Final answer:
More neurotransmitter release from a presynaptic neuron can modify the likelihood of an action potential in the postsynaptic neuron. This change depends on whether the neurotransmitter is excitatory, causing depolarization, or inhibitory, causing hyperpolarization. The effects persist until the neurotransmitter is cleared from the synapse.
Step-by-step explanation:
If a presynaptic neuron releases more of a neurotransmitter, it can increase or decrease the probability of the postsynaptic neuron firing an action potential, depending on whether the neurotransmitter is excitatory or inhibitory.
The synapse is a complex structure where the transmission of nerve impulses between neurons, or from neurons to other cells like muscles, takes place. When a neuron fires an action potential, it causes the synaptic vesicles in the presynaptic neuron to release neurotransmitters into the synaptic cleft. These molecules then bind to receptors on the postsynaptic neuron, leading to changes in its membrane potential. If the neurotransmitter is excitatory, such as acetylcholine, it will generate an excitatory postsynaptic potential (EPSP) and may cause the postsynaptic neuron to also fire an action potential if the depolarization reaches a certain threshold.
On the other hand, inhibitory neurotransmitters like GABA cause inhibitory postsynaptic potentials (IPSPs) by opening Cl- channels and hyperpolarizing the membrane, thus making it less likely to fire. An excess of neurotransmitter can lead to a prolonged effect, either excitatory or inhibitory, on the postsynaptic neuron until it is cleared from the synaptic cleft by diffusion, degradation, or reuptake.