7. Conduction of the Nerve Impulse Flashcards
Name two diseases that affect the conduction of action potentials in the peripheral nervous system.
Landry-Guillain-Barre syndrome.
Charcot-Marie-Tooth disease.
How do diseases affect the conduction of the action potential?
By breaking down and damaging the myelin sheath of axons.
What is diphasic recording?
Extracellular recording of action potentials using two points on the outer membrane of an axon.
What is monphasic recording?
Extracellular recording of action potentials between an undamaged part of an axon and an intentionally damaged axon.
What is the local current theory?
Injection of a current into an axon will cause the resulting charge to spread along the axon and cause an immediate local change in the membrane potential.
What is the length constant?
The distance it takes for the potential to fall to 37% of its original value.
What is capacitance?
The ability to store charge.
What does membrane resistance depend on?
The number of ion channels open, the more ion channels open, the lower the resistance.
How does diameter of axon affect the length constant?
The larger the diameter, the longer the length constant. So the conduction of the action potential and speed of conduction will also be higher.
How does changing resistance affect the length constant?
Increasing Rm increases the length constant.
How does changing the capacitance affect Vmax?
Increasing capacitance decreases the speed of conduction.
How do myelinated and unmyelinated axons differ?
Myelinated axons a have a lower number of ion channels as they are only present at the nodes of Ranvier. But the density of channels at the nodes is very high. Unmyelinated axons have an even distribution of Na+ channels.
How does myelination enable saltatory conduction?
The myelin sheath is an insulator so causes the local circuit current to depolarise the next node above threshold and initiate an action potential.
How does myelination increase conduction velocity?
Myelin sheath increases resistance and decreases capacitance. This means length constant increases and time constant decreases. Conduction velocity = length constant / time constant. So increases.
How does demyelination affect conduction of action potentials?
The density of action current is reduced as there is resistive and capacitive shunting. This means the current passed on doesn’t reach the threshold and can’t shoot action potentials.
