What is the effect of an excitatory neurotransmitter?

An excitatory neurotransmitter is responsible for increasing the likelihood that a neuron will fire an action potential, which is the fundamental mechanism for transmitting signals in the nervous system. These neurotransmitters achieve this by binding to specific receptors on the postsynaptic neuron, leading to depolarization of the neuron's membrane. This depolarization occurs because excitatory neurotransmitters often cause the influx of positively charged ions, such as sodium, which increases the overall positive charge within the neuron. When the membrane potential reaches a certain threshold, an action potential is generated, resulting in neuronal firing.

The role of excitatory neurotransmitters is crucial for various brain functions, including learning and memory, as they enhance communication between neurons. Thus, the correct choice reflects the fundamental process of excitatory transmission in the nervous system.