Insecticides destroy the central nervous system by affecting three molecular targets:
the enzyme acetylcholinesterase,
acetylcholine receptors of the synaptic sodium channels,
and axonal sodium channels.
First, we will discuss the organophosphate and carbamate insecticides
that inhibit acetylcholinesterase.
Acetylcholinesterase acts in association with synaptic sodium channels,
The channel consists of five proteins.
Two of the five proteins are identical and have acetylcholine receptors.
When acetylcholine released by the presynaptic neuron binds to the two receptors,
it activates the channel to open.
The activated channel opens and
sodium ions flow through the channel and into the cell.
When the acetylcholine comes off the channel receptors,  the channel closes.
This stops the sodium flow into the channel.
Acetylcholinesterase breaks the acetylcholine molecule
to keep acetylcholine from continuing to
stimulate the sodium channel receptors and reopening the channel.
During organophosphate and carbamate poisoning, the insecticide molecules
bind to the active site of the acetylcholinesterase enzymes
and block the enzymes from degrading the acetylcholine  from the sodium channel receptors.
This keeps the sodium channels open constantly.
Let us see what happens when this occurs in the synapse.
The insecticide enters the synapse of poisoned insects and blocks acetylcholinesterase.
The sodium channels open in response to release of acetylcholine by the presynaptic neuron.
The insecticide binds the acetylcholinesterase and the enzyme can no longer destroy acetylcholine.
The accumulating acetylcholine constantly stimulates the sodium channel receptors
and keeps the channels open so that sodium flows into the postsynaptic neuron
and produces uncontrolled firing of nerve impulses.
The uncontrolled nerve firing results in the twitching of the limbs
that we observe in organophosphate and carbamate poisoned insects.
We will next discuss how insecticides interact with the enzymes, receptors  and channels of neurons
to disrupt nervous system functions.
