Genesisof Action Potential Flashcards
(39 cards)
Electrotonic potential
Non propagated local potential due to change in ionic conductance due to local change in conductance.
Action potential
Probated impulse
Local responses
Potential changes observed near the site of current passage
Sub threshold current pulses
The size of the potential change observed depends on the distance of the recording electrode from the point of current passage.
The closer the recording electrode to the site of current passage, the larger the potential change
Size of the potential change
Decreases exponentially with the distance to 1/e (37%) of its maximum value.
What is the length of a typical mammalian nerve or muscles cell?
1 to 2 mm
What is the importance of an action potential?
Communication between nerve cells depends on an electrical disturbance.
Action potential
A transient change in the membrane potential that conveys information within excitable cells and the nervous system when excitation occurs. W
When is an action potential triggered?
When the depolarization is sufficient for the membrane potential to reach a threshold value.
What is threshold ?
The critical point in which a membrane must be depolarised in order to initiate a membrane response.
How does the action potential differs from the subthreshold and passive responses?
It is much larger response in which the polarity of the membrane potential actually overshoots.
The action potential is propagated down the entire length of the nerve fibres
The action potential is propagated without decrement( maintains it shape and size.
All or none response
The stimulus either produces a full sized action potential or fails to do so.
Facts about all or none
Stronger stimuli does not increase either size or speed of the action potential
A stimulus of stronger intensity occurs when the frequency of firing increases
involves the flow of ions across the plasma membrane
have a characteristic form ( amplitude, time course and duration)
Stages of action potential
Upstroke: rapid depolarization of membrane
Overshoot: membrane potential is positive
Downstroke: repolarisation phase; rapid return of membrane to its resting potential
Undershoot: membrane becomes more negative that it resting value
Which cells has the fastest action potential?
Cardiac muscle, motor , skeleton
Characteristics of action potential
Threshold, amplitude, duration
Types of subthreshold potential
Local, somatic , receptor
does a subthreshold stimuli elicit an action potential?
NO
does a suprathreshold change the size of an action potential
no
factors affecting the action
1) the gating and permeability of properties of specific types of ion channels. these properties depend on both Vm and time
2) membrane properties that don not depend on Vm and time such as resistance, and the geometry.
3) the intracellular and extra cellular concentrations that pass through these channels.
regulation of Na+ channels is regulated by two gating particles
m and h gates
which gate is the activated channel ?
m is the activated gate while h is the inactivating gate. for na+ to pass through the Na+ channel both gates must be opened
ij the resting potential the activation gates are__________ while the inactivation gates are _______
closed ……. open
describe Na+ channels
its intramembrane domain is known to consist of a number of α helices that span the membrane and surround the ion channel.
The Na+ channel has both an activation gate and an inactivation gate that account for the changes in gNa during an action potential. Groups of charged amino acid residues that form these gates have been tentatively identified. To enter the channel’s narrowest part, known as the selectivity filter, K+ and Na+, it is believed, must shed most of their waters of hydration.
To strip K+ and Na+ of their associated water molecules, negative amino acid residues that line the pore of the channel must have a particular geometric shape; the precise geometry differs for K+ and for Na+. This requirement is believed to confer the specificity of ion channels.
