Structure and function

Students should be able to explain how the structure of the nervous system is adapted to its functions.

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

Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.

stimulus → receptor → coordinator → effector → response

Students should be able to explain how the various structures in a relex arc – including the sensory neurone, synapse, relay neurone and motor neurone – relate to their function. Students should understand why relex actions are important.

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

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Students should be able to extract and interpret data from graphs, charts and tables, about the functioning of the nervous system.

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Students should be able to translate information about reaction times between numerical and graphical forms.

The brain

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

Students should be able to identify the cerebral cortex, cerebellum and medulla on a diagram of the brain, and describe their functions.

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Students should be able to explain some of the difficulties of investigating brain function and treating brain damage and disease.

Neuroscientists have been able to map the regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques. The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult.

The eye

Students should be able to relate the structures of the eye to their functions. This includes:
- accommodation to focus on near or distant objects
- adaptation to dim light.

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

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Students should be able to identify the following structures on a diagram of the eye and explain how their structure is related to their function:
- retina
- optic nerve
- sclera
- cornea
- iris
- ciliary muscles
- suspensory ligaments.

Accommodation is the process of changing the shape of the lens to focus on near or distant objects.

To focus on a near object:
- the ciliary muscles contract
- the suspensory ligaments loosen
- the lens is then thicker and refracts light rays strongly.

To focus on a distant object:
- the ciliary muscles relax
- the suspensory ligaments are pulled tight
- the lens is then pulled thin and only slightly refracts light rays.

Two common defects of the eyes are myopia (short sightedness) and hyperopia (long sightedness) in which rays of light do not focus on the retina.
- Generally these defects are treated with spectacle lenses which refract the light rays so that they do focus on the retina.
- 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.

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Students should be able to interpret ray diagrams, showing these two common defects of the eye and demonstrate how spectacle lenses correct them.

Control of body temperature

Body temperature is monitored and controlled by the thermoregulatory centre in the brain. The thermoregulatory centre contains receptors sensitive to the temperature of the blood. The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre.

If the body temperature is too high, blood vessels dilate (vasodilation) and sweat is produced from the sweat glands. Both these mechanisms cause a transfer of energy from the skin to the environment.

If the body temperature is too low, blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).

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Students should be able to explain how these mechanisms lower or raise body temperature in a given context.