Structure of Membranes - Membrane Biophysics, Biological and Medical Physics, Biomedical Engineering - page 17

Positive Exterior

Fig. 2.2 An approximately

− 70 mV potential in the mem-

brane interior region, relative
to the membrane exterior
region, is a general electrical
condition found in normal
cells. This is due to a resultant
negatively charged interior
and a positively charged exte-
rior of the cell membrane

Negative Exterior

Positive Exterior

Resting Potential and the Neuron Membrane

The brain communicates with other parts of the body through neuron cells. The
resting potentials in neuron membranes help transfer the messages in the form of
electrical pulses. The membrane of a neuron is about 8 nm thick, containing two
thick layers of fat molecules embedding larger protein molecules. In the polarized
state, the membrane effectively maintains a

70 mV resting potential, due to uneven
concentrations of anions and cations on both sides of the membrane. In the polarized
state, the membrane is permeable to K + ions but does not allow larger Na + ions to
cross through it. A nerve impulse is associated with information transfer along the
axon towards the axon terminal. In this way, the transmission of information from
one neuron to other neurons or different types of cells occurs. The nerve impulse or
action potential is created by a depolarizing current. The passage of electrical current
happens due to the movement of sodium and potassium ions across the membrane.

−

Action Potential

An action potential is an electrical event which lasts for a short of period of time
and involves the cell membrane's electrical potential, which rapidly rises and then
falls following a special type of time-dependent trajectory and spatial propagation.
A typical action potential is shown in Fig. 2.3 .
In several types of excitable cells such as neurons, muscle cells, endocrine cells,
etc., action potentials are found to be generated [ 17 ]. An action potential occurs
during the time when a neuron sends a signal down an axon which travels away
from the cell body. These potentials are caused by an exchange of ions across the
membrane of a neuron. Any stimulus first causes sodium channels to open; with it
sodium ions move into the neuron leading the neuron to experience depolarization.
Potassium channels usually take longer to open, but when they do, potassium starts
moving out of the cell, which reverses the depolarization process. Consequently,