SYNAPSE

PRERNA FOR IAS

SYNAPSE

1. Synapse (Definition)

A synapse is the functional junction between two neurons or between a neuron and an effector such as a muscle or gland. It is the site where nerve impulses are transmitted from one cell to another, allowing communication throughout the nervous system. Most synapses in the human body are chemical synapses that use neurotransmitters to carry signals across a small gap called the synaptic cleft. Electrical synapses also exist, where impulses pass directly through gap junctions. Synapses play a vital role in movement, sensation, learning, memory, and reflexes by ensuring rapid and accurate communication between nerve cells.

2. Structure of Chemical Synapse

A chemical synapse consists of a presynaptic terminal, synaptic cleft, and postsynaptic membrane. The presynaptic terminal is the end of the axon and contains synaptic vesicles filled with neurotransmitters. Voltage-gated calcium channels are present in the presynaptic membrane and open during nerve impulse transmission. The synaptic cleft is a narrow gap, about 20–40 nanometres wide, separating the two neurons. The postsynaptic membrane contains receptor proteins that bind neurotransmitters and initiate a new electrical signal. This organized structure allows efficient, controlled, and one-way transmission of nerve impulses between neurons or from neurons to muscles and glands.

3. Transmission of Nerve Impulse (Chemical Synapse)

Transmission across a chemical synapse begins when an action potential reaches the presynaptic terminal. This opens voltage-gated calcium channels, allowing calcium ions to enter the neuron. The calcium influx causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft. These neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane. Binding opens ion channels, producing a new electrical impulse in the receiving cell. Finally, neurotransmitters are removed by enzymatic breakdown or reuptake into the presynaptic neuron, ensuring the signal ends and the synapse is ready for the next impulse.

4. Key Facts