Cardio Myocyte Function

Question 1

Cardiac Muscle

Answer 1

Striated, branched, uninucleated
Involuntary
Intercalated Discs (gap junctions, desmosomes-anchor, fascia adherens- stabilize tissue)

Question 2

EC coupling

Answer 2

excitation-contraction coupling- how an AP along the cardiomyocyte membrane induces contraction

Question 3

AP duration and Contraction
cardio vs skeletal

Answer 3

cardiac:
duration 200 to 300 ms
contraction 300 ms

skeletal
duration 2-5 ms
contraction 75 ms

Question 4

what type of muscle fiber cannot reach tetanus

Answer 4

cardiac

Question 5

Fast Cardiac AP

Answer 5

0- influx of Na+ for ra[id depolarization
1,2- slow Ca2+ channels open
3- repolarization K+ and Ca2+
4- K channels closes, levels off

Question 6

How contraction occurs

Answer 6

1. AP travels to T tubule
2. Voltage sensitive DHP receptors (L type Ca2+ channels) (only voltage sensitive in skeletal muscles)
3. Ca2+ influx causes release from SR
4. Ca2+ finds to troponin C (changes to troponin I), then cross bridge formation
5. SERCE gets Ca2+ back into SR
6. Na+/Ca2+ exchanger lowers intracellular Ca2+ and ends contraction

Question 7

Inotropy

Answer 7

amount of tension a myocyte can produce at any given resting myocte and sarcomere length

fun fact: calcium released from cardiac muscle SR is usually insufficient to produce peak force, but in skeletal muscle it is always enough for peak force

Question 8

What 4 factors increase Ca2+ tension

Answer 8

1. Sympathetic activity
2. Decrease sympathetic activity
3. Drugs
4. Increase in HR

Question 9

How does sympathetic activity increase contraction?
3 ways

Answer 9

NE activation of B1 reception which stimulates cAMP

1) phosphorylates L type Ca2+ increase Ca2+ influx into cell

2) phosphorylates phospholamban, removing inhibition of SERCA, increasing Ca2+ reuptake into SR

3) Phosphorylates Troponin-I which enhances binding of Ca2+ to TN-C, which increases cross bridging (not Ca2+)

Question 10

HR increases contraction by:

Answer 10

Bowditch effect
Increases frequency of AP, increases Ca2+ influx, increases SR Ca2+ release, increases contactivitity

also increasing AP frequency, increase Na+ influx, less efficient ATPase, lowers Na/Ca2+ exchange, increases cytsolic Ca2+, increases Ca2+ SR reuptake

also decreases time in diastole, increases Na and Ca, increases SR Ca stores, increases contraction

Question 11

Parasympathetic effect

Answer 11

Inhibits SNS activity
Lowers HR

Question 12

Beta Blockers

Answer 12

negative inotrope

inhibits B1 receptors/adrenergic effect

Question 13

Digitalis (cariac glycosides

Answer 13

inhibits Na/K ATPase activity

low Na+ gradient, lessens Na/Ca exchanges
Increase cytosolic and SR Ca2+

Question 14

Cardiac muscle and tension relationship

Answer 14

has greater sensitivity than skeletal muscle due to

1. Increased overlap by Actin and Myosin
2. Length dependent increase in calcium sensitivity of troponin C
3. Stretch-activated plasma membrane calcium channels

Question 15

Frank-Starling

Answer 15

Increases ventricular filling, increase stretch, increase tension

SV is dependent on End Diastolic Voluse

Question 16

Inotropy curve up and to the left with greater slope

Answer 16

exercise

Question 17

Inotropy down and to the right with lesser slope

Answer 17

heart failure