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Phys Lect 4

QuestionAnswer
When does the membrane potential equal the nernst potential of a particular ion? When the membrane is selectively permeable to that ion
What makes a membrane selectively permeable to an ion? OPEN channels. **channels are often gated, meaning that there must be some trigger event that causes channel opening.
What ion is MOST responsible for the resting membrane potential? (Remember no ion alone determines the Resting Membrane Potential). Potassium K+ **Since the Ek and Em are so close together, the membrane at rest is most permeable to K+, The graphical deviation of Em from Ek is due to slight permeability of Na. (resting mem pot is less negative)
Which ion is the membrane most permeable to at rest? K+ which is supported by the fact that the Ek and Em are very similar
The membrane potential at a given time is most affected by the ion that is ____ permeable MOST
two factors determine the membrane potential 1.Nernst potentials. 2.Ion permeability
What is the resting membrane potential mV range? What all ions contribute? -60 to -85mV. (Nernst Potentials) 1.Eca: +125mV. 2.Ena: +70mV. 3.Ecl: -50mV. 4.Ek: -90mV.
Does extracellular ion concentration imfluence the resting membrane potential (Em) if the membrane is immpermeable to that ion? NOOOOPPPEEE
Goldman-Hodgkin-Katz Eq How much a given ion's nernst potential influences the overall membrane potential depends on its relative permeability. The P values (permeability) of K, Cl, and Na range b/w 0-1 and add up to equal 1.
The Resting Membrane permeability of Na is ___ the permeability of K 1/100
Hows is Na+ slightly permeable? 2 theories: 1.Na channels that allow Na+ to leak back into the cell. 2.1 Na+ for every 100 K+ enters the cell through a K+ channel.
What is the relative permeability of Ca2+? 0. this is why it is not represented in the GHK equation.
Influence of Cl- in nerve cells Em? Impermeant
Influence of Cl- in Skeletal muscle/ most other cells? is permeant, and is therefore represented in GHK equation. Pcl is much smaller than Pk.
What is actively responsible for maintaining intracellular [Na+] and [K+] concentrations and preventing the membrane potential from simply dissipating once the ion concentrations balanced? Na+/K+ ATPase **Therefore it indirectly maintains the resting membrane potential (Em)
Increase in Extracellular [K+] will cause depolarization b/c Ek becomes more positive (the K+ ions are less likely to move out of the cell).
Decrease in Extracellular [K+] will cause hyperpolarization b/c Ek becomes more negative. (the K+ ions will move out of the cell at a more rapid rate).
A cell has membrane permeabilities of: Na>K>Ca. In what range is the cell's membrane potential likely to lie? 0 to +70mV
HyperKalemia Depolarization/ Less negative Em (Less K+ efflux)
HypoKalemia Hyperpolarization/ More negative Em (More K+ efflux)
Created by: WeeG
 

 



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