Biological Systems MCAT Practice Exam

What is the role of gap junctions in electrical synapses?

1. Unidirectional flow of impulse

2. Bidirectional flow of impulse

3. Fast axonal transport

4. Neurotransmitter release

The correct answer is: Bidirectional flow of impulse

Gap junctions play a crucial role in electrical synapses by allowing the direct passage of ions and small molecules between adjacent cells, facilitating communication. This structure enables a bidirectional flow of impulses because the electrical signals can move freely in both directions across the junction. In contrast, other types of synapses, such as chemical synapses, typically involve neurotransmitter release, which is unidirectional: the signal is initiated in the presynaptic neuron and is received by the postsynaptic neuron after the neurotransmitter is released into the synaptic cleft. The statement regarding fast axonal transport pertains to the movement of materials along the axon but does not involve the rapid electrical communication afforded by gap junctions. Understanding this allows one to appreciate how electrical synapses enable quick, coordinated responses in certain tissues, such as cardiac and some smooth muscle cells, where synchronized contraction is vital. This contrasts with the slower signaling seen in chemical synapses, emphasizing the importance of gap junctions in enabling fast and reliable communication between excitable cells.