Lecture 22 Flashcards
What does the action potential function to do? What type of signal is it?
Action potentials function to send information down a nerves axon, its an electrical signal.
What must be reached to cause an action potential?
The threshold potential (typically -59mV).
What will lead to an action potential?
Stimulus gated Na+ channels opening will allow positive charges to flow in, causing a local depolarisatiom and causing the area to reach the threshold potential.
What event occurs once threshold potential has been reached? How does this cause the action potential to continue along the cell?
Voltage gated Na+ channels will open, leading to rapid local depolarisation. This produces a minor electric field which causes surrounding areas to reach threshold potential (if not inhibited), allowing the signal to continue.
What is the rough maximum value for the membrane potential? What occurs at this point?
+30mV, at this point the Na+ channels will close, hence the membrane potential will no longer decrease. Almost immediately after the Na+ channels shut K+ channels will open, causing the membrane potential to repolarise (hyperpolarisation). The membrane potential will end this point slightly lower than the resting membrane potential and the K+ channels will close.
What functions to restore the RMP once the K+ channels have shut?
The Na+/K+ ATPase ion pump.
What are the four types of potential?
Resting, local, threshold and action.
What prevents action potentials from travelling backwards?
The refractory periods of the sodium channels, there are two types, the absolute, in which the Na+ channel is essentially blocked and hence no action potential can occur or the relative, in which the Na+ channel is difficult to activate due to hyperpolarisation.
What coating allows action potentials to be transmitted quickly? How does this speed conduction?
The myelin sheath coats axons of most neurons and insulates the axon, the myelin is not a full coating, there are gaps in between called nodes of ranvier where ion channels are highly concentrated. This high concentration allows a large electric field to be formed, hence allowing the action potential to jump the insulating myelin sheath to the next node of ranvier. This dramatically increases conduction speed.
What are the three sodium ion channel states?
open, closed and inactive.
