In the central nervous system , a synapse is a small space at the end of a neuron that allows a signal to travel from one neuron to another. Synapses are the place where nerve cells connect with other nerve cells.
The term "synapse" was first coined in 1897 by physiologist Michael Foster in his Physiology Textbook and is derived from the Greek word " synapse " which means "connection."
What synapses do
When a nerve signal reaches the end of a neuron, it cannot just move on to the next cell. Instead, it must trigger the release of neurotransmitters, which can then transmit an impulse across the synapse to the next neuron.
Once a nerve impulse has triggered the release of neurotransmitters, these chemical messengers cross the small synaptic gap and are accepted by receptors on the surface of the next cell.
These receptors act like locks, while neurotransmitters act like keys. Neurotransmitters can excite or suppress the neuron with which they bind.
Think of a nerve signal as an electrical current and neurons as wires. Synapses are plugs or junction boxes that connect power to a lamp (or other electrical device of your choice), allowing the lamp to turn on.
Parts of the synapse
Synapses have three main parts:
- Presynaptic terminal containing neurotransmitters.
- Synaptic cleft between two nerve cells
- Postsynaptic terminal containing receptor sites
An electrical impulse travels along the axon of the neuron and then triggers the release of tiny vesicles that contain neurotransmitters. These vesicles then bind to the presynaptic cell membrane, releasing neurotransmitters at the synapse.
These chemical messengers cross the synaptic cleft and bind to receptors on the next nerve cell, producing an electrical impulse known as an action potential.
There are two main types of synapses:
- Chemical synapses
- Electrical synapses
At a chemical synapse, the electrical activity of a presynaptic neuron triggers the release of chemical messengers, neurotransmitters.
Neurotransmitters diffuse along the synapse and bind to specialized receptors on the postsynaptic cell.
The neurotransmitter then excites or suppresses the postsynaptic neuron. Excitation triggers the action potential, while inhibition inhibits the propagation of the signal.
In electrical synapses, two neurons are connected by specialized channels known as gap junctions.
Electrical synapses allow electrical signals to travel rapidly from the presynaptic cell to the postsynaptic cell, rapidly accelerating signal transmission.
Special protein channels connecting the two cells allow positive current from the presynaptic neuron to flow directly to the postsynaptic cell.
Space between: 20 nanometers
Speed: a few milliseconds
No loss of signal strength
Exciting or inhibitory
Space between: 3.5 nanometers
Speed: almost instantaneous
Signal strength decreases
The gap between electrical synapses is much smaller than that of a chemical synapse (approximately 3.5 nanometers versus 20 nanometers).
Electrical synapses transmit signals much faster than chemical ones. While the rate of transmission at chemical synapses can be as low as a few milliseconds, transmission at electrical synapses is almost instantaneous.
Although electrical synapses have a speed advantage, the intensity of the signal decreases as it travels from one cell to another. Due to this loss of signal intensity, a very large presynaptic neuron is required to affect much smaller postsynaptic neurons.
Chemical synapses may be slower, but they can transmit a message without losing signal intensity. Very small presynaptic neurons are also capable of influencing even very large postsynaptic cells.
Where chemical synapses can be excitatory or inhibitory, electrical synapses are excitatory only.