Question

When curare, a South American arrow poison, is placed on a nerve-muscle preparation, the muscle though a neurotransmitter is still being released from the nerve. Give a possible explanation for the action of curare (be sure to include specific details explaining does not contract when the nerve is stimulated, even how and why).

Answer 1

In a muscle contraction,neurotransmitter acetycholine stimulate the post synaptic membrane of the neuron or the sarcolemma of the muscles cells at the motor end plate .This neurotransmission effect leads to the opening of ligand gated sodium channels.

Therefore action potential(Endplate potential) is transmitted across the synaptic juction to to the muscles to bring about contraction of muscles(effector) .Therefore Acetycholine is refereed to as excitatory hormone.

Curare works as competitive inhibitor of acetycholine at the motor end plate. It prevents the binding of Acetycholine with the endplate.Therefore, ligand gated Na+channels can not open, thus End potential can not be generated due to lack of depolarization, thus contraction of muscles is inhibited.

Thus,despite the fact that the neurotransmitter is produced, the curare has blocked the end plate.So, no muscles contraction will occur because ,no place for the the excitatory acetylcholine to bind with.Hence the the muscle cells are in the permanent state of relaxation (resting membrane potential).

Animals poisoned with this substance usually asphyxiate because of paralysis of the diaphragm, external and internal inter-coastal muscles and collapse of the lungs and therefore failure of the entire respiration muscles and system.Thus lack of oxygen from failed breathing.

Explanation:s

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