Most insecticides affect which system of an insect?

Axon terminal is indicated by which alphabet in the given figure?

The synaptic knob possesses:

The chemical causing the transmission of nerve impulse across synapses is

Arrange the following events in proper sequence during impulse transmission across a chemical synapse:
$(a)$ Fusion of synaptic vesicles with the cell membrane of the presynaptic neuron.
$(b)$ $Ca^{++}$ channels open and $Ca^{++}$ diffuses into the synaptic knob from the extracellular fluid.
$(c)$ Neurotransmitter binds with receptors of the postsynaptic cell.
$(d)$ Release of neurotransmitter by exocytosis.

Nerve fibres conduct impulses in