Resting potential of nerve fibres

2021-06-04 03:19 PM

Functional characteristics of the Na+-K+ pump and of the K+ leak channels. ADP, adenosine diphosphate; ATP, adenosine triphosphate.

The resting potential of the great nerves when they are not transmitting is about -90mV.

Figure. Functional characteristics of the Na+-K+ pump and of the K+ leak channels. ADP, adenosine diphosphate; ATP, adenosine triphosphate. K+ leaky channels also leak Na+ ions into the cell but are much more permeable than K+.

For example, the potential inside the nerve is 90mV more negative than the outside. In the following sections, the transport properties of neuronal membranes with sodium and potassium ions and the factors that determine resting potential levels will be explained.

Active transport of sodium and potassium ions across the membrane- Sodium-potassium pump

Again: all cells in the body have a very powerful sodium-potassium pump that continuously transports sodium out and potassium into the cells, as illustrated in the figure. Note that this is a charge pump because the more positive charge is pumped out than in (3 na going out for 2k in) leaving a positive charge loss inside causing a negative potential inside. membrane

The Na + -K + pump also causes a large concentration gradient for sodium and potassium across the resting neuronal membrane. The difference is as follows:

Na (outside) 142 mEq/l.

Na (inside) 14 mEq/l.

K (outside) 4 mEq/l.

K (inside) 140 mEq/l.

The respective ratios of the two ions inside and outside the membrane are:

Na trog/outside: 0.1.

K inside/out: 35.

Leakage of potassium across neuronal membranes

The right side of the figure shows a protein channel (sometimes called a potassium channel or a potassium leak channel) in the neuronal membrane through which k can leak even when the cell is at rest. These k channels can also leak small amounts of na, but more notably, the membrane permeability fork is about 100 times higher than na. This permeability difference discussed later, is the key to determining the resting membrane potential.