The Nervous System

Prokaryotes

Continuing our practice of giving extra emphasis to certain crucial MCAT topics in these discussions, let us discuss synaptic transmission of nerve impulses. Synaptic transmission involves the passage of electrical or chemical transmission from the axon of a presynaptic neuron to the dendrite of a postsynaptic neuron across the synapse, the junction between the two. Most students are plenty aware of chemical synapses, making the MCAT writers likely to introduce the electrical synapse in a passage. The plasma membranes are in contact in an electrical synapse, sharing cytoplasm through gap junctions, but in a chemical synapse, the plasma membranes are separated by the synaptic cleft, in which neurotransmitters are released and diffuse across this space from the presynaptic cell membrane to the postsynaptic membrane.