Flashcards in Action Potential Deck (17):
What is the difference between electrical wiring and biological nervous systems?
In electrical wiring:
- substrate: metal
- charge is carried by free electrons
- well insulated
In Biological nervous systems:
- substrate: intracellular fluid/cytosol
- charge is carried by ions
- poor insulation between intra- and extracellular spaces.
What properties of membrane channels make them selectively permeable?
Their physical structure and chemical properties (of amino acids)
Some channels are gated. Whether they are open or not depends on...?
The membrane potential and/or binding of a ligand to the channel.
Note: these channels are able to undergo conformational changes.
What percentage of all energy used by the body is used by the brain? How much of the energy used by the brain is used by Na/K ATPase?
20% and 70% respectively.
The Na/K-ATPase utilises:
- Facilitated diffusion
- Passive transport
- Active transport
Active transport as the Na/K ATPase pumps 3 sodiums out and 2 potassiums in against their concentration gradient, which requires ATP.
Is the sodium-potassium pump involved in action potential?
True or false; the action of the Na/K ATPase can be reversed at extremely high sodium and potassium concentrations.
What are the three states of voltage-gated sodium channels and when does each occur?
Closed (active) at -40mV during, during depolarisation
Inactive at > -65mV, following peak of action potential.
They becomes closed and active again once the membrane reaches -65mV.
How many protein subunits is each potassium channel made up of?
Four protein subunits with pore loops.
How many different types of 2-pore-domains (K2P) channels are there? What is their function?
Help set resting membrane potential.
Also contribute to production of metabolic heat.
Where does passive signal transduction normally occur?
In dendrites and neurons with short axons.
What is the maximum rate of action potential and what is it limited by?
The maximum rate is about 1000Hz/second, which is due to inactivation of Navs for 1ms following action potential.
Which channels are open and cause repolarisation following the peak of action potential?
The fact the K2P channels remain open and Navs begin to close, means that the permeability is higher for potassium than it is for sodium.
Define "absolute refractory period".
Period during which Navs are inactive and so action potential cannot be achieved. This limits the rate of action potential to 1000 per second.
Define "relative refractory period".
The period following the absolute refractory period, during which Kavs are open, causing hyperpolarisation. As a result, action potential is possible but will require a greater amount of input for the threshold to be reached than at resting potential.
What are the two ways in which action potential propagates along an axon? Which way is faster and why? Why does action potential travel only in one direction?
Passive conduction and saltatory conduction. Saltatory conduction is faster as action potential does not have to occur at every point along the axon, unlike in passive conduction. Note that the myelin sheath cannot be continuous as current leaks.
Action potential travels in one direction because inactivated neurons that have just been part of AP do not allow depolarisation to occur.