The transmission of nerve impulses

Neurones are responsible for neurotransmission, the conduction of electrochemical impulses throughout the nervous system. Neurone activity is provoked by:

• mechanical stimuli — touch and pressure

• chemical stimuli — from external chemicals or from a chemical released by the body such as histamine.

Nerve impulses are caused by chemical changes in the cell body. Chemical compounds generate electrical charges called ions. Inside the nerve cell body there are potassium ions which cause a negative charge in the cell but outside of the cell are sodium ions which are positively charged.

Whenever there is a change of pressure, temperature or a chemical stimuli a section of the nerve membrane becomes permeable to sodium and the positively charged ions flow in, leaving the outside of the membrane negative. The combination of the negative potassium ions and the positive sodium ions causes an electrical charge which creates the impulse along the length of the nerve cell.

Nerve impulses are the signals of the nervous system that travel along the neurone from dendrite to axon. The function of a neurone is to transmit impulses from their origin to destination. The nerve fibres of a neurone are not actually joined together and, therefore, there is no anatomical continuity between one neurone and another.

The junction where nerve imulses are transmitted from one neurone to another is called a synapse. This is the junction between two neurones or between a neurone and a muscle or gland where they connect to transmit information.

Fig 8.3 The conduction of a nerve impulse across a synapse

Impulses are relayed from one neurone to another by a chemical transmitter substance which is released by the neurone to carry impulses across the synapse to stimulate the next neurone. Synapses cause nerve impulses to pass in one direction only and are important in coordinating the actions of neurones. A special kind of synapse occurs at the junction between a nerve and a muscle and is known as a motor point, which is the point where the nerve supply enters the muscle.


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    How is a nerve impulse conducted anatomy?
    2 months ago

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