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they branch out, stair stepping appearance, 50-100 micrometers long

what do cardiac muscle tissue look like and how long are they

connects muscle fibers

what do intercalated discs do

hold fibers together

what do desmosomes do

allow muscle action potentials to conduct from one musscle to another

what do gap junctions do


what % is mitochondria in the muscles

they are self excitable fibers, responible for lifelong heart beats, stimulate heart to beat even after it is removed from body

what is autorhythmic fibers and what do they do


what % of fibers become autorhythmic fibers

pacemaker and conduction

what are the two important functions of autorhythmic fibers

setting the rhythm of electrical excitation that cause contraction of the heart

what is a pacemaker

network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart. contract in a coordinated manner, make heart an effective pump

what is a conduction system

sinoatrial node, they do not have a stable resting membrane potential and depolarize spontaneously, which is a pacemaker potential,

where does an action potential start

when the pacemaker potential reaches threshold it triggers an action potential, travels throughout both atria via gap junctions in intercalated discs, following potential the atria contract

what creates an action potential and how/where does it travel

potential reaches the atrioventricular node in interatrial septum, then enters the atrioventricular bundle.

after sinoartrial node and and the atria contracts where does the potential go

bundle of his, it is the only place where potential conducts from atria to ventricles

what else is the atrioventricular bundle called and what is its significance

enters right and left bundle branches, which extends through the interventricular septum toward apex of heart

after bundle of his where does the potential go

purkinje fibers rapidly conduct the potential beginning at apex of heart upward to remainder of ventricular myocardium. then the ventricle contract pushing the blood upward toward the semilunar valve

after the potential is in the apex then what happens.

SA node, 100 times per minute, faster than other fibers b/c they spread and stimulate other areas before they generate an action potential on their own

what is teh natural pacemaker of the heart, why and how many potentials does it initate per minute

establish the rhythm

nerve impulses from ANS and hormones modify the timing and strength but do not..


what is the resting membrane potential V

fibers reach threshold due to voltage-gated fast Na+ channels opening, inflow of Na down the electrochemicla gradient produces a rapid depolarization and the channels automatically inactivate and inflow decreases

explain depolarization


period of maintained depolarization

due to Ca2+ inflow when voltage gated slow Ca2+ channels open and K+ outflow when some K+ channels open - increase calcium triggers contraction

explain plateau

closure of Ca2+ channels and K+ outflow when additional voltage gated K+ channels open

explain repolarization

binds to troponin allowing the actina dn myosin and sliding filaments to happen which creates tension, if the flow of Ca2+ is altered so is the strength of contraction

what is the importance of Ca2+

time when second contraction cannot be triggerd, last longer than contraction itself

explain refractory period

this is good because if it could blood flow would cease since ventricles rely on the alteration of contraction

tetanus (2nd contraction during refractory) cant occur, why is this good

ATP mainly from aerobic respiration, at rest comes from fatty acids and glucose, during excersie lactic acid from skeletal muscles

where does the heart get atp from at rest and during exersice and anaerobic or aerobic

a recording of electrical signals which are generated by action potentials and can be dectected at the surface of the body, composite record of action potentials produced by all the heart muscle fibers during each heart beat



instrumnet used to record electrial signals

if conduction pathway is abnorma, heart is enlarged, certain regions are damaged, and cause of chest pain

what can and EKG determine

P wave, QRS complex, T wave

what does the EKG produce (waves)

first wave, small upward deflection, represents atrial depolarizations, spread from SA node through contractile fibers in both atria

P wave - explain

2nd wave, starts down goes upward as a large triangular wave ends as downward wave, represents rapid ventricular depolarization as actio potential spreads through ventricular contractile fibers.

explain QRS complex

3rd wave, dome shpaed upward deflection, indicates ventricular repolarization occurs just as the ventricles are starting to relax

explain T wave

it is flat

during the plateau the EKG is

enlargement of atrium

what does larger P waves indicate

indicate a myocardial infarction

what does larger Q waves indicate

indicates enlarged ventricles

what does larger R waves indicate

heart muscle is receiveng insufficient oxygen

what does flatter T wave indicate

intervals or segments

what is the spans b/w waves mean

beginning of P to beginning of QRS, represents conduction time from beginning of atrial excitation to beginning of ventricular excitation. lengthens when action potential detours around scar tissue

explain P-Q interval and when does it lengthen

begins at end of S wave and ends at beginning of T wave, represents time when ventricular contractile fibers are depolarized during plateau phase. elevated = acute myocardial infarction, depressed = insufficient oxygen

explain S-T segment, when it is elevated and depressed what that mean.

extends from start of QRS complex to end of T wave, beginning of ventricular depolarization to end of ventricular depolarization. lenghened by myocardial damage, decreased blood flow or conduction abnormalities

explain Q-T intereverl and when it is lengthened what does that mean.

phase of contraction


phase of relaxation


depolarization of atrial contractile fiber produces P wave - atrial systole - depolarization of ventricular contractile fibers produces QRS complex - ventricular systole - repolarization of ventricular contractile fibers produces T wave - ventricular diastole relaxation

explain systlole and diastole inrelation to waves produces through out the heart

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