Synapses and the pupil reflexEdexcel International A Level Biology: Flashcards
What these 13 flashcards ask
- What is a synapse?
- Which ions enter the presynaptic knob when an action potential arrives, and why?
- How is acetylcholine released into the cleft?
- What does acetylcholine do at the postsynaptic membrane?
- What enzyme removes acetylcholine from the cleft, and what are the products?
- Why is acetylcholine removed from the cleft?
- Why are mitochondria abundant in the presynaptic knob?
- Why are synapses unidirectional?
- Define temporal summation.
- Define spatial summation.
- What happens to the iris muscles in bright light?
- What happens to the iris muscles in dim light?
- Why is the pupil reflex useful?
Exam questions on Synapses and the pupil reflex
- 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
- 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
- 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
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).