Electrical Excitability and Action Potentials

Question 1

How much biger is the peak of the action potential to Vrest

Answer 1

~100mV

Question 2

What is the overshoot?

Answer 2

part of AP that lies above the 0mV

Question 3

What 3 factors influence the threshold, amplitude, time course, and duration of the action potential

Answer 3

the gating and permeability of ion channels (depend on Vm and time)

2. the intra and extracellular concentration.
3. membrane properties, capacitance resistance and the geometry.

Question 4

What does a brief action potential reflect?

Answer 4

rapid signaling (e.g nerve axon)

Question 5

what does a prolonged repetitive AP tell.

Answer 5

slower rhytmic contractions (cardiac and certain smooth muscle cells)

Question 6

what does endothelin do?

Answer 6

shorten the duration of AP.

Question 7

τ =

Answer 7

RC (product of membrane resistance and capacitance

Question 8

what does happen to graded responses with distance?

Answer 8

decays

Question 9

what happens with AP with distance

Answer 9

magnitude and shaoe stay same. however delay between stimulus and response increases.

Question 10

What are graded voltage changes

Answer 10

yperpolarizations and subthreshold depolarizations

Question 11

what is electrotonic conduction

Answer 11

As the graded response spreads, its magnitude decays exponentially with the distance from the site of stimulation because of passive loss of electrical current to the medium.

Question 12

What kind of velocity do AP propagate

Answer 12

constant (130m/s)

Question 13

Does a large stimulus have a long duration

Answer 13

large stimulus short duration

small stimulus long duration. of spike

Question 14

What is the refractory period

Answer 14

time where it is (nearly ) impossible to fire AP

Question 15

The absolute refractory period lasts from?

Answer 15

initiation to when repolarisation is almost complete

Question 16

What is a feature of the absolute refractory period?

Answer 16

no second AP can be fired

Question 17

whe does the relative refractory period start

Answer 17

after absolute refractory to almost Vrest

Question 18

what is a feature of the relative refractory period

Answer 18

the minimal stimulus necessary for activation is stronger or longer than predicted by the strength-duration curve for the first action potential

Question 19

is the current-voltage relationship between NA+ and K+ macrop or micro scopic? and why

Answer 19

macroscopic because the currents represent many individual ion channels

Question 20

why are the K channels called delayed rectiefier K+?

Answer 20

activate with a time delay

Question 21

ix=gx(Vm-Ex) explain the parameters

Answer 21

ix is the single channel current.

gx is the single channel conductance.

Question 22

what is ohmic in a graph

Answer 22

linear

Question 23

what is Boltzman distribution

Answer 23

The probability of a channel’s being open depends on V m

Question 24

Ix=NPoix

Answer 24

What is P the probability that the channel is open.

Question 25

what are the parameters of Hodgkin and Huxley (not full names)

Answer 25

n,m,h dimensionless parameters between 0 and 1

Question 26

what do the parameters mean of Hodgkin and Huxley (n,m,h)

Answer 26

activation parameter n= the probability that the K + channels are open. activation parameter m= the probability that the Na + channels are open. the inactivation h- Na + current inactivates,

Question 27

when are the parameters of Hodgkin and Huxley measured

Answer 27

at infinite time (e.g steady state)

Question 28

what causes depolarisation

Answer 28

increase in Na + conductance

Question 29

what causes repolarisation

Answer 29

inactivation of Na + conductance and delayed activation of K + conductance

Question 30

what can be the external stimulus to activate Na+ channels at AP

Answer 30

electrode, a synaptic event, or propagation of a depolarizing wave

Question 31

what is a gating current

Answer 31

small movement of charge that should accompany the activasion of voltage gated Na and K channels

Question 32

what are receoptor and synaptic potentials

Answer 32

graded responses

Question 33

what are two ways in improving conduction properties of nerve fibers

Answer 33

increase diameter of axon (higher conductance)or | myelinating the fiber

Question 34

what are Schwann cells

Answer 34

glial cells that produce myelin in the periphery

Question 35

what are oligodendrocytes

Answer 35

glial cells that produce myelin in the brain.

Question 36

what does myelin do

Answer 36

increase membrane resistence which minimizes loss of current.

Question 37

what are the nodes of Ranvier

Answer 37

unmyelinated zones, containing a large density of voltage gated Na+ channels.

Question 38

where are the Na channels in the nodes of ranvier

Answer 38

nodal membrane

Question 39

where are the K channels in the nodes of ranvier

Answer 39

paranodal regions flanking each node

Question 40

what is saltatory conduction

Answer 40

impulse conduction where, Current flow that is initiated at an excited node flows directly to adjacent nodes with little loss of transmembrane current through the internode region

Question 41

what is more effecient and propagates AP faster myelin or larger diameter

Answer 41

myelin (130 m/s)

Question 42

is there a transmembrane current in internodal regions?

Answer 42

no, only capacitative current.

Question 43

what are electrotonic currents

Answer 43

decaying currents that spready away of the location of the electrode.

Question 44

what are the two cable parameters?

Answer 44

time and length constant

Question 45

when myelinated fibers with a very small diameter (<1 µm), is conduction than faster than unmyelinated axons with the same outeer diameter.

Answer 45

no, becasue the resistance of the axoplasm dominates.

Question 46

what is multiple sclerosis

Answer 46

autoimmune disorder in which the myelin sheath surrounding CNS axons is progressively lost, eventually resulting in nerve blockage

Question 47

a high h favors the ...state of the channel.

Answer 47

open