Answer:
a. IV, III, I, II.
Explanation:
This is a pathway of transmission of action potential across a synaptic gap of pre-synaptic and postsynaptic neurons, or from pre-synaptic neuron and a muscles cells at a neuromuscular junction.
It is initiated with the arrival of action potential at the pre-synaptic neuron, which makes voltage gated Ca+ ions to open, vesicles migrates towards the tip of the pre-synaptic neurons, fused and empty contents into the synaptic cleft, the neurotransmitter pass across the synaptic cleft to reach the post synaptic neuron.
The action potential transmitted across the synapse can either be Inhibitory post synaptic or excitatory postsynaptic potential.
The neurotransmitter released into the synapse binds with the receptors on the postsynaptic neurons. And this enabled the Act.potential to be propagated to the postsynaptic neuronal axon, to open many Voltage-Gated Sodium channels for depolarization, and propagation of action potential.
The neurotransmitters can be exictatory or inhibitory. In either case they are broken down to components molecules, by enzymes after short period of binding with the postsynaptic potential. This is important so that they do not exert too much effects on the post synaptic receptors which may affect the action potential in the effectors or in the postsynaptic neurons functions.
