The rest potential or membrane potential
A cell is a structurally functional unit of an organism.
Each organ is represented by a set of cells connected by intercellular structures
About 60% of body weight is represented by liquids.
Most of them are represented by intracellular fluid, and 1/3 are extracellular fluid.
Extracellular fluid is the internal environment of the body
Extracellular fluid contains ions, nutrients, gases necessary for the functioning of cells
The composition of extracellular and intracellular fluids is significantly different.
The cells are covered with a membrane
The membrane is a protein-lipid layer that is permeable only to fat-soluble particles (blood gases).
There are proteins in the membrane: integral (permeate the membrane and are channels for water-soluble substances or carriers) and peripheral.
Excitable tissues
Nerve tissue
Muscle tissue
Secretory tissue
All tissues have property excitability
Properties of excitable tissues
Excitability
Conductivity
Contractility
Automation
Excitability - ability to be excited by irritation
Criteria:
1) The threshold of stimulation is the minimum stimulus force capable of causing tissue excitation (generation of action potential), for the electric stimulus the threshold is called a reobase
2) Excitation threshold (depolarization threshold) is the difference between the resting potential and the Cl (critical level of the membrane potential)
Conductivity - the ability to excite the membrane surface
The conductivity is estimated from the rate of excitation (action potential)
Rate of excitation:
Nerve fibers of group A (120 - 20 m / s);
group B (15 - 3 m / s);
group C (3-0.5 m / s);
Skeletal muscles - 5-8 m / s;
Smooth muscles - 0.5 m / s
Heart muscle - 1 - 4 m / s
Contractility is the ability to contract in response to irritation.
Automation - the ability to be excited without irritation.
Bioelectric phenomena in the excitable tissues
1) The rest potential
2) Local response
3) Action potential
Mechanism of these phenomena Membrane-ion theory explains
Basic principles of the Membrane-ion theory
1) The difference in ion concentrations between the inner and outer sides of the membrane is the concentration gradient;
2) The presence of ion-selective membrane - has a selective permeability for ions: gated and non-gated ion channels;
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3) Potassium-sodium pump (and other pumps) - active mechanism in membrane, provides motion of ions against gradient concentrations with energy.
Threshold stimulus: The stimulus with the intensity equal to threshold
Subthreshold stimulus: The stimulus with the intensity weaker than the threshold
Suprathreshold stimulus: The stimulus with the intensity greater
Depolarization: the membrane potential becomes less negative than the resting potential (close to zero).
Repolarization: restoration of normal polarization state of membrane.
Hyperpolarization: the membrane potential is more negative than the resting level.
The rest potential or membrane potential
Membranes of cells of excitable tissues at rest are negatively charged, are polarized.
The value of the rest potential in different tissues ranges from
-30 to -90 mV.
The rest potential is due to:
1) the release of K + ions from the cell,
2) the weak intake of Na + ions into the cell,
3) the potassium-sodium pump (3 Na + ions are excreted from the cell, 2 K+ are two cells introduced
Local response
local depolarization of the membrane caused by the action of a subthreshold stimulus occurs as a result of the discovery of chemo-sensitive sodium channels
local response can be represented by hyperpolarization of the membrane, it is provided by the opening of potassium or chlorine channels
Local response properties
Action Potential
This rapid oscillation of the membrane potential due to changes in the permeability of the cell membrane and the diffusion of ions into and out of the cell
Two forms of action potentials 1- spiky, 2- plateau
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