Transmission of impulses | Conduction of nerve impulse through a chemical synapse | Synaptic cleft | Types of synapses | Transmission of nerve impulse through synapse

HomeTypes of synapses Transmission of impulses | Conduction of nerve impulse through a chemical synapse | Synaptic cleft | Types of synapses | Transmission of nerve impulse through synapse

The junction between two neurons, across which the impulse passes from one neuron to the next is called synapse. A typical synapse consists of a bulbous expansion of a nerve terminal called a pre-synaptic knob lying close to the membrane of a dendrite. The cytoplasm of the synaptic knob contains numerous synaptic vesicles. Each vesicle contains neurotransmitter (chemical substance). The membrane of the synaptic knob nearest to the synapse forms the pre-synaptic membrane. The membrane of the dendrite is called the post-synaptic membrane. These membranes are separated by a gap, the synaptic cleft.

The post synaptic membrane contains receptor sites for neurotransmitter. The two main neurotransmitters in vertebrate nervous system are acetylcholine (ACh) and noradrenaline although other neurotransmitters also exist.

There are two types of synapses namely.

1- Electrical synapses:- the membranes of pre-synaptic and post-synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses. Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. Electrical synapses are rare in our system.

2- Chemical synapses :- the membranes of the pre-synaptic and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses.

The axon terminals contain vesicles filled with these neurotransmitters. When an impulse arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.

Originally published at https://www.thebioquick.com.