When an action potential arrives at the synapse, the electrical signal of the action potential is transformed into a biochemical signal. This transformation is necessary in order to have the signal cross the small space between two neurons (20 nm).

1. An action potential arrives at the synaptic knob and causes its depolarisation.

2. The depolarisation of the synaptic membrane causes the voltage dependent calcium channels to open. This leads to a quick rise of the intracellular calcium concentration.

3. An increase of intracellular calcium results in the exocytosis of vesicles containing neurotransmitters.

4. The

released neurotransmitters diffuse across the synaptic cleft and can associate and dissociate in a concentration dependent basis with receptors that are localized on the postsynaptic cell. These postsynaptic receptors can be receptor-operated ion channels or G-protein coupled receptors that when stimulated by the neurotransmitter can exert their effect.

5. The action of the receptor is usually focussed on ion channels. By inducing opening of these channels, the postsynaptic membrane can depolarise. Depending on whether this depolarisation reaches the threshold, the signal can be passed over the axon of the postsynaptic cell.


Which of the following statements is true?