Visualize a neuromuscular junction. An impulse has been sent to the effectors (m
ID: 42181 • Letter: V
Question
Visualize a neuromuscular junction. An impulse has been sent to the effectors (muscle cells) for a response. At rest, the endplate region has the following concentrations of sodium and potassium: [Na+in] = 10 mM, [Na+out] = 145 mM, [K+in] = 140 mM, and [K+out] = 5 mM. Remember that when acetylcholine binds to its receptors, a large opening of channels becomes permeable to both sodium and potassium. What is the membrane potential of the endplate region when stimulated by acetylcholine in this response?
Explanation / Answer
Calculate the membrane potential using the formula
(RT/zF)log([X]out/[X]in).
RT/F is approximately 61
Therefore, the equation can be written as
(61/z) ln([X]out/[X]in)
Here,
R is the universal gas constant (8.314 J.K-1.mol-1).
T is the temperature in Kelvin (°K = °C + 273.15).
z is the ionic charge for an ion. For example, z is +1 for K+, +2 for Mg2+, -1 for F-, -1 for Cl-, etc. Remember, z does not have a unit.
F is the Faraday's constant (96485 C.mol-1).
[X]out is the concentration of the ion outside of the species. For example, the molarity outside of a neuron
[X]in is the concentration of the ion inside of the species. For example, the molarity inside of a neuron
= (61/2) ln ([Na+out]+[K+out]/[Na+in]+[K+in])
= 30.5 ln (145+5/10+140)
= 30.5 ln (150/150)
= 30.5 ln (1)
= 30.5*0
= 0
The membrane potential of the endplate region is 0.
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