Electric potentials in neurons and other cells are created by ionic concentration differences across semipermeable membranes. Stimuli change the permeability and create action potentials that propagat...Electric potentials in neurons and other cells are created by ionic concentration differences across semipermeable membranes. Stimuli change the permeability and create action potentials that propagate along neurons. Myelin sheaths speed this process and reduce the needed energy input. This process in the heart can be measured with an electrocardiogram (ECG).
This sequence of events results in a voltage pulse, called the action potential. (See Figure 3.) Only small fractions of the ions move, so that the cell can fire many hundreds of times without depleti...This sequence of events results in a voltage pulse, called the action potential. (See Figure 3.) Only small fractions of the ions move, so that the cell can fire many hundreds of times without depleting the excess concentrations of \(Na^{+}\) and \(K^{+}\). Although the impulse is due to \(Na^{+}\) and \(K^{+}\) going across the membrane, it is equivalent to a wave of charge moving along the outside and inside of the membrane.
Osmosis will be to the right, since water is less concentrated there. (b) The fluid level rises until the back pressure \(\rho gh\) equals the relative osmotic pressure; then, the net transfer of wate...Osmosis will be to the right, since water is less concentrated there. (b) The fluid level rises until the back pressure \(\rho gh\) equals the relative osmotic pressure; then, the net transfer of water is zero. The study of active transport carries us into the realms of microbiology, biophysics, and biochemistry and it is a fascinating application of the laws of nature to living structures.
