Figure 1. Principles of axon navigation. (a) Target area selection. (b) Topographical location. (c) Layer termination. Modified from Tessier-Lavigne and Goodman (1996).

Figure 2. Agrin-induced organization of the neuromuscular synapse. ACh, acetylcholine; MASC, muscle-associated specificity component; MuSK, muscle-specific kinase; p, phosphorylation site. Modified from Kleiman and Reichardt (1996).

Figure 3. Diffusion and trap model. Acetylcholine (ACh) receptors are floating in the postsynaptic muscle membrane, represented by an arrow attached to a filled circle. The size and direction of the arrow indicate the speed and direction of molecular movement. When the ACh receptor is in contact with the trap molecule by chance, it will be trapped and immobilized at the postsynaptic area (green).

Figure 4. Structure of the acetylcholine (ACh) receptor, which consists of five subunits: two , one , one (or ) and one . The subunit has an ACh-binding site. The channel opens when two ACh molecules bind to the receptor.

Figure 5. Maturation of the neuromuscular synapse. (a) Immature synapse. Note that receptor clusters are not necessarily associated with vesicle clusters in the presynaptic terminal. The synaptic current is smaller and slower compared with that in the mature synapse. (b) Mature synapse. A cluster of vesicles in the presynaptic terminal is aligned with postsynaptic receptor clusters, which are located at the mouth of secondary synaptic fold. The basement membrane is surrounding the postsynaptic cell.