BIOL 273 - Unit 3.6

Question 1

Cardiac muscle characteristics

Answer 1

• typical striated muscle (organization of thick/thin filaments)
• contractile fibres organized into sarcomeres
• 1/3 of the cel occupied by mitochondria for ATP production via oxidative metabolism

Question 2

Differentiate between cardiac and skeletal muscle

Answer 2

• cardiac muscle cells are much smaller with single nucleus
• T tubules are much larger and branched
• adjacent cells are joined by intercalated discs with desmosomes and gap junctions

Question 3

What are the type of cells that are not involved in contraction called / how do they communicate

Answer 3

autorhythmic/pacemaker cells

communicate via gap junctions

Question 4

How is cardiac muscle different than skeletal muscle during contraction

Answer 4

• cardiac muscle have calcium entering through calcium channels on cell membrane first AND THEN from the SR (calcium induced calcium release)
• the more cytosolic calcium there is , the greater the force generated (whereas skeletal needed repeated stimuli)

Question 5

Similarities between skeletal and cardiac muscle contraction

Answer 5

both involve the use of calcium released by RyR , binds to troponin on thin actin filament

Question 6

What are the factors influencing Cardiac muscle contraction force (2)

Answer 6

1. Changes in calcium concentration
2. Sarcomere length

Question 7

How does the concentration of calcium influence the cardiac muscle contraction

Answer 7

more calcium -> greater force of contraction (vice versa)

• calcium regulated by epinephrine and norepinephrine (sympathetic pathway) that bind to adrenergic receptors
• binding to receptors activate cAMP second messenger

Question 8

What does the cyclic AMP do once it was activated by the adrenergic receptors during release of calcium in cardiac muscle (2)

Answer 8

1. Voltage gated calcium channels on T-tubules becomes phosphorylated
   - to open the channels that release calcium into the cytosol (first step of calcium induced calcium release)
   - result in more forceful contraction
2. Phosphorylation of protein PHOSPHOLAMBAN
   - acts upon calcium atpase that pumps calcium back into SR at a faster rate
   - result in shorter duration of contraction AND more forceful contraction

Question 9

How does sarcomere length influence the cardiac muscle contraction force

Answer 9

stretching a myocardial muscle cell may also allow more calcium ions to enter through cell membrane calcium channels

Question 10

Cardiac muscle contraction via action potentials: what causes depolarization

Answer 10

The action potential opens voltage-gated Na+ channels
- causing a rapid increase in membrane Na+ permeability
- up to 20 mV

Question 11

Cardiac muscle contraction: what causes the initial repolarization

Answer 11

opening of fast K+ channels and Na+ channels close

Question 12

Cardiac muscle contraction: what causes the plateau

Answer 12

Ca+2 channels slowly open causing an increase in Ca2+ permeability and the fast K+ channels close

causes sustained depolarization

Question 13

Cardiac muscle contraction: what causes rapid repolarization

Answer 13

Ca+2 channels close and the slow voltage gated K+ channels open
- resting permeability is restored