M&R 4.1 - The Action Potential and its Properties Flashcards Preview

ESA 2 > M&R 4.1 - The Action Potential and its Properties > Flashcards

Flashcards in M&R 4.1 - The Action Potential and its Properties Deck (11):
1

What is an action potential?

The change in voltage across a membrane depending on both ionic gradients and relative permeability of the membrane

2

Why is the 'all or nothing' principle of action potentials significant?

Ensures there are no half or double action potentials i.e. they are propagated without getting smaller

3

What is the significance of positive feedback in opening VG Na+ channels during the action potential?

- Positive feedback causes more channels to open so causes more depolarisation

- Ensures depolarisation doesn't stop half way through

4

What is the absolute refractory period?

The period of time at which nearly all the Na+ channels are inactivated meaning the excitability is at 0

5

What is the relative refractory period?

- The period of time at which the Na+ channels are recovering from inactivation so the excitability is returning to normal

- Number of inactivated channels decreases

6

Describe what happens during repolarisation

- Inactivation of Na+ channels = potential returns to RMP

- VG K+ channels open = potential moves towards Ek

7

Describe accommodation

- Longer stimulus = larger depolarisation needed to generate an action potential due to inactivation

- Threshold becomes more positive

- Decreases intensity as initial action potential doesn't reach threshold as more Na+ channels are inactive

8

Describe the structure of Na+/Ca2+ channels

- One peptide of FOUR homologous repeats

- Each repeat has SIX transmembrane domains

- One transmembrane domain is sensitive to changes in voltage (positive amino acid residue)

- ONE pore formed by a dipped Beta sheet in which the inactive particle sits

9

Describe the structure of a VG K+ channel

- FOUR subunits

- Each subunit has SIX transmembrane domains

- One transmembrane domain is sensitive to changes in voltage

- Pore is formed by FOUR subunits

10

Describe the effects of local anaesthetics e.g. Procaine

How are these effects caused?

- Bind to and block Na+ channels = stops AP generation

- Cross membrane in unionised form and block Na+ channels when open

- Have a higher affinity to the inactive state of Na+ channels

11

In what order are local anaesthetics most likely to affect neurons? Why?

- Small myelinated axons

- Non-myelinated axons

- Large myelinated axons

- Tend to affect sensory neurons before motor neurons

Decks in ESA 2 Class (63):