w2 Electrical Activity of the heart Flashcards
What is the driving force of ions?
The difference between the membrane potential and the ions equilibrium potential
What is the deal with ions equilibrium potential?
Give some examples of different ions equilibrium potentials
Ions would like the membrane potential to be the same as their equilibrium potential.
Equilibrium potential is calculated by the Nernst equation.
E^^K =-95mV
E^^Na = +65mV
E^^Ca= + 120mV
What is an ion current?
Ix The movement of an ion across the cell membrane.
What is needed for an ion current to occur?
A driving force to encourage movement of the ion
The membrane needs conductance to that ion, e.g open ion channels so the ion can physically move.
What is the resting membrane potential?
The potential difference across a cell membrane of an excitable cell at rest.
Is normally around -70 to -80 mV.
(note membrane potential is expressed intracellular to extracellular)
Give some examples of diffusion down a chemical and electrical gradient, with Na+ K+ and Ca2+.
What is different between what needs to be considered for an electrical v a chemical gradient?
K+ diffuses out a cell down a concentration gradient, if charges then unbalance as more positive outside will reenter the cell down electrical gradient.
Na+ and Ca2+ diffuse into the cell down a chemical gradient, then would diffuse out of the cell down an electrical gradient.
Note: These electrical gradients only work when ion is considered in isolation. An electrical gradient is affected by other ions, chemical gradient by only the one ion.
Define depolarisation, repolarisation and hyperpolarisation.
Depolarisation - membrane potential becomes more positive
Repolarisation - membrane potential becomes more negative, less than zero
Hyperpolarisation - membrane potential becomes more negative than at rest.
What is undershoot and overshoot in relation to the membrane potential?
Undershoot - membrane potential is less than zero
Overshoot- membrane potential is more than zero.
What is meant by an inward or outward current in relation to membrane potential?
Describes the direction of the flow of positive charge.
Inward - flows into the cell
What is the refractory period in relation to membrane potential?
The period when during an action potential another action potential can not be triggered.
Is spilt into absolute or relative refractory periods.
What is threshold potential in relation to membrane potential?
The membrane potential at which an action potential becomes innevitable.
What is important about the membrane potential relative to the equilibrium potential of K+ and Na+?
How does this relate to their rate of movement?
K+ equilibrium potential is very close to resting membrane potential , so rate of movement of K+ across the membrane in slower.
Na+ equilibrium potential is far way from the membrane potential, so Na+ enter the cell more rapidly when ion channels open when a stimulus is applied.
What are the different types of refractory period?
Absolute - from threshold to halfway through the outward current, no action potential can be generated as the inactivation gates on sodium ion channels are closed.
Rellative - from halfway through outward current and all of hyperpolarisation, due to higher than normal K+ efflux, so greater Na+ influx would be needed. This could potentially be triggered by a greater than normal stimuli.
What is propagation in relation to action potentials?
The movement of waves of depolarisation between conductive cells due to the movement of ions between cells through gap junctions, this activate voltage gated ion channels in the new cells.
What are the two types of cells found in the heart?
Contractile and conducting cells.
What order are conducting cells found in the heart?
SAN
AVN
Bundle of His
Left/Right bundle of His
Purkyne Fibres
