Membrane Potential

Question 1

Describe the all-or-nothing principle

Answer 1

• depolarisation only happens when membrane potentail passes threshold level
• Size of action potential is the same across axon.
• Magnitude of AP is not dependant on how much above threshold but on FREQUENCY of firings (so if there is lots of firing/ depol’s above threhold = the size of the AP will be bigger)

Question 2

Whats the difference between absolute and relative refractory periods

Answer 2

• Absolute refractory period= when cell is undergoes an AP (depol + repol) and cannot do anything else during this time. ~ 1 msec
• Channel that inhibits NA opens, to reset potential.
• Relative RP= after ARP, lasts several msecs until stimulus above threshold triggers next depol. event.

Question 3

Label the following diagram of an action potential recording,

Answer 3

Question 4

* You have prepared lipid vesicles that contain molecules of the K+ -leak channel all oriented so that their cytosolic surface faces the outside of the vesicle. Predict how K+ ions will move under the following conditions and what sort of membrane potential will develop? A. Equal concentrations of K+ ion are present inside and outside the vesicle B. K+ ions are present only inside the vesicle C. K+ ions are present only on the outside of the vesicle

Answer 4

NB: The K+ leak channel works the same regardless of its orientation in the membrane; it always moves K+ down its electrochemical gradient.

A. No NETT movement of ions, membrane potential remains unchanged

B. Nett movement of K+ ions to the outside of the vescilce. Membrane potential with regards to the inside of the vescicle will become more positive until the concentration gradient no longer exists

C. Nett movement of K+ ions to the inside of the vescilce. Membrane potential with regards to the inside of the vescicle will become more negative until the concentration gradient no longer exists

Question 5

Transmitter-gated ion channels open in response to specific neurotransmitters in their environment but are insensitive to the membrane potential; therefore, they cannot by themselves (in the absence of ligand) generate an action potential. T/F?

Answer 5

Activation of the ligand receptor is required to open (or close) the ion channel to which it is coupled. Without the ligand the transmitter-gated ion channels are nonfunctional

translation : ligand channels must have a neurotransmitter in order to open! just like how you must have a special key to open your home.

TRUE