Electrical activity of the heart

How many pumps does the heart have?

2 - left and right side

How is the heart controlled?

by the nervous system but can function without

what are 99% of cardiac cells?

contractile

What are 1% of cardiac cells

capable of spontaneously firing 'autorhythmic'

where are the spontaneously firing cells located?

sino-artial node

atro-ventricular node

bundle of HIs, bundle branched, purkinjie fibres.

how many action potentials per minute in the SA node?

70-80

how many action potentials per minute in the AV node?

40-60

how many action potentials per minute by the purkinjie fibres?

20-40

what occurs when SA node cells are not working?

the AV node cells take over as the natural pacemaker

what is the natural pacemaker of the heart?

SA node

what is the funny current (if)?

allows positive charge to move in the cell and be retained by the cell.

An increase in Na+ influx.

action potential diagram

order of where excitation spreads to?

SA node.

rapidly through atria (1 m/sec).

AV node (0.05 m/sec)

rapidly through bundle of HIs and down purkinjie fibres (1-4m/sec)

through ventricular muscle cells.

what resistance is a gap junction?

low resistance

how do cardiac muscles function?

as a syncitium (single unit)

how is efficient emptying of the blood from atria to ventricles allowed?

coordination of the spread of excitation means atrial excitation and contraction are complete before ventricular contraction due to AV delay.

how do ventricles contract as coordinated units?

ventricular contractions occurs synchronously due to rapid spread down septum and through purkinjie fibres.

action potential of ventricles diagram

how is there an influx of calcium?

it is triggered by the action potential

what does calcium from the action potential trigger?

release of more calcium from the sarcoplasmic reticulum.

what does free calcium activate?

contraction of myocardial fibres = systole

what is systole related to?

contraction in the left ventricle

what does the amount of calcium determine?

cross-bridge cycling and force of contraction

how is free calcium levels lowered?

uptake of it by sarcoplasmic reticulum an extrusion of it by Na/Ca exchange and outward Ca pump.

allows for relaxation = diastole.

what does the plateau phase of AP provide?

long refractory period and protects the heart from tetanus.

sustained fused contraction.

where does ventricular contraction occur from?

inside to the outside (endocardium to epicardium)

apex to the base (bottom of the heart)

how is heart rate increased?

activation of sympathetic nerves (noradrenaline) increases heart rate by activation of Beta 1 adrenoceptors in SA node.

how is heart rate decreased?

activation of parasympathetic nerve system (acetylcholine) decreases heart rate by activation of M2 muscarinic receptors in SA node.

effects of altering plasma K+ ion conc on excitation?

abrupt changes in concertation can initiate arrythmias.

it can alter the excitability of cardiac tissue.