muscle physiology

Question 1

What ion is required for the contraction cycle to take place?

Answer 1

Ca2+

Question 2

What is the role of Ca2+ in the contraction cycle?

Answer 2

Ca2+ binds to troponin causing a conformational change that reveals myosin binding sites on actin. This allows for myosin heads to bind with actin

Question 3

What happens when the muscle relaxes?

Answer 3

repolarization of the sarcolemma & t-tubules leads to reabsorption of Ca2+ back into the sarcoplasmic reticulum

Question 4

Can the contraction occur without Ca2+?

Answer 4

No

Question 5

What is the contractile unit of a muscle called?

Answer 5

Sarcomere

Question 6

Where is Ca2+ stored?

Answer 6

sarcoplasmic reticulum

Question 7

What is the myofibril composed of?

Answer 7

Myofilaments: actin & myosin which are divided into sarcomeres

Question 8

Why can’t myosin bind to actin when there is no nerve impulse (unstimulated) ?

Answer 8

Tropomyosin is blocking the myosin binding sites. No cross-bridges can be formed

Question 9

What allows myosin to bind to actin?

Answer 9

When a nerve impulse is sent, Ca2+ ions are released. Ca2+ binds to troponin which causes a conformational change. This conformational change moves tropomyosin & reveals myosin binding sites on actin.

Question 10

Explain the steps that occur during stimulation of a skeletal muscle cell

Answer 10

1. Signal from nervous system is sent
2. Ach is released into neuromuscular junction
3. Sarcolemma depolarizes
4. T-tubules depolarize
5. Ca2+ is released into myofibril (from sarcoplasmic reticulum)

Question 11

Explain the steps that occur during the muscle contraction cycle

Answer 11

1. Ca2+ binds to troponin causing a conformational change which reveals the myosin binding sites on actin
2. Myosin splits attached ATP into ADP + P (phosphate)
3. Myosin binds to actin
4. Power stroke = myosin heads bend and push actin ; ADP & P are released
5. Myosin binds to ATP again; detach from actin

Question 12

What is the purpose of splitting ATP?

Answer 12

Energizes & reorients the myosin head to attach to actin. It prepares it for the power stroke

Question 13

What is formed when myosin binds to actin?

Answer 13

cross-bridge

Question 14

Name the layers/groupings of the muscle (deep to superficial)

Answer 14

1. Myofibrils = thin & thick filaments (myofilaments)
   - covered by endomysium
2. Fasicle = group of myofibrils
   - covered by perimysium
3. Muscle = groups of fasicles
   - covered by epimysium

Question 15

Where do the t-tubules extend to ?

Answer 15

sarcolemma into the cell

Question 16

What do you call the muscle cell membrane?

Answer 16

Sarcolemma

Question 17

What is the endoplasmic reticulum of a muscle cell wall?

Answer 17

Sarcoplasmic reticulum

Question 18

What is the thin filament composed of?

Answer 18

Troponin, tropomyosin, actin

Question 19

What is the thick filament composed of?

Answer 19

Myosin & myosin heads

Question 20

When does rigor mortis occur?

Answer 20

2-4 hours after death & lasts 1-2 days

Question 21

What do you call temporary stiffness of muscle that occurs after death?

Answer 21

rigor mortis

Question 22

What causes rigor mortis?

Answer 22

excess Ca2+ is released into the muscle fiber, binds to troponin, myosin & actin cant detach –> causing muscles to be rigid & fixed

Question 23

What does the contraction cycle depend on? (hint: 2 factors)

Answer 23

1. ATP availability
2. Ca2+ availability