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Explain how a series of impulses are initiated and transmitted along a neurone and across a synapse.

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Introduction

Explain how a series of impulses are initiated and transmitted along a neurone and across a synapse. When a neurone is stimulated the permeability of the cell surface membrane to sodium ions changes. Sodium channels open allowing Na+ ions to diffuse into the axon of the nerve cell. The large influx of Na+ ions reverses the potential difference across the membrane creating a highly positive area within the axon with respect to the outside. ...read more.

Middle

The time required for this to happen is known as the refractory period. The nerve cannot carry another impulse until this has occurred, ensuring the impulse only travels in one direction. The movement of the wave of depolarisation down the axon of the nerve results in local currents being set up. Positive Na+ ions are attracted to the negative region of the action potential leaving the membrane in this region slightly negative. ...read more.

Conclusion

Calcium channels in the presynaptic membrane open allowing the calcium ions to diffuse into the synaptic knob. These Ca2+ ions cause the vesicles in the synaptic knob to fuse with the presynaptic membrane and release transmitter substance into the synaptic cleft. The transmitter substance then diffuses across the synaptic cleft and binds with receptor sites on the postsynaptic membrane. Sodium channels on the postsynaptic membrane open and allow and influx of Na+ ions into the cell. This creates an action potential which travels down the axon of the nerve. ...read more.

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