Question

One evening during a recent trip to Indonesia, Dr. Marshall Westwood sat down to a meal of puffer fish and rice. Within an hour of returning to his hotel room, Dr. Westwood felt numbness in his lips and tongue, which      quickly spread to his face and neck. Before he could call the front desk, he began to feel pains in his stomach and   throat, which produced feelings of nausea and eventually severe vomiting. Fearing that he had eaten some “bad fish”      for dinner, Dr. Westwood called a local hospital to describe his condition.  The numbness in his lips and face made it   almost impossible for him to communicate, but the hospital staff managed to at least understand the address he       gave them and they sent an ambulance. As Dr. Westwood was rushed to the hospital, his breathing became     increasingly labored.

     The patient presented in the ED with motor dysfunction and an ascending paralysis that started in his legs and spread            to the upper body, arms, face, and head. The patient was cyanotic and hypoventilating. After discussing his case with        his physician, he learned that he had probably been the victim of puffer fish poisoning. The active toxin in the tissues      of this fish is a chemical called tetrodotoxin (TTX). Tetrodotoxin is in a class of chemicals known as neurotoxins   because it exerts its effects on neurons. The specific action of tetrodotoxin is that it blocks voltage-gated sodium ion       channels.

Part A)  Describe the normal physiology of an action potential in a neuron. Describe the conditions that a neuron         maintains at rest, and the stimuli that may disrupt these conditions. Does every disruption to resting      conditions result in an action potential? What structures and chemicals are involved in the generation of an action potential?

Part B)  As mentioned in the case description, TTX blocks voltage-gated sodium channels. If TTX’s effect is in neurons,    why did Dr. Westfall experience both numbness and paralysis?

Answer 1

* In physiology, action potential occurs When membrane potential of neuron rapidly rises and falls. This depolarization then causes adjacent locations to Similarly depolarize. * In neuron, action potential play a central role in cell to cell Communication by providing to saltatory conduction, assisting the propagation of signal along nearon's axon towards Synaptic boutons Situated at ends of an axon. Action potentials are generated by special types of voltage - gated ion channels embedded in a cell's plasma membrane. these channels are shut when membrane Potential is near resting potential of the Cell, but they rapidly begin open if membrane potential increases to a

Precisely defined threshold voltage, depolarising the transmembrane potential. When the channel open, they allow an inward flow of sodium ions, which Changes electrochemical gradient, which in turo produces a further rise in membrane potential. This then causes more Channels to open, producing a greater electric current. Rapid influx of sodium ion causes polarity of plasma membrane to reverse and ion channels then rapidly inactivate. potass sodium channel close, Potassium channels are then activated. and there is Outward current of Potassium ions; returning electrochemical gradient to the resting state.