Question

Neurons can communicate with other neurons via both gap junctions and synapses, but there are important differences between the two. Compare and contrast the structure and function of gap junctions and synapses.

Answer 1

At a synapse, one neuron sends a message to a target neuron which is another cell. At a chemical synapse, an action potential triggers the presynaptic neuron to release neurotransmitters. These molecules bind to receptors on the postsynaptic cell and make it more or less likely to fire an action potential. A chemical synapse is not a gap junction, because of the 20 to 40-nanometer distance that separates the presynaptic and postsynaptic neurons.

Gap junctions are aggregates of intercellular channels that permit direct cell-cell transfer of ions and small molecules. Initially described as low-resistance ion pathways joining excitable cells (nerve and muscle), gap junctions are found joining virtually all cells in solid tissues. Now a gap junction is called an electrical synapse in neurons and nerves. So an electric synapse is a specific type of gap junction, namely the electrically conductive link between two neighbouring neurons.  In a gap junction, cells are about 3.5 nanometers apart.