Nervous coordination

Sample questions

Original practice questions written in the style of the exam.

1. Question 15 marks

   Describe how an impulse is passed across a cholinergic synapse.

   Mark scheme

   • An action potential arrives at the presynaptic membrane and voltage-gated calcium ion channels open, so Ca²⁺ diffuses in (1)
   • Vesicles containing acetylcholine move to and fuse with the presynaptic membrane, releasing acetylcholine by exocytosis (1)
   • Acetylcholine diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane (1)
   • Sodium ion channels open, Na⁺ enters and the postsynaptic membrane depolarises; if threshold is reached an action potential is generated (1)
   • Acetylcholinesterase breaks down acetylcholine, so the channels close and the signal stops (1)
2. Question 24 marks

   Explain how light falling on a rod cell leads to an action potential in a neurone of the optic nerve.

   Mark scheme

   • Light breaks down rhodopsin into retinal and opsin (bleaching) (1)
   • Opsin triggers the closing of sodium ion channels, so the rod cell hyperpolarises (1)
   • The rod cell stops releasing its inhibitory neurotransmitter (glutamate) onto the bipolar cell (1)
   • So the bipolar cell depolarises and stimulates an action potential in the optic nerve (ganglion) neurone (1)