human phys 14.2

intercalated discs

specialized connections between myocardial cells containing gap junctions and desmosomes

act as one, all cells depolarize and contract at same time, connected via intercalated discs

properties of cardiac muscles

transverse tubules

System of tubules that provides channels for ion flow throughout the muscle fibers to facilitate the propagation of an action potential.

sinoatrial node

pacemaker of the heart

purkinje fibers

fibers in the ventricles that transmit impulses to the right and left ventricles, causing them to contract

SA node, AV node, AV bundle, right and left bundle branches, purkinje fibers

structures that contain autorhymic fibers

ensures chambers contract in a coordinated way

conduciton system

act as pacemaker, form conduction system

functions of autorhytmic fibers

SA node cells spontaneously depolarize and generates AP, moves to AV node, AV bundle, right and left bundles, purnkinje fibers

steps in AP conduction system

first half is K+ channels close and F type Na+ opens, second is T type Ca2+ opens

pacemaker potential: pacemaker phase (YELLOW)

L type ca2+ channels open

pacemaker : depolarizing phase (GREEN)

L type Ca2+ close, K+ channels open

pacemaker : repolarizing phase

produce force, don't depolarize on its own, AP produced only in response to signals from nodal cells

contractile cells

fast Na+ channels open

contractile AP: depolarizing phase

Na+ closes, K+ opens

contractile AP: intial repolarizing phase

L type Ca2+ opens, fast K+ close, slow K+ partially opens

contractile AP: plateau phase

L type Ca2+ closes, slow K+ fully open

contractile AP: final repolarizing phase

Ca2+ induced Ca2+ release

influx of Ca2+ causes release of more Ca2+ from SR through ryanodine receptors

long, almost as long as duration of contraction

refractory period of cardiac muscle

electrocardiogram

A recording of the electrical activity of the heart

atrial depolarization, spreads from SA node to contractile fibers

P wave

ventricular depolarization, AP spreads through ventricular contractile fibers

QRS complex

ventricular repolarization, smaller and wider than QRS complex

T wave

time from beginning of P wave to beginning of QRS complex

P-R interval

time when ventricular contractile fibers are depolarized during plateau phase of AP

S-T segment

time from beginning of QRS to end of T wave

Q-T interval

P wave, P-R interval, QRS complex, S-T segment, T wave, Q-T interval

components of ECG/EKG

systole

Contraction of the heart

diastole

Relaxation of the heart

depolarization of atrial contractile fibers produces P wave, atrial systole contraction

step 1 of ECG waves

depolarization of ventricular contractile fibers produces QRS complex, ventricular systole contraction

step 2 of ECG waves

repolarization of ventricular contractile fibers produces T waves, ventricular diastole relaxation

step 3 of ECG waves

cardiac cycle

A complete heartbeat consisting of contraction and relaxation of both atria and both ventricles

passive ventricular filling

Blood flows into ventricles without atrial contraction.

AV valves open, blood flows from atria into ventricles, no contractions

passive ventricular filling

atrial contraction

Atria contract to push blood into ventricles.

isovolumetric ventricular contraction

ventricles contract, all 4 valves are closed, pressure rises

ventricles contract, all 4 valves close, pressure rises, ventricular volume remains same

isovoluemtric ventricular contraction

ventricular ejection

as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected

pressure rises, semilunar valves open, blood pumped out of heart

ventricular ejection

isovolumetric ventricular relaxation

all valves closed, no movement of blood in early diastole

all valves closed, pressure falls

isovolumetric ventricular relaxation

passive ventricular filling, atrial contration, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular relaxation

5 phases of cardiac cycle

lubb

closure of the tricuspid and mitral valves at the beginning of systole

dubb

closure of the aortic and pulmonary valves at the end of systole

louder and a bit longer, caused by vibrations with closure of AV valves

first sound - Lubb

shorter and not as loud, caused by vibrations with closure of SL valves

second sound - Dubb