Chapter 5

Question 1

Nerst Potential (Definition)

Answer 1

-Defined by the diffusion potential which inhibits the net diffusion of a particle

Question 2

Nerst Equation:

Answer 2

EMF= +/- 61 (log [Ci]/[Co])

• the sign is (+) for a (-) ion and (-) for a (+) ion.
• determined by the ratio of concentrations of that specific ion of the two sides of the membrane. the greater the ratio, the greater the tendancy of the ion to move in one direction and therefore the greater the force required to resist this movement.

Question 3

How to measure the membrane potential:

Answer 3

• using a micropipette which is slowly advanced inside of the cell and abruptly changes potential from 0mV to -90mV.
• average Na ratio (out/in) (142/14)
• Average K ratio (140/4)

Question 4

RMP is maintained by:

Answer 4

-Leaky K+ channels which allow for the slow leak of K+ out of the cell

Question 5

RMP contributors:

Answer 5

• K+ ions are the only contributors to RMP
• almost all of the diffusion potential of -86mV is determined by the K+ membrane potential
• additional 4mV provided by the constant action of Na/K ATPase
• accounts for -90mV

Question 6

Stages of the nerve action potential:

Answer 6

• Resting stage
• depolarizing stage
• Repolarizing stage

Question 7

Resting Stage:

Answer 7

-Membrane is polarized to -90mV

Question 8

Depolarizing Stage:

Answer 8

• Stimulus pushes the charge to threshold and Na+ gated channels open
• Na+ floods the nerve fiber and cause it to rapidly depolarize
• Commonly overshoots the “0mV” and becomes positive

Question 9

Repolarizing Stage:

Answer 9

• K+ channels open and cause an efflux of K+ (down it’s concentration gradient to repolarize the membrane
• Na/K ATPase re-establishes the RMP

Question 10

How many doors does the Na+ gated channel have and what are they called?

Answer 10

• 2 doors
• Outer activation gate and inner inactivation gate

Question 11

What is the conformation of Na+ gates at RMP?

Answer 11

-activation gate is closed and the inactivation gate is open

Question 12

Conformation of Na+ gates when activated?

Answer 12

-Both the activation and the inactivation gates are open

Question 13

Conformation of Na+ gates once 0mV is reached?

Answer 13

-The inactivation gate closes and the activation gate is still open

Question 14

Conformation of the K+ gate at RMP?

Answer 14

-Gate closed

Question 15

Whe does the K+ gate open?

Slowly or quickly?

Answer 15

• When the membrane potential is more + or close to zero.
• they work slowly

Question 16

What tissues have action potentials with a “plateau” and why?

Answer 16

• Common in heart muscle nerves
• Slow voltage gated Ca2+ channels prolong the entry of (+) chagred ions.
• Slower than usual K+ channels are delayed and prolong the potential
• Allows for a porlonged contraction of the heart muscle and full pumping action

Question 17

Order and timing of Ion movement in AP?

Answer 17

Question 18

Repetitive or Rhythmic AP is caused by:

Answer 18

• Less negative RMP (-60 to -70mV) is not able to keep the Na+ channels close all of the way.
• This causes the slow influx of Na+ ions to the point of threshold

Question 19

How is a delay between heart AP ensured?

Answer 19

-the delay is ensured by the slow K+ channels causeing hypermolarization.

Question 20

Nerve conductance observed in myelinated nerves?

Answer 20

Saltitory Conductance: allows fo rthe rapid conductance of AP by jumping from node to node of ranvier.

• 5 to 50 fold increase in velocity
• conserves energy by less ion loss

Question 21

Whch channels are inactivated in the absolute refractory persiod?

Answer 21

• Na+ and Ca2+ channels are inactiated so no further AP can be generated
• Occurs in the first 2/3 of the AP

Question 22

What is the relitive refractory period?

Answer 22

-the last 1/3 of the AP when a new AP can be generated if the stimulus is stron enough.

Question 23

How does Ca2+ inhibit AP?

Answer 23

• Ca2+ decreases Na+ permiability (more (+) already on the inside) and reduces the excitability
• Called a stabilizer

Question 24

Action of Local anesthetics?

Answer 24

• inhibit the activation gate of Na+ channels
• No AP generated or can not propagate efficiently
• Eg. End in -caine, tetracain, procain