Title: Psychology / Biopsychology / 03_MembranePotential
Tags: Biopsychology::03_MembranePotential Biopsychology::Semester_1

Q: What is meant by the "Equilibrium Potential" of the membrane?
A: Ions have two sources of attraction:
1. they want to move along the concentration gradient
2. positively charged ions are attracted by negativity (and vice versa)
When those two attractions cancel each other out, ions do not move even if there are open ion channels
This is the "equilibrium"

Q: How do Potassium and Sodium differ in equilibrium potential?
A: Potassium: -80mV
Sodium: +62 mV

Q: What is the resting potential of a neuron?
A: Add up all of the equilibrium potentials of the respective ions.
→ resting membrane potential is about -65 mV

Q: What are the elemental symbols denoting Sodium and Potassium respectively?
A: Potassium: K+
Sodium: Na+

Q: What part of the cell is responsible for the different concentrations of ions inside/outside the cell?
A: The sodium-potassium pumps
→ Proteins that are part of the cell membrane and move ions against the concentration gradient.
(2 states that attract and move different ions)

Q: What do sodium-potassium pumps need that ion channels do not?
A: As they move ions against the concentration gradient, they need energy in the form of ATP in order to change shape and pump the ions.

Q: Under what circumstance is action potential generated in a neuron?
A: When the membrane potential reaches the threshold of -40 mV.

Q: What are voltage-gated sodium channels?
A: They are ion channels with positively charged elements inside → they change their shape when a certain membrane potential is reached.

Q: How do voltage-gated ion channels and transmitter-gated ion channels differ in location?
A: Voltage-gated channels are located on the axon, while transmitter-gated channels are mostly found on the soma and dendrites.

Q: What is the refractory period of the cell membrane?
A: The time period in the "falling" phase of the action potential graph, where the channels are set up in a way that makes it impossible or highly unlikely for another action potential to be triggered at that patch of the cell membrane.

Q: What is the difference between the absolute and relative refractory period of the cell membrane?
A: Absolute: Falling phase, no AP can be initiated
Relative: Undershoot, only a very strong input can initiate AP

Q: Where in the neuron is the action potential initiated?
A: In the Axon hillok (the beginning of the axon, the first part where a high density of voltage-gated channels can be found)

Q: How does voltage travel down the axon?
A: The voltage-gated channels along the axon open as ions diffuse.

Q: How does the axon make sure that the action potential only travels in one direction?
A: After a patch of axon membrane triggered the action potential, it needs some time to restore as the Na-channels cannot open, and the Na-K-pumps are working on restoring the membrane potential.
(a new AP can only be triggered after the Na-channels are ready to open again)

Q: What are the 4 phases of the action potential?
A: Synaptic input makes the membrane potential less and less negative, threshold is reached
-> 1. Rising Phase (The Na+ channels open up and positively charged Sodium enters the cell)
-> 2. Overshoot (The positivity reaches its peak and K+ channels open completely, making Potassium stream out of the cell)
-> 3. Falling Phase (Membrane potential gets more and more negative)
-> 4. Undershoot (Membrane potential is now more negative than resting, Na-K-Pumps work on restoring it)

Q: Repeatedly triggering action potential along the axon is quite slow. How did mammals fix this?
A: Myelination → Insulating the axon, so that internally, Na can diffuse for a certain distance without ion channels and pumps getting activated.
The AP only gets reactivated in each of the gaps of isolation (Node of Ranvier) instead of constantly along the axon.

Q: How much faster are myelinated axons compared to non myelinated axons?
A: 100x as fast

Q: What is the name for the fast propagation of AP due to myelinisation?
A: Saltatory conduction

Q: What part of the nervous system does multiple sclerosis affect?
A: The myelin sheaths insulating the axons.

Q: In what form is information coded by neurons?
A: Digitally, as every action potential looks the same, it can only give a pulse or give no pulse.
→ the information is encoded in the firing rate (number of APs in a time interval)

Q: During the neuron's resting phase, where are more Sodium Ions? Inside or outside of the cell?
A: More Na+ outside of the cell.

Q: During the neuron's resting phase, where are more Potassium Ions? Inside or outside the cell?
A: More K+ inside the cell.

Q: How does the neuron's cell membrane's permeability differ for K+ and Na+?
A: The cell membrane is 40 times more permeable for K+ when compared to Na+

Q: Why are dendrites unable to elicit action potential?
A: Because they would need voltage-gated ions channels for that (those are mostly found on axons).

Q: Why is the cell membrane more permeable for K+ during the resting phase?
A: The K+ channels are always slightly opened