A synapse is the junction between two neurons that allows a signal to pass between them. Neurons are cells that transmit information between your brain and other parts of the central nervous system. Synapses are found where neurons connect with other neurons.

Function of Synapses

Synapses connect neurons and help transmit information from one neuron to the next. They pass sensory signals such as pain or touch from the nervous system to the brain, and they help you move the muscles in your body. They are also involved in memory processing and storage.

Types

There are two main types of synapses:

• Chemical synapses
• Electrical synapses

Chemical Synapses

In a chemical synapse, the electrical activity in the presynaptic neuron triggers the release of chemical messengers, the neurotransmitters. Most synapses are chemical.

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 electrical impulse known as an action potential, while inhibition prevents the propagation of a signal.

Chemical 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

Electrical Synapses

In electrical synapses, 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 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

The gap between electrical synapses is much smaller than that of a chemical synapse (about 3.5 nanometers⁸ compared to 20 nanometers).

Electrical synapses transfer signals much faster than chemical synapses.⁹ While the speed of transmission in chemical synapses can take up to several milliseconds, the transmission at electrical synapses is nearly instantaneous.

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 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.

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