the lens onto the ________, which lines the inside of the eye.
The retina contains the photoreceptor cells.
______impulses from the photoreceptor cells are carried from the retina to the brain by the _______nerve, which is a bundle of neurones. Where the optic nerve leaves the eye is called the blind spot- there aren’t any photoreceptor so its not sensitive to ______.
The Eye
Photoreceptors are receptors in the eye that detect light.
Light enters the eye through the pupil and the amount of light that enters is controlled by the iris. Light rays are focused by the lens onto the retina, which lines the inside of the eye.
The retina contains the photoreceptor cells.
Nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve, which is a bundle of neurones. Where the optic nerve leaves the eye is called the blind spot- there aren’t any photoreceptor so its not sensitive to light.
The human eye has 2 types of photoreceptor-rods and cones.
Rods are found mainly on the ___________parts of the retina. Cones are found mainly packed together in a ________area called the fovea.
The human eye has 2 types of photoreceptor-rods and cones.
Rods are found mainly on the peripheral parts of the retina. Cones are found mainly packed together in a central area called the fovea.
Rods and cones convert ______ energy into an ____________impulse Light enters the eye, hits the photoreceptors and is absorbed by light sensitive pigments
Light bleaches the _________, causing a chemical change and increasing membrane permeability to ________
A ___________potential is created and if it reaches a ____________, a nerve impulse is sent along a bipolar neurone
Bipolar neurones connect _________________to the ______nerve which takes impulses to the brain
Rods and cones convert light energy into an electrical impulse Light enters the eye, hits the photoreceptors and is absorbed by light sensitive pigments
Light bleaches the pigments, causing a chemical change and increasing membrane permeability to sodium
A generator potential is created and if it reaches a threshold, a nerve impulse is sent along a bipolar neurone
Bipolar neurones connect photoreceptors to the optic nerve which takes impulses to the brain
Rod cells contain a pigment called ___________.
The rhodopsin molecule breaks down when exposed to light into a pigment called retinal and the protein _____. This is called bleaching.
The breakdown of rhodopsin begins a series of chemical reactions that result in the release of a __________________substance by the rod cell. The transmitter substance stimulates a chain of events that may result in an impulse being passed to the brain along a nerve fibre in the ______nerve.
Rob cells contain a pigment called rhodopsin.
The rhodopsin molecule breaks down when exposed to light into a pigment called retinal and the protein opsin. This is called bleaching.
The breakdown of rhodopsin begins a series of chemical reactions that result in the release of a neurotransmitter substance by the rod cell. The transmitter substance stimulates a chain of events that may result in an impulse being passed to the brain along a nerve fibre in the optic nerve.
Rods are sensitive to light. This is because many rods synapse with one bipolar neurone.
Dim light results in the production of only a small amount of transmitter substance by each rod cell, Individually, this is insufficient to overcome the __________of the bipolar cell, but the total amount of ________________ substance produced by several rods is sufficient to overcome the __________ and trigger an ________potential.
This gives rod cells high visual ____________.
Dim light results in the production of only a small amount of transmitter substance by each rod cell, Individually, this is insufficient to overcome the threshold of the bipolar cell, but the total amount of neurotransmitter substance produced by several rods is sufficient to overcome the threshold and trigger an action potential.
This gives rod cells high visual sensitivity.
Cone cells are less sensitive than rod cells because each ____ cell joins one bipolar neurone. It therefore takes more fight to reach the ___________and trigger an _______ potential. Cones have low visual sensitivity.
Cone cells are less sensitive than rod cells because each cone cell joins one bipolar neurone. It therefore takes more fight to reach the threshold and trigger an action potential Cones have low visual sensitivity.
However, cone cells high visual acuity.
Visual acuity is the ability to tell apart points that are close together. When light from two points hits two cones, two _______potentials (one from each cone) go to the brain- so you can distinguish two points that are close together.
Rods have low visual acuity because many rod cells join the same __________ neurone, which means that light from two points cannot be told apart.
However, cone cells high visual acuity.
Visual acuity is the ability to tell apart points that are close together. When light from two points hits two cones, two action potentials (one from each cone) go to the brain- so you can distinguish two points that are close together.
Rods have low visual acuity because many rod cells join the same bipolar
neurone, which means that light from two points cannot be told apart.
Rods and cone cells contain different pigments making them sensitive to different wavelengths.
Rods contain the pigment rhodopsin and cones the pigment iodopsin.
Rods only give information in black and white, but cones give information in colour. There are three types of cone cells, each of which has a different sensitivity to
light. There are red-light sensitive receptors, green-light sensitive receptors and
blue-light sensitive receptors. However the ranges of sensitivity overlap and
most wavelengths of light stimulate at least 2 types of cone.
Rods and cone cells contain different pigments making them sensitive to different wavelengths.
Rods contain the pigment rhodopsin and cones the pigment iodopsin.
Rods only give information in black and white, but cones give information in colour. There are three types of cone cells, each of which has a different sensitivity to
light. There are red-light sensitive receptors, green-light sensitive receptors and
blue-light sensitive receptors. However the ranges of sensitivity overlap and
most wavelengths of light stimulate at least 2 types of cone.
Card 1
- Where are rod and cones cells found on the retina?
Rods mainly on the periphery: cones packed together in central area called the fovea.
Explain how a generator potential is reached.
When a stimulus is detected the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell. This alters the potential difference across the membrane and therefore produces a generator potential
What is the pigment in rod cells
What is bleaching
rhodopsin
Chemical change to the pigment caused by light which increases the membrane permeability to sodium.
Why are rod cells sensitive to very low light intensity?
In dim light each rod cell only produces a small amount of neurotransmitter but because many rod cells synapse with one bipolar neurone the total amount of neurotransmitter produced by all the rod cells is sufficient to overcome the threshold and trigger an action potential..
Why do cone cells have low visual sensitivity?
One cone cell joins with one bipolar neurone so it takes more light to reach the threshold and trigger an action potential.
In strong light, rhodopsin is broken down quicker than it can be reformed. In dim light, breakdown of rhodopsin is much slower, so production keeps up with breakdown. The pigment in cone cells is lodopsin which is broken down only by high light intensity.
- Why can’t we see very well when we first enter a poorly lit room from a brightly lit area
When in a brightly lit area much of the thodopsin in the rods has been broken down: time is needed to resynthesize it before the rods can become sensitive to light again The low light intensity does not stimulate the cones so although their pigment is resynthesized much more quickly, they are not of Use in dim light.
- At night, it is often easier to see a star in the sky by looking slightly to the side of it rather than directly at it. Suggest why this is so.
Light reaching the earth will be of low intensity. Looking directly at a star, the light will be focused on the fovea where there are only cone cells Cone cels respond only to high light intensity so will not be stimulated by the low light intensity. Looking to one side, means that light from the star is focused fowards the outer regions of the retina where there are mostly rod cels. These are stimulated by low light intensity and therefore the stor is seen.
