A person touches a hot plate and quickly moves their hand away. This is a reflex action.
(a) Name the effector in this reflex. [1]
(b) Explain why a reflex action is fast. [1]
(c) Describe how a nerve impulse passes across a synapse from the sensory neurone to the relay neurone. [3]
- (a) muscle (in the arm); accept biceps; reject 'hand' / 'arm' alone(1)
- (b) does not involve the conscious part of the brain / no thinking needed; accept impulse goes through the spinal cord (not to the brain) / few synapses / short pathway (only three neurones)(1)
- (c) (impulse causes) neurotransmitter / chemical to be released from end of sensory neurone(1)
- (c) neurotransmitter diffuses across the gap / synapse(1)
- (c) binds to receptors on the relay neurone, starting a new impulse(1)
- Answer: (a) arm muscle (b) no conscious thought / few synapses (c) neurotransmitter released, diffuses across gap, binds to receptors on next neurone
- Examiner tip: The effector is the muscle, not the hand — name the tissue that responds.