Formation of Resting Potential

Cells possess a negative charge due to the presence of numerous macromolecules like proteins and nucleic acids.
These macromolecules, when balanced out, contribute significantly to the overall negative charge within the cell.

The resting membrane potential is the initial charge of the cell. It is affected by the movement of ions in or out of the cell.
The specific ions involved dictate whether the resting membrane potential becomes more positive or negative.
Macromolecules, being large, cannot traverse the membrane, thus maintaining the negative charge inside the cell.

Cells strive for electroneutrality, maintaining equal amounts of positive and negative ions to balance charges.
Potassium ions (K^+) are the most abundant positively charged ions inside the cell.

Despite the presence of potassium ions, the resting membrane potential remains negative because membranes are permeable (leaky) to K^+.
K^+ ions leak out, while negatively charged macromolecules remain trapped inside.
This leakage results in a buildup of negative charge within the cell.
Variations in the distribution of macromolecules can cause some areas to have more negative charges than others (e.g., high negative charge in the nucleus due to DNA).

An equilibrium is established when the number of K^+ ions leaking out equals the number being drawn back into the cell.
This equilibrium stabilizes the resting membrane potential.
The balance between K^+ ions leaving and entering results in a consistent resting membrane potential.

The outflow of K^+ ions is driven by the high concentration inside the cell compared to the outside.
Sodium-potassium pumps counteract this by actively transporting K^+ ions against their concentration gradient, pulling them back into the cell.

Electrical potential, or voltage, measures the tendency of positive and negative ions to move towards each other.
It quantifies the desire or potential for ions to flow together.
Voltage is measured in volts.

Current arises when positive and negative charges are actually moving towards each other.
It represents the actual flow of ions.
Current is measured in amperes (amps).

Electrochemical equilibrium defines the balance between the chemical gradient (concentration gradient of a specific ion) and the electrical potential (voltage).
It takes into account both the ion's concentration gradient and the electrical charge of the environment it is moving into.
When moving K^+ ions back into the cell, movement occurs against the concentration gradient.
However, the negative charge inside the cell attracts the positively charged potassium, facilitating its movement inward.
The balance between the chemical gradient and electrical potential determines ion movement.