The black mamba’s toxin kills prey by preventing their breathing. It does this by inhibiting the enzyme acetylcholinesterase at neuromuscular junctions. Use your knowledge of muscle contraction to explain how this prevents breathing.

By inhibiting the enzyme acetylcholinesterase, the neurotransmitter acetylcholine does not get broken down. This causes acetylcholine to build up in the synapse between the motor neurones and muscles of respiration (also known as the neuromuscular junction. This in turn causes the acetyl choline to stay bound to its receptor on the sarcolemma (the outer membrane of the muscle cells). This causes the sarcolemma to continue to remain in its depolarised state as sodium ions continue to cross the membrane. This continued depolarisation prevents the respiratory muscles from relaxing and maintains them in a contracted state, thus preventing breathing and causing death of the prey.