State how the distribution of membrane proteins and organelles ensures that synaptic transmission is unidirectional.

Figure 1 shows the changes in membrane potential in a postsynaptic neurone after separate and rapid successive stimulations of a single presynaptic neurone, $X$.

Draw on this

Name and explain the type of summation shown in Figure 1.

Myasthenia gravis (MG) is an autoimmune disease where the body produces antibodies that block, alter, or destroy nicotinic acetylcholine receptors on the postsynaptic membrane of neuromuscular junctions.

Suggest and explain how MG causes muscle weakness. Do not include details of myofibril movement or muscle contraction in your answer.

Pyridostigmine is a drug used to treat MG. It acts as a reversible inhibitor of the enzyme acetylcholinesterase in the synaptic cleft.

Explain how pyridostigmine can help in the treatment of MG.