How Nerves Work 4 Flashcards
What does a diagram of an action potential look like?
What is the threshold to fire an action potential?
-55mV
Explain the ionic basis of the firing of an action potential?
- Leaky K+ channels bring the cell to threshold (graded potential)
- Voltage gated channels open allowing Na+ to flow in and bring the cell to +40mV
- More K+ channels open and bring the cell down to -90mV
What channel is faster, and which is slower, out of Na+ and K+?
Na+ channels open faster and K+ stay open for longer
Explain how the excitability of a cell changes?
The greater the membrane potential, the greater the excitability of a cell
What does excitability of a cell mean?
How easy it is to fire an action potential
What is the absolute refractory period?
When all gates are opened and the action potential fires (low excitability)
What is the relative refractory period?
Gates are closing and recovering (excitability increasing)
Is the size of an action potential proportional to the size of the stimulis?
No, they are all the same size
How does the size of a stimulis impact an action potential?
The bigger the stimulis, the more action potentials are fired (increased frequency) but the size is the same (same amplitude)
Are action potentials self-propogating or decremental?
Self propogating
What does self propogating mean?
Keep making new ones for themselves
How does the self propogation of action potentials work?
Depolarisation spreads across a membrane decrementally, opening more channels
Why do action potentials technically not spread backwards?
They do, but the gates are not opened so nothing happens and it decremenates into nothing
How can you increase conduction velocity?
Larger axons
Myelination
Why do larger axons increase conduction velocity?
They decrease conduction resistance
What two cells form myelin sheath?
Schann cells (PNS)
Oligodendrocytes (CNS)
Where are the voltage gates on a myelinated axon?
Not in the myelinated section, but in the gaps between (nodes)
How does depolarisation spread along a myelinated axon?
Spreads from node to node without decaying much to to the high insulation
What are some diseases that de-myelination causes?
Multiple scerosis
Gwillain-Barre syndrome
Why does de-myelination cause disease?
Signal decays quicker and doesn’t reach threshold at the next node
What is a nerve?
A bundle of axons
What varies within the axons of a nerve?
The size and extent of myelination
What is the compound action potential?
Signal recorded extracellularly from large populations of axons
What does each bump in the graph of a compound action potential represent?
An action potential going past at that point in time, each one being from the same stimuli
What are the different waves and speeds in a compount action potential?
Which end of the spectrum of waves is most sensitive to anoxia and local anaesthetic?
Aa is most sensitive to anoxia
C is most sensitive to local anaesthetic
What is anoxia?
An absence of oxygen
