5 cardiac and skeletal muscle cells differences.
- 1. Gap junctions- absent in skeletal muscle and present in cardiac muscle. Slow down signals in the AV node and gives time for ventricles to fill with blood before contracting.
- 2. The source of Ca+ in skeletal muscle is the sarcoplasmic reticulum and in cardiac muscle its the sarcoplasmic reticulum and extracellular fluid. Ca+ in ECF flow into the cell when the gates open slowly and bing to ligand regulated Ca+ channels in the sarcoplasmic reticulum. SR responsible for a lot of Ca+ being released in cytosol, accounts for 90-98 % of Ca+ needed for contraction.
- 3. Nervous stimulation is not required in cardiac muscle but is in skeletal.cardiac muscle needs to function without stimulation to sustain itself. It has a pacemaker in the SA node that fires at regular intervals and the muscle can contract rhythmically and independently.
- 4. Cardiac muscle has a greater amount of mitochondria than skeletal muscle and relies on aerobic respiration. Cardiac muscle is very resistent to fatigue unlike skeletal muscle.
- 5. Skeletal muscle has a brief twitch when contracting and caridiac muscle sustains contractions so that blood can eject from the heart to chambers.
What causes the ventricular cardiac muscle cell action potential to look different then those from neurons?
In ventricular contraction action potentials open volatge regulated slow calcium channels producing a long plateau in the action potential. The prolonged depolatization creates a plateau that is not seen in neurons.
The cardiocyte in figure 19.14 has a absoute refractory period of approximately 0.20 seconds. Assuming all of the cells in the heart have the same absolute refractory period, what would be the maximum heart rate in beats per minute?
During an absolute refractory period no stimulus of any strength will trigger a new action potential. Within 60 seconds the cardiocyte will produce an action potential every 0.20 seconds. 60s/0.20s= 300bpm
The absoute refractory period of a skeletal muscle is much shorter (approximately 0.002 seconds). What is the benefit of having such a long absoute refractory period in cardiac muscle?
A long absolute refractory period in cardiac muscle helps with the prevention of wave summation that would stop the heart from pumping and a sustained muscle contraction.
What caused the action potential from the pacemaker cells (fig 19.13) to appear different than the action potential of a ventricular cardiocyte?
- SA node doesnt have stable resting potential it starts at -60mV and drifts upward with gradual depolarization and a slow inflow of Na+.
- Ventricular cardiocytes have a stable resting potential of -90mV and only depolarize when stimulated. Na+ rapid inflow.
Moving paper chart used to detect electrical currents in the heart by means of electrodes applied to the skin.- composite recording of all action potentials by the nodal and myocardial cells.
The 4 Heart Chambers
-superior pole (base)
Right and Left atria- thin walled chambers for blood returning to the heart by way of the great veins.
The 4 Heart Chambers
-inferior pole (base)
Right and left ventricles- pumps that eject blood into the arteries and keep it flowing around the body.
constitutes most of the anteror aspect of the heart
forms the apex and inferiorposterior aspect
- -ensure a one way flow
- -between each atrium and its ventricle and another at the exit from each ventricle into its great artery.
- - no valves where the great veins empty into the atria.
Atrioventricular (AV) Valves
regulate the openings between the atria and ventricles.
right av valve has three cusps
left av valve has has two ( mitral valve)
- (pulmonary and aortic valves)
- regulate the flow of blood from the ventricles into the great arteries.
controls the opening from the right ventricle into the pulminary trunk
controls the opening from the left ventricle into the aorta.
How do the valves open and close?
pushed open and closed by changes in blood pressure that occur as heart chambers contract and relax
AV Valves open?
- during diastole, ventricles expland and their pressure drops below that of the atria
- -blood flows into ventricles
- -ventricular pressure rises
- -artrial pressure falls
- -marked by slower filling
- - P wave occurs at end of diastole, depolarization of atria
-completes filling porcess
AV valves close
- -pressure in ventricles rises sharply and reverse pressure gradient between atria and ventricles.
- - AV close as ventricular blood surges back against the cusps.
- -heart sound S1 occur at begining of this phase-produced by left ventricle
AV and semiulnar valve closed
- -phase called isovolumetric
- -ventricles contract but do not eject blood and there is no change in volume
- -pressure in aorta and pulmonary trunk greater than in the ventricles
- -blood can not go anywhere
- - in graph at the end of diastole point of shift in atrial and ventricular pressure.
Aortic semiulnar valves open
- -ejection of blood begins when ventricular pressure exceeds atrial pressure pressure peaks at 120mm hg in left ventricle.
- -forces semiulnar valves open
Aortic semiulnar valve closes
- - begining of ventricular diastole blood from aorta and pulmonary trunk briefly flow backward through the semiulnar valves.
- - backward flow fills cusps and closes valves
- - heart sound S2 occurs
contraction of any heart chamber
heart relaxed and fills with blood
one complete heart beat atrial and ventricles contract and relax
When are the AV valves closed?
During isovolumetric contaction
What events within the heart causes the AV valves to open?
When ventricular pressure exceeds arterial pressure the semiulnar valves are forced open and blood ejects.
When are semiulnar valves closed?
- -during isovolumetric phase
- -ventricles contract but do not eject blood
- -no change in volume
- -oppose opening of semilulnar valves, pressure in aorta and pulmonary trunk greater.
- -when ventricles expand internal pressure falls
- -when ventricle contracts internal pressure rises
- - the greater the volume the lower the pressure and vice versa
What events causes the semiulnar valves to open?
ventricular pressure ecxceeds large arteries pressure leaving the heart
Are both sets of valves closed during any part of the cycle?
Yes, sovolumetric contraction and relaxation
Are both sets of valves open during any part of cycle?
At what point in the cardiac cycle is the pressure in the hear the hightest?
At what point in the cardiac cycle is the pressure in the hear the lowest?
what event results in the pressure deflection called the dicrotic notch?
aortic semiulnar valve snaps shut and aortic pressure increases.
If an individuals heart rate is 80 bpm, what is the length of cardiac cycle.
0.75 = 60 sec/80bpm
what portion of the cardiac cycle is shortened by this more rapid heart rate?
what two factors promote the movement of blood through the heart?
- 1.alternate contraction and relaxation of myocardium
- 2.opening and closing of valves
What organelle are less developed in cardiac muscle than in skeletal muscle? what ones are more developed? what is the functional significance of these differences between muscle type?
Mitochondria are more developed and T tubules in cardiac muscle. Skeletal muscle has satelite cells and cardiac doesnt. not having satelite cells cause repair to be fibrosis. the large mitochondria assist with metabolism of aerobic respiration.
what is an intercalcated disc and what function is served by each of its components?
- how cardiocytes are joined end to end by thick connections
- increase surface area, prevent pulling apart during contraction, help with electrical stimulation of neighbor cardiocyte.
Benefit of not using anaerobic fermentation to generate ATP?
not prone to fatigue
Where is the pacemaker of the heart located? What is it called?
Pacemaker is in the SA node in the right atrium
Trace the path of electrical excitation from the SA node to a cardiocyte of the left ventricle,name each component of conduction system?
- 1. SA node fires in the right atrium
- 2. spread through atrial myocardium
- 3.the AV atrioventricular node fires
- 4.spreads down atrioventricular bundle
- 5.purkinje fibers distribute excitation through ventricular myocardium
Why does the heart have a nerve supply since it continues to beat even without one?
sympathetic and parasympathetic nerves modify heart rate and contraction strength