muscles iii

Question 1

What is Excitation Contraction coupling, generally?

Answer 1

The events from electrical stimulation of the sarcolemma leading up to contraction of muscle cells

Question 2

Describe the receptors in the T-tubules

Answer 2

• Dihydropyridine receptors (DHP)
• voltage sensitive
• linked to calcium release channels in SR membrane (ryanodine receptors)
• AP causes shape change in DHP receptors which results in calcium outflow from SR into sarcoplasm

Question 3

What does the calcium in the sarcoplasm do?

Answer 3

It binds to troponin which pulls tropomyosin off the myosin binding sites, allowing the myosin to pull on actin

Question 4

what happens to the parts of the sarcomere during muscle contraction?

Answer 4

• z discs get closer together
• H zone gets smaller and can disappear
• A band and I band get smaller

Question 5

4 Steps of Contraction with the Sliding Filament Model

Answer 5

1. ATP hydrolysis = reorients and energizes myosin head
2. Formation of crossbridge = myosin head attaches to myosin binding site
3. Power stroke = myosin folds and cross bridge rotates towards center of sarcomere, sliding the filaments
4. Detachment of myosin from actin = ATP binds to myosin head, causing it to let go of actin

Question 6

How long does contraction cycle repeat?

Answer 6

until ATP is no longer available or calcium levels drop

Question 7

ATP use during muscle contraction

Answer 7

• ATPase hydrolyzes ATP so that myosin head can bind
• ATP binds to myosin head to detach it
• ATPase pumps calcium into SR and out of axon terminal
• ATPase is used by sodium/potassium pump to reestablish the RMP of the sarcolemma

Question 8

3 ways that muscle fibers make ATP

Answer 8

1. creatine phosphate
2. anaerobic cellular respiration
3. aerobic cellular respiration

Question 9

Creatine Phosphate metabolism

Answer 9

• excess ATP is used to synthesize creatine phosphate
• creatine phosphate transfers its high energy phosphate to ADP, making ATP
• creatine phosphate/ ATP provide enough energy for 15 secs of contraction

Question 10

Anaerobic respiration in muscle cells

Answer 10

• Glucose is taken from the blood and from glycogen stored in muscle fibers
• Glycolysis breaks glucose into Pyruvic Acid –> 2 ATP
• Pyruvic acid is converted to lactic acid and taken away by blood
• provides energy for 30-40 seconds of muscle activity

Question 11

Aerobic respiration

Answer 11

• Still uses glucose
• Pyruvic acid enters mitochondria and is oxidized, generating ATP, CO2, O2, H2O, and heat
• each glucose makes 36 (-38) ATP
• Muscles get oxygen from hemoglobin in blood and myoglobin in muscle cells (both bind oxygen)
• provides ATP for muscle activity > 30 secs
• 90% of ATP for > 10 min exercises

Question 12

Muscle fatigue

Answer 12

-inability of muscle to maintain contraction after long activity
-Factors that contribute to muscle fatigue:
not enough calcium from SR
depletion of creatine phosphate
not enough oxygen
depletion of glycogen
buildup of lactic acid/ ADP
not enough Ach

Question 13

Oxygen debt or Excess Postexercise Oxygen Consumption (EPOC)

Answer 13

• extra oxygen taken into body after exercise
• used to restore muscle cells in 3 ways:
  1. converts lactic acid into glycogen
  2. synthesizes creatine phosphate and ATP
  3. replaces oxygen removed from myoglobin