Question

Describe the resting membrane potential and the forces at play in a resting neuron concisely, but thoroughly. At minimum, the following terms/concepts should be explained in your response: membrane potential, ion channels (and the two main ions involved, and their relative distribution), the two types of forces/pressures acting on each of the ions, and the special transporter of these two ions (and what it does). Here is a previous answer I got(it was great!)- please build off it though, and make it more cohesive.

Answer 1

The membrane potential of a cell is defined as the difference in total charge between the inside and outside of a cell.

A neuron at rest is negatively charged: the inside of a cell is approximately 70 millivolts more negative than the outside (i e, −70 mV, this vary from cell to cell). This voltage is called the resting membrane potential; it is caused by differences in the concentrations of ions inside and outside the cell. This charged membrane results in conduction of various signals through our nervous system.

But, these neurons are lipid bilayered membrane which does not allow the charged moelcules Or ions for entry or exit into neuron cell. For this entry or exit of charged particles, there are special proteins called ion channels which allow there movement. These ion channels have different configuration; they may be open, closed or inactive. These ion channels also change their structure according to the voltage difference , known as voltage gated ion channel. Voltage-gated ion channels regulate the relative concentrations of different ions inside and outside the cell.

There are Positively charged (cations): Sodium (Na+) and potassium (K+) ions

Negatively charged (anions): Chloride (Cl-) and organic anions.

Na+ and K+ ions are the two mains ions which are responsible for maintenance of the voltage difference across cells. It's concentration within extracellular and intracellular are given below --

Ion	Extracellular concentration (mM)	Intracellular concentration (mM)	Ratio outer/inner
Na+	145	12	12
K+	4	155	0.026
Cl-	120	4	30

In a resting neuron, the concentration gradient is maintained between the Na+ and K+ ions. The membrane is more permeable to K+ ions than to Na+ ion because there are more K ion channels.

  In most neurons, K+ and organic anions (such as those found in proteins and amino acids) are present at higher concentrations inside the cell than outside. In contrast, Na+ and Cl- are usually present at higher concentrations outside the cell. This means there are stable concentration gradients across the membrane for all of the most abundant ion types.

When a potassium ion channel opens, it results in the outward movement of k+ ion creating a negative charge inside the membrane and positive charge outside the cell membrane.

The electrical and diffusional forces that influence movement of K+ across the membrane jointly form its electrochemical gradient. This later results in no net movement and this equilibrium is achieved. This was the case when only K+channels were open and allowed ion movementmovement creating a negative membrane potential.

Similarly, when only Na+ channel were active, it would result in Na+ influx and create a positive membrane potential.

Usually ,in an resting membrane of neuron, sodium potassium pumps (maintained by activity of Na+ - K+ Atpase) are effective which allow Na+ and K+ ion to move across concentration gradient.

The energy for this "uphill" movement comes from ATP hydrolysis (the splitting of ATP into ADP and inorganic phosphate). For every molecule of ATP that's broke down, 3 Na+ ions are moved from the inside to the outside of the cell, and 2 K+ ions are moved from the outside to the inside. As more cations are expelled from the cell than taken in, the inside of the cell remains negatively charged relative to the extracellular fluid. It should be noted that calcium ions (Cl–) tend to accumulate outside of the cell because they are repelled by negatively-charged proteins within the cytoplasm

Diagram representing Na+ - K+ exchange pump.