Chemicals which are released at the synaptic junction are called

Muscle contraction is initiated by a signal sent by the central nervous system by the release of . . . . . . .

What is the difference between electrical transmission and chemical transmission?

Define/Explain the following terms:
$(1)$ Synapse
$(2)$ Node of Ranvier

Which of the following inhibits the enzyme acetylcholinesterase?

True about electrical synapses:
$(I)$. Pre and postsynaptic neurons are in very close proximity.
$(II)$. Pre and postsynaptic neurons are separated by a synaptic cleft.
$(III)$. Impulse transmission is very fast.
$(IV)$. Electrical synapses are common in our system.
Select the correct option.