Describe three different ways that chemical transmission at the synapse results in more complexity than action potentials along an axon.

Question

What will be an ideal response?

Answer 1

Neurotransmitters are not all-or-none events. Instead, neurotransmitters can have effects that vary in intensity and duration, which contributes to complexity in the nervous system. For example, once released into the synapse, the action of a neurotransmitter can be limited through removal of the neurotransmitter from the synapse, which can occur through enzymes that break down the neurotransmitter, reuptake of the neurotransmitter, or absorption by glial cells. The amount of neurotransmitter that is released into a synapse can be modified through axoaxonic synapses, so that inhibitory or excitatory signals from other neurons can impact the amount of calcium that comes into the axon terminal, and thus the amount of neurotransmitter that is released once an action potential reaches the axon terminal. Autoreceptors on a presynaptic neuron can also detect the amount of neurotransmitter in a synapse and adjust release based on this. Glial cells can release gliotransmitters, which can alter release of neurotransmitter by the presynaptic neuron or responses by the postsynaptic neuron. Not all neurotransmitters have the same effects on postsynaptic neurons; some are inhibitory, reducing the chances of an action potential occurring, and others are excitatory, increasing the chances of an action potential occurring. Even the same neurotransmitter can have different effects at different receptors. Through spatial and temporal summation, where the inputs from even thousands of different neurons over a period of time can be added together, any one neuron's activity can be impacted by stimulation or inhibition coming from multiple different sensory inputs. In addition, ionotropic receptors respond quickly to neurotransmitters with direct opening of ion channels, while metabotropic receptors respond more slowly and have less direct impact on ion channels.