homeostasis and response Flashcards
(32 cards)
Define homeostasis
the regulation of internal conditions to maintain a stable internal environment
Name the 3 things that homeostasis has to control to maintain a stable environment
1) water levels
2) body temperature
3) blood glucose concentration
Explain how negative feedback counteracts when levels of something (e.g water or temperature) are too high
RECEPTORS detect a a stimulus levels is too high
COORDINATION CENTRE receives and processes the information then organises a response.
EFFECTORS carry out response so levels drop which counteracts the change which restores optimum level.
Explain how negative feedback counteracts when levels of something (e.g water or temperature) are too high
RECEPTORS detect stimulus level is too low.
COORDINATION CENTRE receives and processes the information then organises a response..
EFFECTORS carry out response so levels decrease to counteract the change which restores optimum level.
What are receptors? give an example
The cells that detect stimuli.
e.g taste receptors on tongue
sound receptors in ears
What makes up the Central Nervous system in mammals?
Brain
Spinal cord
Connected to the body by:
Sensory neurones
Motor neurones
What are sensory neurones?
Neurones that carry information as electrical impulses from receptors to the CNS.
What are the motor neurones?
Neurones that carry information as electrical impulses from the CNS to the ffectors.
What are the effectors?
Muscles which contract in response to a nervous impulse or glands that secrete hormones in response.
Explain what happens in the nervous system when a bird sees a cat.
The receptors in the bird’s eye are stimulated.
Sensory neurones carry the information (as electrical impulses) from receptors to CNS.
CNS decides what to do about it.
The CNS sends information to the bird’s wings (the effectors) via motor neurones.
The muscles contract and the bird flies away to safety.
How does information moves between neurones?
Electrical impulse travels along to the end of neurone where it triggers the release of chemicals which diffuse across the synapse to the next neurones which then set of a new electrical impulse.
What are reflex actions?
Actions that are automatic and do not involve the conscious part of the brain.
Explain the stages of the reflex arc
A stimulus is detected by the receptors.
Impulses are sent along a sensory neurone which triggers chemicals to diffuse across synapse to the relay neurone (in CNS) to set of new electrical impulse.
When impulse reaches a synapse between relay neurone and motor neurone the same thing happens (electrical-chemical-electrical).
Impulse travel along motor neurone to the effector (e.g a muscle which contracts to pull limb away from danger).
Define:
cornea
iris
pupil
lens
Cornea- transparent outer layer that refracts light into eye
Iris- contains muscles that allow it to control the diameter of the pupil therefore how much light enters
Pupil- hole in middle of eye and allows light through
Lens- focuses light onto retina. It changes shape to see objects near and far.
What is the job of:
sclera
retina
ciliary muscles and suspensory ligaments
optic nerve
Sclera- tough, supporting wall of eye
Retina- contains receptors that are sensitive to light intensity and colour
Ciliary muscles and suspensory ligaments control the shape of the lens
Optic nerve- carries impulses from retina to the brain
How does the eye accommodate when focusing on a near object?
Ciliary muscles contract, which slacken suspensory ligaments. Lens becomes more curved which increases the amount by which it refracts light.
How does the eye accommodate when focusing on a far object?
The ciliary muscles relax, which allows suspensory ligaments to pull tight. Lens becomes less curved so it refracts light by a less amount.
What happens when bright light hits your eye?
When light receptors in the eye detect bright light, a reflex triggers the pupil to become smaller. The circular muscles in the iris contract and the radial muscles relax which reduces amount of light that can enter eye.
What does the eye do in dim light?
The opposite: The circular muscles relax and the radial muscles contract which makes the pupil wider (dilated)
Explain why some people are long sighted (hyperopia)?
The lens is the wrong shape and doesn’t refract enough or the eyeball is too short. The images of near objects are brought into focus behind the retina.
What glasses would people with long-sightedness (hyperopia) wear?
Convex lens (curves outwards) which refracts light rays so they focus on retina.
Explain why some people are short sighted (myopia)?
The lens is wrong shape and refracts too much or eyeball is too long. The images of distant objects are brought to focus in front of the retina.
What glasses would people with short-sightedness (myopia) wear?
Concave lens (curves inwards) so that light rays focus on the retina.
What new technologies are treatments for eye defects?
.Contact lenses
.Laser eye surgery
.Replacement lens surgery
