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Chapter: The Massage Connection ANATOMY AND PHYSIOLOGY : Nervous System

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An Overview of Electrical and Ionic Events in Receptors

The receptors convert the adequate stimuli into action potentials, similar to the electrical changes (EPSP and IPSP) that occur at the synapse.

AN OVERVIEW OF ELECTRICAL ANDIONIC EVENTS IN RECEPTORS

The receptors convert the adequate stimuli into action potentials, similar to the electrical changes (EPSP and IPSP) that occur at the synapse. However, the electrical changes here are known as generatorpotentials or receptor potential. For example, ifpressure is applied over a receptor that responds to this stimuli and the electrical changes are recorded using microelectrodes inside and outside the nerve, the inside of the nerve ending which is originally neg-ative depolarizes. This is caused, in most cases, by opening of sodium channels on the cell membrane of the nerve endings and sodium rushing in. This seems to trigger an action potential down the nerve. It has been shown that if the stimuli are more intense, many action potentials at greater frequency are gen-erated. In this way, by differences in the frequency of the action potentials, the brain is able to discern the intensity of the stimulus applied.

If a stimulus is applied for a prolonged period, the frequency of the action potentials generated declines. This phenomenon is adaptation. The degree to which receptors adapt varies with sense organs. In receptors that do not adapt quickly, the action poten-tials continue for as long as stimuli are applied. These are the slow adaptors or tonic receptors. Certain receptors trigger action potentials at the beginning and end of the application of stimulus, the rapidlyadapting receptors or phasic receptors. Both typesare valuable for survival. Pain and cold receptors are slow adapting and help warn the body regarding in-jury. Similarly, the stretch receptors that regulate blood pressure are slow adaptors. This is because the blood to the brain must be constantly monitored.


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