A+P 2--17.3: Cardiac Muscle Tissue A&P
electrocardiogram, contractile, dysrhythmia
An _____ (ECG, EKG) is a graphic depiction of the electrical activity occurring in all the cardiac muscle cells over a period. -electrodes are placed on patient's skin: 6 on chest, 2 on each extremity --the electrodes record changes in electrical activity from unique positions in the heart, which register on the ECG as deflections, or waves -the ECG shows changes in ___ cells-there are not enough pacemaker cells to measure; the ECG appears flat when pacemaker cells have APs ------------------------------------------------- -ECGs reveal info on the *structure, conduction pathways, and overall health of heart*. --> it can detect ______ (aka arhythmia)
pacemaker, sinoatrial node, right, fastest, ANS, atrioventricular node, tricuspid valve, slower, Purkinje fiber, slowest, atypical, AV bundle, skeleton, bundle branches, terminal branches, contractile
Cardiac Conduction System > Pacemaker Populations -this system consists of a group of interconnected ____ cells; it includes the following 3 populations: ==> ___ ____: (SA) -located on the ____ atrium, slightly inferior and lateral to the opening of the SVC -under normal conditions, the pacemaker cells of this node have the ____ intrinsic rate of depolarization-about 60-70 more times per minute; however, this changes depending on input from ____ ==> ____ ____: (AV) -located posterior and medial to ____ ____ -their intrinsic rate of depolarization is ____ than that of SA; it is about 40-50 APs/min ==> ___ ____ system: -they have the ____ rate of intrinsic depolarization (20 APs/min) -the cells are sometimes called *____ pacemakers* because their APs rely ion different ion channels and they function slightly differently --there are 3 components in this system: --> __ ____: penetrates into fibrous ____ in the inferior interatrial septum and superior interventricular septum --> R and L ___ ____: course along R and L sides of interventricular septum --> ___ ____ (of Purkinje fibers): penetrate ventricles and come into contact with _____ cells
intercalated discs, vg Na, depolarizes, slowly, inactivation, K, plateau, 0, slow, Ca, outflow, slow, resting, K, -85
Cardiac Contractile Cells > Action Potentials -APs generated by pacemaker cells are rapidly transmitted to contractile cells via ____ ____ -the contractile cells then have an AP, which occurs via the following process: *1- rapid depolarization phase:* pacemaker potential causes change in membrane ∆V > this activates __ ____ channels > they open, causing rapid influx of Na (membrane ____ rapidly) -- the upstroke in membrane ∆V occurs much faster in contractile cells than in pacemaker cells because the vg Ca channels in pacemaker cells activate more ___ *2- initial repolarization phase:* -occurs due to abrupt ____ of vg Na channels and very brief opening of ___ channels that cause very small outflow of K *3- ___ phase* -in this phase, depolarization is sustained at about __ mV -this critical phase is due to ___ opening of __ channels and resulting influx of Ca ions (certain Na channels also remain open) --very little change in potential, because there is ___ of K in addition to inflow of Ca -the Ca channels are ____ to close, making this plateau phase last longer than initial depolarization *4- Repolarization phase:* -both Na and Ca channels return to ____ states and most ___ channels are open > this results in outflow of positive charge > membrane ∆V returns to resting state of ___ mV
sarcolemma, T-tubules, sarcoplasmic reticulum, troponin, crossbridge, Ca, Ca, ECF, troponin, SR, calcium ion-induced calcium ion release, amplifies, positive
Cardiac contractile Cells > Excitation-Contraction Coupling -this occurs through the sliding-filament mechanism and is similar to the process in skeletal muscle fibers: --> depolarization propagates through the ____ and its __-____ > ___ ____ releases Ca > Ca ions bind to ____ > actin can bind to myosin and ____ cycle begins ------------------------------------------------ -There are differences between cardiac and skeletal excitation-contraction coupling: --> skeletal muscle cells have very extensive sarcoplasmic reticula that are well-connected to T-tubules > their SR release all the ___ required for contraction; they are not affected by extracellular [Ca] --> in contrast, the SR of cardiac myocytes are not as extensive; many ___ ions required for contraction diffuse into cardiac muscle cells from the ___ and into T-tubules --->> in cardiac muscle, Ca ions bind to ____ and also stimulate the ___ to release more Ca ions in a process called ___ ___-_____ ____ ___ ____ > this ____ the overall response, ensuring a sufficiently strong contraction with each AP (this is an example of a ____-feedback loop)
nervous, pacemaker cells, action potentials, contractile, autorhythmicity
Cardiac muscle cells do not require ____ stimulation to initiate contraction; rather, their electrical activity is coordinated by a small, unique population of myocytes called ____ ____, which generate ___ ____ rhythmically and spontaneously; these APs trigger _____ cells --Cardiac muscle tissue has the property of ______-it sets its own rhythm without need for input from the NS.
SA node, gap junctions, atrial, atrial conducting fibers, AV, slows, low, fibrous skeleton, AV node delay, bundle, atria, blood, backward, bundle branches, Purkinje fibers, ventricles, faster, ventricles
Conduction Pathway through the Heart -the following events occur in each heartbeat: *1- __ ____ generates an AP that spreads rapidly via ___ _____ to surrounding ___ cells* -next, in a process that takes about 0.03 sec, specialized ___ ___ ____ conduct the impulse to the AV node *2- upon reaching the ___ node, impulse conduction ____ for 2 reasons:* (1) - ____ number of gap junctions between AV nodal cells (2) - the presence of the nonconducting ___ ____ that surrounds the AV node -this slow conduction, called the __ ____ ____, lasts about 0.13 sec --> the time it takes for the AP to spread from the SA node to the AV _____ allows time to depolarize (and contract) the ____ before the ventricles, giving the ventricles time to fill with ____ --> it also prevents current from flowing ____ to the atria -the AP is then conducted from the AV bundle to the R and L ___ ____ *3- depolarization spreads along the ___ ____ to the contractile cardiac muscle cells of the _____* -in spite of their slow rate of depolarization as pacemaker cells, the Purkinje fibers conduct APs ____ than any other cell in the myocardium -in 0.06 sec, the entire mass of the R and L ____ is depolarized, for a total AP duration of 0.22 sec
ECG, bradycardia, tachycardia, heart block, P-R, defibrillation, asystole
Dysrhythmias -can be detected by ___ -they have 3 basic patterns: 1- disturbances in HR --> ____: HR < 60 bpm --> ____: HR > 100 bpm -sinus tachycardia is regular, fast rhythm 2- disturbances in conduction pathways -can be caused by ____ _____: blockage along cardiac conduction system, most often found in *AV node* --> in this ^ case, the ____ interval is longer than normal due to increased time it takes for APs to spread to ventricles form AV node --> there may also be an extra P wave (indicating that some APs from the SA node are not being conducted through the AV node at all) --heart block amy also occur along R / L bundle branch; the result in *wider QRS complex* 3- Fibrillation: -electrical activity of heart goes "haywire" --> atrial fibrillation: generally not life-threatening -appears on ECG as "irregularly irregular" that lacks P waves --> ventricular fibrillation: immediately life-threatening; appears on EcG as chaotic activity -->> it is treated with _____, an electric shock to the heart, which depolarizes all ventricular myocytes simultaneously > they are thrown into refractory period; ideally, SA will resume pacing the heart -it is distinct from "flat-lining" = ____ (treated with CPR and drugs that start heart, like atropine and E)
intervals, segments, R-R, AP, HR, P-R, SA, atria, ventricles, AV node delay, Q-T, ventricles, S-T, flat, plateau phase, depression
ECG -periods between waves include important AP phases, as well as the spread of electrical activity through the heart --> _____ include a component of at least 1 wave --> _____ do not include any wave components ------------------------------------------------ -There are 3 significant intervals: ==> ___ interval: -time between 2 successive R waves -represents entire duration of generation and spread of ____ through the heart -can be measured to determine ___ ==> ____ interval: -period between start of P wave to start of QRS complex -represents the time it takes for an AP to spread from the ___ node through the ___ and _____; it includes the ___ ___ ___ ==> _____ interval: -from beginning of QRS complex to end of T wave -represents time in which ___ are undergoing APs ------------------------------------------------ -Significant segments: ==> ___ segment: -end of S wave to beginning of T wave -it is _____ because it is recorded during ___ _____ of ventricles, so no net change occurs in electrical activity -* elevation/ _____ of this segment is seen in clinical conditions (myocardial ischemia, MI)
depolarization, repolarization, P, atrial, SA node, upward, SA node, QRS complex, ventricular depolarization, Q, R, S, ventricles, repolarize, T, ventricular repolarization, upward, inverted
ECG > Waves -an ECG recording consists of 5 waves, each of which represents the active ____ or _____ of different parts of the heart; they may be upward or downward ==> ___ wave: -small initial wave -represents depolarization of all ___ cells except for those of ___ ____ -nearly always registers as ___ wave on ECG -the flat segment immediately preceding this wave represents the time in which the __ ___ depolarizes ==> ___ _____: -represents ___ _____ -it is 3 separate waves --> __ wave: first downward deflection --> __ wave: large upward deflection --> __ wave: second downward deflection -it is much larger than P wave because ____ are larger than atria -the atria _____ as ventricles depolarize; this does produce a small electrical signal, but it is obscured by the large QRS complex, so it is not observed on the ECG ==> ___ wave: -represents ___ ____ -under normal conditions, it is an ____ deflection; however, some pathological states (myocardial ischemia) may cause T waves to become ____ as a result of functional changes in the cells' activity
SA node, other
Each of the 3 populations of pacemaker cells can pace the heat; however, the fastest-the ___ ____-dominates. The _____ populations may pace the heart only if the fastest ceases to function.
slow, hyperpolarized, -60, HCN channels, more, threshold, -40, Ca, depolarization, upstroke, time, K, repolarize, minimum, HCN
Generation of Pacemaker Potential *1- ____ initial depolarization phase:* -the plasma membrane is in a ____ state with minimum membrane potential (___mV) -this hyperpolarized state triggers ___ _____ to open, allowing ___ Na to leak in than K leaking out > this results in an overall slow depolarization to ____ *2- full depolarization phase:* -when the threshold (____mV) is reached, vg ____ channels open, allowing Ca inflow > this causes full _____, and is responsible for the slow ____ of membrane potential *3- Repolarization phase:* -Ca ion channels are ___-gated, and close after 100-150 msec -simultaneously, vg ___ channels begin to open, allowing for K outflow as the membrane begins to _____ *4-minimum potential phase:* -K channels remain open until the membrane reaches _____ potential > when this happens, the hyperpolarized state triggers K channels to close and ___ channels to open, and the cycle begins again!
Purkinje fibers, gap junctions
In spite of their slow rate of depolarization as pacemaker cells, the ____ ____ conduct APs *faster* than any other cell in the myocardium (as much as 150x faster than AV node). This is due to differences in their ion channels and large numbers of ___ _____ in their membranes. -in 0.06 sec, the entire mass of the R and L ventricles is depolarized, for a total AP duration of 0.22 sec
intercalated discs, electrical synapses, pacemaker, contractile, unit, heartbeat, functional syncytium
Intercalated Discs The gap junctions of ____ ____ that join cardiac muscle cells function as ___ ____. --> the electrical activity from ____ cells can be transmitted directly to ____ cells, allowing the heart to contract as a ____ to produce a coordinated ____ -->> for this reason, heart cells may be referred to as a ____ ____ (term for a large multinucleated cell)
1, 3, cardiac conduction system
Pacemaker Cells -they make up ___% of all the cardiac muscle cells -there are ___ cell populations that fire APs spontaneously to set pace of the heart --> these populations are collectively called the ___ ___ ____
reversal, -60, 10, pacemaker potential, depolarization, lack, oscillate, HCN channels, hyperpolarization, depolarization
Pacemaker Cells > Action Potentials -APs in a pacemaker cell result from a ____ in membrane potential --> the inside of the plasma membrane swings from negative (___ mV) to momentarily positive (___ mV) --> these changes occur due to vg-ion channels and Ca, Na, and K concentrations -a pacemaker AP = ____ _____ ----these APs are very different from those of other cells: -> ____ occurs much more slowly-partially because of ____ of Na ion channels in the sarcolemma of many pacemaker cells -> pacemaker potentials _____; they never remain at a resting level and instead occur in cycles, with the last event triggering the first -->> ___ ____ are what allows this to happen; they are vg and open in response to _____; by letting Na in and K out, they start a slow _____
1
Pacemaker cells make up about ___% of the total number of cardiac muscle cells.
SA node, sinus rhythms, AV node, AV bundle, cannot, slow, ectopic pacemaker, irregular
Pacing the Heart: Sinus Rhythm -the __ ____ is the normal pacemaker of the entire heart --> ___ ____ are the electrical rhythms generated and maintained by the SA node -the AV bundle and Purkinje system normally only conduct APs generated by the SA node; however, if it ceases t function, the ___ ____ can pace the heart (slowly) -the ____ _____ of the Purkinje system is the only connection between the AV node and the ventricles --> if this is blocked, the SA node ____ pace the ventricles -> the Purkinje system can pace the heart; however, it has a ____ rate of depolarization that is not adequate to sustain life beyond a short time **in the case of an ____ _____, a group of regular contractile cells or pacemaker cells other than the SA node attempt to pace the heart at the same time as the SA node; this could lead to ___ heart rhythms
striations, sarcoplasmic reticulum, tension, sliding-filament mechanism, myoblasts, branched, 1, shorter, myoglobin, mitochondria, intercalated discs, desmosomes, gap junctions
Properties of Cardiac Muscle Cells ----Cardiac and Skeletal Muscle similarities: --> _____ :alternating dark and light bands that arise from arrangement of contractile proteins within myocytes --> both types have *T-tubules* and a ___ ____ (for storing and releasing Ca ions) --> both function to generate _____, and they do so via the ____-____ _____ of contraction -----Cardiac and Skeletal Muscle differences: --> skeletal muscle arises from the fusion of _____ to form large fibers; this is not the case in cardiac muscle ---->> cardiac myocytes are individual, typically _____ cells with ____ nucleus; they are also ____ and wider than skeletal muscle cells --> cardiac muscle cells have abundant _____ --> nearly 50% of their cytoplasmic volume is composed of _____ --> cardiac myocytes are joined by ____ _____; they joint pacemaker > contractile > other contractile cells --->> cardiac myocytes are *highly folded* when they meet at these discs; at the end of the folds are ___ that hold myocytes together; where the flat parts of the membranes touch are ___ _____ that allow ions to pass between joined cells' cytoplasms
pacemaker, Ca, time, nonselective, HCN channel, hyperpolarization, Na, K
Sarcolemma of Cardiac Muscle Cells -the sarcolemma of cardiac myocytes have ion channels that facilitate changes in membrane ∆V: ==> vg Na ion channels: -these are present in all cardiac muscle cells *except for some _____ cells* ==> ___ ion channels: -present in all cardiac myocytes -* they are vg-opening but ___-gated closing-they close after a certain period, regardless of ∆V ==> K ion channels: -all cardiac myocytes have one ore more types of potassium channels (there are lg- and vg) ==> ____ ion channels: -these are unique to certain pacemaker cells is the ___ _____, a type of nonselective channel; it is a vg channel that opens in response to _____ --> when opened, it allows ____ to enter and ___ to exit the cell
plateau phase, slows, fill, strength, force, Ca, effective refractory period, tetany, refractory period, blood
The ___ ___ is what makes the depolarization of cardiac contractile cells different from that of skeletal muscles. --> it lengthens the cardiac AP to 200-300 msec, which ____ HR, providing the time for the heart to ____ with blood --> it also increases the ____ of contraction: --->> the prolonged AP makes the muscle twitch last long, so it can develop more ____, and it allows ___ ions to enter the cell, which are needed for cell contraction in sliding-filament mechanism --> it lengthens the ___ ____ ____: this action prevents ___ (sustained contraction) from occurring in the heart -this period is similar to the absolute refractory period of skeletal muscle (but they result from different reasons) ->> in skeletal muscles, the refractory period is so short that tetanus can be induced with repeated stimulation; this cannot occur in cardiac muscle due to the much longer effective ___ ____ --> the extended r. p. gives time for the heart to refill with ___ before ventricles are stimulated to contract again
cardiac conduction system
The group of pacemaker cells in the heart are collectively called the ___ ___ ____.
SA node
What pacemaker population has the fastest rate of intrinsic depolarization?
