electrical signalling Flashcards
What is current
The net ion flow through channels
charge/unit time
what do ion currents do
change membrane potential and therefore regulate voltage gated channels to conduct info/provide mechanical response
what is the issue with recording firing patterns of a cell
many variables = current, voltage, time
describe the intracellular electrophysiological method of illustrating neuronal firing patterns
the membrane potential and current changes as a function of time
so you can inject current to shift the baseline and induce action potentials
what shapes firing patterns
Kv channels
which types of neurons have short action potentials and fast firing rates and how are these enabled
inhibitory CNS
through fast activation KC channels
(there are then neurons w/slow firing + long aps that have slow act. Kv channels)
What happens when you block a Kv channel using TEA
decrease firing rate, increase time for cells to depol and ap
how can the firing pattern be controlled
governed by types of Kv channels -> currents available
Describe the mechanisms of a voltage clamp
controls V to measure current as function of time
illustrates ionic mechanisms of function
uses one electrode to monitor V, one to inject current
what does the current required to inject into a cell tell you about what’s happening inside the cell
allows you to measure the current inside the cell because you need to inject equal and opposite current
current flow depends on driving force and open channels
How does probability relate to ion currents
when the V is constant, all changes in current are due to open probability, which shows the rates of transitions between open and closed states
Describe what a patch clamp is and the different types
recording pipette with conductive saline, suctioned onto a membrane. channels activity is measures as step changes in current
cell attached = IC signals from whole cell = total cell current
inside out = access to IC side
outside out = access to EC side
what are the single channels probability properties
same probability properties as entire populations of channels in membrane
What does the ball and chain describe
the inactivation particle will find and bind to its site in a matter of time to cause inactivation, even when the channel is closed, no current is passing through until that happens
what does the time course of decay back to zero show
the range of inactivation
What are the K subtype channels for inactivation
fast inactivating and relatively non inactivating (delayed rectifier)
What is the total K current a sum of
delayed rectifier + inactivating K channels
What is shown in Drosophila Kv channels
the spectrum of inactivation properties
What does the shaker gene encode for
gives rise to fast and slow inactivating channels
encodes 4 subtypes of kV channels
What’s important about the amino terminal domain on shaker genes
the exons that codes for the amino acid terminal has fast inactivation properties nad is necessary + sufficient for inactivation
What is double pulse protocol
measures the rate of recovery from inactivation
What does the rate of recovery from inactivation depend on
time and membrane potential + voltage
What encourages faster recovery and describe how this impacts closed vs open states
more -ve membrane potential, the faster the recovery because this is governed by probability
if channel open wants to be closed => require -ve mempot
is channel closed wants to be open => require +ve mempot
What can happen to Na+ channels during sustained firing
the proportion of inactivated Na+ channels accumulates
inactivation block = mempot is highly depolarised so the Nav channels can’t recover from inactivated state
