Membrane Potential / Resting Potential / Resting Membrane Potential [Biology, Neurobiology, High School]

The video introduces the concept of membrane potential in neurobiology, highlighting that cells maintain an isotonic state despite an unequal distribution of specific ions like sodium and potassium. Inside the cell, there are more potassium ions, while outside, there are more sodium ions. Despite this, both sides are electrically neutral due to other negatively charged ions.

Despite electrical neutrality, an electrical charge difference, known as an electrical potential, exists across the cell membrane. The inside of the membrane is negatively charged relative to the outside, typically around -70 millivolts. This membrane potential is crucial for various biological functions.

The unequal distribution of sodium and potassium ions drives them to diffuse to equalize concentrations. The cell membrane is selectively permeable, allowing some substances through while blocking others, like charged ions. However, specific protein channels in the membrane facilitate the passage of certain ions. Potassium ion channels are abundant, allowing potassium to flow out of the cell down its concentration gradient.

As potassium flows out, it leaves behind uncompensated negative charges, creating an electrical gradient where the inside of the cell becomes more negative and the outside more positive. This negative charge inside attracts positively charged ions like sodium and some potassium back into the cell. An equilibrium is reached when the outward diffusion of potassium due to concentration gradient is balanced by the inward pull of negative charges, resulting in the resting membrane potential.

The membrane potential, often called 'leak currents,' is maintained by potassium's outward diffusion and subsequent return due to electrical attraction. Additionally, the sodium-potassium pump actively transports three sodium ions out and two potassium ions into the cell, consuming ATP. This pump is vital for sustaining the unequal distribution of ions and thus the membrane potential.

Nearly all living cells exhibit a membrane potential. In nerve, muscle, and sensory cells, it's particularly known as the resting membrane potential. Neurons, for instance, can be activated to rapidly change their membrane potential. This potential is not only important for substance transport but also plays a critical role in the transmission of excitations, which will be discussed in the next video.