Synapses and the pupil reflexEdexcel International A Level Biology: Mind map

Exam questions on Synapses and the pupil reflex

1. A neurophysiologist is studying a cholinergic synapse between two neurones in a tissue sample. She stimulates the presynaptic neurone and records the electrical changes in the postsynaptic neurone.
   Explain why an impulse can cross this synapse in one direction only.2 marks
2. In a second experiment, the researcher finds that a single stimulus to the presynaptic neurone does not produce an action potential in the postsynaptic neurone, but several stimuli delivered in rapid succession do.
   Explain why a single stimulus failed to produce an action potential in the postsynaptic neurone, but several rapid stimuli did.2 marks
3. An optician shines a bright torch into one eye of a patient sitting in a dim room. The pupil quickly becomes smaller. When the torch is switched off and the room lights are dimmed, the pupil gradually becomes wider again.
   Describe how the reflex pathway and the iris muscles bring about the change in pupil size when the bright light is shone into the eye.3 marks