Electrolytes like sodium (Na+) and potassium (K+) play a key role in the transfer of nerve impulses. Nerve impulses are created by stimuli in the environment such as sight, sound, smell, taste and touch. If the stimulus is strong enough, reaching a threshold of -55 mV, an action potential is triggered. In other words, the neuron is said to “fire”. The action potential begins with neurotransmitters binding to receptors on the neuron, causing ligand-gated sodium channels to open and allow Na+ to flow in. This causes a change in the resting potential of the cell from its usual -70 mV to the threshold voltage of -55mV. Once this threshold is reached, voltage-gated sodium channels are opened in the membrane causing more Na+ to flow in, further raising the voltage to 35 mV. This raise in voltage from -70 to 35 mV is called depolarization. Shortly after, the voltage-gated Nachannel closes and voltage-gated Kchannels open to pump Kacross the membrane, repolarizing it in an attempt to restore resting potential. This process is somewhat over-corrected in that too much K+ is pumped out leading to hyperpolarization as the cell’s voltage drops to -80 mV. However resting potential is soon normalized back to -70 mV as leaky K+ channels allows K+ to flow back in freely. The depolarizing/repolarizing event is known as an action potential and encodes the message to be passed along the neuron. The message is able to move along the length of the neuron because every time there is an inflow of Nain one part of the neuron it causes a drop in voltage in the neighboring section ahead, and hence another action potential. Therefore the message will be transferred via  a series of many action potentials.  

Cell at resting potential

Depolarization

Repolarization 

The stimuli is encoded in the resulting changes in voltage along the neuron 

Action potential relay

Reference: Thompson,&  J., Manore, M., Vaughan, L. (2020). The science of nutrition (5th ed.). New York. Pearson

Courtney Simons
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Courtney Simons is a food science professor. He holds a BS degree in food science and a PhD in cereal science from North Dakota State University.
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