Cardiac Excitation Flashcards
excitation pathway
sinus rhythm - HR controlled by SA node
action potential activates atria
atrial AP activated AV node
AV node activates bundle of His/purkinje fibres
purkinje fibres activate ventricles
features of AV node
small cells
slow conduction velocity
introduces delay of 0.1s
myogenic
generates own action potentials spontaneously
e.g. cardiac muscle
action potential development at SA node
spontaneous
AP conduction from cell to cell
via intercalated discs with gap (nexus) junctions
what is the SA node essentially
the pacemaker of the heart
SA node action potential - pacemaker potential
increased gCa
increased gNa
decreased gK
SA node action potential - AP upstroke
increased gCa
SA node action potential - repolarisation
increased gK
decreased gCa
SA node action potential - noradrenaline
increased gNa
increased gCa
SA node action potential - acetyl choline
increased gK
decreased gCa
neurogenic
needs a nervous impulse to initiate a contraction
e.g. skeletal muscle
length of skeletal muscle AP
50msec
length of cardiac muscle AP
500msec
what does the action potential control in the heart vs skeletal muscle
controls during of contraction in heart
in skeletal it acts only as a trigger
what does g mean - i.e. gK, gNa, gCa
conductance
ion currents during action potential - skeletal vs cardiac
skeletal - simple
cardiac - complex
currents responsible for cardiac AP - depolarisation
large gNa
currents responsible for cardiac AP - plateau
small gNa
increased gCa
decrease gK
currents responsible for cardiac AP - repolarisation
decrease gCa
increase gK
what is released from the sarcoplasmic reticulum
calcium
Ca entry from outside required for heart cells - ‘Ca induced Ca release’
relaxation (Ca reduction) - uptake of Ca by sarcoplasmic reticulum
via an ATP driven Ca pump
modes of exit of Ca from a cell
ATP driven Ca pump (weak)
Na-Ca exchange protein (energy from Na entry gradient)
