Potentials Flashcards
True/False: A diffusion potential is caused by diffusion of ions.
True
What depends on the size of the driving force?
Magnitude of DP
What depends on the charge of the diffusing ion?
Sign
What happens to the net diffusion of a diffusion potential when reaching equilibrium?
Ions slows and stops
What happens when a diffusion potential balances or opposes the tendency for diffusion?
Electrochemical equilibrium
What is used to calculate equilibrium potentials?
Nerst equation
What values go into calculating the nerst equation?
Charge on ion, constant 60 mV @37C, intracellular concentration, extracellular concentration
What is the typical equilibrium value of Na+?
+65 mV
What is the typical equilibrium value of K+?
-95 mV
What is the typical equilibrium value of Ca2+?
+120 mV
What is the typical equilibrium value of Cl-?
-90 mV
True/False: The driving force for charged solutions is the concentration difference.
False. Uncharged solutions
What does the driving force consider?
Potential difference of concentration and electrical potential difference (Em-Ex)
True/false: When the driving force is (+), that ion will enter the cell and if (-) it will leave the cell.
False. The opposite is true (-) to (+)
When does an ionic current (Ix) occur?
Movement across the CM
What is the formula for ionic current?
Ix= Gx(Em-Ex)
Ions will move across the CM to ion channels if there is what two things?
Conductance (Gx) and Driving Force (Em-Ex)
What is the potential difference that exists across a membrane of excitable cells in the period between action potentials (rest)?
Resting Membrane Potential
What is the typical range of resting membrane potential?
-70 to -80 mV
What is the phenomenon of excitable cells in which a rapid depolarization is followed by a rapid repolarization of the membrane potential?
Action Potential
Briefly discuss the ionic basis of action potential (in 4 steps).
- RMP is at -70mV. K+ conductance is high and channels are open for diffusion. 2. Inward current causes depolarization to thresholf (60 mV). Na+ activation gates open and depolarization occurs. 3. Upstroke is terminated and MP repolarizes to RMP from Na+ inactivation gates and depolarization opens K+ channels. 4. Undershoot of RMP to closer to Ek but eventually it returns to resting level, ready to go again.
What is the toxin that blocks Na+ channels, preventing the occurence of APs?
Tetrodotoxin
What blocks K+ channels resulting in no outward current of K+ so no repolarization?
Tetraethylammonium (TEA)
What is responsible for the upstroke of AP in nerve and muscle?
Nerve Na+ channel
What are the three gate positions?
Closed, but available. Open. Inactivated.
When does the refractory period move from absolute to relative?
during undershoot
True/False: Depolarization opens activation gates for Na+ for upstroke to occur.
False. Depolarization closes inactivation gates and upstroke cannot occur b/c of insufficient Na+ channels available
What condition increases K+ serum in the body?
Hyperkalemia
What does the increase of K+ do to the action potential?
Causes depolarization of RMP so the body is less likely to fire an AP from the Na+ gates being closed.
Is the cell interior at rest negatively or postively charged?
Negatively
Is the cell interior negatively or positively charged at depolarization?
Positively
What is considered the speed at which an action potential is conducted along a nerve/muscle fiber?
Conduction Velocity
True/False: Conduction velocity determines the speed at which info is transmitted to the nervous system?
True
What are the two cable properties that influence conduction velocity?
Time constant and length constant
What two things affect the time constant?
Membrane Resistance and Membrane capacitance
What two things affect the length constant?
Membrane resistance and internal resistance
Ultimately, the __ the membrane resistance and the __ the membrane conductance results in higher conduction velocity.
Lower, Higher
Ultimately, the __ the membrane resistance, the ___ the diameter, and the __ the internal resistance, the higher the conduction velocity is.
higher, smaller, lower
What two mechanisms can increase conduction velocity?
Myelination and increasing nerve diameter
A man sustains a burn to over 60% of his body, which leads to a decrease in the serum [K+] from normal (4) to 2.5 Eq/L. What happens to the RMP and K+ Nernst Potential in the cardiac myocyte after the injury?
RMP = more negative, K nernst potential = more negative.
Where does potassium conductance exceed sodium conductance?
At rest and after repolarization
What happens during the upstroke of the nerve action potential?
Net inward current and cell interior becomes less negative
What is responsible for the change in membrane potential occurring between RMP and Ena+ depolarization?
Movement of Na into cell
What is responsible for the change in membrane potential between depolarization and repolarization?
Movement of K+ out of the cell
What would increase the velocity conduction of APs along a nerve?
Myelinating the nerve (also, increasing the diameter)
What are the three characteristics of action potentials?
Stereotypical size and shape, propagation, and all-or none response
What happens during the hyperpolarizing afterpotential?
Following repolarization when the MP is more negative than at rest. Another word = undershoot
What is overshoot?
Period of AP when it is more positive (depolarization)
What is the meaning of the term influx?
Positive charge entering the cell
What is the meaning of the term outflux?
Positive charge leaving the cell
