Introduction 
postsynaptic cell 
Action potential 
triggers entry of 
calcium ions (Ca^*) 
into the presynaptic 
terminal 
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Synaptic vesicles 
fuse with the presynaptic 
membrane, releasing 
transmitter. 
The transmitter binds to proteins 
in the postsynaptic membrane, 
changing their conformation and 
either opening an ion channel or 
activating a second messenger 
system within the postsynaptic cell 
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The transmitter is removed 
from the synaptic cleft, and 
the postsynaptic receptors 
revert to their original 
conformation. 
Figure 7. A summary of the essential events at a chemical synapse following the arrival of an action potential in the axon 
terminal. 
Adapted from Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K., and Watson, J. D. 1989. Molecular Biology of the Cell, 2nd 
edition. New York: Garland, p. 1077. 
Figure 8. A: A section of human skin stained with an anti- 
body against the protein keratin. Note how the cells are 
packed together to form the distinctive structure of skin. The 
dark structures within each cell are the nuclei that do not 
contain keratin and so are not labeled. 
B: A fluorescence micrograph showing the presence of kera- 
tin filaments in cultured skin cells. The keratin filaments 
have been revealed by a fluorescently labeled antibody 
against the keratin protein. 
Courtesy of Elaine V. Fuchs. 
