3. Impulse sent along sensory neuron

4. Impulse passed along relay neuron (message also sent to brain)

2. Pain receptor stimulated

1. Stimulus (heat)

5. Impulse sent along motor neuron

6. Effector muscle contracts (response)

Y11 Biology Homeostasis & Response

Homeostasis: Maintaining a constant internal environment in response to internal and external change - through both nervous and hormonal (chemical) control.

Key words: 1. Homeostasis: Maintaining a constant internal environment 2. Receptor: Detect a change in the environment 3. Effector: Muscle or gland that carries out a response 4. Stimulus: A change in the environment 5. Sensory neurone: Carries an electrical impulse from the receptor to the

CNS 6. Relay neurone: Carries the impulse from the sensory neurone to the motor

neurone 7. Motor neurone: Carries the impulse from the CNS to the effector 8. Synapse: A tiny gap between 2 neurones 9. Reflex: An automatic response that does not require processing, helps an

organism survive 10. CNS: Central Nervous System – the brain and spinal cord 11. PNS: Peripheral Nervous System – the neurones that connect the rest of

the body to the CNS

Examples of factors controlled by homeostasis include: 1. Blood glucose 2. Temperature 3. Water levels

All homeostatic control systems include: 1. Cells call receptors – which

detect stimuli. 2. Coordination centres – E.g.

the CNS (brain and spinal cord) or the pancreas

3. Effectors – Muscles or glands which bring about responses to restore optimum levels

STIMULUS RECEPTOR SENSORY NEURONE

CNS MOTOR

NEURONE EFFECTOR RESPONSE

A change in the internal or external

environment

Detects the stimulus and causes an impulse in the…

Carries the impulse from the receptor

to the CNS

The brain or relay neurones in the

spine

Carries the impulse from the CNS to the

receptor

A muscle contracts or a gland releases

a chemical

The body responds to the stimulus

The Stimulus-Response Chain: ALL nervous responses, whether voluntary or involuntary, follow this pattern:

.

Synapse (gap between 2 neurones)

The Reflex Arc Reflexes are automatic or involuntary responses to a stimulus. The brain is not involved in the response, so the response is faster and automatic: reflexes protect us from harm. Special relay neurones in the spine carry impulses from the sensory neurone directly to a motor neuron. The impulse is then sent to an effector for a super-fast response!

A synapse is a tiny gap between one neuron and the next one. The electrical impulse has to be transmitted across that gap using chemicals called neurotransmitters as follows: 1. As the nervous impulse arrives at the synapse it causes a

chemical/nerotransmitter to be released into the synapse 2. The chemical/nerotransmitter diffuses across the synapse 3. The chemical/neurotransmitter binds to receptors on the second neurone,

which causes a new impulse to be generated in that neurone. If a drug has a similar shape to the neurotransmitter it can block the receptor, which blocks the impulse from being passed on. Some painkilling medicines work in this way. Crossing a synapse slows down the speed of a nervous response!

Y11 Biology Homeostasis & Response

The thermoregulatory centre of

the brain, found in a structure

called the hypothalamus,

detects and responds to body

temperature.

Too high a body temperature

can lead to enzymes denaturing,

and therefore death

Thermoregulation (controlling body temperature)

Monitoring body temperature: The Thermoregulatory centre in the hypothalamus of the brain monitors blood temperature using temperature receptors. Temperature receptors in the skin also send impulses along sensory neurones to the thermoregulatory centre. Body temperature too low: 1) Impulses stop being sent along motor neurones to sweat glands, so sweating stops 2) Vasoconstriction occurs – blood vessels in the skin constrict so less blood flows near the skin’s surface and less heat is transferred to the environment Body temperature too low: 1) Impulses sent along motor neurones to sweat glands and sweating starts. Sweat cools the body as it evaporates. 2) Vasodilation occurs – blood vessels in the skin dilate (open up) so more blood flows near the skin’s surface and more heat energy is transferred to the environment

Y11 Biology Homeostasis & Response

Required practical activity 7: plan and carry out an investigation into the effect of a factor on human reaction time.

Ruler drop method Online method

The person being tested rests their arm on a table with their hand over the edge. They hold their thumb and forefinger a short and fixed distance apart. The ruler is held so that the top of the ruler is in line with the top of the person’s forefinger. Ensure the ruler is held in the same place in any further tests. Without warning, the ruler is dropped and the person attempts to catch the ruler as quickly as possible. The distance on the ruler at the top edge of the person’s thumb is recorded, and a conversion table is used to convert this into a reaction time. Repeat tests can be taken and a mean average calculated. Computer based reaction time tests can offer more accurate results as there is less room for human error

The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions, as shown above. The complexity and delicacy of the brain, along with the crucial processes it controls, make it difficult to investigate. Neuroscientists have been able to map the regions of the brain to particular functions in 3 main ways: 1) Studying patients with brain damage (e.g. Phineas Gage). 2) Electrically stimulating different parts of the brain. 3) Using MRI scanning (magnetic resonance imaging).

Y11 Biology Homeostasis & Response The Eye and Accomodation

Distant object Near object

Light rays

nearly parallel Diverge

Lens Thin lens so only slight refraction of light rays needed

Thick lens refracts rays

Y11 Biology Homeostasis & Response

Object Ciliary muscles Suspensory ligaments

Lens shape Light rays

Near Contract Loosen Thick Refracted more strongly

Far Relax Tight Thin Refracted less strongly

Normal vision Myopia Hyperopia

Where is the image formed?

On the back of the retina In front of the retina Behind the retina

Why does this happen?

Light is correctly refracted by the cornea and lens in the eye.

The lens is too strong, or the eyeball is too long.

The lens is too weak or the eyeball is too short.

What can be done to correct this, if necessary?

Use a concave lens Use a convex lens

Compare and contrast normal vision, myopia and hyperopia:

Y11 Biology Homeostasis & Response

Questions 1. Define homeostasis. 2. Give 3 examples of things controlled by

homeostasis. 3. What is the CNS and what does it consist of? 4. What two things are effectors? 5. Write out the parts of the stimulus response

chain in order. 6. Explain the differences between a voluntary

response and an involuntary response (a reflex)

7. A person steps on a pin and moves their leg away. Describe what happens in their nervous system to bring about this response.

8. What is a synapse? 9. Describe how an impulse is passed from one

neurone to another across a synapse. 10. Why do synapses slow down the speed of a

nervous response? 11. What is thermoregulation? Why is it

important? 12. Explain how your body temperature is

monitored. 13. Describe and explain what happens when

you are too hot. 14. Describe and explain what happens when

you are too cold. 15. Why is it wrong to say ‘blood vessels move

closer to the skin when you are too warm’?

16. Describe how you could measure the effect of caffeine on reaction time using the ruler drop method.

17. Why might it be preferable to use a computer based reaction time measurer?

18. Draw a rough outline of a brain. Label the 4 main parts and state what they are for.

19. What is the brain made of? 20. Why is it difficult to study the brain, and

what are the main ways that scientists can do it?

21. A person has a region of their brain electrically stimulated by an external device, and finds it impossible to type a text message on their phone while it is happening. Suggest what part of their brain is likely being stimulated.

22. List the parts of the eye and state what they do.

23. A doctor shines a torch into a patient’s eye. Describe what the doctor expects to see and explain how it happens.

24. Draw labelled ray diagrams to show how near and distant objects are focussed onto the retina.

25. Compare and contrast myopia and hyperopia including how lenses can be used to correct them. Draw diagrams showing this.

26. Describe and explain the roles of the ciliary muscles and suspensory ligaments in accommodation in the eye