What Is a Synapse?

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A synapse is a small gap at the end of a neuron that allows a signal to pass from one neuron to the next. Synapses are found where nerve cells connect with other nerve cells. The term synapse was first introduced in 1897 by physiologist Michael Foster in his Textbook of Physiology and is derived from the Greek synapsis, meaning "conjunction."

What Do Synapses Do?

When a nerve signal reaches the end of the neuron, it cannot simply continue to the next cell.

Instead, it must trigger the release of neurotransmitters which can then carry the impulse across the synapse to the next neuron.

Once a nerve impulse has triggered the release of neurotransmitters, these chemical messengers cross the tiny synaptic gap and taken up by specialized receptors on the surface of the next cell. These receptors act much like a lock and the neurotransmitters function much like a key. This process then converts the chemical signal back into an electrical signal. If the signal is strong enough, it will be propagated down the next neuron by an action potential until it once again reaches a synapse and the process is repeated once more.

The Parts of the Synapse

Synapses are composed of three main parts:

  • The presynaptic ending that contains neurotransmitters
  • The synaptic cleft between the two nerve cells
  • The postsynaptic ending that contains receptor sites

An electrical impulse travels down the axon of a neuron and then triggers the release of tiny vesicles containing neurotransmitters.

These vesicles will then bind with the membrane of the presynaptic cell, releasing the neurotransmitters into the synapse. These chemical messengers cross the synaptic cleft and connect with receptor sites in the next nerve cell, triggering an electrical impulse known as an action potential.

Different Types of Synapses

There are two main types of synapses:

The first is the chemical synapse in with the electrical activity in the presynaptic neuron triggers the release of chemical messengers. The neurotransmitters diffuse across the synapse and bind to the specialized receptors of the postsynaptic cell. The neurotransmitter then either excites or inhibits the postsynaptic neuron. Excitation leads to the firing of an action potential while inhibition prevents the propagation of a signal.

However, there are also electrical synapses in which two neurons are connected by specialized channels known as gap junctions. Electrical synapses allow electrical signals to travel quickly from the presynaptic cell to the postsynaptic cell, rapidly speeding up the transfer of signals. The gap between electrical synapses is much smaller than that of a chemical synapse (about 3.5 nm compared to 20 nm). The special protein channels that connect the two cells make it possible for the positive current from the presynaptic neuron to flow directly into the postsynaptic cell.

Electrical synapses transfer signals much faster than chemical synapses. While the speed of transmission in chemical synapses can take up to several milliseconds, the transmission at electrical synapses is nearly instantaneous.

Where chemical synapses can be excitatory or inhibitory, electrical synapses are excitatory only.

While electrical synapses have the advantage of speed, the strength of a signal diminishes as it travels from one cell to the next. Because of this loss of signal strength, it requires a very large presynaptic neuron to influence a much smaller postsynaptic neurons. Chemical synapses may be slower, but they can transmit a message without any loss in signal strength. Very small presynaptic neurons are also able to influence even very large postsynaptic cells.

More Psychology Definitions: The Psychology Dictionary


Freberg, L.A. (2010). Discovering biological psychology, Second edition. Belmont, CA: Wadsworth, Cengage Learning.

Freberg, L.A. (2016). Discovering behavioral neuroscience. Boston: Cengage Learning.

Tansey, E.M. (1997). Not committing barbarisms: Sherrington and the synapse, 1897. Brain Research Bulletin, 44,(3), 211–212. doi:10.1016/S0361-9230(97)00312-2.

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