2-Minute Neuroscience: Membrane Potential

October 26, 2019 0 By Jose Scott

Welcome to 2 minute neuroscience, where I
simplistically explain neuroscience topics in 2 minutes or less. In this installment
I will discuss membrane potential. Membrane potential refers to the difference
in electrical charge between the inside and the outside of a neuron. This is the plasma
or cell membrane of the neuron. It separates the inside of the cell from the outside environment;
we’ll say this is the inside and this is the outside of the neuron. The difference
in electrical charge develops due to the grouping of ions on the inside and outside of the membrane.
Ions are atoms that have either lost or gained electrons and thus have a positive or negative
charge. There are several ions that play an important
role in the membrane potential of neurons. There are positively charged sodium ions,
represented by these blue circles and negatively charged chloride ions, represented by these
green circles. When a neuron is at rest, the sodium ions and chloride ions are more prevalent
outside of the cell. There are also positively charged potassium ions, represented by these
yellow circles and various negatively charged ions, often referred to as organic anions
represented by these grey circles (anion is simply a term for a negatively charged ion).
When a neuron is at rest, the potassium ions and organic anions are more prevalent inside
the cell. At rest, the inside of the neuron is more negatively charged than the outside,
causing the resting membrane potential of an average neuron to be around -70 millivolts. One way this potential is maintained is through
a mechanism known as the sodium-potassium pump. This is a transport protein that uses
energy to constantly pump three sodium ions out of the cell while at the same time pumping
two potassium ions into the cell. Because there are more positive ions being pumped
out than in, it helps to keep the membrane potential negative. Unlike other ions, potassium tends to move
fairly easily across the cell membrane through ion channels, which are membrane spanning
proteins that allow ions to pass through. Potassium will pass out of the neuron until
it reaches the point where it is at an equilibrium – when forces like diffusion aren’t pushing
it in one direction or the other. At this point, the membrane potential of the neuron
is around -65 to -70 mV, which is known as the resting membrane potential.