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The messages are transmitted in the form of electrical impulses along the fibres of the neurons.
The impulse is received by the dendrites and passed through the cell body to the axon. An impulse is an electrical disturbance.
All along the nerve fibre, the cytoplasm is more electronegative than the outside and is thus having a potential. This is due to the differential distribution of sodium and potassium ions across the membrane. This potential is called the resting potential. When the dendrite receives the neurotransmitters, they change the properties of the cell membrane which in turn changes the distribution of the ions across the membrane.
This results in a different potential called the action potential. The change in potential is then transmitted along the neuron to the ends of the axon. Here, the impulse induces the release of the neurotransmitter. In this manner, the message is transmitted as a wave of impulse along the lengths of connecting neurons.
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An instrument called electro encephalograph can record electrical activity of brain. The activity of the brain is recorded as electric potentials. Such a record is called electro encephalogram (EEG). By placing two electrodes on the scalp and leading via suitable amplifier to ink-writing device, a record of four different types of waves is obtained. These waves are named as alpha, beta, delta and theta. They vary in their frequency. These waves give the characteristic activity of the brain and that is very useful for clinical purposes.
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The junction between the axon and the dendrites of the next neuron is called the synapse. At the synapse, the axon fibres and dendrites are not in direct contact. The space between them is called synaptic cleft. Within the axons are synaptic vesicles having chemicals called nuerotransmitters. The impulses that reach the ends of the axon fibres make the vesicles release these chemicals into the synaptic cleft. The chemicals reach the dendrites of the next neuron. This sets up a new impulse which is transmitted to the axon. The speed of transmission is about 120 m/s.
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