Membrane & Action potential Flashcards
What is the Nernst Equation used for?
Calculating the equilibrium potential of a specific ion.
E_x = RT/zF * ln(X_out / X_in)
Why does the Nernst equation not generalize for calculation of continiously updated membrane potentials?
The Nernst equation can be expanded to include several Ions but does not account for changes in conductance/permability.
Which equation is used repsectively for calculating membrane potentials with a known ion permability/conductance?
- The Goldman equation is used for calculating the membrane potential with a known permability.
- The Millman equation is used when an ion conducantance is provided.
Explain conductance and permability and how it can be affected.
Conductance and permability is both measures for the ability of current to flow in specific path.
Differences:
Permability: is an intrinsic property of the membrane, independent of ion concentration. How easily can ions move across the membrane even if they do not move at all (e.g. is there an ion channel present).
- Directly proportional to the number of open ion-channels.
Conductance: measures of movement of charge across the membrane is dependent on the concentration gradients.
- depdent on the number of open ion-channels and the electro-chemichal gradient.
https://www.ncbi.nlm.nih.gov/books/NBK538338/
What is a membrane potential?
The differences in electrical potential between the extracellular and intracellular environment. The difference is quantified relative to the extracellular electrical potential.
I.e., -70mV corresponds to the intracellular electrical potential beign -70mV lower than the extracellular.
What is an action potential?
An action potential (AP) is a rapid series of changes in membrane potential. Depolarizing the cell all the way to the AP threshold (-50: -55 mV) activating the voltage-gated sodium channels in the axon-initial segment. Cascading the signal all the way through the axon.
What is a graded membrane potential?
A change in the relative electrical potential. The change can be gradual and isn’t an “all or nothing” signal as the action potential.
**Types of graded membrane potentials: **receptor potentials, electrotonic potentials, subthreshold membrane potential oscillations, slow-wave potential, pacemaker potentials, and synaptic potentials.
Does the amplitude of the action potential depend on the intensity/amplitude of stimulus (e.g., synapse or electrical stimulation)
No the action potential (AP) is an all or nothing signal. The only way to modulate the amplitude of an AP is to the change the concentration gradient or ionic conductance in the axon.
How do neural signalling pathways encode intensity?
The strength of signal is encoded by the frequency of firing (Hz) rather than the amplitude.
Does Na+ have a higher intracellular or extracellular concentration in a neuron at rest?
A neuron at rest: Extracellular…
Na+ has an intracellular concentration of 5-15mM
Na+ has an extracellular concentration of 145mM
Does K+ have a higher intracellular or extracellular concentration in a neuron at rest?
A neuron at rest: intracellular…
K+ has an intracellular concentration of 140mM
K+ has an extracellular concentration of 5mM
Does Cl- have a higher intracellular or extracellular concentration in a neuron at rest?
A neuron at rest: extracellular…
Cl- has an intracellular concentration of 4-30mM
Cl- has an extracellular concentration of 110mM
K+ & Na+ is inversely proportional in their concentration distribution and Cl- has a higher extracellular concentration for a neuron at rest. How come the resting membrane potential is negative?
Various negatively charged intracellular proteins and organic phosphates that cannot cross the cell membrane are also contributory.
What is passive transportation?
What is active transportation?
