Neuronal Excitability Wk1 Flashcards
What determines how a nerve cell responds to electrical activation? (4)
- When at rest, if a neurone is activated, its membrane potential will depolarise from the RMP
- The level of depolarisation will be proportional to the strength of stimulation applied
- Such responses of the cell are known as graded depolarisations of the membrane
- If the membrane is sufficiently depolarised to a certain critical level of depolarisation, it will suddenly generate an all-or-nothing event known as an action potential
Describe electrical activation of the cell (2)
- Cells are happy at -90mV
- Electrical impulse applied and membrane depolarises - amount of depolarisation is proportional to the stimulus (but nerve cells have an exponential response)
What is the threshold level for generations of an action potential? (3)
- The level of membrane potential at which graded depolarisations become and action potential is known as the threshold value
- Different neuronal cell types have different threshold levels
- Generally, most neurone produce action potentials when their membrane potentials reach approx -65mV
Action potential graph explanation (2)
- Originally exponential, but changes when an action potential is generated (when you increase the stimulus to a certain level, the cell’s response completely changes)
- “All of nothing” principle dictates that the threshold value must be reached before an action potential is generated
What does the threshold level depend on? (3)
- Level of excitability
- Type of cell
- These are not the only two factors but some
Describe the changes in membrane potential when a neurone discharges its resting membrane potential (5)
- When a neurone fires an action potential, its membrane potential changes very briefly, in a very distinctive way
- The plot of the membrane potential against time is often a steep incline and decrease
- Nerve action potentials last between 1 and 2 seconds
- Amplitude of the action potential remains the same at all times
- The membrane potential will jump from resting membrane potential to various level throughout
What happens to the movements of ions when the nerve cell is at rest? (3)
- K+ are under a concentration gradient in favour of them diffusing to the outside. Negatively charged particles prevent diffusion of K+ to the outside.
- Large concentration of Na+ under a concentration gradient in favour of them diffusing intracellularly
- Membrane potential hardly changes
What is the Nernst Equation? (1)
E(ion) = RT/zF x ln((ion)o/(ion)i))
What are the things in the Nernst equation? (5)
E = Equilibrium potential of ion in equation R = Gas constant T = Temperature in K Z = Valency of the ion F = Faraday's number
What happens at 37 degrees Celsius? (1)
By also converting into Log10, the Nernst equation can be simplified to E(ion) = 61mVlog10{[ion]out/[ion]in}
What is the Goldman Hodgkin Katz Equation? (1)
Em = (RT/zF)ln{P(Na)/P(Na) x [Na+]out/[Na+]in + Pk[K+]out/Pk[K+]in}
You should have an understanding of why this is relevant
Resting membrane potential summary (4)
- There is a slow leak of Na+ ions into the cell and of K+ out.
- The Na+, K+ ATPase is electrogenic but contributes only 5 to 10 mV towards the resting membrane potential
- At rest, the amount of Na+ entering is the same as K+ leaving, but because the permeability to K+ is much greater, the resting membrane potential is much closer to Ek.
- In neurones, Ecl is very close to the resting potential and there is relatively little Cl- movement
What happens to the membrane potential when a neurone discharges its RMP? (4)
- Initial entry of Na+ ions into the cell leads to depolarisation of the cell from resting membrane potential - opening of voltage gated sodium channels
- If the cell is sufficiently depolarised to reach threshold potential, the cell will then produce an unstoppable, all or nothing event, known as an action potential - gradient indicated large movement of ions
- Steep depolarisation brings about even further depolarisation of the membrane of the cell
- Then at the peak, it stops increasing and is suddenly reversed and becomes negative
What happens during the upstroke (depolarisation) of the action potential? (12)
- Na+ enters the cell
- Membrane depolarises
- Depolarisation to threshold
- Na+ channels open - depolarisation as a result
- Begins again (cycle)
5b (after depolarisation).
6a. Opens K+ channels
7b. K+ efflux
6b. Inactivated Na+ channels
7a. Na+ influx stopped - Repolarisation
- Recovery after an action potential
What does ARP and RRP stand for? (2)
ARP = Absolute refractory period RRP = relative refractory period
