cardiac physiology Flashcards
heart muscle
stimulated by nerves and is self-excitable (automaticity)
contracts as a unit
has a long (250 ms) absolute refractory period
cardiac muscle contraction is similar to skeletal contraction
sinoatrial node
generates impulses about 75 times per minute
atrioventricular node
delays the impulse approximately 0.1 second
Bundle of His
Bundle of His slits into two pathways in the interventricular septum.
1. Bundle branches carry the impulse toward the apex of the heart
2. Purkinje fibres carry the impulse to the heart apex and ventricular walls
Autorhythmic cells
- initiate action potentials
- have unstable resting potentials called pacemaker potentials
- use calcium influx for rising phase of action potential.
resting potential
High concentration of sodium outside of the cell as well as potassium but inside cell.
voltage gated sodium and potassium gateway.
relative distribution of Na and K when resting.
phase 0
depolarisation phase
Myositis is stimulated
fast acting Na channels open and allow extracellular space to move inside the cell.
influx of sodium ions through voltage gate
efflux of K ions moving through voltage gate.
phase 1
at 40
early repolarisation phase
high Na inside
high K outside
closes sodium channels haunting influx of Na ions
brief opening of K ions which iniciate repolarisation of cell.
Phase 2
repolarisation sequence begins
opening of calcium channels
influx of calcium ions infler triggers release of calcium from different intracellular stores this is important for contraction of myositis
phase 3
rapid repolarisation
membrane potential eventually restored to resting values
calcium is being used in cell
extrinsic innervation of the heart
usually 75-80 AP generated per minute
can be regulated externally:
The heart is stimulated by the sympathetic cardioaccelerator centre
Heart is inhibited by the parasympathetic cardioinhibitory centre
