Chapter 14 part 2 Flashcards
Coordination: Sense Organs, Hormones
What is a Sense organ?
A sense organ is a group of sensory cells that respond to specific stimuli.
ex: light, sound, touch, temperature, and chemicals.
What are Receptors?
Receptors are structures (specialised cells) in the cell membranes that detect stimuli.
What happens when a receptor receives a stimulus?
The receptor will respond to the stimulus and send nerve impulses to the brain, making us aware of the sensation.
What is the special property of sensory cells and sense organs?
These can convert one form of energy into another. (ex: into nerve impulses)
What are the parts of the eye?
The eye consists of the Sclera, Cornea, iris, pupil, lens, retina, optic nerve and blind spot.
What is the Sclera?
The Sclera is the tough, white, outer coating.
What is the Cornea and its function?
The Cornea is the front part of the Sclera. A transparent, curved layer.
- The function is it allows light to enter the eye.
What is the Iris and its function?
The iris is a disc of tissue infront of the eye lens. Its a colored ring of circular and radial muscle.
- It controls the size of the pupil
What is the Pupil?
The pupil is a hole in the center of the iris. It is black because of the black pigment Choroid, which absorbs light.
What is the Lens?
The lens is a transparent, jelly-like structure that is held in place by a ring of fibres called Suspensory Ligaments.
- The lens refracts light to focus on the Retina.
What is the Retina?
The Retina is a light sensitive layer in the back of the eye. It consists of Rods and Cones.
- When light falls on the Retina, it sends nervous impulses that travel in nerve fibres to the Optic Nerve.
What is the Optic Nerve?
The Optic Nerve transmits the nerve impulses from the Retina to the Brain.
What is the blind spot?
The blind spot is the part of Retina directly INFRONT of the Optic Nerve.
- This has no light-sensitive cells.
What is tear fluid?
Tear fluid is produced by tear glands which keep the eyes surface moist, and washes away dust particles and foreign substances from the eye.
What is Lysozyme?
Lysozyme is an enzyme present in tear fluid.
- It attacks bacteria.
How does the Cornea and lens refract light?
When light enters the eye, the curved surfaces of the Cornea and Lens refract the rays to direct the light into the Retina.
How do we see an image? (regarding a pattern of nerve impulses to the brain)
When an image is formed in the Retina, it is upside down and smaller than the object.
- The pattern of sensory cells will produce a pattern of nerve impulses and send them to the brain.
- The brain will now interpret the pattern, and form an impression of the size, distance and upright nature of the object.
Explain the pupil reflex: (light intensity and diameter of pupil)
Change of the size of pupil is caused by exposure of the eye to different light intensities.
- At high light intensity; The diameter of the pupil decreases, restricting the amount of light reaching the retina.
- At low light intensity; The diameter of the pupil increases to allow as much light in as possible to stimulate the retinas cells.
Explain pupil reflex in terms of Circular and Radial muscles:
- At high light intensity; the Circular muscle fibres in the iris contracts, reducing the pupil size and restricting light from entering the eye.
*This is a protective function - At low light intensity; the Circular muscle relaxes, and the Radial muscle fibres in the iris contract, causing the pupil to enlarge.
- This is involuntary and antagonistic action.
What is meant by Antagonistic action?
The circular and radial muscles in the iris are Antagonistic.
- This means that they oppose each others actions.
- When Circular contracts, it constricts the pupil.
- When Radial contracts, it dilates the pupil.
How does the lens accommodate to near and distant objects?
When the eye is focused on a near object; The ciliary muscle contracts to a small circle, removing tension from suspensory ligaments.
- This makes the lens fatter to focus on near objects.
When the eye is focused on a distant object; The Ciliary muscle relaxes. Outward pressure of humours on sclera pulls suspensory ligaments, and stretches the lens.
- This makes the lens thin to focus on distant object.
What is the Ciliary muscle and its function?
The Ciliary muscle forms a circular band of muscle in the Ciliary body.
- Its function is to contract or relax, changing the shape of the lens to focus on near or distant objects.
What are Cones?
Cones are light sensitive cells in the Retina that allow us to see colours.
There are 3 types of cones for each primary colour, absorbing light and colours.
- In the Fovea, cone cells are concentrated.
What are Rods?
Rods are light sensitive cells in the Retina that are sensitive to low intensities, and work well for night vision.
