A striated muscle cell (muscle fibre) contracts after stimulation by a motor neurone at a neuromuscular junction. Air temperature can influence the temperature of striated muscle cells. Investigations have shown that the efficiency of contraction of striated muscle cells falls as air temperature falls. Suggest reasons why lower temperature can reduce the efficiency of contraction of striated muscle cells.
The greater blue-ringed octopus, $Hapalochlaena\ lunulata$, secretes tetrodotoxin (TTX). TTX is a neurotoxin. If a mammal is bitten by this octopus, TTX can lead to the death of the mammal. Fig. 7.1 shows a greater blue-ringed octopus. TTX attaches to voltage-gated sodium ion channels in the axon of a neurone and alters the tertiary structure of the channel protein. Suggest how TTX may affect the functioning of a motor neurone.