Action Potentials Flashcards
Open when membrane is depolarized, slow inactivation, depolarizes after AP
Delayed rectifier K channel
Where is the selectivity filter of the VG Na channel?
The loop between subunits 5 and 6
What initiates closure of the inactivation gate in VG Na channels?
Outward movement of S4 (voltage sensor)
Many properties displayed by the AP are due to properties of this channel
VG Na channel
How does water play an important role in determining selectivity of the VG Na channel pore?
The size of a partially hydrated Na ion can fit but a partially hydrated K ion cant
What are used to record APs?
Intracellular and extracellular electrodes
What happens in the rising phase?
Na going into the cell, high Na conductance (how easy it is for ions to move), inside becoming positive
From puffer fish, block VG Na channel
Tetrodotoxin
What happens in the falling phase?
ABSOLUTE REFRACTORY. Na channels close and won’t open, K channels open, high K conductance
Sea anemone toxins are active here
Site 3
When the AP looks like it is jumping from noble to node
Saltatory conduction
Channel with selective ion conductance for Na
VG Na channel
When AP conduction is started from the end and moves toward cell body (rare)
Antidromic
Are the a helical segments of the VG Na channel
S1-S6
These two things help convey info about the neuron ion channels
Rate and pattern of firing
Set by K channels
Relative refractory period
These two VG channels structures are related
VG K and VG Na channels
Why cant an AP be faster than 1 ms?
The absolute refractory period
When do toxins have an effect on the VG Na channel?
When there is an AP. No effect if it is at rest
Opening the inactivation gate is also tied to doing what with it?
Closing it
What is deinactivation of the inactivation gate and when does it occur?
It is when the VG Na channel is not activated and the ball and chain falls out. It happens around -65 mV
Tetrodotoxin and saxitoxin are active here
Site 1
The voltage sensor of the VG Na channel that moves outward when the cell depolarizes
S4
What does tetraethyl-ammonium do to cells?
Blocks K current outward
What happens to channels behind the AP that the AP has already passed?
They are refractory bc Na channels are inactivated
When AP conduction is started from the cell body
Orthodromic
Block pore and selectivity filter, specific amino acids required
Tetrodotoxin and saxitoxin
What is length constant?
How far current flows before it leaks out, before it is reduced to 37%
Used to deduce the nature of the AP
Voltage clamp and squid giant axon
Segment of VG Na channels that mostly line the pore
S6
These don’t open right after depolarization, they are delayed
VG K channels
Composed of 4 subunits, each similar to one domain of the VG Na channel
VG K channels
Axon placed in saline solution, reference electrode in solution, electrodes hooked up to ultimately measure current at specific voltages
Voltage clamp
From a dinoflagellate, occurs in calms, shellfish, and mussels. Block VG Na channel
Saxitoxin
Na channels inactivated, cant be deainactivated until Vm is more negative
Absolute refractory period
This gate is less accessible after depolarization in the VG Na channel
Inactivation gate
What does I ion = g ion represent?
Current of the ion = conductance of the ion (Like Ohms law Vm - Eion)
What is needed to initiate an AP?
Depolarization of membrane due to generator potentials beyond some threshold (around -40 mV)
What are spike initiation zones?
In unmyelinated neurons, they are areas of high Na channel concentration
Part of the VG Na channel sensitive to proteases and antibodies
Inactivation gate
Used voltage clamp to determine ionic permeability changes during the AP
Hodgkin and Huxley
VG Na channels contain 4 of these
Four homologous domains
What is the maximum rate of an AP?
1000 Hz = 1 ms
Na channels inactivate, K channels open, large driving force for K to leave cell
Falling phase
Toxins that affect channel inactivation
Scorpion and sea anemone toxins
Techniques used to record electrical activity from single neurons or single channels
Patch clamp techniques
What are membrane conductance changes dependent on?
Time and voltage