The deathstalker scorpion, Leiurus quinquestriatus, is one of the most dangerous scorpions on Earth. Its venom contains charybdotoxin, a neurotoxin that binds to voltage-gated potassium (K+\text{K}^+K+) channels in the axon membrane.
Using this information, explain how charybdotoxin affects the electrical activity of neurones during an action potential.
A severe symptom of deathstalker scorpion stings is respiratory distress due to paralysis of the diaphragm. Explain how paralysis of the diaphragm leads to a lack of ventilation in the lungs.
Charybdotoxin also prevents the repolarisation of cardiac muscle cells, causing myocardial hyperexcitation and uncoordinated contractions of the heart chambers. Suggest and explain the effect this would have on the ability of the heart to maintain systemic blood pressure.
Some invertebrates, such as the giant squid (Loligo forbesii), rely on exceptionally wide, unmyelinated axons to conduct nerve impulses. Why is the conduction velocity of action potentials along an unmyelinated axon significantly slower than along a myelinated axon of a similar diameter?
22 exam-style questions on OCR A A Level Biology Neuronal communication. Each one has a worked solution and a mark scheme showing where the marks go.