The threshold potential is the critical level to which the membrane potential must be depolarized in order to initiate an action potential. Threshold potentials are necessary in order to regulate and propagate signaling in both the central nervous system (CNS) and the peripheral nervous system (PNS).
The threshold potential is simply a specific measurement of the difference in charge across a cellular membrane. Most often the threshold potential is between -40 and -55 mV, but it can vary based upon several factors. A neuron's resting membrane potential (-70) can be altered to either increase or decrease likelihood of reaching threshold via sodium and potassium ions. An influx of sodium into the cell through open, voltage-gated sodium channels can depolarize the membrane past threshold and thus excite it, while an influx of potassium or chloride can hyperpolarize the cell and thus inhibit threshold from being reached.
Read more about Threshold Potential: Discovery, Physiological Function and Characteristics, Tracking Techniques, Clinical Significance
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