Revise
The Nervous System • • • •
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The nervous system enables humans to react to their surroundings Spinal cord and coordinate their behaviour. Information from receptors passes to the central nervous system (CNS) (the brain and spinal cord). The CNS coordinates the response of effectors, i.e. muscles contracting or glands secreting hormones. 2 Sensory neurone Reflex actions are automatic and rapid so they can protect the body. They do not involve the conscious 3 Relay part of the brain: neurone 1 The pain stimulus is detected by receptors. Motor 4 Spinal neurone 2 Impulses from the receptor pass along a sensory nerve neurone to the CNS. 3 An impulse then passes through a relay neurone. 4 A motor neurone carries an impulse to the effector. 5 The effector (usually a muscle) responds, e.g. to 5 Effector cells, in this case a muscle withdraw a limb away from the source of pain. Neurones are not directly connected to each other. 1 Receptor They communicate with each other via synapses (gaps Hot plate between neurones). (stimulus) When an electrical impulse reaches a synapse, a chemical is released that diffuses across the gap between the two neurones. A Synapse This causes an electrical impulse to be generated in the second neurone. Neurone A
REQUIRED PRACTICAL
Neurone B
Investigating the effect of a factor on human reaction time. Sample Method Reaction time can be investigated by seeing how quickly a dropped ruler can be caught between finger and thumb: 1. The experimenter holds a metre ruler vertically from the end. 2. The subject has their finger and thumb a small distance apart, either side of the ruler, on the 50cm line. 3. The experimenter lets go of the ruler and the subject has to trap it. 4. The distance the ruler travels from the 50cm line is noted. 5. The experiment is repeated on subjects that have just drunk coffee or cola and subjects that have not.
Considerations, Mistakes and Errors • It is very difficult to control the variables in this experiment. • To obtain reliable results, large numbers of subjects need to be tested and averages taken.
Variables • The independent variable is whether the subject has taken in caffeine or not. • The dependent variable is the distance that the ruler travels. • The control variables are the age, sex and mass of the subjects.
Hazards and risks • There are limited risks with this experiment.
Key Words
Quick Test 1. Which type of neurone is responsible for sending impulses from the receptors to the CNS? 2. What is the gap between two neurones called? 3. Which two structures make up the CNS?
homeostasis receptors effectors HT negative feedback central nervous system (CNS) synapse
Homeostasis and Response: Revise
227841 AQA Higher Tier Combined Science All-in-One_P032_055.indd 51
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6/29/16 10:56 AM