BIOLOGY 2401 – ANATOMY & PHYSIOLOGY 1

Bad Fish: A Case on Nervous Tissue

Your favorite uncle Mr. Marshall Westwood is in Indonesia on a busines trip.  One evening he sat down to eat a meal of puffer fish and rice. Within an hour of returning to his hotel room, Mr. 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, Mr. 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 Mr. Westwood was rushed to the hospital, his breathing became increasingly labored.

The patient presented in the ED with diaphoresis, motor dysfunction, paresthesias, nausea, 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. Within 30 minutes of presenting in the ED, Mr. Westwood developed bradycardia with a BP of 90/50 mmHg. Atropine was administered in response to the bradycardia. Intravenous hydration, gastric lavage, and activated charcoal followed a presumptive diagnosis of tetrodotoxin poisoning that was based on the clinical presentation in the ED. Five hours after treatment, the following vital signs were noted:

• BP 125/79 mmHg
• HR 78 bpm
• Oxygen saturation: 97% on room air

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.

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Your aunt back home in US is very concerned about her husband’s condition and turns to you for answers.  Write a letter to your aunt explaining the mechanism behind food poisoning.  Your letter should address the following components of the nervous system in detail:

• Define the following phrases and terms associated with the signs and symptoms of Mr. Westwood’s TTX poisoning:  diaphoresis,motor dysfunction, paresthesias,cyanotic, hypoventilating, bradycardia, gastric lavage, oxygen saturation.
• As mentioned in the case description, tetrodotoxin is a molecule that blocks voltage-gated sodium ion channels. What is a voltage-gated sodium ion channel and what is its function?
• When nerve cells are at rest, there is an unequal amount of positive and negative charges on either side of a nerve cell membrane. This charge difference creates an electrical potential. Describe how the resting membrane potential (resting potential) is generated.
• What is happening to the electrical potential of a neuron when it generates an action potential? What is the function of the action potential in neurons?
• Describe the role of sodium ions and sodium channels in generating an action potential.
• What would happen to a neuron if it was exposed to tetrodotoxin? Be specific regarding its effect on the ability of a neuron to communicate.
• Now that you have addressed some of the basic biology of this case, explain why Dr. Westwood experienced numbness after eating the puffer fish meal.
• Paralysis is a term used to describe the loss of muscle function. If tetrodotoxin’s effect is on neurons, why did Dr. Westwood experience paralysis?