Site author Richard Steane
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Passage of nervous impulses

1) Along the axon/dendron

Electrochemical impulses: - partly electrical in nature, so can be detected by electronic methods (electrodes connected to amplifiers & oscilloscopes etc): also the basis for ECG, EEG and electrical stimulation of muscles; also explains electrocution!

- partly chemical in nature, so very different from current passing down conductor, as in mains electricity/telephone systems.

The nervous impulse is a change in potential (voltage) resulting from wave of change in membrane permeability which travels at a steady speed, but is not instantaneous.

Nerve fibres (axons and dendrons) are in a state of readiness to pass impulses due to a small electrical potential (only millivolts) caused by an imbalance of Na+ & K+ ions in the cytoplasm of the fibre (compared with fluid outside). These ions are moved by active transport (Na+ pumped out of cytoplasm), so energy is required (from respiration) to set up the potential in the first place.

2) Between neurones

The impulse arriving at the end of the axon of the first cell cause the release of a neurotransmitter substance from vesicles fusing with cell membrane.

The neurotransmitter substance diffuses into synaptic cleft (i.e. gap) towards the second cell.

When the neurotransmitter substance is detected by the second cell, an impulse (as above) may* be generated in the axon leading out of that cell.
*depending on the number/type of impulses
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