Answer
Strychnine is a alkaloid plant toxin produced by the plant Strychnos nux-vomica. The symptoms of strychnine poisoning include twitching, tremors, hyperreflexia, convulsions, periods of stiffness and relaxation, arching of the back (opisthotonus) and dyspnea . These manifestations are due to the heightened excitability of muscles secondary to the blocking of the inhibitory action of glycine (IPSPs) by the binding of strychnine to postsynaptic glycine receptors.
Work Step by Step
When an action potential ( neural stimuli) is triggered in a sensory nerve, it travels to the presynaptic membrane where voltage -gated calcium channels open to allow the entrance of calcium ions. The Calcium ions cause excitatory neurotransmitter vesicles (ACH or glutamate) to fuse with the pre- synaptic membrane and release their contents by exocytosis into the synaptic cleft. The excitatory neurotransmitter will bind with receptors on the postsynaptic membrane and open ligand-gated ion channels. In the case of the neuron to neuron transmission, cation channels (Na+/K+) channels are opened ; the preponderance of in-streaming Na+ ions depolarizes (lowers the negativity) of the post synaptic cell. Ordinarily, where an an inhibitory interneuron is involved in this circuit, it will release an inhibitory neurotransmitter (glycine or GABA) in response to the neural trigger. Glycine will bind to postsynaptic membrane and open anion channels that will permit a flow of Cl- ions through post synaptic membranes. This will hyperpolarize the post synaptic cell (motor neuron or skeletal muscle) and make the reaching of threshold, and firing more difficult. Strychnine is a competitive antagonist to glycine (and Acetylcholine) receptors. It binds to glycine receptors at a different site than does glycine. Thus it opposes the inhibitory action of glycine on glutamate; this causes extreme depolarization of postsynaptic cells, and makes muscles (and the whole nervous system) more excitable and sensitive to stimuli of all kinds. Twitches, tremors, bouts of convulsions ensue in a victim of strychnine poisoning. Eventually, severe impairment in function of respiratory muscles will lead to asphyxiation and death, unless the patient is treated appropriately, and placed on a respiratory ventilator.
