Synapse

Definition

A specialized junction between two excitable cells—typically neurons, or a neuron and an effector cell such as a muscle fiber—where signals are transmitted from one cell to another. Synapses may be chemical, involving the release of neurotransmitters across a narrow synaptic cleft, or electrical, employing gap junctions for direct ionic coupling. In arthropods, chemical synapses dominate the nervous system and are the principal targets of neurotoxic insecticides.

Etymology

From Greek synapsis, 'conjunction,' from syn- (together) + haptein (to fasten).

Example

In the escape response of a cockroach, giant interneurons form fast, reliable synapses with motor neurons in the thoracic ganglia, enabling millisecond-scale reaction to wind stimuli detected by cercal hairs.

Synonyms

• neural junction
• synaptic junction

Related Terms

• Neurotransmitter
• synaptic cleft
• Axon
• Dendrite
• ganglion
• neuromuscular junction
• gap junction

Usage Notes

In arthropod neurobiology, 'synapse' typically refers to chemical synapses unless specified otherwise; electrical synapses are less common in insects than in some other invertebrate groups. The term excludes non-junctional forms of neuronal communication such as ephaptic coupling or volume transmission. When describing arthropod neuroanatomy, 'synapse' is often used interchangeably with 'synaptic bouton' or 'synaptic terminal' in reference to the presynaptic specialization.