Question

What is a synapse? How does the nerve impulse cross the synapse?

Answer 1

A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron. There are two types of synapses- electrical synapses and chemical synapses. Neurotransmitters are the chemicals which are involved in the transmission of nerve impulses across chemical synapses. These chemicals do not participate in the transmission of nerve impulses at electrical synapses.

When a wave of depolarisation reaches the pre-synaptic membrane, calcium channels, open up. Due to the opening of calcium channels, $C{a}^{2+}$ diffuse inside the cytoplasm of synaptic knob from the extracellular fluid. The $C{a}^{2+}$, in some way stimulate the movement of synaptic vesicles towards the pre-synaptic membrane. Thereafter, the membrane, of synaptic vesicles fuses with the plasma membrane of synaptic knob, i.e., pre-synaptic membrane, resulting in the rupture of the synaptic vesicles. This results in the release of neurotransmitters in the synaptic cleft. These released neurotransmitters rapidly pass to the other side of the gap. These released neurotransmitters bind to their specific receptors present on the post-synaptic membrane. This binding opens the ion channels in the post-synaptic neuron, allowing the entry of ions. This entry of ions generates a new potential or nerve impulse in the post-synaptic neuron.