Lecture 11 - Graded and Action Potentials Flashcards
What starts a graded potential?
An injection of ion which changes the Vm
Graded Potential: Spatial Decay occurs because
diffusion of ion, current leakge
Rod photoreceptor are _______ in the dark and ________ when a photon strkies
Depolarized Hyperpolarized (closes Na+ channels)
Graded potentials occur where?
Occurs usually in dendrites and soma
Action potentials occur where?
Start at axon hilock, move through axon.
all or nothin
It is the location where the graded potentials are evaluated and either result in firing or not of an action potential.
Axon hilock
Threshold level of action potentials
-55 mV
Explain how an action potential happens
a stimulus opens the Na channels, letting Na into the cell, depolarizing it. Gate closes and then K leaves the cell, repolarizing it, then it returns to normal.
Synthetic local anesthetics derived from cocaine. How?
Reversibly block voltage-gated Na+ channels when in the open state.
-Tetrodoxin produced by some fish such as puffer fish.
-Saxitoxin produced by dinoflagellates (red tide) this accumulates in some shell fish and they become toxic.
-mu-conotoxin (cone snail).
What do they do?
Bind to voltage gated Na+ channels
The larger the axon diameter, the_______ the action potential propagates down its length.
Faster
Why is current faster in myelinated axons?
-no current leakage in the internode myelinated section,
opening
-Na+ channels takes time. Fewer membrane patches where Na+ channel opening is required, a process which takes time, and thus propogation accelerated.
Disease:
2.3 million patients worldwide.
Autoimmune.
Demyelination of neurons in CNS.
80% of patients have a form with relapses followed by remissions.
During relapse acute inflammation of CNS with demyelination resulting in conduction failure.
Multiple sclerosis
Causes of abnormal conduction:
Axonopathy – damage to axons
Conduction block
Demyelination
