Nerve Firing Questions Key

Baronet Despard Murgatroyd has been found dead in his library. There is no sign of violence, but his body is contorted, his muscles stiff and contracted, and his face frozen in a grimace of terror. The detective suspects poison, and has come up with a list of four possible poisons. Evaluate them and explain why you think they could or could not have caused the baronet's death.

a. Tetrodotoxin would stop all nerve firing by blocking Na+ gates. This would leave him limp, not contorted.

b. an injection of Potassium would raise resting potential, making the neurons fire more easily. If it raised resting potential above threshold, the neurons would fire once and be unable to ‘reset’ themselves. Potassium also can cause pain at the injection site, which might explain his grimace.

c. Acetylcholinesterase inhibitor is most likely. This slows down the destruction of acetylcholine at the synapse, so the muscles keep firing and contracting.

d. epinephrine could have killed him by speeding up his heart too much or raising his blood pressure too high. It doesn’t have a direct effect on skeletal muscle contraction, though.