The human nervous system — AQA GCSE Biology

Revision notes

8 short notes, in the order of the specification. Each one in short:

1. Structure and function of the nervous system

   The nervous system enables humans to react to their surroundings and to coordinate their behaviour. Receptors detect a stimulus, and neurones carry information as electrical impulses to the central nervous system (CNS), which is the brain and spinal cord. The CNS coordinates the response of effectors: muscles contracting or glands secreting hormones.

2. Reflex actions and the reflex arc

   A reflex action is an automatic and rapid response that does not involve the conscious part of the brain. In a reflex arc, an impulse passes from a receptor along a sensory neurone to the CNS, through a relay neurone, then along a motor neurone to an effector. Reflexes protect the body from harm.

3. Required practical: reaction time

   Practical

   Reaction time is the time taken to respond to a stimulus. In this required practical, a partner drops a ruler without warning and the volunteer catches it as fast as possible: a shorter distance fallen means a faster reaction. You change one factor, such as caffeine or practice, keep the other variables the same, and repeat to calculate a mean.

4. The brain

   Triple only

   The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions. The cerebral cortex is responsible for consciousness, intelligence, memory and language. The cerebellum coordinates muscular activity and balance. The medulla controls unconscious activities such as heart rate and breathing.

5. The eye: structures and their functions

   Triple only

   The eye is a sense organ containing receptors sensitive to light intensity and colour, found in the retina. The cornea refracts light, the iris controls the size of the pupil, and the optic nerve carries impulses to the brain. In dim light the pupil gets wider so more light enters; in bright light it gets narrower, which protects the retina.

6. Accommodation

   Triple only

   Accommodation is the process of changing the shape of the lens to focus on near or distant objects. For a near object the ciliary muscles contract, the suspensory ligaments loosen and the lens becomes thicker, so it refracts light strongly. For a distant object the ciliary muscles relax, the ligaments are pulled tight and the lens is pulled thin.

7. Defects of the eye

   Triple only

   Myopia (short sightedness) and hyperopia (long sightedness) are defects of the eye in which light rays do not focus on the retina. In myopia rays focus in front of the retina and a concave lens corrects it. In hyperopia they focus behind the retina and a convex lens corrects it. Contact lenses, laser surgery and replacement lenses are newer treatments.

8. Control of body temperature

   Triple only

   Body temperature is monitored and controlled by the thermoregulatory centre in the brain, which contains receptors sensitive to the temperature of the blood. Temperature receptors in the skin also send impulses to it. If body temperature is too high, blood vessels dilate and sweat is produced. If it is too low, blood vessels constrict, sweating stops and skeletal muscles shiver.