Cardiac muscle

Question 1

Describe the flow of ox and de ox blood through the major blood vessels of the heart

Answer 1

• Dexoxygenated blood goes into the vena cava and leaves through the pulmonary artery to the lungs (pulmonary circuit)
• Oxygenated blood from the lungs enters through the pulmonary vein and leaves through the aorta to the entire body (systemic )

Question 2

What is cardiac muscle called?

Answer 2

Myocardium

Question 3

Describe the structure of cardiac muscle

Answer 3

• Striated - repeated sarcomeres
• one or two central nuclei
• adjacent cells connected though intercalated disks (desmosomes)
• has troponin and tropomyosin like skeletal muscle
• branched cells (myocytes)

Question 4

What is the func of intercalated disks?

Answer 4

1. provide strong anchorage
2. for electrical communication

Question 5

Why does the left side of heart have a thicker myocardium?

Answer 5

• needs much more force than RHS as it is pumping blood around the body

Question 6

Describe the term pacemaker potential

Answer 6

• no steady RMP
• instead it undergoes a slow depolarisation called a pacemaker potential
• brings MP to threshold where AP’s are generated

Question 7

What are nodal cells?

Answer 7

• Cells that produce an electrical impulse through a pacemaker potential
• eg the SA node in the right atrium of the heart
• the hearts natural pacemaker cell - constantly produces AP’s

Question 8

Describe the excitation - contraction coupling in the myocardium - generation of AP

Answer 8

• Na+ entry into cell causes depolarisation
• this depolarisation causes L type Ca2+ channels to open in T tubules
• Trigger Ca2+ enters cytosol and binds to the ryanodine receptor on SR
• Ca2+ then flows into cytosol
• Ca2+ binds to troponin and cross bridge cycle begins - sliding flilament mech

Question 9

What controls cardiac muscle ?

Answer 9

• Spontaneous electrical activity
• ANS - sympathetic increases heart rate and parasympathetic decreases heart rate
• note hormonal secretions and stretch have effect to

Question 10

What is phase 0 of ventricular AP?

Answer 10

• when the AP reaches the myocyte & depolarization begins
• fast Na+ voltage gated channels open but they inactivate rapidly

Question 11

What is phase 1 of ventricular AP?

Answer 11

• after Na+ channels become inactivated, there is a period of brief repolarization
• K+ channels open and outward flow of K+

Question 12

What is phase 2 of ventricular AP?

Answer 12

• consists of a plateau period where Ca2+ enters the cell through L type (long opening) voltage gated Ca2+ channels

Question 13

What is phase 3 of ventricular AP?

Answer 13

• as the plateau progresses, K+ efflux increases due to the opening of voltage gated K+ channels
• these channels are called slowed rectifier K+ channels

Question 14

What is phase 4 of ventricular AP?

Answer 14

• the resting membrane is re- established
• 75-90% of the raised Ca2+ in the cytosol is pumped back to the sarcoplasmic reticulum via the Ca2+- ATPase