Critical Thinking Assignment 6: Cardiac Muscle Animal victims of the blue ringed

Question

Critical Thinking Assignment 6: Cardiac Muscle Animal victims of the blue ringed octopus are often fully conscious and paralyzed as the octopus consumes them, because the venom blocks voltage-gated sodium channels causing paralysis of skeletal muscle. This means that their brain and heart are stil functioning despite the fact the peripheral nervous system is failin potentials. 1. a) Explain why your heart would continue to beat despite being bitten by a blue ringed octopus. (2 pts) b) After biting you and injecting you with venom, the octopus realizes that you are too big to eat, and slimes away. Assuming that you are not bleeding from the bite, what will cause your heart and brain to stop functioning after a number of minutes? Be very specific and think about what cells need to function! (2 pts) c) A surfer comes along almost immediately, before your heart and brain stop functioning and notices the blue-ringed octopus crawling away. So despite the fact that you can't talk, he cleverly deduces the cause of your predicament. What life-saving measu surfer administer to you? (2 pts) res can the 2. If a coronary artery becomes blocked, blood flow to the heart is reduced. Hint: look up myocardial infarction in Silverthorn! a) How does lack of blood flow affect oxidative metabolism and why? (2 pts) b) What will happen to the pH of the affected heart cells? (2 pts) c) What will happen to levels of ATP in the affected heart cells? (1 pt) do wIna ill lapen tocalcium levels in the eytosol f the afleted bear cell and why? (3 pts)

Explanation / Answer

1a) The skeletal muscles are paralyzed after the blue-ringed octopus bite. The venom blocks the voltage gated sodium channels in the neural membranes. The venom consists of a neurotoxin tetrodotoxin or TTX that blocks movement of sodium ions across neural membranes. The neurotoxin attaches to the sodium channel receptor thereby blocking the sodium channels. The nerve impulses in myelinated nerve fibers are blocked causing paralysis of voluntary muscles. As a result, muscles of chest wall and diaphragm are affected causing respiratory failure. However, the heart keeps beating until extreme asphyxia sets in. The inability of TTX to cross the blood brain barrier prevents any effect on brain.

The purkinje fibers that are essential for maintaining the rhythm of the heart are affected by TTX only at higher concentration. When the octopus bites the animal, it takes a while for the TTX to reach the heart. Hence, initially its concentration is too low to cause any effect on the heart. There are two types of currents in these fibers: the slow and the fast currents. TTX blocks the channels through which fast currents work. However, it has no effect on the slow channels thorough which sodium or calcium ions can enter. Calcium ions would in that case substitute for sodium ions. Hence, in the initial phases of venom action, the slow channels are active in presence of TTX.

b) TTX does not pass through the blood brain barrier. Hence, it has no effect on the neurons of the brain.

TTX induces respiratory failure in the victims. This causes loss of oxygen to the heart and the brain. Respiratory failure induces ischemia in the heart and the brain. Paralysis of the respiratory musculature causes anoxia (no oxygen). Further, there is rapid and severe hypotension or low blood pressure is observed. The heart and the brain require oxygen to function. Lack of oxygen to these tissues induces failure of activity in them.

c) TTX has not anti dote. The octopus injects its toxin by biting. The swimmer can use an elastic bandage to tightly wrap or immobilize the bite area in limb or toe to prevent the spread of the venom. However, care must be taken so that circulation is not affected. This is a pressure immobilization technique. Mouth –mouth ventilation can be tried if the patient is having difficulty breathing.

Neostigmine (Prostigmin Bromide) and edrophonium (Enlon, Tensilon) that have been tried for tetrodotoxin intoxication. The patient must be transported to the hospital for further treatment.

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