Phospholipid 70%

Cholesterol 20%

Glycolipid 10%

lipid bilayer Head polarity hydrophilic Hydrophobic non-polar tail is a two-dimensional fluid

Integrin 70%

Surface protein 30%

All located on the outer surface of the lipid membrane

cell membrane permeability

Transport power: concentration difference; potential difference; osmotic pressure difference

Passive transport: along the concentration gradient, from high concentration to low concentration, without consuming energy

Active transport: against the concentration gradient, from low concentration to high concentration, consuming energy

vesicle transport

Signal transduction of most growth factors and some peptide hormones

When living cells are not stimulated, there is a potential difference on both sides of the cell membrane. The polarity is positive on the outside and negative on the inside, which is called the resting potential.

Transmembrane diffusion of K⁺: Normal intracellular K⁺ concentration is much greater than the extracellular K⁺ concentration, K⁺ has a tendency to diffuse outward, and the cell membrane is highly permeable to K⁺ At this time, the potential difference across the membrane is the equilibrium potential of K⁺

Endoleak of Na⁺: At the resting potential, the cell membrane has a certain permeability to Na⁺, making the resting potential slightly smaller than the equilibrium potential value of K⁺

Electrogenic effect of sodium pump (less impact)

When excitable cells are stimulated, rapid, reversible and spreading potential changes occur on both sides of the cell membrane.

①All or no phenomenon, does not change with stimulation intensity

②Does not attenuate conduction and does not change with conduction distance

③Pulse-type emission, cannot be merged or superimposed with each other

Go to extremes

Repolar phase

Resting state (m gate closed) Inactive state (h gate closed)

The inactivated Na⁺ channel cannot be activated directly and must return to the polarized state (standby state or resting state)

If the difference between threshold potential and resting potential is large, the cell excitability is low (not easy to be excited); if the difference is small, the excitability is high (easy to be excited)

The action potential is conducted as a local current

Absolute refractory period: Na⁺ channel inactivation state, no matter how strong the stimulation is, the cells cannot be excited again

Relative refractory period: Na⁺ channels are gradually resurrected and have not returned to normal levels. Excitation can occur after stimulation, and the stimulation intensity is greater than the threshold intensity.

Supernormal period: Na⁺ channels basically return to the resting state, the gap between the membrane potential and the threshold potential is small, and the excitability is higher than the normal value.

Low normal phase: The Na⁺ channel has completely returned to the resting level, the gap between the membrane potential and the threshold potential is large, and the excitability is lower than the normal value.