DSA Contractility

Question 1

What are the steps in excitation-contraction coupling in cardiac muscle?

Answer 1

1. Autorhythmic cells (pacemaker) depolarize; AP travels through dyad t-tubules
2. Ca2+ enters the cell from the ECF during the plateau via L-type Ca2+ channels (dihydropyridine receptors)
3. Ca2+ mediated Ca2+ release: more Ca2+ is released from the SR via ryanodine R.
   
   1. Because influx from ECF is not enough to initiate contraction
4. Ca2+ binds to troponin C
5. Cross-bridge cycle results in contraction

Question 2

Amount of tension in cardiac muscle is dependent on what?

Answer 2

INTRACELLULAR Ca2+, which directly depends on Ca2+ released from SR during excitation-contraction coupling.

Question 3

How does cardiac muscle relax?

Answer 3

Ca2+ ATPase moves Ca2+ back into the SR and extrudes the Ca2+, which entered the cell during the plateau phase of the AP, out of the cell with the help of Ca2+-Na+ exchanger in the sarcolemma membrane.

• Pumps Ca2+ out of the cell against its gradient.

Question 4

The difference between cardiac muscle and skeletal muscle is that …

Answer 4

Cardiac muscle uses Ca++ to come from the ECF.

With skeletal muscle, all of the Ca++ was from the inside.

Question 5

The cardiac muscle is arranged just as skeletal muscle. It is composed of sarcomeres that run from z to z line. Composed of thick and thin filaments. What makes up each?

Answer 5

Thick: myosin, globular heads with actin binding sites and ATPase activity.

Thin: actin, tropomyosin, and troponin (troponin removes tropomyosin from binding site, allowing actin and mysoin to bind)

Question 6

Contraction occurs via the sliding filament model which states?

Answer 6

When cross bridges form between myosin and actin and then break, the thick and thin filaments move past each other, causing tension

Question 7

(T) tubules invaginate cardiac muscle cells at Z lines and function to carry action potentials to the cell interior. The T tubules form what?

Answer 7

Dyads with the sarcopaslmic reticulum, which is the site of storage and release of Ca2+ for excitation contraction coupling.

Question 8

Another word for contractility

Answer 8

Ionotropism- intrinsic ability of cardiac muscle cell to develop force at a certain length.

Question 9

+ ionotropic effects

Answer 9

increase contractility.

Increase rate of tension development and peak tension

Question 10

Negative ionotropic effects

Answer 10

Decrease rate of tension development and peak tension

Question 11

Do cardiac glycosides have positive or negative inotropic effects?

Answer 11

Positive:

increase rate of tension

& peak tension

Question 12

What fuels the cross bridge cycle?

Answer 12

ATP. It will continue as long as intracellular Ca2+ is enough to bind to troponin C

Question 13

+ ionotropic events an increase in both..

Answer 13

1. Rate of tension development

2. Peak tension