homeostasis

homeostasis

homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes.

what does homeostasis maintain

Homeostasis maintains optimal conditions for enzyme action and all cell functions.

In the human body, these include control of:

• blood glucose concentration

• body temperature

• water levels.

what do automatic control systems may involve

These automatic control systems may involve nervous responses or chemical responses

0. All control systems include:

• cells called receptors, which detect stimuli (changes in the environment)

• coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors

• effectors, muscles or glands, which bring about responses which restore optimum levels.

what do nervous systems enable humans to do

The nervous system enables humans to react to their surroundings and to coordinate their behaviour.

what 2 parts make up the nervous system

CNS (brain and spinal cord)

-other nerves running to and from the central nervous system

describe a pathway through nervous system

a stimuli will be detected by the receptors and this will send electrical impulses down neurones to CNS (coordination centre) and this now sends electrical impulses down other neurones to effectors and they will bring about a response

stimulus receptor coordinator effector response

what do effectors tend to be

which may be muscles contracting or glands secreting hormones.

the CNS

The CNS is the brain and spinal cord. The CNS coordinates the response of effectors

reflex arc of when you touch a hot object

-stimulus (heat) is detected by a receptor

-electrical impulses now pass from the receptor along a sensory neurone to the CNS

-reach a synapse where a chemical is released and diffused to a relay neurone where it triggers an electrical impulse

-the electrical impulse passes across the relay neurone and reaches another synapse. Once again, a chemical is released

-this chemical triggers an electrical impulse in a motor neurone

and the electrical neurone will pass down the effector (in this muscle

-muscle now contracts and pull hand away from heat

reflex actons

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.

what is reaction time

• Reaction time is the time taken to respond to a stimulus; reactions are usually very quick responses typically taking less than a second to occur

what factors can affect reaction time

age, stress or use of drugs

outline method to investigate reaction time

1. sit down on the chair and place your forearm of your weaker/non-dominant hand on the table with your hand hanging over the end of the table

2. have your partner hold a ruler with the bottom end in between your fingers so you can practise holding the ruler with 2 fingers

3. have your partner hold the ruler and remove your finger

4. have your partner hold the ruler in line so that the 0 mark is level with the top of your thumb

5. your partner will drop the ruler without telling you beforehand, and you will catch the ruler as quickly as possible

6. note and record the number level with the top of your thumb after you have caught ruler in a table

7. repeat test at least 5 times

8. find reaction times by using a conversion table to convert the ruler measurements

9. The process is then repeated after a condition is changed (the person drinks a can of caffeinated drink or has to repeat the experiment when loud background music is playing)

   • Remember to only change one factor (independent variable) in your investigation

independent variable

dependent variable

control variable

• amount of energy

• reaction time

• same hand, same ruler, same height which is being dropped from

sources of error

-participants may have different experiences in performing a similar task previously i.e some participants may already be practiced in this task

-samples size may be too small to make a valid conclusion

why is using computer program to measure reaction times likely to be more valid tan the method using a dropped ruler

1. removes human errors from measurements

2. reaction time can be measured in milliseconds which is more accurate than seconds

brain

The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.

cerebral cortex

-outer part

-function include language, memory and consciousness

cerebellum

controls balance and co-ordinates movements

medulla

controls our heart rate and breathing rate

 explain some of the difficulties of investigating brain function and treating brain damage and disease.

-brain is protected by skull so it is very tricky to access

-the structure of the brain are extremely complex meaning it is difficult to work out which parts of the brain carry out specific functions

-very delicate and easy to damage

3 ways that scientists use to investigate the brain

1. Many scientists look at patients who have suffered brain damage by looking to see where the damage has taken place they can try to link that part of the brain to its function

2. we can electrically stimulate different paarts of the brain and look at the effects on the person’s behavioiur and that allows us to narrow down specific regions to their functions

3. we can use MRI scanning to loook at which parts of the brain are most active during different activities

eye

The eye is a sense organ containing receptors sensitive to light intensity and colour.

cornea

transparent layer in front t of the eye where light passes through and its function is to start the focussing of the light rays

iris

the muscle surrounding the pupil - the coloured part of the eye

pupil

the space in the centre of the iris which light passes through

lens

the light rays will through it after going through the pupil and its job is to focus the light rays onto the back of the eye

-it can change its shape allowing us to focus on distant or near objects (accommodation)

retina

where the image is formed at the back of the eye and the retina will contain receptor cells for light which allow us to detect light intensity and light colour

optic nerve

the receptor cells in the retina now send electrical impulses down the optic nerve to the brain

sclera

the white part of the eye surrounding the eye-this tough outer structure protects the eye

ciliary muscles and suspensory ligaments

work with the lens to allow focus on distant or near objects

what happens to the size of the pupil when you enter a dark room

the light entering is low and this drop in light intensity is sensed by light receptors in the retina and these send electrical impulses to the brain. the brain then sends electrical impulses to specific muscles in the iris and these muscles contract causing pupil to become larger -circular muscles relax and radial muscles contract

what happens to the size of the pupil when you enter a bright room

the light entering is high and this increase in light intensity is sensed by light receptors in the retina and these send electrical impulses to the brain. the brain then sends electrical impulses to specific muscles in the iris and they causing pupil to become smaller -circular muscles contract and radial muscles relax

accommodation

the ability to change the shape of the lens to focus on near or distant objects

focusing on distant objects

the light only needs to be focused by a small amount

-the ciliary muscle relaxes and the suspensory ligaments are pulled tight and the lens will be pulled thin meaning that light rays will only be slightly refracted

focusing near objects

light from near objects need to be focused a large amount meaning that ciliary muscles contract and suspensory ligaments loosen. the lens is thicker and refracts the light rays more strongly

long sightedness

-hyperopia

-cannot focus on nearby objects

-many cases eyeball is too short meaning that the light is focused at the point behind the retina

-in other cases, especially in the elderly the lens becomes less elastic meaning that lens cannot become thick enough to focus on near objects

how can longsightednesses be treated

by using glasses with convex lenses which partially focus the light before they enter the eye and it is potruding outwards

short sightedness

-myopia

-cannot focus on distant objects

-eyeball can be too long and so the light is focused at a point in front of the retina

-can also be caused when the lens is too thick meaning that again the light is focused infront of the retina

how can shortsightedness be treated

can use concave lens (going inwards) to partially unfocused the light before it enters the eye

instead of using glasses what can we use

• New technologies now include hard and soft contact lenses, laser surgery to change the shape of the cornea and a replacement lens in the eye.

how can body temperature is measured

Body temperature is monitored and controlled by the thermoregulatory centre in the brain.

the thermoregulatory centre in the brain

The thermoregulatory centre contains receptors sensitive to the temperature of the blood.

what does the skin contain

The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre

what happens if temperature is too high

If the body temperature is too high, blood vessels dilate (vasodilation) meaning that more blood flows through the capillaries meaning that heat can transfer out of blood and sweat is produced from the sweat glands.the sweat will evaporate and this takes energy from the body, cooling the body down. Both these mechanisms cause a transfer of energy from the skin to the environment.

what happens if body temperature is too low

If the body temperature is too low, blood vessels constrict (vasoconstriction),-les blood flows through and less heat lost from the body sweating stops and skeletal muscles contract (shiver)- to generate energy for this contraction the muscle cells increase their rate of respiration and this releases heat