9. Biochem 1 - Contractility

Question 1

What are the four layers of the heart? And describe the composition of each [cells wise]

Answer 1

Endocardium - endothelial cells
Myocardium - myoctes
Epicardium - mesothelial cells and connective tissues
Pericardium - fibrous sac

Question 2

Describe skeletal muscle.

Answer 2

Striated
Unbranched
Multinucleated
Bundles
Contract quickly but get fatigued

Question 3

Describe smooth muscle

Answer 3

Non striated
Involuntary
Uninucleated
In sheets - unbvranched
Contract slowly
Don’t fatigue

Question 4

Describe cardiac muscle

Answer 4

Between striated and non striated
Involuntary
Uninucleated
Branched
Contract quickly and rhythmically
Don’t get fatigued

Question 5

What are cardiac myocytes separated by?

Answer 5

Intercalated discs

Question 6

What are demosomes?

Answer 6

Strong connections that tie adjacent calls together that allows force created in one cell to be transferred to the adjacent cell

Question 7

What is the function of gap junctions?

Answer 7

Electrically connect cardiac muscle cells to eachother
Allow waves of depolarisation to spread rapidly from cell to cell to allow cardiac cells to contract almost simultaneously

Question 8

What are cardiac myocytes composed of?

Answer 8

Bundles of myofibrils that contain myofilaments
Myofibrils have sarcomeres

Question 9

What are sarcomeres

Answer 9

Basic contractile units of the myocyte
Have thick myosin filaments and thin actin filaments

Question 10

What can long QT syndrome lead to?

Answer 10

V fib

Question 11

What is the name for sustained contraction?

Answer 11

Tetanus

Question 12

If a non pacemaker cell is stimulated during the absolute refractory period what would happen?

Answer 12

No response

Question 13

If a non pacemaker cell is stimulated between the absolute refractory period and the effective refractory period what would happen?

Answer 13

A non propagated response

Question 14

If a non pacemaker cell is stimulated after the effective refractory period what would happen?

Answer 14

Gives rise to a new propagated action potential

Question 15

Describe excitation contraction coupling ECC

Answer 15

Action potential enters from adjacent cell
Voltage gated L type Ca2+ channels open. Ca2+ enters cell
Ca2+ induces Ca2+ release through ryanodine receptor channels RyR
Local release causes Ca2+ spark
Summed Ca2+ spark create Ca2+ signal
Ca2+ ions bind to troponin and initiate contraction
Relaxation occurs when Ca2+ unbinds from troponin
Ca2+ pumped back into sarcoplasmic reticulum for storage
Ca2+ exchanged with Na+ by NXN antiporter - gradient maintained by na k pump

Question 16

Describe the different stages in cross bridge cycling in muscle contraction

Answer 16

1. Myosin heads split atp and become reorientated and energised and changed shape
2. Myosin heads bind to actin forming cross bridges
3. Myosin heads rotate towards center of sarcomere [power stroke]
4. As myosin heads bind to atp, the cross bridges detach from actin