Most people know to eat a banana if they are getting cramps while working out. That is common knowledge especially in the athletic community. Some people know to salt their food if they are feeling like they are lacking in performance or strength. Not all should be adding extra salt to their foods if they already have a high sodium diet. For those who do not have a high sodium diet can consider that for an increase in their performance.
WHY IS THIS?
SCIENCE AND STUFF, THAT’S WHY. Check out the vlog below on the benefits of sodium and potassium for action potential generation. Aka, one of the many steps for us to be able to do things like squat, run, and how I can type all of this up.
SCIENCE STUFF: How Action Potentials Are Created
Action Potential Generation terms to know:
Action Potential: A nerve impulse formed from sodium ions diffusing into the neuron until a threshold is reached.
Depolarization: An increase in cell membrane permeability to potassium to let potassium leave a cell and for sodium to enter the cell
Repolarization: Returning resting membrane potential
Neurotransmitter: Chemical messenger that is a communicator for neurons
Excitatory transmitter: Neurotransmitters to cause depolarization
Excitatory Postsynaptic Potentials (EPSPs): graded depolarizations that add up through temporal summation or through spatial summation to create an action potential
Temporal Summation: The sum of different EPSPs that arrive at different times
Spatial Summation: The sum of different EPSPs that arrive from different presynaptic inputs
Inhibitory Postsynaptic Potential (IPSP): hyperpolarization of the cell membrane to develop a negative resting membrane potential
Action potentials are how our afferent fibers transmit signals from our peripheral nervous system to our brain in the central nervous system (Powers & Howley, 2018). The nerve impulse formed from each neuron is an action potential and each signal is formed after depolarization occurs in the cell membrane (Powers & Howley, 2018). A resting cell membrane has a greater amount of sodium ions outside of the membrane and a greater amount of potassium inside the membrane (Powers & Howley, 2018). Resting cell permeability closes all sodium channels and a few potassium channels are open for potassium ions to leak out, causing a negative membrane potential (Powers & Howley, 2018). To prevent a loss in the slightly negative resting membrane potential, a sodium/potassium pump powered by ATP maintains a resting ion concentration (Powers & Howley, 2018). This active transport pump move three sodium ions out of the cell and two potassium ions out of the cell (Powers & Howley, 2018). When depolarization occurs the membrane permeability increases which opens channels for potassium ions to leave the cell and sodium ions to enter bringing the cell closer to threshold for an action potential to occur (Powers & Howley, 2018). Sodium and Potassium ions switch places from ions naturally going from an area of high concentration to an area of low concentration (Powers & Howley, 2018). Multiple graded depolarizations need to add up to reach threshold for an action potential (Powers & Howley, 2018).
For a graded depolarization to occur neurotransmitters communicate with other neurons through synaptic transmission (Powers & Howley, 2018). When excitatory transmitters release into the synaptic cleft they bind to the target membrane receptors to create graded depolarizations (Powers & Howley, 2018). Acetylcholine is also a neurotransmitter that binds onto the receptors of the postsynaptic membrane to open sodium channels (Powers & Howley, 2018). These graded depolarizations are excitatory postsynaptic potentials (EPSPs) and are added up through temporal summation and spatial summation (Powers & Howley, 2018). Temporal summation is controlled by time and is the sum of different EPSPs that arrive at different times (Powers & Howley, 2018). Within a single excitatory presynaptic neuron it’s been estimated that fifty EPSPs may be enough to create an action potential (Powers & Howley, 2018). The time of adding up graded depolarizations open more open ion channels for a greater amount of sodium ions to go into the cell membrane (Powers & Howley, 2018). Spatial summation is the sum of EPSPs that arrive from different presynaptic inputs (Powers & Howley, 2018). Around fifty EPSPs from spatial summation are also needed to create an action potential (Powers & Howley, 2018). The more EPSPs compared to inhibitory postsynaptic potential (IPSP), the close the cell will be to threshold (Powers & Howley, 2018).
A threshold will not be reached causing action potential to not occur if the number of EPSPs are similar to IPSPs (Powers & Howley, 2018). To avoid chronic depolarization, acetylcholine breaks down into acetyl and choline through the enzyme acetylcholinesterase (Powers & Howley, 2018). This break down removes the depolarization stimulus and inhibitory transmitters increases the negativity of the postsynaptic membrane (Powers & Howley, 2018). IPSPs resist depolarization and repolarization the postsynaptic membrane to resting membrane potential (Powers & Howley, 2018).
It is important that resting membrane potential returns in the postsynaptic membrane. Short term variability (SV) of heart rate can be affected by action potential duration (Nanasi, Magyar, Varro, & Ordog, 2017). In multicellular cardiac tissues SV was smaller compared to singular cellular tissues (Nanasi et al., 2017). The longer duration of an action potential lead to increasing SV (Nanasi et al., 2017). This was discovered through inward and outward current pulses and was considered to be ion-channel-independent manipulation (Nanasi et al., 2017). Factors like allergy medications, antibiotics, anti-inflammatory drugs, and grapefruit juice all were found to reduce repolarization of a cell (Nanasi et al., 2017). Without repolarization, the postsynaptic membrane can’t return to resting membrane potential potential leading to an increase in SV (Powers & Howley, 2018; Nanasi et al., 2017).
Powers, S. K., & Howley, E. T. (2018). Exercise physiology: theory and application to fitness and performance (10th ed.). New York, NY: McGraw-Hill Education
Nanasi, P. P., Magyar, J., Varro, A., & Ordog, B. (2017). Beat-to-beat variability of cardiac action potential duration: underlying mechanism and clinical implications. Canadian Journal of Physiology and Pharmacology, 95, 1230-1235. dx.doi.org/10.1139/cjpp-2016-0597