membrane potentials n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Membrane potentials 膜电位 PowerPoint Presentation
Download Presentation
Membrane potentials 膜电位

Loading in 2 Seconds...

play fullscreen
1 / 65

Membrane potentials 膜电位 - PowerPoint PPT Presentation


  • 181 Views
  • Uploaded on

Membrane potentials 膜电位. Xia Qiang, PhD Department of Physiology Room C518, Block C, Research Building, ZJU School of Medicine Tel: 88208252 Email: xiaqiang@zju.edu.cn. Objectives.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Membrane potentials 膜电位' - madeline-kosta


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
membrane potentials

Membrane potentials膜电位

Xia Qiang, PhD

Department of Physiology

Room C518, Block C, Research Building, ZJU School of Medicine

Tel: 88208252

Email: xiaqiang@zju.edu.cn

objectives
Objectives

To understand the shape and form of the action potential and understand how it arises in terms of the changes in the underlying Na+ and K+ channels

To explore how action potentials are conducted in axons and how this is affected by myelin

slide3

Electrocardiogram

ECG(心电图)

slide4

Electroencephalogram

EEG(脑电图)

slide5

Electromyogram

EMG(肌电图)

slide8

Opposite charges attract each other and

will move toward each other if not separated

by some barrier.

slide9

Only a very thin shell of charge difference

is needed to establish a membrane potential.

resting membrane potential
Resting membrane potential(静息电位)

A potential difference across the membranes of inactive cells, with the inside of the cell negative relative to the outside of the cell

Ranging from –10 to –100 mV

slide12

(超射)

Overshoot refers to

the development of

a charge reversal.

A cell is

“polarized”

because

its interior

is more

negative

than its

exterior.

Repolarization is

movement back

toward the

resting potential.

(复极化)

(极化)

Depolarization

occurs

when ion

movement

reduces the

charge

imbalance.

Hyperpolarization is

the development of

even more negative

charge inside the cell.

(超极化)

(去极化)

slide13

electrochemical balance

- - - - - - - - - - - - - - - - -

++++++++++++++++

chemical driving force

electrical driving force

slide14
The Nernst Equation:

K+ equilibrium potential (EK) (37oC)

R=Gas constant

T=Temperature

Z=Valence

F=Faraday’s constant

(钾离子平衡电位)

slide15

Begin:

K+ in Compartment 2,

Na+ in Compartment 1;

BUT only K+ can move.

Ion movement:

K+ crosses into

Compartment 1;

Na+ stays in

Compartment 1.

At the potassium

equilibrium potential:

buildup of positive charge in Compartment 1 produces an electrical potential that exactly offsets the K+ chemical concentration gradient.

slide16

Begin:

K+ in Compartment 2,

Na+ in Compartment 1;

BUT only Na+ can move.

Ion movement:

Na+ crosses into

Compartment 2;

but K+ stays in

Compartment 2.

At the sodium

equilibrium potential:

buildup of positive charge in Compartment 2

produces an electrical potential that exactly

offsets the Na+ chemical concentration gradient.

slide17

Difference between EK and directly measured resting potential

Mammalian skeletal muscle cell -95 mV -90 mV

Frog skeletal muscle cell -105 mV -90 mV

Squid giant axon -96 mV -70 mV

Ek Observed RP

slide19

Role of Na+-K+ pump:

  • Electrogenic
  • Hyperpolarizing

Establishment of resting membrane potential:

Na+/K+ pump establishes concentration gradient

generating a small negative potential; pump

uses up to 40% of the ATP produced by that cell!

origin of the normal resting membrane potential
Origin of the normal resting membrane potential
  • K+ diffusion potential
  • Na+ diffusion
  • Na+-K+ pump
action potential
Action potential(动作电位)

Some of the cells (excitable cells) are capable to rapidly reverse their resting membrane potential from negative resting values to slightly positive values. This transient and rapid change in membrane potential is called an action potential

slide23

A typical neuron action potential

Positive

after-potential

Negative after-potential

Spike potential After-potential

slide25

The size of a

graded potential

(here, graded

depolarizations)

is proportionate

to the intensity

of the stimulus.

slide26

Graded potentials can be: EXCITATORY or INHIBITORY (action potential (action potential

is more likely) is less likely)

The size of a graded potential is proportional to the size of the stimulus.

Graded potentials decay as they move over distance.

slide28
Local response(局部反应)
  • Not “all-or-none” (全或无)
  • Electrotonic propagation: spreading with decrement(电紧张性扩布)
  • Summation: spatial & temporal(时间与空间总和)
slide29
Threshold Potential(阈电位): level of depolarization needed to trigger an action potential (most neurons have a threshold at -50 mV)
membrane potentials1

Membrane potentials膜电位(续)

Xia Qiang, PhD

Department of Physiology

Room C518, Block C, Research Building, ZJU School of Medicine

Tel: 88208252

Email: xiaqiang@zju.edu.cn

objectives1
Objectives

To understand the shape and form of the action potential and understand how it arises in terms of the changes in the underlying Na+ and K+ channels

To explore how action potentials are conducted in axons and how this is affected by myelin

review
Review

Intracellular and extracellular recording

Resting membrane potential (definition and mechanism)

Action potential (definition)

Local response (Graded potential)

Threshold potential

slide34

Nobel Prize in Physiology or Medicine 1963

  • "for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane"
  • Eccles Hodgkin Huxley
  • Voltage Clamp
slide35

Nobel Prize in Physiology or Medicine 1991

  • "for their discoveries concerning the function of single ion channels in cells"
  • Erwin Neher Bert Sakmann
  • Patch Clamp
slide36

From:

doi:

10.1111/j.1469-7793.2000.t01-1-00593.x

June 15, 2000 The Journal of Physiology, 525, 593-609

Figure 2 Instantaneous I–V data reveal that IK has a more hyperpolarised reversal potential than IA

A, tail current family for IK, recorded in 5 mM 4-AP. Following a 100 ms step to +53 mV, the membrane potential was stepped to a level ranging from +53 to -117 mV in 10 mV increments. Each trace is an average of 12 interleaved episodes. Leak currents have been subtracted. B, plot of peak instantaneous IK, from extrapolated exponential fits to the tail currents (Methods), versus tail potential for this patch. The superimposed curve is a quadratic polynomial. The reversal potential for this patch was -86.4 mV. C, tail current family for IA, recorded in 30 mM TEA and shown expanded in the inset. The pulse protocol was as in A, except the duration of the prepulse to +53 mV was 1.5 ms. Each trace is an average of 6 interleaved episodes. Leak currents have been subtracted. The slowly rising trace in the inset is the estimated time course of the contaminating IK at +53 mV in this patch. At 1.5 ms the contamination is about 10 % of IA. D, plot of peak instantaneous IAversus tail potential for this patch. The fitted quadratic polynomial gives a reversal potential of -68.7 mV.

slide37

Blocker:

Tetrodotoxin (TTX)

(1) Depolarization(去极化):

Activation of Na+ channel

(2) Repolarization(复极化):

Inactivation of Na+ channel

Activation of K+ channel

Blocker:

Tetraethylammonium

(TEA)(四乙胺)

slide39

The rapid opening of voltage-gated Na+ channels

explains the rapid-depolarization phase at the

beginning of the action potential.

The slower opening of voltage-gated K+ channels

explains the repolarization and after hyperpolarization

phases that complete the action potential.

slide42

An action potential

is an “all-or-none”

sequence of changes

in membrane potential.

The rapid opening of

voltage-gated Na+ channels

allows rapid entry of Na+,

moving membrane potential

closer to the sodium

equilibrium potential (+60 mv)

Action potentials result

from an all-or-none

sequence of changes

in ion permeability

due to the operation

of voltage-gated

Na+ and K + channels.

The slower opening of

voltage-gated K+ channels

allows K+ exit,

moving membrane potential

closer to the potassium

equilibrium potential (-90 mv)

how to re establish na and k gradients after action potential
How to re-establish Na+ and K+ gradients after action potential ?

Concentration gradient of Na+ and K+

Extracellular (mmol/L) Intracellular (mmol/L)

Na+ 150.0 15.0

K+ 5.0 150.0

slide47

For a television game show, 16 contestants volunteer to be stranded on a deserted island in the middle of the South China Sea. They must rely on their own survival instincts and skills. During one of the challenges, one team wins a fishing spear. They catch a puffer fish and cook it over the open flames of their barbecue. None of them are very skilled in cooking, but they enjoy the fish anyway. One of the contestants, a worldwide traveler, comments that it tastes like Fugu. After dinner, they all develop a strange tingling around their lips and tongue. They all become weak, and their frailty progresses to paralysis. They all die.

What is the mechanism of toxicity?

    • A Blockage of the sodium gates
    • B Blockage of the potassium gates
    • C Interference with the release of acetylcholine
    • D Antibody directed against the acetylcholine receptor
    • E Maintaining the sodium channel in an open state
slide48

For a television game show, 16 contestants volunteer to be stranded on a deserted island in the middle of the South China Sea. They must rely on their own survival instincts and skills. During one of the challenges, one team wins a fishing spear. They catch a puffer fish and cook it over the open flames of their barbecue. None of them are very skilled in cooking, but they enjoy the fish anyway. One of the contestants, a worldwide traveler, comments that it tastes like Fugu. After dinner, they all develop a strange tingling around their lips and tongue. They all become weak, and their frailty progresses to paralysis. They all die.

What is the mechanism of toxicity?

    • A Blockage of the sodium gates
    • B Blockage of the potassium gates
    • C Interference with the release of acetylcholine
    • D Antibody directed against the acetylcholine receptor
    • E Maintaining the sodium channel in an open state
conduction of action potential
Conduction of action potential(动作电位的传导)

Continuous propagation in the unmyelinated axon

slide50

Saltatory propagation in the myelinated axon

http://www.brainviews.com/abFiles/AniSalt.htm

slide51

Saltatorial Conduction: Action potentials jump from one node to the

next as they propagate along a myelinated axon.

(跳跃性传导)

excitation and excitability
Excitation and Excitability(兴奋与兴奋性)
  • To initiate excitation (AP)
    • Excitable cells
    • Stimulation
      • Intensity
      • Duration
      • dV/dt
slide54

Threshold intensity(阈强度) & Threshold stimulus(阈刺激)

Four action potentials, each the result of a stimulus strong enough to cause depolarization, are shown in the right half of the figure.

slide55
Refractory period following an AP:

1. Absolute Refractory Period: inactivation of Na+ channel(绝对不应期)

2. Relative Refractory Period: some Na+ channels open(相对不应期)

slide57

The propagation of the action potential from the dendritic

to the axon-terminal end is typically one-way because the

absolute refractory period follows along in the “wake”

of the moving action potential.

factors affecting excitability
Factors affecting excitability
  • Resting potential
  • Threshold
  • Channel state
slide59

A well-meaning third year medical student accidentally pushes an unknown quantity of KCl IV to a patient. If the concentration of potassium outside a neuron were to increase from 4 mEq/L to 8 mEq/L, what would you expect to happen to the minimal stimulus required for initiation of an action potential?

    • A The minimal stimulus required for initiation of an action potential would remain the same
    • B The minimal stimulus required for initiation of an action potential would increase
    • C The minimal stimulus required for initiation of an action potential would decrease
    • D The minimal stimulus required for initiation of an action potential would stay the same, but the amplitude of the peak of the action potential would increase
    • E The minimal stimulus required for initiation of an action potential would stay the same, but the conduction velocity of the action potential down an axon would slow
slide60

A well-meaning third year medical student accidentally pushes an unknown quantity of KCl IV to a patient. If the concentration of potassium outside a neuron were to increase from 4 mEq/L to 8 mEq/L, what would you expect to happen to the minimal stimulus required for initiation of an action potential?

    • A The minimal stimulus required for initiation of an action potential would remain the same
    • B The minimal stimulus required for initiation of an action potential would increase
    • C The minimal stimulus required for initiation of an action potential would decrease
    • D The minimal stimulus required for initiation of an action potential would stay the same, but the amplitude of the peak of the action potential would increase
    • E The minimal stimulus required for initiation of an action potential would stay the same, but the conduction velocity of the action potential down an axon would slow
slide61

Sydney Ringer and his work on ionic composition of buffers

Sydney Ringer published 4 papers in the Journal of Physiology in 1882 and 1883, while working as a physician in London.

He found that

133mM NaCl,

1.34mM KCl,

2.76mM NaHCO3

1.25mM CaCl2

could sustain the frog heart beat.

He wrote “The striking contrast between potassium and sodium with respect to this modification (wrt refractoriness) is of great interest….because, from the chemical point of view, it would be quite unlooked for in two elements apparently so akin”

Ringer found that in excess potassium the period of diminished excitability is increased, and frequnecy of heart beats diminishes.

1835-1910

J Physiol 2004, 555.3; 585-587

Biochem J 1911, 5 (6-7).

slide62

A rather somber application note: Death by lethal injection

This explains what Sydney Ringer observed in frog hearts in 1882!

Lethal injection is used for capital punishment in some states with the death penalty. Lethal injection consists of (1) Sodium thiopental (makes person unconscious), (2) Pancuronium/tubocurare (stops muscle movement), (3) Potassium chloride (causes cardiac arrest).

It seems a bit sick, but we can understand how this works from what we know about electrical signalling. Recall that

summary
SUMMARY
  • Resting potential:
    • K+ diffusion potential
    • Na+ diffusion
    • Na+ -K+ pump
  • Graded potential
    • Not “all-or-none”
    • Electrotonic propagation
    • Spatial and temporal summation
slide64

Action potential

    • Depolarization: Activation of voltage-gated Na+ channel
    • Repolarization: Inactivation of Na+ channel, and activation of K+ channel
  • Refractory period
    • Absolute refractory period
    • Relative refractory period