deck_533571 Flashcards
What is a membrane potential?
An electrical potential difference across a cell membrane
What is used to measure membrane potential?Give the characteristics for the unique component of the measuring device/
Microelectrode with a micropipette– one electrode measures the extracellular fluid & a micropipette measures voltage inside the cell membrane– teh micropipette has a diameter of >1micrometres and is filled with a conducting solution (KCl/solution which is a s similar as possible to intracellular fluid to prevent excess disruption)
How is a membrane potential expressed?
A value which is relative to the outside of the cell
What is the range for membrane potential for animal cells?
-20mV to -90mV
What is the membrane potential range for cardiac muscle?
-80mV to -90mV
What is the membrane potential range for nerve cells?
-50mV to -75mV
Why do membrane potentials occur?
The membrane is selectively permeable to different ions due to transmembranous channel proteins.
What are the charactersitics of ion channels?
- Are specific to one/ a few ion species2. Gating – teh channel can be opened or closde by a conformational change in the protein molecule3. Ion flow always occurs down the electrochemical gradient
What is specific about potassium channels?What movement of K+ ions occur at rest?
They are voltage insenstive and tend to open at resting potential – Increased K+ inside cell so ions move out down chemical gradient– Negative charge on the inside of the cell so ions are attracted bck into the cell down an electrical gradient
How is a membrane potential generated?
K+ channels are open so K+ can diffuse out down a conc. gradientAnions cannot follow (cant diffuse through the membrane) so negative anions build up in cell. Negative charge is present on inside in comparison to the outside. Membrane potential opposes K+ outward diffusion so equilibrium arises.
What is an equilibrium potential?
The membrane potential where the electrical and diffusion forces balance each oter so there is no further net movement of an ion
What equation crayon use to calculate the potassium equilibrium potential?
Nernst equation
What are the two terms which can be used to describe changes of the membrane potential from its resting level and describe them.
HYPERPOLARISATION – an increase in the membrane potential so the inside becomes less negativeDEPOLARISATION – a decrease in the membrane potential so the inside becomes more negative
What will cause depolarisation of cells?
Opening Ca2+ or Na+ channels
What will causes hyperpolarisation of cells?
Opening K+ or Cl- channels