Discussion
Which one of the following statements is incorrect ? Calcium ions are necessary for :
Answer: C
The incorrect statement is that calcium is necessary for the propagation of action potential in a neuron.
A nerve impulse travels along the axon by the opening of voltage-gated sodium channels, which depolarise the membrane, followed by voltage-gated potassium channels, which repolarise it. Calcium ions are not needed for this conduction along the axon.
The other roles are genuine. Calcium binds troponin to allow muscle contraction. Its entry into the presynaptic terminal triggers vesicle fusion and the release of neurotransmitter. And it is itself a second messenger, released for example by IP3, mediating the action of other signals through proteins such as calmodulin.
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