Neuroscience · BEGINNER LESSON
Synapse
A synapse is a specialized contact point where one neuron communicates with another neuron, usually across a tiny gap called the synaptic cleft. It is measured by how signals are passed from a presynaptic side to a postsynaptic side using neurotransmitters and, in the receiving cell, receptors.
What it is
A synapse is the place where communication between neurons happens. One neuron’s axon, the long outgoing fiber that carries signals away from the cell body, comes very close to another neuron’s dendrite, the branch-like part that usually receives signals. The two sides are separated by a very small gap called the synaptic cleft. The sending side is called presynaptic, and the receiving side is called postsynaptic. [0,2]
[1] Reference Guide on Neuroscience - NCBI [3] Molecular Physiology of the Neuronal Synapse - PMC - NIH
How signaling works
When the presynaptic axon becomes active, it releases chemical messengers called neurotransmitters into the synaptic cleft. These molecules bind to matching receptors on the postsynaptic side, usually on the dendrite. This can make the receiving neuron more likely to fire, less likely to fire, or sometimes produce no obvious immediate change. Because many synapses can converge on one neuron, the final response is a sum of multiple inputs. [0,1,2]
[1] Reference Guide on Neuroscience - NCBI [2] Brain Synapses: Neurons, Astrocytes, and Extracellular ... - PMC [3] Molecular Physiology of the Neuronal Synapse - PMC - NIH
What happens inside the cells
Synaptic communication is partly electrical and partly chemical. Inside neurons, charged particles called ions move across the membrane, creating electrical currents that travel along the axon. At the presynaptic terminal, this activity can trigger neurotransmitter release. The release depends on organized protein machinery and, in modern descriptions, calcium-driven steps that control vesicle fusion and recycling. Vesicles are small membrane sacs that store neurotransmitters. [0,2]
[1] Reference Guide on Neuroscience - NCBI [3] Molecular Physiology of the Neuronal Synapse - PMC - NIH
Why synapses matter
Synapses are the main functional units of communication in the central nervous system. Their strength can change over time, a property called synaptic plasticity. This changing strength is part of learning and memory, and it depends on how release, receptors, and vesicle recycling are regulated. Some synapses also include support from astrocytes, a type of glial cell, so the structure can be more than just two neurons meeting. [1,2]
[2] Brain Synapses: Neurons, Astrocytes, and Extracellular ... - PMC [3] Molecular Physiology of the Neuronal Synapse - PMC - NIH
Limits and caveats
A synapse is not a simple on-off switch. The effect depends on many inputs, receptor types, and molecular steps, so the same general structure can produce different outcomes. Also, newer descriptions emphasize that synapses involve more than just a fixed gap: supporting cells, extracellular spaces, and vesicle recycling all shape how communication works. [0,1,2]
[1] Reference Guide on Neuroscience - NCBI [2] Brain Synapses: Neurons, Astrocytes, and Extracellular ... - PMC [3] Molecular Physiology of the Neuronal Synapse - PMC - NIH
SEE THE IDEA
How a synapse passes information
Sends the signal and can release neurotransmitters when active.
Tiny gap between the two cells where neurotransmitters diffuse.
Detects neurotransmitters and changes the receiving neuron’s response.
The receiving neuron may fire, be inhibited, or show no clear immediate change.
Signal flows from the presynaptic side across the cleft to the postsynaptic side, using chemicals as the messenger.
A synapse converts an electrical event in one neuron into a chemical message and then back into a cellular response in another neuron.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.