Outline the structural similarities between a neuromuscular junction and a cholinergic synapse.
ATP hydrolysis during muscle contraction liberates inorganic phosphate ($P_i$). In the sarcoplasmic reticulum, calcium ions ($\text{Ca}^{2+}$) can combine with $P_i$ to form insoluble calcium phosphate. This may mean that fewer power strokes occur in sarcomeres. Suggest why calcium phosphate formation in the sarcoplasmic reticulum may result in fewer power strokes occurring in sarcomeres.
Adrenaline is a hormone that can influence muscle contraction. It attaches to G-protein-coupled receptors on T-tubule membranes. The signalling pathway triggered by adrenaline is similar to the one in liver cells when glucagon binds. Fig. 7.1 gives an outline of the cell signalling pathway of adrenaline. Identify the molecules represented by A and B in Fig. 7.1.