MCAT Content / Plasma Membrane / Membrane Potential

Membrane potential

Topic: Plasma Membrane

A cell’s membrane potential is negatively charged when it is resting and non-signalling and is determined by the concentrations of ions across the membrane.

For a cell’s membrane potential, the reference point is the outside of the cell. In most resting neurons, the potential difference across the membrane is about 30 to 90 mV, with the inside of the cell more negative than the outside. That is, neurons have a resting membrane potential of about -30 to -90 mV. The resting membrane potential is determined by the uneven distribution of ions (charged particles) between the inside and the outside of the cell, and by the different permeability of the membrane to different types of ions.

Because there is a potential difference across the cell membrane, the membrane is said to be polarized. If the membrane potential becomes more positive than it is at the resting potential, the membrane is said to be polarized.

If the membrane potential becomes more negative than it is at the resting potential, the membrane is said to be hyperpolarized.

 


Practice Questions

Khan Academy

Demyelinating disease and aging

MCAT Official Prep (AAMC)

Practice Exam 4 B/B Section Passage 10 Question 53


Key Points

• A non-signalling cell has a voltage across its membrane called the resting membrane potential. It is therefore polarized.

• The resting potential is determined by concentration gradients of ions across the membrane and by membrane permeability to each type of ion.

• Movement of these ions can cause the membrane to depolarize and the voltage to change, as is the case in neuron transmission of action potentials.


Key Terms

Resting membrane potential: non-signalling neuron has a voltage of about -30 to 90 mV

Depolarized: membrane potential is more positive than it is at the resting potential

Hyperpolarized: membrane potential is more negative than it is at the resting potential

Membrane potential: a measurement of the potential gradient that forces ions to passively move in one direction across a membrane

Neurons: nerve cells

Polarized: the electrical charge on the outside of the membrane is positive while the electrical charge on the inside of the membrane is negative



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