Lecture 2: Membrane and action potentials Flashcards
Does Na+ want to flow into the cell or outside?
Wants to flow inside the cell
Does K+ want to flow inside the cell or outside
outisde
What is the definition of Resting Membrane Potential (Vm)
Electical potential difference across the membrane
What do you call it when you there is a potential difference across the membrane?
POLARIZED
What would happen if the membrane was ONLY permeable to K+/Na+
K+/Na+ would diffuse down its concentration gradient until the electrical potential (diffusion potential) across the membrane counters the K+ diffusion
If membrane was only permeable to K+, when would diffusion stop?
When the concentration difference=electrical difference
What is another name for NERST potential?
equilibrium potential?
Define Nerst Potential (equilibirum potential)
the electrical (diffusion) potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane
What is the nerst equation
Β±61 logβ‘(πππππππ‘πππ‘πππ πππ πππ (πΎπ)/(πππππππ‘πππ‘πππ ππ’π‘π πππ (πΎ0)
How do you determine the sign for the nerst potential equation?
-The sign of the potential is positive if the ion diffusing is negative
and it is negative if the ion is positive
The electrical potential that counters net diffusion of Na+ is calledβ¦
The Na+ equilibrium potential OR
Nerst potential for Na+
What does the Goldman ( Goldman-Hodgkin-Katz ) equation assess
Equilibrium Potential of Membrane Permeable to Several Different Ions
What 3 factors does the Goldman ( Goldman-Hodgkin-Katz ) equation depend on?
1) CONCENTRATION: of respective ions on the inside (i) and outside (o) of the membrane
2) PERMEABILITY: of membrane (P) to each ion
3) polarity of the electrical charge of ions positive or negative
Why is the resting membrane potential so close to the equlibrium potential for K+ in comparison to Na+
The membrane is far more permeable to K+ than to Na+
What is the equlibrium potential for na+ and k+
na+= 61 mV K+= -94mV
What are the 2 Transport Properties of Resting Nerve Membrane
1) Leak channels much more permeable to K+ than Na+ (~ 100 times)
2) Na+/K+ pump: Net increase of 1 positive charge outside: More Negativity inside
What is the resting membrane potential for large nerve fibers? for small neurons?
- 90mV for large nerve fibers (e.g. motoneurons)
- 70 mV for small neurons of nervous system
Resting membrane potential of nerves depends on what 3 factors?
- Diffusion of potassium and sodium ions (K+ : Inside to Outside,
Na+: Outside to Inside (less degree) - Permeability of ions through leak channels
P to K+»_space; P to Na+ (~ 100 times). - Na+/K+ Pump
Creates more negativity inside (transports 3 Na+ ions to outside vs 2 K+ ions to inside).
The resting membrane potential is closer to the equilibrium potential for the ion with the BLANK permeability (i.e. K+).
HIGHEST PERMEABLITY
What is action potential?
AP is a very rapid change in the membrane potential from β-β to β+β values and return back to initial resting potential level
True or false and explain: AP is an all or nothing event?
TRUE: either it occurs fully or it does not occur at all (amplitude of AP never change)
Where does AP propagate
along nerve fiber until it comes to the end of the fiber
What are the 3 functions of AP
1) transmitting nerve signals
2) rapid transmission over distance
3) encoding information (neuronal language)
Explain the 3 functions of AP
1) Transmitting nerve signals
- Transfer all sensory information from the periphery to central nervous system (CNS)
- Transfer all motor information from CNS to periphery (e.g. muscles, endocrine systemβ¦etc)
- Transfer information between different parts of CNS
2) Rapid Transmission over distance
Note: speed of transmission (conduction velocity) depends on fiber size (how big the axon is) and whether it is myelinated
3) Encoding Information (neuronal language)
- The frequency of APs encodes information
What does speed of transmission of AP depend on?
depends on fiber size (how big the axon is) and whether it is myelinated
In which of these examples the AP will travel at the highest speed?
a) Twisting your ankleβ¦ouch! It hurts!!!
b) Feeling the position of my limbs in space
c) Feeling a pressure on my skin
Feeling the position of my limbs in space
What encodes information? the frequency or the amplitude of the AP
THE FREQUENCY
What are the 5 sequence of events for AP
1) resting state
2) depolarization
3) repolarization
4) undershoot
5) back to resting
be able to identify the sequence of events for Ap on a diagram
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Explain resting stage of nerve AP
-90 mV, membrane is balanced