script #4 Action Potential

8/3/2019 script #4 Action Potential

1/8


2/8

Action Potential

chapter 3

How can we picture Action potential:- idea about A.P

#We are talking about stages polarization, depolarization , repolarization. we have

to know the differences between them and between hyper polarization, overshoot:-

Becomes positive inside as predicted by the Ena & undershoot:- Return to

membrane potential to a more negative potential than at rest

#ions exchange through the cell membrane or in another word diffusion of ions

diffusion either intracellular from inside to the outside or extracellular from outside

to the inside

# movement mainly either Na or k extracellular / intracellular respectively

other ions create a minor role in Action Potential :- Ca involved in slow Ca/Na

channel. when we are talking about Na fast Na channel

>>>>>>


3/8

brainsympathetic

spinal cord parasympathetic

so in the brain death case, sympathetic nervous will be effected, the pressure will

decrease/increase

not our subject:- the doctor talked about medulla oblongata which located beneath

the brain

Helps control bodys autonomic function, It is responsible for maintaining vital

body functions, such as breathing and heart rate, group of nuclei control blood

pressure

>>>>>>>>>


4/8

NOTE:- ATP is not needed in Na/K leak channel and Na/K

Ca channelrole in A.P in smooth muscle / heart where is theres no fast Na

channel

Causes transient change in membrane potential

Changes in ion permeability is bigger by transient depolarization of the membrane

We said that we have extractable tissue

***Extractable tissue in the body:

1. The nervous system

2. Muscular

Action potential in deferent variable: transmission of impulse

Anything that Im doing is action potential...

***its response to sensory ((sterilite)) by ((moto)) is action potential

If you are exposed to any alarm or harmful thing you will move your hand away or

whatever this is sensory...

Sensory impulse is action potential and this action potential is being transmitted

from one nerve cell to another

This is the pathway to integrated center and the to the (( etherant )) pathway

((moto )) action potential transmitted from the nerves to the muscles

Impulse : action potential

*** There is a question that i cant hear it ***

*** The doctor answered that it pump the sodium and then it goes out

*** Nerve fibber either be: myelinated (myelin sheath) big nerve fibbers

We have the axon inside and we have the node of ranvier

Action potential in nerve fibber are created to be node of ranvier


5/8

And the saltatory transmitted from one node to another inside the axon

The creation of action potential in the node and the saltatory (jumping) inside the

axon

Action potential has been created in the node and jumping inside the axon from

one node to another

So its created in the node of ranvier

The state of action potential is -60 its the start of reaction potential

Action potential have threshold ( )

For everything in this life we have threshold (level at which action potential is

starting)

Membrane potential: electronegativity inside the cell is -90

When action potential starts it becomes 15 to 30 MV and more in the 65-60 the

initiation of action potential starts (threshold of action potential)

Below action potential will not be initiated which means the rule of ALL OR

NONE

Either action potential is be initiated or not

If the stimulate is enough there is action potential

If the stimulate is NOT enough no action potential

Question: you said that action potential related to the brain the brain send the

signals??

Answer:

Its not the brain,

(Its sensory) Source of harm


6/8

Motor order comes from the brain the impulse is action potential

If something harmful touches you it may just receive to the spinal cord not the

brain and its action potential

Conductance how many charges (ions) enters or leaves cell (inverse of

resistance)

Conductance:

Controlled by:

1. Number of channels

2. Ion concentration

...sodium and potassium voltage channels from outside there is activation agates..

There is two gates (activation and inactivation)

Activation gate from outside

Inactivation gate from inside

When action potential is started at the end of depolarization sodium voltage gate

channels are close (inactivation gate/inside)

At the beginning of the opening activation gate channels are open (outer)

Outer and the inner gates are opened during the action potential but at the end of

action potential the inner gate close


7/8

sodium potassium pump is not involved during the action potential, during action

potential the sodium potassium voltage gated channel.

Now there is a subject in action potential called Nernst equation , it talks about

diffusion potential and concentration gradient but what is the relationship between

the diffusion potential and concentration gradient ?

ans : as the diffusion potential decreases the concentration gradient

What is the main role in diffusion ?

ans : concentration

Nernst equation = +_ log ( inside / outside) but I will not ask you to calculate , just

I want you to know the principleNow characteristics of an action potential , first triggered by depolarization , a less

negative membrane potential that occurs transiently . and as we mentioned before

about the threshold depolarization , it is needed to trigger the action potential .

Numbers are not important .*

All or none : either to be or not to be , also the muscles either being contracted orrelaxed

So we talked about action potential , depolarization , hyperpolarization and

repolarization

In repolarization there is a closure of sodium channels at the end of depolarization

and opening of potassium voltage gated channels , so potassium is going outside

and storing the electro negativity of the membrane .

Refractory period : is the period during which it is impossible to initiate another

action potential , once an action potential is created it is impossible to create

another action potential at the same time .

The repolarization results of potassium going outside but if excessive potassium is

pumped outside it is called hyperrepolarization .


8/8

Sodium voltage gated channels are sensitive to sodium , and potassium voltage

gated channels are sensitive to potassium , it means that sodium voltage gated

channels don't permit potassium to enter and vice versa , but calcium voltage gated

channels permit sodium to enter so we have calcium pump and it pumps calcium

outside the cell and helps in the electro negativity , and calcium voltage gatedchannels which permit sodium to enter , but the difference between calcium

channels and sodium channels that sodium channels are fast and that's why we

called it fast sodium channels , and calcium channels are slow and that's why we

called it slow calcium channels or slow calcium-sodium channels ( in the heart ) .

In the intestine the main factor that makes the action potential is the slow calcium

channels or calcium-sodium channels .

In the heart also ( cardiac muscle ) we have two kinds of channels , we have thefast sodium channels and the slow calcium-sodium channels , later on we will talk

about the depolarization in the heart and the action potential there .

M gates are the activation gates and it is the outer , H gates are inactivation gates

and it is the inner .

Channel density : how many channels in a unit area of plasma membrane .

Forgive us if there is any mistake

Done by : Nour HejazinAraam Odeibat

Elias Abu rahmoun

Documents

script #4 Action Potential