Homeostasis & Resting Potential Flashcards
What is the internal environment of an animal that cells are bathed in?
Extracellular fluid
Why carry out homeostasis?
Protect cells from changing external environment
‘Constancy of the internal environment is the condition of free life’ - ?
Claude Bernard 1872
What is the composition of extracellular fluid?
1/5 blood plasma
4/5 interstitial fluid
What does homeostasis mean?
Maintaining the internal environment of an organism different from the external
Who invented the name ‘homeostasis’?
Walter Cannon
What is the lipid bi-layer membrane a barrier for?
Water, ions, sugars
Is there a difference between the environments inside (cytoplasm) and outside the cell?
Yes, inside the cell is maintained ideal for biological molecules to work
What is the electrical voltage difference between the inside and outside called?
Resting membrane potential
What is ‘the cells electrical battery’?
The resting potential
What is the value for the resting potential?
-60 to -80 mV
The inside is 60-80mV negative to the outside
What can the resting potential be used for?
Make electrical signals
Movement across membrane
How is the resting potential measured?
Intracellular microelectrodes:
Measure the voltage difference between inside and outside an axon, amplify it
What are the 2 cell membrane proteins responsible for the resting potential?
Sodium-potassium exchange pump
Potassium ion channel
Sodium-potassium exchange pump: what does it do and how?
Expels Na+; imports K+ (3:2 ratio)
Using ATP
So conc of K+ is greater inside the cell
Potassium ion channel: what does it do?
Contains a gate
If gate is open, potassium moves through by diffusion
Direction of diffusion depends upon the electrochemical gradient across membrane
Who created equation for calculating K+ equilibrium potential?
Nernst (Nernst equation)
Who conducted experiment on frog muscle cells and what did they find?
Hodgkin & Horowicz (1959)
Varying external K+ conc alters membrane potential as predicted by Ernst
What causes the large voltage difference if only a bit more Na+ is being removed than K+ being pumped in?
K+ moves down its conc gradient out of the cell, increasing voltage difference
What is the equilibrium potential for K+
When the voltage difference balances the concentration difference
