Synapse

Synapse (syn: together, apse: gap/window) is the point of contact between the terminal branches of the axon of a neuron with the dendrites of another neuron separated by a fine gap.

or

The junction between two nerve cells having a minute gap called synaptic cleft through which nerve impulse is transmitted by neurotransmitters is called synapse.

• Synapse = gap junction between two nerve cells, allowing impulse transmission via a neurotransmitter bridge.
• Two types — Electrical (direct, via gap junctions, cardiac/smooth muscles) | Chemical (via neurotransmitters, in PNS, CNS, neuromuscular junction).
• Chemical Synapse Steps — Impulse arrives → Ca²⁺ influx → synaptic vesicles release neurotransmitters (exocytosis) → bind postsynaptic receptors → excitatory/inhibitory response → cholinesterase destroys neurotransmitter → ready for new impulse.
• Chemical Synapse — Gap = 20–40 nm, Unidirectional, Slower.
• Electrical Synapse — Gap = 3.8 nm, Bidirectional, Faster, Found where the quickest response is needed (e.g. defence reflexes).