Genesisof Action Potential

Question 1

Electrotonic potential

Answer 1

Non propagated local potential due to change in ionic conductance due to local change in conductance.

Question 2

Action potential

Answer 2

Probated impulse

Question 3

Local responses

Answer 3

Potential changes observed near the site of current passage

Question 4

Sub threshold current pulses

Answer 4

The size of the potential change observed depends on the distance of the recording electrode from the point of current passage.

The closer the recording electrode to the site of current passage, the larger the potential change

Question 5

Size of the potential change

Answer 5

Decreases exponentially with the distance to 1/e (37%) of its maximum value.

Question 6

What is the length of a typical mammalian nerve or muscles cell?

Answer 6

1 to 2 mm

Question 7

What is the importance of an action potential?

Answer 7

Communication between nerve cells depends on an electrical disturbance.

Question 8

Action potential

Answer 8

A transient change in the membrane potential that conveys information within excitable cells and the nervous system when excitation occurs. W

Question 9

When is an action potential triggered?

Answer 9

When the depolarization is sufficient for the membrane potential to reach a threshold value.

Question 10

What is threshold ?

Answer 10

The critical point in which a membrane must be depolarised in order to initiate a membrane response.

Question 11

How does the action potential differs from the subthreshold and passive responses?

Answer 11

It is much larger response in which the polarity of the membrane potential actually overshoots.

The action potential is propagated down the entire length of the nerve fibres

The action potential is propagated without decrement( maintains it shape and size.

Question 12

All or none response

Answer 12

The stimulus either produces a full sized action potential or fails to do so.

Question 13

Facts about all or none

Answer 13

Stronger stimuli does not increase either size or speed of the action potential
A stimulus of stronger intensity occurs when the frequency of firing increases
involves the flow of ions across the plasma membrane
have a characteristic form ( amplitude, time course and duration)

Question 14

Stages of action potential

Answer 14

Upstroke: rapid depolarization of membrane
Overshoot: membrane potential is positive
Downstroke: repolarisation phase; rapid return of membrane to its resting potential
Undershoot: membrane becomes more negative that it resting value

Question 15

Which cells has the fastest action potential?

Answer 15

Cardiac muscle, motor , skeleton

Question 16

Characteristics of action potential

Answer 16

Threshold, amplitude, duration

Question 17

Types of subthreshold potential

Answer 17

Local, somatic , receptor

Question 18

does a subthreshold stimuli elicit an action potential?

Answer 18

NO

Question 19

does a suprathreshold change the size of an action potential

Answer 19

no

Question 20

factors affecting the action

Answer 20

1) the gating and permeability of properties of specific types of ion channels. these properties depend on both Vm and time
2) membrane properties that don not depend on Vm and time such as resistance, and the geometry.
3) the intracellular and extra cellular concentrations that pass through these channels.

Question 21

regulation of Na+ channels is regulated by two gating particles

Answer 21

m and h gates

Question 22

which gate is the activated channel ?

Answer 22

m is the activated gate while h is the inactivating gate. for na+ to pass through the Na+ channel both gates must be opened

Question 23

ij the resting potential the activation gates are__________ while the inactivation gates are _______

Answer 23

closed ……. open

Question 24

describe Na+ channels

Answer 24

its intramembrane domain is known to consist of a number of α helices that span the membrane and surround the ion channel.
The Na+ channel has both an activation gate and an inactivation gate that account for the changes in gNa during an action potential. Groups of charged amino acid residues that form these gates have been tentatively identified. To enter the channel’s narrowest part, known as the selectivity filter, K+ and Na+, it is believed, must shed most of their waters of hydration.
To strip K+ and Na+ of their associated water molecules, negative amino acid residues that line the pore of the channel must have a particular geometric shape; the precise geometry differs for K+ and for Na+. This requirement is believed to confer the specificity of ion channels.

Question 25

regulation of the K+ channels

Answer 25

The K+ channel has one gating potential that covers the extra cellular side of the K+ channels. the “n” gate must be opened for K+ to flow through the K+ channel.

Question 26

structure of potassium channel

Answer 26

made up of 4 alpha subunits as well as a cytoplasmic beta subunit.

Question 27

what is the resting potentiali of a cell?

Answer 27

-70 to 90mV

Question 28

Na+ channels are closed by

Answer 28

“n” gate but the h gate is open

Question 29

Depolization

Answer 29

When the membrane is depolarized to threshold, a positive feedback (regenerative) process produces the all-or-none upstroke of the action potential.

The response of the membrane to the stimulus (opening of “m” gates) causes an effect (membrane depolarization) that produces an even greater response.

Question 30

Repolization

Answer 30

Inactivation of the Na+ channels & flow of Na+ into the cell stops

Activation the K+ channels, & K+ flows out of the cell, causing the membrane to repolarize

Question 31

hyperpolization

Answer 31

“n” gates close slowly & membrane repolarizes

K+ conductance (gK) is higher at the end of the AP than during the resting state

The high gK causes the membrane to hyperpolarize (i.e., become more negative than the resting membrane potential).

Eventually, the “n” gates close & the membrane potential returns to its resting level

Question 32

the role of Na/ K pump

Answer 32

it pumps 3 Na outside the cell and 2 K inside the cell using atp .

Question 33

Local anaesthetics

Answer 33

lidocaine, novocaine, benzocaine - prevent action potential from being progated.

Question 34

Na channels blockers

Answer 34

Tetrodotoxin- potent poisin. its binds to the extracellular side of its channel.
Saxitoxin - produced by reddish dinoflagellates that are responisible for the so call red tide

Question 35

K+ channel blockers

Answer 35

Tetraeythylammonium - It enters the K+ channel from the cytoplasmic side and blocks the channel because it cannot pass through the channel.

Question 36

absolute refractory period

Answer 36

Period from initiation & extends into the down-stroke

2nd AP absolutely cannot be initiated during this period.

“m” gates in Na+ channels are opening rapidly during the up-stroke

“h” gates produce inactivation of Na+ channels during early part of the down-stroke

Question 37

Relative refractory period

Answer 37

No. of inactivated Na+ channels is reduced by repolarization

Voltage-gated K+ channels are open.

2nd AP can be initiated

Membrane is hyperpolarized (-80mV).

AP are more difficult to generate during this period relative to the resting potential (-70mV).

Question 38

increase potassium in the ECF does what to the mebrane?

Answer 38

depolarises the membrane.

Question 39

decrease calcium in the ECF does what to the membrane

Answer 39

allows the activation of the sodium channels at the more negative potential