Conduction Of Nerve Impulses Flashcards
In disease states which affect action potential conduction, what is the common problem?
Breakdown or Damage to myelin sheath
What is the difference between diphasic and monophasic recording?
In monophasic, the potential only changes in one direction because the second electrode is attached to damaged nerve tissue.
Why do we get different measurements at different points on nerve fibres?
Nerve fibres are made of multiple axons, so they will all have slightly differing conduction velocities and so this will affect measurements.
What is local current theory?
This is the theory that if we inject current into an area of the axon then it will spread locally by currents.
Name two factors which will affect the local spread of current in a membrane.
The capacitance of the membrane and the resistance of the membrane (number of ion channels open)
What is the significance of sodium channel inactivation on the direction which action potentials move?
Sodium channel inactivation keeps the action potential moving in a single direction as one cannot be fired in the area directly behind the action potential due to sodium channel inactivation.
What is the difference in ion channel density at the node of ranvier compared with under the myelin sheath on an axon?
There is a much higher density of ion channels at the node of ranvier compared with under the myelin sheath.
Describe the sodium channel distribution on an Unmyelinated axon
The sodium channels are equally distributed along the whole axon.
What is saltatory conduction?
This is where depolarisation can spread from one node to the next on a myelinated axon and so the action potential is passed along the axon.
Why does myelin sheath increase rate of conduction?
Myelin sheath is a good insulator and so causes local currents to depolarise the next node.
What factors lead to myelin sheath causing an increase in conductance?
Membrane resistance increase, membrane capacitance decreases, length constant increases and time constant decreases slightly.
Why is there failed transmission in a demyelination area of an axon?
Conductance decreases because there is decreased resistance and increased capacitance so the membrane can store more charge. This means that there is less spread of local current - not as far as the next node.
