Membrane and Action Potentials Flashcards
ion concentrations in cells: for K+/ Na+/ Cl-
[K+] is high inside the cell relative to outside
[Na+] is low inside the cell relative to inside
Lots of Cl- ions outside the cell
sodium potassium pump is fuelled by?
breakdown of ATP
Sodium/Potassium Pump:
Actively transports 3 Na+ ions outside the cell & then intakes 2 K+ ions inside the cell
Active transport process
Resting potential
membrane potential of the cell that isn’t sending signals
e.g epithelial cells are always in a resting state
Equilibrium potential
the membrane potential at which the electrical & chemical gradients of a specific ion are balanced
Ek
potassium equilibrium potential
ENa
sodium equilibrium potential
Goldman equation:
Used to calculate the resting membrane potential of a cell taking into account multiple ion permeabilities
Depolarisation
membrane potential is more positive than resting potential
Repolarisation
membrane potential returns to resting potential after depolarisation
Hyperpolarisation
membrane potential is more negative than the resting potential
If depolarisation shifts the membrane potential sufficiently, it results in?
action potential
Neuronal action potential
Neurons receive signals &transmit them down the axon
At the end of the nerve terminal something will happen e.g. release a neurotransmitter, stimulate another nerve (electrically/chemically)
The stimulus needs to cause sufficient depolarisation to raise the voltage above the threshold
threshold
-55mV
mechanism of action of drugs such as local anaesthetics relieve pain how?
Work by blocking these channels (Na+ e.g) which means that neurons can’t fire action potentials–> can’t feel pain in that region because the action potentials transmit information electrically
If signal isn’t sent–> don’t feel pain
How nerves send electrical signals:
Action potential spreads along the axon
Depolarisation of the first part of the axon will spread to the next part of the axon etc.
At the synapse, an action potential will result in the release of neurotransmitters
Receptors on the post-synaptic membrane receive the signal
Cardiac action potential has how many phases
longer process than in neuronal cells: 4 phases
Phase 0- phase 4
cardiac action potential phase 0
depolarisation
Na+ channels open
cardiac action potential phase 1
repolarisation begins
Na+ inactivate and K+ channels open
cardiac action potential phase 2
Plateau
K+ channels still open, but some channels are activated too which results in plateau
Intake of Ca+ is important
cardiac action potential phase 3
repolarisation
Ca2+ channels close
K+ channels open
cardiac action potential phase 4
most Na+ and K+ channels closed
