Ionic Basis of Excitation Flashcards
What is the name for the voltage difference across cell membrane?
How is it used?
membrane potential
used as a bettery and for signaling purposes
What are the typical intracellular and extracellular concentrations of:
Na+
K+
Ca2+
Cl-
- Na+
- intracellular: 15 mM
- extracellular: 140 mM
- K+
- intracellular: 140 mM
- extracellular: 4mM
- Ca2+
- intracellular: 0.0001 mM
- extracellular: 2.5 mM
- Cl-
- intracellular: 6 mM
- extracellular: 100 mM
What is the relationship between energy and concentration gradients?
It takes energy to move something against its concentration gradient, but it releases energy to move something down its concentration gradient
What two forces are generated by the uneven distribution of ions acros the membrane?
chemical and electrical
What are the 4 factors influencing teh ion distribution across the cell membrane?
- Membrane permeability (ion channel)
- Concentration gradient (chemical force)
- Voltage gradient (Vm; electrical force)
- Active transport of the ion (Na-K-Pump)
- restores membrane potential from (Na/K movement due to leak or action potentials)
Nenst potential
Equilibrium potential (ion specific)
membrane potential at which there is no net movement of ions
electrical and chemicla forces are equal but opposite in direction
chemical > electrical
Based on the Nerst euqation, what is the deiving force and current flow when the following ion channels are opened?
K+
Na+
Ca2+
Cl-
- K+: -25 mV : outward current; negative
- Na +: +130 mV: inward current; positive
- Ca2+: +205 mV: inward current; positive
- Cl-: -5 mV: outward current; negative
What is the definition of ionic current?
direction of cation flow?
- Inward (+) current:
- inward movement of cations
- outward movement of anions
- Outward (-) current:
- outward movement of cations
- inward movement of anions
If conductance in 0, what is the driving force and current?
there is no driving force, there is no current flow
Regardless of driving force, if there are not open channels, then ther will be no current
Moving the membrane potential more positive?
Moving the membrane potential more negative?
positive: depolarization
negative: hyperpolarizaion
Influence of Eion on Vm
for K+, Na+ and Cl-
Vm is closest to the equilibrium potential of the ion with the highest what?
What ion is this?
Permeability
K+
What types of stimulation can induce channel opening?
- mechanical (stretch)
- electrical (voltage-gated)
- transmitter
- G-proteins
- pH
- drugs
What channels are most important for altering Vm?
- Potassium channels
- to establish resting Vm–> some always open for K+; some to restore Vm following excitation (voltage-gated)
- Sodium channels
- elicit action potentials (voltage-gated)f
- Lidocaine: topical anesthetic that blocks Na channels
- elicit action potentials (voltage-gated)f
- Na-K pump
How does the Na-K ATPase work?
- ATP-dependent electorgenic displacement K+ and Na+
- 3 Na+ out for eery 2 K+ in
- blocked by Ouabain (cell depolarize)
- If activity decreases
- [Na+] will increase
- [K+] will decrease
- Vm will depolarize
Consider a neuron in the central nervous system. What would you typically expect in regards to the following properties?
A high number of negatively charged anions that do not cross teh cell membrane are found
- A: on both sides of cell membrane
- B: on inside of the cell
- C: on the outside of the cell
- D: nowhere, anoins usually carry a positive charge
B: on inside of the cell
Consider a neruon in the central nervous system. What would you typically expect in regards to the following properties?
Vm with approdimately -70mV
- A: leak potassium currents
- B: sodium permeability
- C: the equilibrium potential of chloride
- D: the ion with the lowest permeability
- E: Na-K pump
A: leak potassium currents
b/c at resting state, mostly determined by leak potassium current
Na-K pump, important to restore ion concentrations
- What type of change is required to alter Ex?
- Only a ‘global’ change in [X]in and or [X]out alters Ex
- ‘local’ events (EPSP/IPSP/AP) have not effect on Ex
- What is the only variable with regardsto ion X can change Vm?
- Only a change in membrane permeability for ion X can influence Vm
- closed ion channels cannot determine Vm (however, closing of ion channel can change Vm
What is hyper/hypokalemia?
What pathologies are associated?
increase/decrease of extracellular K+ concentration
- Pathologies
- changes in Ek with cocomitant changes in membrane excitability
- for increa K+: dyspnea, arrhythmias, palpations, chest pain, paraesthesia, diarrhea
- acidosis, alkalosis coupeld to exracellular K+
What are examples of channelopathies?
What channelopathy causes “the fainting goat”?
epilepsy, long QT syndrome, myotonia congenita (fainting goat)
- fainting goat (in humans = Thomsen types and Becker type)
- mutation CIC-1, major skeletal muscle Cl- channel
- exagerate response to stimula dur to failure to restore normal resting Vm
- CIC-1 helps to re-establish resting Vm
- delayed relaxation of the muscles
- hereditary genetic disorder
- exagerate response to stimula dur to failure to restore normal resting Vm
- mutation CIC-1, major skeletal muscle Cl- channel
