Action potential L8 Flashcards
action potential=
rapid change in electrical potential across the plasma membrane of a cell.
Cells that generate action potentials (3)
neurons (nerve cells) Muscle fibres (muscle cells) Endocrine cells
Action potential in neurons
initiates cell to cell communication
action potential in muscle
initiates steps leading to muscle contraction
Action potential in endocrine
initiates hormone release
Graded response=
the response is proportional to the amount of excitation it receives.
What is the space between cell body and axon called
axon hillock
Where does an action potential first arrive
dendrites
How do action potentials pass from the dendrites to soma
passively (graded response)
What happens to negative and positive electronic potentials in the soma
they are integrated (summed)
Sum of action potentials reaches the _____
axon hillock
What response ensues at the axon hillock
all or nothing action potential
What need to happen for an action potential at the hillock;
net electric potential> threshold
What is a non-decremental spread
all or non response
membrane potential=
the difference in electrical potential between inferior and exterior of a cell.
What is a membrane potential measured in
volts or millivolts
Stages of an action potential
stimulus depolarisation action potential repolarisation refractory period resting state
What is the normal resting membrane potential
-70 mv
The charge of the inside of a neuron is
negative
The charge of the outside of a neuron=
positive
main ions involved in neurons action potential
sodium (Na+)
potassium (K+)
The extracellular fluid contains lots (2)
sodium ions and chloride
The inside of the cell contains (3)
negative proteins
phosphate ions
potassium ions
leak ion channels are
always open, continually leak specific ions across membrane
voltage-gated ion channels=
open or close in response to voltage change
ligand gated ion channels=
open or close in response to chemical or drug
Na+/ K+ pump is powered by
active transport (needs ATP)
Na+/K+ ratio
pumps 3 Na+ out for every 2 K+ in
Three main factors that set up the resting membrane potential
- low protein permeability ( negative proteins can’t leave)
- Na+/K+ pump
- High K+ permeability (moves freely through leak channels)
More Na+ is
extracellular
Equilibrium potential=
voltage at which ion’s net flow across membrane is 0
Equation that can predict a single ions equilibrium potential
nernst equation
equilibrium potential for K+
-80mV
Equilibrium potential for Na+
+61mV
2 main things nernst equation considers
valence (charge)
Concentration gradient
What equation can measure the resting membrane potential
goldmans equation
Why is the resting membrane potential close to equilibrium potential of K
Because neurons are highly permeable to K+
explain resting state of AP
-70mV
all voltage-gated Na+ and K+ channels closed
Only leak channels open
Explain depolarisation (AP)
-55mV voltage sensitive (fast activation) gates of Na+ channels open----> sodium rushes into cells making it more positive
What is threshold potential
-55mV
explain repolarisation (AP)
+40mV
Voltage sensitive K+ channels open—> potassium rushes out of cell making the inside of the cell more negative again
Explain after hyperpolarisation
-80mV
voltage sensitive K+ channels stay open and Na+ fast activation gates close
below threshold what determines the action potential
magnitude of graded response
Above threshold what determines the response
Frequency of action potentials (strong stimulus–> rapidly fire)
What ensues one-way propagation of the action potential
refractory period (previous Na+ channels are inactivated)
What happens on a myelinated axon
saltatory conduction
2 things axon conduction velocity depends on
axon diameter
myelination
unmyelinated axons are better for
smaller axons
Myelinated axons are needed for
larger diameter axons
In myelinated axons velocity ;
linear with diameter
(3) myelinated axons
A alpha
A beta
A delta
unmyelinated axon=
C fibres
What does Tetrodotoxin do
Na+ channels blocker
What is multiple sclerosis
T-cells attack myelin sheaths causing inflammation
What does local anaesthetic do
reversibly block voltage-gated sodium channels
