Cardiac muscle (exam 1) Flashcards
Which of the following represents the first thing that happens after Ach binds to the ligand-gated channels on the Sarcolemma
An end-plate potential is created on the muscle fiber (local potential)
The resting potential of -85mV is a characteristic of what phase of the fast cardiac AP
Stage 4
name the characteristics of cardiac muscle
Sarcomeric arrangement (striated), mono nucleated, central nuclei, syncytium, intercalated discs, cells may branch
Are cardiac mono nucleated or multinucleated
Mononucleated
Where is the nuclei of cardiac muscle
Centrally located
what is the average AP in ventricular AP
105mV
What is the range of AP in ventricular cardiac muscles
-85-+20mV
How long does the Ventricular fiber remain deploarized
about 0.2 seconds
What are purkinje fibers derived from
Modified cardiac muscle cells
Where are the T-Tubules in skeletal muscle fibers located
At the ends of the thick filaments, where the A and I filaments meet
Where are the T-Tubules in Cardiac Muscle fibers located
Found along the z-line
How many T-tubules are there per Sarcromere in skeletal muscle cells
2
How many T-Tubules are there per sarcromere in cardiac muscles
1
in what type of muscle are triads formed and what composes them
Triads are formed in skeletal muscles, composed of two T-tubules and one SR
In what type of muscle are diads formed and what composes them
Cardiac muscle, One T-Tubule and one SR
Is the SR more extensive in skeletal muscle or cardiac muscle
The SR is more extensive in Skeletal muscle
What is a syncytium
a single cell or cytoplasmic mass containing several nuclei, formed by the fusion of cells or by division of nuclei
What types of muscle cells form a syncytium
Cardiac muscle cells
Where are fast cardiac muscle cells found
Atria, ventricles, and conduction system and Purkinje fibers (which are non-contractile)
Where are slow cardiac muscle cells found
SA and AV nodes
What do Purkinje fibers not have in common with other fast AP muscle cells
Purkinje fibers are not contractile while the Atria and ventricles are
What is the amplitude of the fast AP cardiac tissue
about 100mV
What is the amplitude of the slow AP cardiac tissue
Low amplitude (60mV)
What leads to the automatic depolarization of the slow cardiac tissue
They possess leak ion channels
Do slow cardiac muscle cells depolarize automatically
Yes
What is the resting potential phase of fast action cardiac muscles
Phase 4
What is the rapid depolarization phase of fast action potential
Phase 0
What is the initial, incomplete repolarization phase of fast AP cardiac muscles
Phase 1
What is the plateau phase of fast acting cardiac muscles
Phase 2
What is the Repolarization phase of fast cardiac muscles
Phase 3
What ions are responsible for the fast action potentials of cardiac muscle cells
Potassium, sodium, and calcium conductance
What factors increase the rate of conduction velocity of cardiac muscles
Greater AP amplitude, more rapid rate of rise of phase 0, larger cell diameter
An increase in cell diameter would have what effect on the conduction velocity of cardiac muscle
It would increase the speed of velocity
Slow cardiac muscle AP does not have fast sodium ion gates
True
The upstroke of action potential is due to what ion in slow cardiac muscles
Calcium
What is the resting phase of slow cardiac muscle
-60mV
Do slow cardiac cells have a smaller or larger amplitude than that for fast action cardiac cells
Smaller
At what phase do the SA and AV nodal tissue spontaneously depolarize
Phase 4 (resting phase)
Name three basic characteristics of fast type contractile myocytes
large diameter, high amplitude, rapid onset of AP
name three characteristics of slow type non-contractile myocytes
Small diameter, low amplitude, and slow rate of depolarization
Which type of non-contractile myocyte has a small diameter
Slow non-contractile
Purkinje fibers would have what size of diameter
Very large
Which have a larger diameter fast non-contractile myocytes or fast contractile myocytes
Fast non-contractile
describe the characteristics of fast type non-contractile myocytes
Very large diameter, very rapid upstroke
What causes the AP for Ventricular fibers
Fast sodium channels (as in skeletal muscle) and also slow calcium-sodium channels (fast sodium channels are responsible for the initial spike
What is responsible for the initial spike of Ventricular fibers
Fast sodium channels
What is largely responsible for the calcium necessary in cardiac muscles for electro-mechanical coupling
Dihydropyridine Receptors (DHP) and ryanodine receptors
what are the L-Type voltage-dependent calcium channels in T-Tubles called
Dihydropyridine receptors (DHP)
what would the diameter size of a ventricular myocyte be
Large
Calcium influx is directly more affected by DHP receptors in skeletal or cardiac muscle
Cardiac
What is the absolute refractory period
The period when it is impossible to generate another AP
What is the relative Refractory period
The period when a stronger than normal stimulus can generate an AP
What would shorten the refractory period
Gates return to their phase 4 stage faster (resting phase)
What would lengthen the refractory period
Ion channels and gates take longer to get to their phase 4 stage
What node depolarizes more rapidly than the others
SA node
What node is referred to as the pacemaker
SA node
The rate of depolarization of the heart determines what
The rhythmicity
what tissues will gradually depolarize during Phase 4 in cardiac muscle
SA and AV nodes, as well as the perkinje fibers
what happens at the action potential plateau in cardiac muscle
Sodium channels close rapidly, but calcium channels open slowly and stay open for a longer period of time
also a delay in the potassium channels opening
the large concentration of both calcium ions and potassium ions is responsible for the plateau
Are there fewer calcium-induced calcium release channels in cardiac muscle compared to skeletal muscle
Yes, allow for fine control over the sarcoplasmic calcium concentration and contractility
Relaxation of Cardiac muscle is a result of what two transporters
SERCA and Sodium-calcium exchanger in sarcolemma
What is SERCA stimulated by
Phosphorylation via an integral SR protein called phospholambian which, when phosphorylated, reduces its ability to inhibit the SERCA pump
When does SERCA return calcium to the SR
During Diastole
When does the Aortic valve close
When the pressure of the left ventricle equals pressure in the aorta
What are the primer pumps
The Atria
About what percent of blood flows form the atria to the ventricles before the atria contract
80%
About percent of blood flow in the ventricles is secondary to atrial contraction
20%
The AV values are closed during what
Ventricular Systole
When do the AV valves open
At the end of ventricular systole caucus of increased pressure in Atria
what third of diastole is the period of rapid filling
The first third
What is diastasis
The middle third of diastole
- a small amount of blood flows into the ventricles representing blood that continues to flow into atria during diastole
When might diastasis be lost
During periods of increased heart rate
What happens in the last third of diastole
The atria contract to push last 20% of blood into the ventricles
When is the isometric (isovolumic) contraction
ventricles contract pressure rises causing the A-V valves to close. Than an additional 0.02 to 0.03 seconds is required for ventricle to build up sufficient pressure to push the semilunar valves open.
Describe the period of rapid ejection
occurs when the left ventricular pressure is a little above 80mm Hg and right ventricular is slightly above 8mm Hg
semilunar valves open
about 70% of blood in ventricle is ejected
occurs during the first 3rd of ejection
During what 3rd is the period of rapid ejection
the 1st third of ejection
What percent of the ventricular blood is ejected during the period of rapid ejection
70%
What 3rd does the period of slow ejection occur
the last 2 thirds of ejection
how much blood is ejected during the period of slow ejection
30% of blood is ejected from the ventricles
Frank-Starling Law
The greater the heart muscle is stretched during filling the greater the force of contraction and the greater the quantity of blood pumped into the aorta
- the stretching of the cardiac muscle brings the actin and myosin filaments to a more nearly optimal degree of overlap of force generation
what is the equation for ejection fraction
SV/EDV
How can stoke volume be increased
increasing EDV ( End-diastolic-volume) and decreasing ESV (end-systolic volume)
What is stroke volume
The difference between EDV and ESV
What is the mean velocity of blood in the proximal aorta
40cm/s
What is the range of velocity in the proximal aorta
120 cm/s (during systole) to negative value before aortic valves close in diastole
Why is the forward flow of distal aorta and arteries continuous
the elastane of vessel walls during diastole
The rate of blood flow to each tissue is
usually precisely controlled in relation to tissue need
Active tissues may need how much more blood flow than ones at rest
20 to 30 times more
Cardiac output cannot exceed what
407 times greater than when at rest
What monitors each tissues blood need
Microvessels
Needs of tissues acts directly on what
Local blood vessels
_______ and _________ also help control tissue blood flow
nervous control and hormones
at normal heart rate of 72 beats per minute the systole comprises of about _____
0.4 of the entire cardiac cycle
what is the pressure in the left ventricle at the start of phase I
Phase 1 is the period of filling and the pressure is about 2 to 3 mm Hg. There is about 50 milliliters blood from the en systolic volume
How much does the pressure in the left ventricle change by the end of phase I
Phase one is the period of filling and the pressure changes from 2-3mm Hg to 5-7 mm Hg. This is due to the increase of blood from 50 milliliters to 120 milliliters
What is the pressure in the left ventricle at the beginning of phase II
120mm Hg
What is happening in Phase II
Isovolumic contraction
What is the pressure in the left ventricle at the end of phase II
80mm Hg
What depicted in phase III
Period of ejection
Why does pressure rise in the ventricle during phase three
The ventricle is still contracting
What marks the beginning of phase III
The aortic valve opens
What marks the beginning of Phase IV
The aortic valve closes
when the heart pumps large quantities of blood what happens to the area of work diagram
it becomes much larger. it will extend faster to the right because the ventricle fills with more blood during diastole, it rises much higher because the ventricle contracts with greater pressure, and it usually extends farther to the left because the ventricle contracts to a smaller volume. especially if stimulated by the sympathetic nervous system
What is the preload in cardiac contraction
Is end diastolic volume and is related to right atrial pressure
What is the after load in cardiac contraction
the pressure in the aorta leading from the ventricle. or even the resistance to circulation
an increase in preload in the left ventricle would cause what
Pre-load is directly associated with the end diastolic volume if you increased the EDV then the SV would increase
as would the pressure curve
this would lead to increased blood volume and decreased venous capacity
Increased after load would result in what in the left ventricle
Increased after load would mean that the aortic valve has an increased pressure this means that the heart is having to work against a higher pressure gradient thus we would have an increased end-systolic volume, thus a smaller SV, and decreased pressure loop
What affect would the increase in heart contractility have on the end-styolic volume
it would decrease it. and thus increase stroke volume
Right atrial pressure and cardiac output increases with what innervation
sympathetic
