The threshold of excitation represents the critical level of membrane potential that a neuron must reach to initiate an action potential. This specific charge level (approximately -55mV) is attained when an influx of positive ions enters the cell, making the internal environment sufficiently positive. Once this exact threshold is surpassed, the neuron becomes active and inevitably triggers an action potential.

Threshold of Excitation

When a neuron receives signals at its dendrites, typically from neurotransmitters released by an adjacent neuron binding to its receptors, small pores or gates open on the neuronal membrane. This event allows sodium (Na+) ions, propelled by both charge and concentration differences, to flow into the cell. With this influx of positive ions, the cell's internal charge becomes more positive.

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Neuronal receptors are specialized proteins located on a neuron's cell surface, typically on the dendrites, where neurotransmitters attach. The shape of each receptor is specific, allowing it to bind only with particular neurotransmitters, functioning like a lock that only a specific key can open.

Neuronal Receptors

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Based on the principle that specialized proteins on a neuron's surface interact with chemical messengers like a lock and key, provide the most likely explanation for why the new medication described in the case study is causing unintended side effects.

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