Neuronal Excitability Flashcards
What will happen to a neurone when it is activated?
The membrane potential of the neurone will depolarise from the resting membrane potential.
What is the relationship between the level of depolarisation and the strength of the stimulation applied?
They are proportional
What is a graded depolarisation of the membrane?
A neurone’s membrane depolarising from the resting membrane potential.
What determines how a neurone responds to electrical activation?
Whether or not a certain critical level of depolarisation is reached.
What happens if the critical level of depolarisation is reached?
The neurone will generate an all or none event known as an action potential.
What is the threshold level
The level of membrane potential where the graded depolarisation becomes an action potential.
What is the most common threshold level
Different neurones have different threshold levels, but most neurones produce action potentials at around -65mV
How long is the resting membrane potential maintained for?
Until the cell is either activated or inhibited.
What happens to the movement of Na+ ions when the neurone is at rest?
Since the concentration of Na+ ions are higher in the extracellular environment the diffusion gradient makes it favourable for them to move into the intracellular environment.
What happens to the movement of K+ ions when the neurone is at rest?
Since the concentration of K+ ions are lower in the extracellular environment the diffusion gradient makes it favourable for them to move out of the cell into the extracellular environment
What happens to ion movement when the nerve cell is at rest
- Concentration gradient is in favour of K+ diffusing to the extracellular environment. This is prevented by negatively charged particles.
Concentration gradient is in favour of Na+ moving into the intracellular environment
-
What is used to calculate the membrane potential at equilibrium for each of the ions
Nernst Equation NOT REQUIRED
What is the equilibrium potential for Na+
+71MV
What is the equilibrium potential for K+
-95MV
How do ions affect the RMP
Na+ ions leak into the cell and K+ ions leak out of the cell.
What maintains the ionic concentration gradient over time despite being electrogenic
Na, K ATPase
What is the relationship between the amount of Na+ entering the cell and the amount of K+ leaving the cell
They are the same
What does the permeability of K+ being much greater mean
The resting membrane potential is much closer to Ek-
What is the relationship between Ecl and the RMP
They are very close as there is little Cl- ,movement
What is the Goldman Hodgkin Katz (GHK)
A modification of the Nernst Equation which takes into account relative permeabilities of ions in question.
What does initial entry of Na+ ions into the cell lead to
Depolarisation of the cell from RMP
What will happen if the cell is depolarised enough to reach threshold potential
The cell will produce an unstoppable all or nothing event (action potential)
What does this action potential cause
A Further, steeper depolarisation.
What happens right after depolarisation
K+ channels open at the same time that Na+ ions are inactivated
What does the opening and deactivating of the ion channels do
Causes a K+ efflux and stops the Na influx
What does the efflux of K+ ions and no influx of Na + ions cause
repolarisation
What happens in the hyperpolarisation phase
K+ continue to be activated and inactivation of Na+ ions is removed
In the propagation of AP across the axon, what are the charges at the ends of the axon
Region where the AP is +ve
Region where AP is heading or has been is -ve
What causes Na+ ions to diffuse along the inside of the axon
Attraction to the negative charge ahead
What does the forward movement of Na+ plus cause
Depolarisation which triggers the opening of sodium voltage gated ion channels. This results in more Na+ entering the cell causing more depolarisation and an action potential
What happens to the Na+ that diffuse backwards
They won’t cause an AP as this part of the axon is in its absolute refractory period and Na+ channels are inactivated
What happens due to the myelin sheath insulating sections of the axon
Increases speed of AP conduction, also mean no leak of charge so SP can travel further
Why do myelinated neurones transfer impulses faster than non-myelinated cells
Na+ ions only enter at the nodes of Ranvier causing depolarisation and an AP
What is saltatory conduction
the AP jumping from one node to another by flow of ions
Why can saltatory conduction speed up depolarisation across an axon
Every time channels open and close it takes time so reducing the number of places this happens saves time
What is multiple sclerosis
A demyelinating disease
Compare the conduction velocities of myelinated and non-myelinated neurones
0.1 metres/second Unmyelinated vs 100 metres/second myelinated
How does the size of the axon affect the speed of conduction
The larger the diameter of the axon the faster the conduction.
