topic.9. powerpoint 9.2 Flashcards
(32 cards)
What is the main difference between neurogenic and myogenic hearts?
Neurogenic hearts are controlled by the nervous system, while myogenic hearts have contractions initiated within the heart.
Gap junctions are found where?
gap junctions are located in the intercalated discs of cardiac muscle cells.
What is the function of intercalated discs in cardiac muscle cells?
Intercalated discs allow action potentials to spread between cardiac cells[due to ion movement], due to ga junctions that produce uniform depolarization of the heart muscle.
Intercalated disc are found where?
cardiac muscle cells, more specifically the Z line of sarcomere
Draw the parts of a sarcomere
z-disk, actin filament, I band, A Band, H zone, M line
Auto-rhythmicity
The ability of the heart to stimulate itself to contract at regular intervals.
How is the heart able to stimulate itself to contract at regular intervals[auto-rhythmicity]?
uses pacemaker cells aka excitable cells in the sinoatrial (SA) node of the heart to spontaneously generate action potentials to regulate the heartbeat. Action potentials occur pacemaker specialized cell membrane that allow Na+, K+, Ca++ to cross
T/F only parasymapehtic nerve fibers influence SA nerve?
false, both can.
-Sympathetic input increases, and norepinephrine binds to receptors on the SA node, leading to an increase in the permeability of sodium (Na+) and calcium (Ca++) channels in pacemaker cells. Depolarization
-parasympathetic input increases, acetylcholine (ACh)binds to receptors on the SA node cells. This binding leads to a decrease in the permeability of sodium (Na+) and calcium (Ca++) ions, as well as an increase in the permeability of potassium (K+) ions. Hyperolarization
Sino Atrial Node found in what part of the heart?
right atrium
WHat is another name for heart muscle cells?
cardiomyocytes
How do cardiomyocytes move ions across cell membranes in order to generate AP?
depolarization and repolarization of cell membranes
Summarize heart electrical acitivty in SA node
Pacemaker cells in SA spontaneously generate AP, spread slowly through atria to AV then rapid spread of AP to large connecting fibers[Bundle of His] then to L and R bundle branches to the Purkinje fibers that goes to ventricular wall to causing rapid ventricular contraction
T/F There is electrical connection between the muscle cells of
the atria and the muscle cells of the ventricles.
false; There is no electrical connection between the muscle cells of
the atria and the muscle cells of the ventricles. There is (just
connective tissue between them)
How can AP rapidly spread down connective tissue if there is is no electrical connection between the muscle cells of the atria and the muscle cells of the ventricles?
The rapid spread of action potentials down connective tissue in the heart is facilitated by specialized conducting fibers. These conducting fibers have small diameters, allowing for the rapid transmission of electrical signals between the atria and the ventricles.
What effect will the small diameter have on the conduction
velocity of the action potential?
increases the velocity of the action potential
Why would you want the action potential to go though
the atria to the ventricles slowly? in SA node
When discussing heart electrical activity, pacemaker cells in SA spontaneously generate AP and spread slowly through atria to AV. There is a delay between the contraction between the atria
and the ventricle because you don’t want the atria and ventricles to
pump at the same time
Explain AP in SA node
1.permeability to K+[flows out], gradual rise in MP
2.Na+ travel through funny channels which are open at low MP and close as MP rises
3.Funny channels close and Ca++ enters
4. Threshold reached due to Ca++ influx
5. Repolarization K+ out
Explain how AP in SA Node spread slowly through atria to AV then rapid spread of AP to large connecting fibers[Bundle of His] then to L and R bundle branches to the Purkinje fibers that goes to ventricular wall to causing rapid ventricular contraction
2 voltage-dependent calcium channels impact cardiac muscle
-L-type, respond to higher MP, open slowly and remain open longer than the T-type
-L-type sustains AP which t-type initiate AP
What are funny channels?
allow the passage of both sodium (Na+) and potassium (K+) ions
-activated by voltage and cAMP
What if the permeability to Na+ and Ca2+ was increased?
Sympathetic effect
-slow rise to depolarization become quicker due to increase in channels openings Na+ and Ca2+
**norepinephrine is responsible
What can we expect in term of the permeability of Na+ and Ca2+ is we think about the parasympathetic effect?
Decrease permeability o Na+ and Ca2=, aka channels close and a slower rate of depolarization
How does AP in skeletal muscle differ from cardiac muscle?
AP in cardiac muscle longer than because it has a longer refractory period, meaning it can’t generate another AP until the muscle is finished contracting.
What would we expect if cardiac muscle AP has a shorter refractory period?
Another AP generated before muscle finished contracting, meaning ventricles won’t fill up completely with blood from atrium
What is the difference between cardiac muscle AP and SA node AP?
cardiac muscle AP are driven by the
output from the SA node
1. K+ flows out in Ap in SA node but in cardiac muscle AP some K+ channels actually close, increase in permeability to k+ is delayed
2.When Na+ travel through funny channels in SA node AP, the AP in ventricular muscle peaks.
3.plateaus after peak in cardiac muscle AP is explained by Ca+ channels opening for long time
4. Permeability to K+ is delayed, causing repolarization to take long time
