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Initiation or generation of a nerve impulse
 

Initiation or generation of a nerve impulse

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    Initiation or generation of a nerve impulse Initiation or generation of a nerve impulse Document Transcript

    • Initiation or Generation of a Nerve Impulse (Action Potential)  At rest, the voltage-sensitive sodium and potassium gates in the channels in the plasma membrane of a nerve cell are nearly closed and the Na+/K+ pump moves 3 Na+ ions to the ECF and 2 K+ ions to the ICF.  This contributes to the formation of a resting membrane potential of -70 millivolts (mV).  Resting Membrane Voltage (RMV) Initiation of the Nerve Impulse Continued:  The sodium/potassium pump also contributes to the resting membrane potential by pumping out three sodium ions to the ECF and pumping in two potassium ions to the ICF.  The effect of this process is to make the outside of the nerve cell positive compared to the inside of the cell which becomes negative (-70 mV).
    •  At rest, the ICF of an axon has a voltage of about -70 mV When the membrane of the axon is properly stimulated, Na+ ions begin to leak into the ICF. This causes the voltage to change to a less negative state. When ICF voltage reaches a threshold of about - 55 mV, sodium gates open. As sodium gates open, Na+ flow through sodium channels increases and quickly changes the voltage from a resting level of - 70 mV to + 30mV. This rapid shift from a negative to a positive state is called DEPOLARIZATION. At +30 mV, the sodium gates close. When the sodium gates close at +30 mV, the depolarization process stops. Interestingly, the + 30 mV condition causes the potassium gates to open and allows potassium to flow from the ICF to the ECF. The potassium flow quickly reverses the potential from + 30 mV to about - 70mV. This is called REPOLARIZATION. The rapid depolarization and repolarization process generates a a voltage pulse peak that is called the ACTION POTENTIAL or NERVE IMPULSE. The formation of a nerve impulse stimulates the formation of still another nerve impulse in the next section of the axon membrane
    • Overview of Transmission of Nerve Impulse  Action potential→ synaptic knob→ opening of Ca+ channels → neurotransmitter vesicles fuse with membrane → release of neurotransmitter into synaptic cleft → binding of neurotransmitter to protein receptor molecules on receiving neuron membrane → opening of ion channels → triggering of new action potential  Neurotransmitter is broken down by enzymes & ion channels close -- effect brief and precise  How a synapse works