2/22: Skeletal Muscle and Reflexes

Question 1

Where do muscle fibers run?

Answer 1

Length of skeletal muscle

Question 2

What is the dark band?

Answer 2

A band

Question 3

What is the light band?

Answer 3

I band

Question 4

What is the functional unit of cardiac and skeletal muscle?

Answer 4

Sarcomere

Question 5

What components makes up skeletal muscle?

Answer 5

A. Whole muscle
B. Muscle fascicles
C. Muscle fibers (cells)
D. Myofibrils
E. Myofilaments (thick and thin) arranged in sarcomeres

Question 6

What do alternating A bands and I bands create?

Answer 6

Striated appearance in skeletal and cardiac muscle

Question 7

What is the composition of A band?

Answer 7

Entire length of thick filaments

Question 8

What is the composition of I band?

Answer 8

Only thin filaments

Question 9

What is the composition of H zone?

Answer 9

Only thick filaments

Question 10

What is the composition of Z line?

Answer 10

Thin filaments anchored here

Question 11

What is the composition of M-line?

Answer 11

Link the central regions of thick filaments

Question 12

When do sarcomeres shorten?

Answer 12

During contraction

Question 13

What does the muscle look like during contraction?

Answer 13

• zone of overlap increases
• I band decreases
• H zone decreases
• A band stays the same

Question 14

What is the thin filament composed of?

Answer 14

Actin (with G-actin molecules), tropomyosin, and troponin

Question 15

What is the active site which binds myosin?

Answer 15

G-actin molecules

Question 16

What does troponin bind?

Answer 16

Actin, tropomyosin, and calcium

Question 17

What makes up thick filaments?

Answer 17

Myosin

Question 18

Describe the cross-bridges of the thick filament?

Answer 18

Multiple cross-bridges where the “heads” can bind to the G-actin molecule

Question 19

What functions as an ATPase enzyme?

Answer 19

Myosin

Question 20

What are the globular proteins of troponin?

Answer 20

T, C, and I

Question 21

What does dystrophin protein connect?

Answer 21

Thin filaments to glycoproteins in sarcolemma

Question 22

What does dystrophin-glycoprotein complex provide?

Answer 22

Scaffolding for sarcomeres

Question 23

What are muscular dystrophies?

Answer 23

A. Duchenne
B. Beckers
C. Myotonic
D. Oculopharyngeal
E. Limb girdle

Question 24

What does the alpha motor neuron release?

Answer 24

ACh

Question 25

What does the alpha motor neuron bind to?

Answer 25

A nicotinic ACh receptor on the muscle fiber

Question 26

What does botulinum toxin A inhibit?

Answer 26

The release of ACH at the neuromusclar junction

Question 27

What is botox used for in dentistry

Answer 27

Bruxism, sialorrhea, masseteric hypertrophy

Question 28

What are the 3 phases of a muscle twitch?

Answer 28

Latent, contraction, relaxation

Question 29

What must happen for contraction to occur?

Answer 29

The intracellular calcium in the muscle fiber must increase

Question 30

What does tropomyosin prevent in resting muscle?

Answer 30

A strong bond between the myosin head and G-actin molecules

Question 31

What happens when troponin binds to cytosolic Ca++?

Answer 31

Tropomyosin is pulled away from the myosin binding site, and allows for the power stroke

Question 32

What is released from the sarcoplasmic reticulum?

Answer 32

Calcium

Question 33

What is the sarcoplasmic reticulum?

Answer 33

Modified ER that sequesters Ca2+

Question 34

What is transverse (T)-tubules?

Answer 34

Invaginations of sarcolemma

Question 35

What is terminal cisternae?

Answer 35

Portion of SR that contact T-tubule

Question 36

Where does the AP travel?

Answer 36

Down T-tubules and activates voltage-sensitive dihydropyridine (DHP) receptors on the T-tubules

Question 37

What happens when the voltage-sensitive dihydropyridine receptors are activated?

Answer 37

The calcium channels (ryanodine receptors) open on the SR

Question 38

What happens when the calcium channels open?

Answer 38

Goes from SR to the sarcoplasm

Question 39

What does the intracellular structure of myocytes ensure?

Answer 39

The spread of action potential (and calcium) throughout the cell

Question 40

What is ATP necessary for?

Answer 40

Contraction

Question 41

What does ATP binding to the myosin head cause?

Answer 41

A break in the cross-bridge (connection between actin and myosin)

Question 42

What does energy release from ATP hydrolysis by the myosin head provide?

Answer 42

Energy for cocking the myosin head (myosin is now in the high energy form)

Question 43

What does release of inorganic phosphate from the myosin head provide energy for?

Answer 43

The power stroke

Question 44

What is the power stroke?

Answer 44

Myosin head pulling actin towards the center of the sarcomere

Question 45

What shortens the sarcomere?

Answer 45

The power stroke

Question 46

Muscle cells only have enough ATP for how many twitches?

Answer 46

~8

Question 47

What produces ATP for muscle fibers?

Answer 47

A. Aerobic and anaerobic metabolism B. Phosphocreatine

Question 48

What does contribution of aerobic and anaerobic metabolism on each specific muscle depend on?

Answer 48

(1) the metabolic enzymes are present in the cell (ex. glycolytic fibers versus oxidative fibers) (2) the intensity of the exercise

Question 49

What are measurements of creatine kinase levels in the blood done to determine?

Answer 49

If damage to muscle tissues (skeletal and cardiac) has occurred (ex: heart attack or muscular dystrophy)

Question 50

What 3 things are associated with fatigued muscles?

Answer 50

1.have decreased tension generation, 2.take longer to contract 3.relax more slowly and may not completely relax

Question 51

What are theories that lead to fatigue?

Answer 51

1.Change in membrane potential 2.Decreased ACH 3.Blockage of blood flow 4.Central Fatigue 5.Increased metabolic byproducts 6.Depleted glycogen

Question 52

What must be present for cross-bridge cycling?

Answer 52

both calcium AND ATP

Question 53

Describe the steps of the cross-bridge cycling (sliding filament theory)

Answer 53

A. Rigor State: myosin and actin are tightly bound B. ATP binds myosin, decreases its affinity for actin, and the two separate C. Myosin head moves in the direction of the Z line, ATP is hydrolyzed D. Myosin binds the next actin (one closer to Z line) and power stroke occurs (pulls actin toward the M Line) E. ADP is released and the actin and myosin resume the brief rigor state