Cardiac muscle traits and terms

Question 1

Characteristics of Cardiac Muscle

Answer 1

1. Sarcomeric arrangement (striated)
2. Mononucleated
3. Central nuclei
4. Syncytium
5. Intercalated discs
6. Cells may branch

Question 2

Comparison Between Skeletal and Cardiac Muscle

1. T tubules
2. number per sarcoplasmic reticulum
3. triads/vs diads
4. motor unit arrangement

Answer 2

1. t tubules at z disc in cardiac muscle, at I-A band in skeletal tissue
2. two in each
3. form triads in sekeltal muscle and diads in cardiac
4. cardiac muscle cells form syncytium (all connected). skeletal muscle = one never fiber/one skeletal muscle fiber

Question 3

Cardiac Action Potential

Answer 3

105 mV potential difference across membrane

-85 inside/+20 outside

remains depolarized for about .2 seconds following initial spike, followed by protracted plateau, then repolarization

Question 4

Types of Cardiac Action Potentials

Answer 4

Fast and Slow

fast have
high amplitude (100 mV)
in atria and ventricles and conduction system
rapid but non-contractile fibers (Purkinje fibers)
found in atria, ventricles, and conduction system

slow

found in the SA and AV nodal tissues
conducts slowly
automatically depolarizes during resting phase (result of leaky Na channels)
Low amplitude (60 mV)

Question 5

Phases of a Fast Action Potential

Answer 5

4) resting potential
0) depolarization
1) initial incomplete repolarization
2) plateau
3) repolarization

Question 6

The gates responsible for fast vs slow action potentials

Answer 6

Fast action potentials in cardiac muscle are basically the same as those in skeletal muscle. Slow action potentials are due to two things 1) calcium is the principle ion responsible for depolarizing the inside of the myoctes, and there’s a reduced permeability in the membrane to potassium. This culminates in longer positive charge inside (due to the slower reuptake of calcium) and added potassium charge, so the dihydropryodine receptors remain open longer

Question 7

Describe the difference in T-Tubule behavior between a cardiac muscle fiber and a skeletal one

Answer 7

t-tubles in both cells respond to depolarization from the sarcolemma. the difference in the extracellular matrix: a large quantity of calcium resides in order to rush through the dihydropyrodine receptors

when this happens, the calcium causes a conformational shift in ryanodine receptors/channels on the sarcoplasmic reticulum cisternae. excess calcium flows into the cell from

Question 8

How does calcium return to the SR cisternae?

Answer 8

two ways

1) SERC

Sarcoplasmic Reticulum Calcium Re-uptake carriers in the cisternae are phosphorylated by an enzyme called phosolambian

2) sodium/calcium symporters

Question 9

SERC

Answer 9

sarcoplasmic reticulum calcium ATPase

stimulated by phohpholambian, which, when phosphorylated, is inhibited from preventing the SERCA pump to operate