An experiment was conducted to study synaptic integration in a postsynaptic neurone. Two presynaptic neurones, X X\,X and YYY, synapse with a single postsynaptic neurone ZZZ. The resting membrane potential of neurone Z Z\,Z is -70 mV, and its threshold potential is -55 mV.
The table shows the peak membrane potential recorded in neurone Z Z\,Z following different stimulation patterns of neurones X X\,X and YYY.
| Trial | Presynaptic neurones stimulated | Time interval between successive stimuli (ms) | Peak membrane potential of neurone ZZZ (mV) |
|---|---|---|---|
| 1 | XXX (1 stimulus) | N/A | -62 |
| 2 | YYY (1 stimulus) | N/A | -75 |
| 3 | XXX (2 stimuli) | 25 | -62 |
| 4 | XXX (2 stimuli) | 1.5 | +35 |
| 5 | XXX (1 stimulus) and YYY (1 stimulus) simultaneously | N/A | -67 |
Which of the following is a correct deduction from these data?
The neurotransmitter released by neurone YYY causes ligand-gated K+\text{K}^+K+ or Cl−\text{Cl}^-Cl− channels to open on the postsynaptic membrane.
The peak potential in Trial 3 indicates that neurone XXX releases an inhibitory neurotransmitter when stimulated at a lower frequency.
Trial 5 demonstrates that spatial summation of inputs from neurones XXX and YYY results in cooperative depolarisation to exceed the threshold.
In Trial 4, the rapid successive stimulation of neurone XXX triggers an action potential via spatial summation.
22 exam-style questions on OCR A A Level Biology Neuronal communication. Each one has a worked solution and a mark scheme showing where the marks go.