Lesson 7 of 11 · 10 min
Transmission of impulses
NCERT §18.3.2
The command to run had to jump from one nerve cell to the next many times before it reached Meher's muscles. At each gap, electricity alone was not enough.
The lesson in notes
In short
Impulses pass from neuron to neuron at junctions called synapses. Each synapse is built from two membranes, one of the pre-synaptic neuron and one of the post-synaptic neuron; a gap, the synaptic cleft, may or may not lie between them.
There are two types of synapse: electrical and chemical.
At an electrical synapse the two membranes lie very close together and current flows directly from one neuron into the next. Transmission is much like conduction along a single axon, and is always faster than at a chemical synapse. Our body has few electrical synapses.
At a chemical synapse the membranes are separated by a fluid-filled synaptic cleft, and chemicals called neurotransmitters carry the signal across. The axon terminals contain vesicles filled with neurotransmitter.
When an impulse arrives at the axon terminal, it makes the synaptic vesicles move to the membrane, fuse with it and release neurotransmitter into the cleft.
The neurotransmitter binds specific receptors on the post-synaptic membrane. This opens ion channels; the ions that enter can set up a fresh potential in the next neuron.
The new potential may be excitatory or inhibitory.