The junction (microscopic gap) between the axon of one neuron and the dendrite of other neuron or effector cell is termed as synapse.

Synapse has following parts

1. End bulb

An action potential proceed along an axon.  It reaches the end of the branching axon terminal is termed as end bulb.

2. Synaptic cleft

The gap between the end bulb and the dendrite of the next neuron is called synaptic cleft.

3. Presynaptic neuron

Such neuron carrying the action potential towards a synapse is called presynaptic neuron. The presynaptic cells are always a neurons.

4. Postsynaptic neuron

The receptive segment of the second neuron is known as postsynaptic neuron. The postsynaptic cell can be a neurons, gland cells, or muscle cells.

Types of synapses or Nature of synapses

Synapses can be

1. Electrical Synapse

In this type, positively charged ions travels from one neuron to the next neuron. Therefore, nerve impulse transmit directly from neuron to neuron. These positively charged ions depolarize the postsynaptic membrane. An electrical synapse can rapidly transfer impulses in both directions. These synapses are very common in fishes. Electrical synapses helps fishes to move away rapidly from the predators.

2. Chemical Synapse


In this type of synapse, two cells communicate by means of a chemical agent is called a neurotransmitter.

It is released by presynaptic neuron. A neurotransmitter changes the RP (resting potential) in the plasma membrane of the post-synaptic cell. It generates the action potential in the next cell. This cell continued the transmission of the nerve impulse.

Mechanism of action of neurotransmitters

1. Release of neurotransmitter

Impulse reaches at the end bulb. Nerve impulse stimulates the storage vesicles. These vesicles contains neurotransmitter. These vesicles intermix with the plasma membrane. The vesicles deliver the neurotransmitter by exocytosis into the synaptic cleft. The common neurotransmitters are

Acetylcholine and norepinephrine

More than 50 other neurotransmitters are known.

2. Stimulation of postsynaptic membrane

The neurotransmitters bind with receptor protein. These proteins are present in the photosynthetic membrane. Its causes depolarization in the presynaptic cell. The special enzyme acetylcholinesterase rapidly inactivates acetylcholine. On the other hand, if acetylcholine is not inactivated,  it continuously produces nerve impulses. It cause a disease. The active ingredients in most flea sprays and powders is parathion. It prevents the breaking of acetylcholine in the fleas. It cause disease in it & kill them.

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