cell membrane

Examples of cell membrane in the following topics:

• Electric Potential in Human

  • Electric potentials are commonly found in the body, across cell membranes and in the firing of neurons.
  • In humans, they are seen in cell membranes and nerve impulses in particular.
  • Resting membrane potential is approximately -95 mV in skeletal muscle cells, -60 mV in smooth muscle cells, -80 to -90 mV in astroglia, and -60 to -70 mV in neurons.
  • Potentials can change as ions move across the cell membrane.
  • Active transport of ions across a cell membrane is also a possibility.

• Nerve Conduction and Electrocardiograms

  • A voltage is created across the cell membrane of a neuron in its resting state.
  • The cell membrane is semipermeable, meaning that some ions may cross it while others cannot.
  • In its resting state, the cell membrane is permeable to K+ and Cl−, and impermeable to Na+.
  • The action potential is a voltage pulse at one location on a cell membrane.
  • How does it get transmitted along the cell membrane as a nerve impulse?

• Physics and Other Fields

  • On the microscopic level, it helps describe the properties of cell walls and cell membranes.

• Molecular Transport Phenomena

  • Less sophisticated, single-celled organisms still rely totally on diffusion for the removal of waste products and the uptake of nutrients.
  • Many substances regularly move through cell membranes; oxygen moves in, carbon dioxide moves out, nutrients go in, and wastes go out, for example.
  • Diffusion through membranes is an important method of transport.
  • Membranes are generally selectively permeable, or semipermeable.
  • In other types of membranes, the molecules may actually dissolve in the membrane or react with molecules in the membrane while moving across.

• Blood Flow

  • Blood is the viscous fluid composed of plasma and cells.
  • The composition of the blood includes plasma, red blood cells, white blood cells and platelets.
  • In microcirculation, the properties of the blood cells have an important influence on flow.
  • An alteration of the osmotic pressure difference across the membrane of a blood cell causes a shift of water and a change in cell volume.
  • Therefore, a change in plasma osmotic pressure alters the hematocrit (the volume concentration of red cells in the whole blood) by redistributing water between the intravascular and extravascular spaces.

• Biological and Medical Applications

  • The capillaries connect to venules, into which the deoxygenated blood passes from the cells back into the blood.
  • The heart, vessels and lungs are all actively involved in maintaining healthy cells and organs, and all influence the fluid dynamics of the blood.
  • Less sophisticated, single-celled organisms still rely totally on diffusion for the removal of waste products and the uptake of nutrients.
  • Similarly, dialysis is the transport of any other molecule through a semipermeable membrane due to its concentration difference.
  • A semipermeable membrane with small pores that allow only small molecules to pass through.

• The Battery

  • One half-cell includes electrolyte and the anode, or negative electrode; the other half-cell includes electrolyte and the cathode, or positive electrode.
  • Some cells use two half-cells with different electrolytes.
  • A separator between half-cells allows ions to flow, but prevents mixing of the electrolytes.
  • Each half-cell has an electromotive force (or emf), determined by its ability to drive electric current from the interior to the exterior of the cell.
  • The net emf of the cell is the difference between the emfs of its half-cells, or the difference between the reduction potentials of the half-reactions.

• Electric Activity in the Heart

  • In the atria the electrical signal moves from cell to cell (see section on nerve conduction and the electrocardiogram) while in the ventricles the signal is carried by specialized tissue called the Purkinje fibers which then transmit the electric charge to the myocardium. shows the isolated heart conduction system.
  • It is a group of cells positioned on the wall of the right atrium.
  • These cells are specialized cardiomycetes (cardiac muscle cells).
  • It is a group of cells positioned on the wall of the right atrium.
  • These cells form the atrioventricular node (AV node), which is an area between the atria and ventricles, within the atrial septum.

• Surface Tension

  • The tendency of the surface of a liquid to resist a force and behave like a membrane and is a result of cohesion between liquid molecules.

• Charging a Battery: EMFs in Series and Parallel

  • Usually, the cells are in series in order to produce a larger total emf .
  • A battery is a multiple connection of voltaic cells.
  • The disadvantage of series connections of cells in this manner, though, is that their internal resistances add.
  • But, if the cells oppose one another—such as when one is put into an appliance backwards—the total emf is less, since it is the algebraic sum of the individual emfs.
  • This schematic represents a flashlight with two cells (voltage sources) and a single bulb (load resistance) in series.