Chapitre 4: Potentiel d'Action Flashcards
Que se passe til durant la communication du systeme nerveux
Stimulus sensoriel : via visuelle, cutanée , musculaire etc
il est converti en code neurale : à travers des potential action converti dans potential post synaptique
Interprétation/action: le potentiel dAction est interpreté par le cerveau ou par action motrice
what is a potentiel d’Action
Transfert l’information sur de longues distances
caractéristique d’un code neurale
fréquence : is there more pics or less pic in a span of time
patron de décharge : 2 pictures with 6 pics but one of them has a longer gap
Quelles sont les phases d’un potentiel d’action
Potentiel de repos - neurone en repos
Phase ascendante (dépolarisation de la cellule)
Dépassement until the pic - raising above 0mV
Phase descendante très rapide (repolarisation)
Hyperpolarisation (periode refractaire absolue followed by relative)
Action potentiel can be generated by what
Stimulation electrique
chimique
mecnique
What is the concept of tout ou rien
everytime we generate an action potentiel , it will always give the same pic/shape .
Reaction en chaine
boucle de rétrpaction postivie durant un potentiel d’action
ou il y a des ouverture des canaux perméable au ions sodium
La fréquence de décharge dépend de :
L’amplitude du courant injecté
Si un research injecte du courant et veut lire l’amplitude de la cellule .. que ce passe til si:
La stimulation est trop faible
La stimulation est au dela du seuil
La stimulation est plus forte
La stimulation trop faible - elle dépolarise la membrane mais il n’y aura pas de potentiel action
Juste au dela du seuil: on vera quelque potentiel d’action
Stimulation plus forte: on vera une augmentation de décharge (nombre de pic par un temps donné)
Qui ont étudier l’expérience avec les calmar
Huxley and Hodgin
What was the purpose of the calmar experiment by Huxley and Hodgin
to determine the permeabilité of Na and K
to determine the model mathématique
Decrire le simple modèle d’un potentiel d’action
1) Repos: quelque K channels are open. to exit the membrane and reduce the vM
2) ouverture des canaux Na, dépolarisation –> leads to more canaux Na to open up une fois que ca depasse le seuil
3) une fois rendu à un pic, les canaux Na se ferment, et les canaux K s’ouvrent (repolarisation)
4) Retour au repos: quelque canaux K+ restent ouvert comme au début
Quelle est le Problème majeur avec ce modèle simple (2)
on ne pouvait pas expliquer comment les canaux Na se fermaient à un Vm dépolarisé
et comment est ce qu’il restent fermés lors que les canaux K repolarise la membrane
What is electrophysiologie cellulaire
une technique qui nous aide à observer l’activité electrique d’un neurone
permet de comprendre le comportement d’un courant à différent potentiel membranaire
What happens in an electrophysiologie
We place a cell inside a bath with ions. we attach 1 electrode to the cell and the other electrode is place inside the bath.
we let the circuit pass through the cell – and use the formula of OHM to record the electrode
What is the issue with the electrophysiology
we cannot measure both voltage (Vm) and Current (Im) at the same time.
it can only be 1 of the 2
How can we use the electrode in electrophysiologie then (how can we measure Im and Vm)
you can find Voltage by imposing a current (Im) - current can be positive or negative
you can find the current (Im) by imposing a Voltage (Vm) - we are curious to see what happens to our current if the potentiel membranaire is at a specific value
What are the 2 techniques to find the current or voltage
current clamp
voltage clamp
what is current clamp
classic
inject/impose a current and we look at the potentiel membranaire aka Vm (are there any action potential)
What is voltage clamp
we are using equipment to maintain our potentiel membranaire at a specific voltage (Vm)
then i will be able to record the current during that membrane potential change
(observe les propriétés des canaux ionique en suivant leurs conductance)
Quelle est le probleme avec les voltage clamp.
the purpose of voltage clamp is to adjust the membrane potential to visualize the current
however, when we adjust the voltage or the membrane potential, this will result in opening and closing of channels to return the membrane back,
we will then use equipment that will neutralize and maintain the potential membrane.
How do we read voltage clamps:
We know that voltage clamp is when we want to maintain a certain membrane potential and want to see the current during that specific membrane potential.
We have equipment that injects the current that neutralizes and keeps the membrane potential stable. but those currents are actually opposite current to what the membrane is producing . so when we read a voltage clamp. we invert the current that is recorded to deduct what the membrane is producing
if current injected is 2amp then the current of the membrane is -2amp
example : Si-dessous, vous voyez des enregistrements voltage-clamp d’un courant ionique qui est activé par la dépolarisation de la membrane (voir le haut du panneau F pour la stimulation imposée par les auteur.e.s de l’étude). Pouvez-vous déterminer si c’est un courant dépolarisant ou hyperpolarisant?
membrane was hyperpolarisant cus the machine injected courant depolarisante
How did they figure what happens to Na and K with the voltage clamp
they noticed 2 caracteristiques in the courbe produced by the machinery
a curve that dipped (negatif by the machine aka depolarisation) and then a delay and slower curver that formed a bump at a positive value aka hyperpolarizarion
we then applied the same membrane potential but with drugs applied to sodium then another where we put drugs to inactivate the potassium : we find out that the sodium is involved in the depolarisation of the membrane and that potassium is involved in the hyperpolarisation. na channels closes more abruptly at the same time as when K channels open and remains open longer
What is patch clamping and what was its purpose
Using an electrode , you take a patch of the membrane that only contains 1 ionic channels (ie Na channel) and you study the current of that channel alone
here they used it to study a bunch of single na channels to make a summary of what they perform. same for the potassium
What is the structure of the sodium channels
selective to sodium
consiste of 4 domains just like the potassium channels
has a specific segment called S4 that are sensitive to membrane potential and influences the opening of the pores
quelle est le mécanisme du canal sodium durant action potential (new and reviewed mecanism)
- so Na opens but the fermeture rapide is done by the balle attaché au canal. il bloque le courant
PA needs to reach hyperpolarisation afin que le balle se détache du canal
Differences between channel K and Na during action potentials
both depend on depolarisation. they open
K+ has 4 sous unité , Na has 4 domaines qui sont liés ensemble
K+ opens more slowly compared to Na, but only Na s’inactive
K+ rectify and recharge le potential membranaire, it is also important to bring Na back from its inactive state
what is the mecanisme of potentiel d’action avec les correction de huxley and hodgkin
1) Etat de repos ; some K+ remains open , permeability to K+
2) depolarisation from a stimulation that opens some Na+ channels ,, this further depolarises the membrane and opens more Na+ where we end up in the phase ascendante
3) rendu au pic, the Na channels are blocked by ball d’inactivation and then we have another type of K+ channels that opens to allows ion to leave the membrane (phase descendante) aka repolarisation
4) phase descendante continue further down from the membrane de repos to undergo hyperpolarisation. K+ channels takes their time to close and this helps us remove the inactivation balls from the Na+ channels .
5) once the Na+ inactivation balls are removed, the Na+ will be able to restabilize the membrane potential back into its resting state (-65mV)
Propagation du potentiel d’action
Difference between potentiel action orthodromique et potentiel action antidromique
orthodromique : PA voyage vers les terminaison axonales/nerveuse
antidromique: PA voyage des terminaison vers les dendrites
quelle est la vitesse ou la durée d’une potentiel d’action
2ms
Quelle est la velocité typique de conduction
10m/s
What is myelin
– isolant electrique –
– couches de lipide multiple sur l’axone
– Peu de canaux Na+
– bloque le passage des ions
– consiste de cellule de schwann et oligodendrocytes
Noeud de ranvier
– les bouts des bandes de myeline
– contient bcp de Na+ channels qui permettent de regenerer le potentiel d’action
Permet le passage d’Ion
Conduction saltatoire
PA se regenere at chaque neoud de randier. as though they jump from one noeud de ranvier to the next one
difference entre conduction electrotonique aka passive
conduction active
electrotonique: passive diffusion of Na ions , myeline prevents the loss of Na ions
active: PA avec canaux sodique
WHat are the exception in the PA intiation of a neurone
majority of neurone AP start at the cone axonique
but in some neurones like neurone sensorielle , PA commence dans les terminaison nerveuse or sensorielle
