Figure 1. Neuromuscular synapse.

Figure 2. The triune receptor concept, describing neurotransmitter receptors as signal converters turning an extracellular signal into an intracellular effect.

Figure 3. The nicotinic acetylcholine receptor. (a) Electron-microscopic picture of the membrane bound receptor (left: longitudinal section; right: cross-section showing the pentameric structure. (b) Schematic of the receptor protein showing the pentameric complex in its membrane environment (left) and a summary of the known functional domains (right): the helices depict the wall of the ion channel proper; the ellipses represent the location of the ligand-binding sites at the interface between subunits. (c) Schematic representation of the transmembrane folding of the receptor subunits: M1–M4 represent the four membrane-spanning sequences connected by extramembrane loops. N and C are the N- and C-termini, respectively, of the polypeptide chain.

Figure 4. Schematic representation of AChR aggregation in the postsynaptic membrane triggered by agrin. Synaptic differentiation involves at least five steps: (1) redistribution of AChRs, which are initially distributed on the entire myotube surface, to the subsynaptic part of the postsynaptic membrane; (2) increased transcription by synaptic nuclei of mRNAs encoding AChR subunits; (3) decreased transcription by extrasynaptic nuclei; (4) rearrangement of membrane cytoskeleton; (5) retrograde signal from the postsynaptic to the presynaptic side. ‘AAAA’ indicates polyadenylation. Reproduced from Hoch, (1999), with permission from the author.