Homeostasis and the nervous system

5. Homeostasis and Response

Homeostasis is the regulation of the conditions inside your body to keep a stable internal environment, so that cells and enzymes can work properly whatever is happening outside.

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185 questions5 subtopicsFoundation and Higher1 required practical

What homeostasis and the nervous system covers

Every subtopic below has its own questions, mark schemes and notes.

4.5.1Homeostasis

Homeostasis is the regulation of the conditions inside your body to keep a stable internal environment, so that cells and enzymes can work properly whatever is happening outside.

4.5.2.1The nervous system and reflexes

The nervous system lets you react to your surroundings and coordinate your behaviour, carrying information as electrical impulses along neurones. Reflexes take a short cut that misses out the conscious brain.

4.5.2.2The brain

The brain is made of billions of interconnected neurones, and different regions do different jobs. Mapping those regions is difficult, and so is treating the brain when it goes wrong.

4.5.2.3The eye

The eye is a sense organ containing light receptors. It changes the shape of its lens to focus, and changes the size of its pupil to control how much light gets in.

4.5.2.4Controlling body temperature

Core body temperature is held near 37 degrees Celsius, the optimum for your enzymes, by a control centre in the brain that switches effectors in the skin on and off.

Key terms

The definitions examiners expect, in the wording that earns the mark.

Homeostasis — The regulation of internal conditions to maintain optimum conditions for function, in response to internal and external change.

Stimulus — A change in the environment, either inside or outside the body.

Receptor — A cell that detects a stimulus.

Coordination centre — A structure such as the brain, spinal cord or pancreas that receives and processes information from receptors and organises a response.

Effector — A muscle or gland that carries out the response.

Negative feedback — A mechanism in which a change in a level triggers a response that counteracts that change.

Neurone — A nerve cell, which carries information as an electrical impulse.

Central nervous system — The brain and spinal cord.

Sensory neurone — A neurone carrying impulses from receptors to the central nervous system.

Relay neurone — A neurone inside the central nervous system that connects a sensory neurone to a motor neurone.

Motor neurone — A neurone carrying impulses from the central nervous system to an effector.

Synapse — The junction between two neurones, crossed by chemicals that diffuse over the gap.

Reflex arc — The pathway taken by information in a reflex, from receptor to effector.

Reaction time — The time taken to respond to a stimulus.

Cerebral cortex — The folded outer layer of the brain, responsible for consciousness, intelligence, memory and language.

Cerebellum — The region at the lower back of the brain that coordinates muscle activity and movement.

Medulla — The region at the base of the brain that controls unconscious activities such as breathing and heart rate.

Neuroscientist — A scientist who studies the brain and nervous system.

MRI scan — A scanning technique that produces a detailed image of the brain and shows which regions are active.

Accommodation — The changing of the shape of the lens so that light is focused on the retina.

Refraction — The bending of light as it passes into or out of a transparent material.

Hyperopia — Long-sightedness - near objects are focused behind the retina.

Myopia — Short-sightedness - distant objects are focused in front of the retina.

Convex lens — A lens that curves outwards and increases refraction, used to correct long-sightedness.

Concave lens — A lens that curves inwards and reduces refraction, used to correct short-sightedness.

Thermoregulatory centre — The region of the brain that monitors and controls body temperature.

Vasodilation — The widening of the blood vessels supplying the skin capillaries, increasing energy transfer to the surroundings.

Vasoconstriction — The narrowing of the blood vessels supplying the skin capillaries, reducing energy transfer to the surroundings.

Shivering — Rapid automatic contraction of skeletal muscles, which increases respiration and releases energy that warms the body.

Antagonistic effectors — Effectors that produce opposite effects, allowing finer control.

Where marks get lost

The mistakes that come up again and again in this topic.

A definition of homeostasis that only says 'keeping things the same' will not score - say regulation of internal conditions to maintain optimum conditions for function.
Receptors are cells. The eye and the ear are organs that contain receptor cells; they are not themselves receptors.
Do not call the brain an effector. It is the coordination centre; the effector is the muscle or gland that acts.
Negative feedback does not mean a bad response - it means a response that opposes the change.
Impulses travel along neurones electrically but cross synapses chemically - say which is which or the mark is lost.
Reflexes do involve the brain in some cases, but never the conscious part of it. 'Does not involve the brain' is not a safe answer; 'does not involve the conscious part of the brain' is.
The reflex arc has three neurones. Missing out the relay neurone is the most common way to drop marks on a 'describe the pathway' question.
In the ruler test you measure a distance, not a time. Say 'the distance the ruler fell', then explain what that tells you.
'Repeat and take a mean' scores; 'repeat to make it accurate' usually does not. Say it reduces the effect of random error.
Spell and place the three regions carefully - cerebral cortex on the outside, cerebellum at the lower back, medulla at the base.
The medulla controls unconscious activities. Saying it 'controls breathing' alone is fine, but 'controls the lungs' is not.
When asked for difficulties of studying the brain, give a property of the brain (complex, delicate, hard to reach) rather than just saying 'it is hard'.
A question about risks of treatment wants consequences for the patient, such as loss of speech, not just 'the operation might go wrong'.
The iris is the ring of muscle; the pupil is the hole. Saying 'the pupil contracts' loses the mark - the muscles of the iris contract.
For accommodation, name all three of the ciliary muscle, the suspensory ligaments and the lens. Two out of three rarely gets full marks.
The ciliary muscle contracts for near objects, which feels backwards to most students. Near - contract - fat lens.
Long sight focuses behind the retina and needs a convex lens; short sight focuses in front and needs a concave lens. Getting these the wrong way round is the single most common error on this page.
The retina contains receptor cells. It is not itself a receptor.
Blood vessels do not move up and down in the skin, and capillaries do not dilate. It is the vessels supplying the skin capillaries that widen or narrow.
Sweat only cools you as it evaporates. 'Sweat is produced' on its own is half an answer.
Shivering warms you because the extra muscle contraction increases respiration - say that link, not just 'shivering makes heat'.
Use 'transfers energy to the environment' rather than 'loses heat'.

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