A presynaptic neuron is the neuron that sends a signal across a synapse by releasing neurotransmitters from its axon terminal. In Intro to Brain and Behavior, it is the sending cell in chemical communication between neurons.
A presynaptic neuron is the sending neuron at a synapse in Intro to Brain and Behavior. It does not directly “touch” the next neuron with the signal. Instead, it converts an electrical impulse into a chemical message by releasing neurotransmitters from its axon terminals.
Here is the sequence. An action potential travels down the axon and reaches the presynaptic terminal. That depolarization opens voltage-gated calcium channels, calcium flows into the terminal, and the calcium signal triggers synaptic vesicles to fuse with the presynaptic membrane. The neurotransmitter is then released into the synaptic cleft, the tiny gap between neurons.
After release, the neurotransmitter diffuses across the cleft and binds to receptors on the postsynaptic neuron. That binding can make the next neuron more likely to fire, less likely to fire, or change how it responds to later input. The presynaptic neuron is the side that controls the amount and timing of transmitter release, so it has a lot of influence over whether the message is strong, weak, fast, or short-lived.
This is why the presynaptic neuron matters in synaptic transmission. The same neurotransmitter can have different effects depending on how often the presynaptic neuron fires, how much calcium enters, and how many vesicles are available for release. A fast burst of firing can increase transmitter release, while fatigue or feedback can reduce it.
A common mistake is thinking the presynaptic neuron is the one that receives the message. It is actually the sender. In a simple diagram, look for the axon terminal, the vesicles, and the synaptic cleft. Those features usually mark the presynaptic side.
Drugs and toxins often act here too. Some change neurotransmitter release at the presynaptic terminal, while others interfere with receptors on the other cell. That is why this term comes up not only in basic neuron diagrams but also in discussions of medication effects, brain signaling, and disorders tied to altered communication between neurons.
The presynaptic neuron is the starting point for chemical signaling in the nervous system, so this term shows up anytime the course moves from “a neuron fires” to “another cell responds.” It gives you the before part of the before-and-after story: action potential first, neurotransmitter release second, receptor binding after that.
That sequence is the backbone of topics like neurotransmitters, synapses, and brain-based behavior. If you are trying to explain how dopamine, GABA, or acetylcholine changes behavior, you need to know where the signal begins and how the presynaptic cell controls release. The same is true when you compare fast signaling with slower modulatory effects.
This term also helps with real course examples. If a lab image shows vesicles clustered near a membrane, or a quiz asks what happens when calcium enters a terminal, you are working with the presynaptic neuron. If a case study describes a drug that changes transmitter release, you need to trace the effect back to the presynaptic side.
It also sets up the logic of many neurological and psychiatric treatments. Some medications reduce transmitter release, some increase it, and some change how long the signal lingers in the synapse. Without the presynaptic neuron, those effects look like isolated facts instead of one connected communication system.
Keep studying Intro to Brain and Behavior Unit 2
Visual cheatsheet
view gallerySynapse
The presynaptic neuron is one side of the synapse. The synapse is the full communication site, including the sending cell, the synaptic cleft, and the receiving cell. When you identify a synapse in a diagram, the presynaptic neuron is the cell with the axon terminal that releases neurotransmitters into the gap.
Neurotransmitter
Neurotransmitters are the chemical messengers the presynaptic neuron releases. The presynaptic cell determines when and how much neurotransmitter enters the synaptic cleft, which affects the strength of the signal. In class examples, you often trace behavior or drug effects by following what happens to the neurotransmitter after release.
Postsynaptic neuron
The postsynaptic neuron is the receiving cell. It has receptors that respond to neurotransmitters released by the presynaptic neuron. Comparing the two is a common way to make synaptic transmission clearer, because one side sends the signal and the other side changes its activity in response.
Ionotropic Receptors
Ionotropic receptors are one of the main ways the postsynaptic neuron responds after the presynaptic neuron releases neurotransmitters. They open quickly and can change the postsynaptic membrane potential fast. That makes them a useful contrast with the presynaptic step, which is about release rather than reception.
A quiz question might show a neuron diagram and ask you to label the presynaptic side, or it may describe calcium entering an axon terminal and ask what happens next. You should be able to trace the process from action potential to vesicle release to neurotransmitter binding. In short-answer responses, use the term when you explain why a signal starts in one neuron and changes activity in another.
If you get a case about a drug, toxin, or disorder, check whether the effect happens before the neurotransmitter reaches the receptor. If so, you are probably dealing with the presynaptic neuron. That distinction is useful in lab write-ups, too, especially when you describe synaptic transmission step by step rather than just naming the molecules involved.
These two are easy to mix up because both are part of the same synapse. The presynaptic neuron sends the chemical message by releasing neurotransmitters, while the postsynaptic neuron receives that message through receptors. A quick memory trick is this: pre means before, so the presynaptic cell comes first in the signaling chain.
The presynaptic neuron is the sending neuron at a synapse, and it releases neurotransmitters from its axon terminal.
Its signal is triggered when an action potential reaches the terminal and calcium enters the cell.
This is the step that turns electrical activity into chemical communication between neurons.
The presynaptic neuron controls how much neurotransmitter is released, which affects the strength and timing of the signal.
When you study synaptic transmission, look for the presynaptic neuron whenever the question focuses on release, calcium, or vesicles.
It is the neuron that sends the signal at a synapse by releasing neurotransmitters from its axon terminal. In this course, it is part of the chemical communication system that links one neuron to the next. The presynaptic cell starts the process, and the postsynaptic cell responds.
An action potential reaches the axon terminal, which opens calcium channels. Calcium enters the terminal and triggers vesicles to fuse with the membrane, releasing neurotransmitters into the synaptic cleft. That release is the chemical step that lets the message cross to the next cell.
The presynaptic neuron sends the message, and the postsynaptic neuron receives it. The presynaptic side releases neurotransmitters, while the postsynaptic side has receptors that detect them. If you are looking at a diagram, the presynaptic neuron is usually the axon terminal side and the postsynaptic neuron is the receiving side.
A drug or toxin can change how much neurotransmitter is released or how long it stays available in the synapse. That can strengthen, weaken, or block communication between neurons. In brain and behavior topics, this is one way medications and poisons can change mood, movement, or cognition.