Nervous system
Stimulus and response
• A stimulus is a change in an animal’s internal or external environment
• A response is a reaction to that change.
• A receptor organ is one which detects a stimulus.
• Coordination centres (brain, spinal cord and pancreas) process information from receptors
• An effector is muscle or gland which carries out the response.
Nerve cells (Neurones)
The CNS (central nervous system) is comprised of spinal cord, brain and all the nerves
3 types of neurones and their functions:
Relay neurone – pass signals in the brain from sensory to motor neurone
Sensory neurone – pass signals from the receptor to the coordination centre
Motor neurone – pass signals
Complete the flow diagram below to show the sequence of a nervous response:
Stimulus
Ball thrown towards
you
Reflex action/arc
- Reflex actions are unconscious processes which happen in grey and white matter of the
brain across the reflex arc
- They are quicker because thinking about them is not needed
- Their purpose is to provide quick responses to different stimuli, in order to avoid danger and
damage to body as well as control of different required processes, such as heart beat and
breathing
, Synapses
1. impulse arrives at the synapse, causing 2. neurotransmitter is released and diffuses
vesicles (scas) containing transmitter to fuse across the snapse. It binds to the receptors on
with the membrane the surface of the next neurone
3. new impulse is generated
Q1. Three students measured their reaction times.
The students used a computer program.
The image below shows the image displayed on the computer screen.
This is the method used:
1. Sit facing the computer screen.
2. Click the mouse button as quickly as possible when the computer screen
turns green.
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