4.2 - Conduction Of The Nerve Impulse Flashcards
Explain the local current theory
When there is a change in the membrane potential of part of an axon, this charge spreads to adjacent areas, i.e. a local current spreads
Conduction velocity is determined by how far along the axon these local currents can spread
How can you measure conductance velocity?
Place an anode at one end of the axon and a cathode at the other
Stimulate the cathode and record when the action potential reaches the anode
Conduction velocity = distance/time
What is the length constant?
The distance it takes for the action potential to fall to 37% of its original value
How is conductance velocity linked to fibre diameter?
Larger diameter means lower cytoplasmic resistance which means a larger current so action potentials travel further
Conduction velocity is therefore increased
How does resistance affect conduction velocity?
A higher resistance means a higher potential difference so more voltage across the membrane
This means more voltage gated Na+ channels are open so it is easier to reach the threshold, hence and increased conduction velocity
How does membrane capacitance affect conduction velocity?
Capacitance is the ability to store charge so at a low capacitance it takes less time to charge hence a quicker conduction velocity
What is the affect of myelination on conduction velocity?
Myelination increases conduction velocity as it reduces capacitance
Describe salutatory conductance
In myelinated neurones action potential jump between the node of Ranvier, gaps in the myelin sheath where there is a high concentration of ion channels
What happens in Multiple Sclerosis?
Myelin is destroyed in patches in certain areas of the CNS
Causes problems to propagation of action potentials
The density of the action current is reduced due to increased capacitance and decreased resistance
