TOPIC 5 - HOMEOSTASIS AND RESPONSE Flashcards
What is homeostasis?
Maintaining a stable internal environment.
The conditions inside your body need to be kept steady , even when the external environment changes. This is really important because your cells need the right conditions in order to function properly, including the right conditions for enzyme action.
What is homeostasis (simple)?
The regulation of the conditions inside your body (and cells) to maintain a stable internal environment, in response to changes in both internal and external conditions.
Give examples of some automatic control systems.
Nervous and hormonal communication.
What are the three components that your automatic control systems are made of?
Cells called receptors
Coordination centres (brain, spinal cord, pancreas)
Effectors
What is negative feedback?
Negative feedback counteracts changes. When the levels of something gets too low or too high your body uses negative feedback to bring it back to normal.
What happens when a receptor detects a stimulus - level is too high?
The coordination centre recieve and processes the information, then organising a response.
Effectors produces a response, which counteracts the change and restores to optimum level - the level decreases.
How long will effectors continue to produce a response?
As long as they are stimulated by the coordination centre. This could cause the opposite problem - making a level change too much, away from the ideal.
However, the receptor detects if the level becomes too different and negative feedback starts again.
What is the CNS (central nervous system)
In vertebrates this consists of the brain and the spinal cord only.
In mammals, the CNS is connected to the body by sensory neurones and motor neurones.
What are sensory neurones?
The neurones that carry information as electrical impulses from the receptors to the CNS.
What are motor neurones?
The neurones that carry electrical impulses from the CNS to effectors.
What are effectors?
All your muscles and glands, which respond to nervous impulses. Egmuscles contract in response to a nervous impulse, whereas glands secrete organs. They respond to nervous impulses and bring about a change.
What are receptors?
Receptors are cells that detect stimuli. There are many, eg taste receptors on the tongue and sound receptors in the ear. They can also form part of larger, complex organs eg the retina in the eye is covered in light receptor cells.
What does the CNS do?
Coordinates the response. It receives information from the receptors and then coordinates a response. The response is carried out by receptors.
What are synapses?
The connection between two neurones is called a synapse. The nerve signal is transferred by chemicals which diffuse (move) across the gap. These chemicals then set off a new electrical signal in the next neurone.
Why are reflexes important?
They help to prevent injury.
What are reflexes?
They are rapid, automatic response to certain stimuli that don’t involve the conscious part of the brain. The passage of information in a reflex (from receptor to effector) i called a reflex arc.
Explain the reflex arc.
The neurone in reflex arcs go through the spinal cord, or through an unconscious part of the brain.
When a stimulus is detected by receptors, impulses are sent along a sensory neurone to a relay neurone in the CNS.
When impulses reach a synapse between the sensory neurone and the relay neurone, they trigger chemicals to be released. These chemicals cause impulses to be sent along the relay neurone.
When the impulse reach a synapse between the relay neurone and a motor neurone, the same thing happens. Chemicals are released and cause impulses to be sent along the motor neurone.
The impulses then travel along the motor neuone to the effector.
What is the brain responsible for?
Complex behaviours.
What is the cerebral cortex?
Outer wrinkly bit. It is responsible for things like consciousness, intelligence, memory and language.
What is the medulla?
Controls unconscious activities such as breathing and your heart beat.
What is the cerebellum?
Responsible for muscle coordination.
How do neuroscientists study people with brain damage?
If a small part of the brain has been damaged, the effect this has on the patient can tell you a lot about what the damaged part of the brain does. Eg if the area at the back of the brain was damaged by a stroke and the patient went blind, you know that that area had something to do with vision.
How can doctors electrically stimulate the brain?
The brain can be stimulated electrically by pushing a tiny electrode into the tissue and giving it a small zap of electricity. By observing what stimulating different parts of the brain does, it is possible to get an idea of what those parts do. Eg when a certain part of the brain (known as the motor area) is stimulated, it causes muscle contraction and movement.
What is the sclera?
Tough supporting wall of the eye.
What is the cornea?
Transparent outer layer found at the front of they eye. It refracts light into the eye.
What is the iris?
Contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye.
What is the lens?
Focuses the light onto the retina.
What is the retina?
Contains receptor cells sensitive to light intensity and colour.
How is the shape of the lens controlled?
Ciliary muscles and suspensory ligaments.
What is the optic nerve?
Carries impulses from the receptors on the retina to the brain.
How does the eye adjust for bright light?
When light receptors in the eye detect a very bright light, a reflex is triggered that makes the pupil smaller.
The circular muscles in the iris contract and the radial muscles relax.
How does the light adjust for dim light?
The radial muscles contract and the circular muscles relax. This makes the pupil wider.
What is accomodation?
The way that the eye focuses light on the retina by changing the shape of the lens.
How does the eye look at near objects?
The ciliary muscles contract, which slackens the suspensory ligaments. The lens becomes more curved. This increases the amount by which it refracts light.
How does the eye look at distant objects?
The ciliary muscles relax, which allows the suspensory ligaments to pull tight.
This makes the lens go less curved.
So it refracts light by a smaller amount.
What is the medical term for long-sightedness?
Hyperopia.
What does it mean if a person is long sighted?
They are unable to focus on near objects.
This occurs when the lens is the wrong shape so doesnt refract the light enough, or the eyeball is too short. The images of the near objects are brought into focus behind the retina.
What lens do people who are long sighted need to wear?
Convex lenses
They are curved outwards so the light is refracted onto the lens.
What is the medical term for short-sightedness?
Myopia.
What does it mean if a person is short sighted?
They are unable to focus of distant objects.
This occurs when the lens is the wrong shape and refracts the light or the eyeball is too long.
The images of the distant objects are brought into focus in front of the retina.
What lens should a short sighted person wear?
You can use glasses with a concave lens.
The lens curves inwards. This makes sure that the light rays focus on the retina.
What are three treatments for vision defects?
Contact lenses
Laser eye surgery
Replacement lens surgery
Why might a person want to wear contact lenses?
Lightweight and invisible.
More convenient for activities such as sport.
What are the two types of contact lenses?
Hard and Soft
People usually prefer soft as they are more comfortable, but they carry a higher risk of infection than hard lenses.
What is laser eye surgery?
A laser can be used to vaporise tissue, changing the shape of the cornea and so changing how strongly it refracts light into the eye. Changing the shape so that it is more powerful will improve long sight.
What is replacement lens surgery?
Sometimes long-sightedness may be more effectively treated by replacing the lens of the eye. The natural lens is removed and and an artificial lens, made of clear plastic, is inserted in its place. As it involves work inside of the eye, it carried a higher risk of infection than laser eye surgery. (including possible damage to the retina which could lead to loss of sight.
What is the thermoregulatory centre in the brain?
It contains receptors that are sensitive to the temperature of the blood flowing through the brain. It also receives impulses from temperature receptors in the skin, giving information about skin temperature.
What happens when the temperature receptors detect that core body temperature is too high?
The thermoreguatory centre acts as a coordination centre - it receives information from the temperature receptors and triggers the effectors automatically.
Effectors eg sweat glands produce a response and counteract the change.
What mechanism allows a more sensitive response to a change in body temperature?
Some effectors work antagonistiaclly eg one effector heats and another cools.
What do the effectors do when you are too hot?
Sweat
and Dilate blood vessels
How does sweat help to cool you down?
It evaporates from the skin which transfers energy to the environment.
How does you blood vessels dilating help to cool you down?
More blood flows closer to the surface of the skin. This is called vasodilation. This helps to transfer energy from the skin to the environment.
