Nervous coordination (A-level only)

Medium
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Question 8
Medium
a.

State two anatomical or physiological features of a chemical synapse that ensure transmission of an impulse is unidirectional.

[2]
b.

Figure 1 shows the changes in membrane potential in a postsynaptic neurone after separate and simultaneous stimulation of two different presynaptic neurones, A A\,A and BBB.

A line graph showing membrane potential in mV against time. The y-axis ranges from -100 mV to +75 mV, with key values marked at -70 mV (resting potential), -50 mV (threshold), and +35 mV. The first region represents stimulation of presynaptic neurone A alone, showing a small depolarisation peak reaching -60 mV before returning to resting potential. The second region represents stimulation of presynaptic neurone B alone, showing a small depolarisation peak reaching -58 mV before returning to resting potential. The third region represents simultaneous stimulation of both A and B, showing two depolarisations that summate to reach the -50 mV threshold, triggering a full action potential spike that peaks at +35 mV before repolarising back to -70 mV. Time moves from left to right on the x-axis with an arrow.

Name and explain the type of summation shown in Figure 1.

[2]
c.

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease where antibodies target and destroy voltage-gated calcium ion channels in the presynaptic membrane of neuromuscular junctions.

Suggest and explain how LEMS can cause muscle weakness. Do not include details of myofibril movement or muscle contraction in your answer.

[2]
d.

Amifampridine is a drug that blocks voltage-gated potassium channels in the presynaptic neurone, which prolongs depolarisation during an action potential. Amifampridine is used to treat LEMS.

Explain how Amifampridine can help in the treatment of LEMS.

[3]

Nervous coordination (A-level only) Questions

  1. A Level
  2. /Biology
  3. /Nervous coordination (A-level only)