Muscle Contraction

Question 1

What does each muscle fiber contain?

Answer 1

Myofibrils

Question 2

What two myofibrils make up a muscle fiber?

Answer 2

Actin and myosin

Question 3

What myofibril is a globular protein consisting of two alpha-helical twisted strands?

Answer 3

Actin

Question 4

Which myofibril is made up of a heavy chain pair of alpha-helical tails and two light chain pairs of “heads”?

Answer 4

Myosin

Question 5

Which component of myosin has an actin binding site that binds and hydrolyzes ATP?

Answer 5

The “Heads” (Light chains)

Question 6

What is the basic contractile unit of a muscle fiber?

Answer 6

Sarcomere

Question 7

Which myofibril is covered in tropomyosin?

Answer 7

Actin

Question 8

What does tropomyosin function to do?

Answer 8

Covers Actin-myosin binding site at rest, moves from that site at AP

Question 9

Which myofibril is associated with troponin?

Answer 9

Actin

Question 10

What does troponin function to do?

Answer 10

Release Ca2+ for binding to tropomyosin allowing it move for Cross-Bridge cycling

Question 11

What structure is the middle of the sarcomere?

Answer 11

M line

Question 12

What structure is surrounding each side of the M line until actin site?

Answer 12

Bare zone (no overlap)

Question 13

What structure is on each side of the actin?

Answer 13

Z disks

Question 14

What makes up the I band of a sarcomere?

Answer 14

Actin lines

Question 15

What makes up the A band of a sarcomere?

Answer 15

Actin and myosin lines

Question 16

What actin-binding protein anchors the myofibrillar array to the CM?

Answer 16

Dystrophin

Question 17

What large protein extends from the M line to Z disks, partly passing through the myosin?

Answer 17

Titin

Question 18

What protein extends from one end of actin to the other, setting the length?

Answer 18

Nebulin

Question 19

What protein anchors actin to Z disk?

Answer 19

Alpha Actinin

Question 20

What structure does a contraction reach the muscle fiber via?

Answer 20

Transverse tubules

Question 21

Through what structure does the contraction get to the SR from the Transverse Tubules?

Answer 21

Dihydropyridine receptors

Question 22

What structure is the storage and release site of Ca2+ for E-C Coupling?

Answer 22

SR

Question 23

What structure on the SR does Ca2+ flow through to get to muscle?

Answer 23

Ryanodine Receptors

Question 24

What substance pumps calcium back to the SR?

Answer 24

Ca2+ ATPase (SERCA)

Question 25

Summarize the mechanism of Excitation-contraction coupling of Skeletal Muscle. (seven steps)

Answer 25

1. AP -> T-tubules for depolarization from the surface to interior of muscle fiber. 2. Depolarization of t-tubule causes dihydropyridine receptors to open Ryanodine receptors for Ca@+ release. 3. Ca2+ is releases from SR to muscle fiber. 4. Ca2+ binds to troponin, 5. That bind causes tropmyosin to unbind and move to allow for actin-myosin cross bridge. 6. Myosin and actin bind. ATP binds to myosin head. ATP is hydrolyzed to ADP+P providing the energy to walk along the actin filament. ADP is releases and myosin is returned to OG state and continue walking until Ca2+ unbinds to troponin. 7. Relaxation occurs when Ca2+ unbinds and is reaccumulated in SR by SERCA. Tropomyosin returns to binding sites to stop cross bridge cycling for relaxation.

Question 26

Summarize the mechanism of Smooth Muscle E-C Coupling. (6 steps)

Answer 26

1. depolarization opens Ca2+ channels in SR. Influx increases concentration and if threshold is reached, AP can occur and further depolarization occurs opening Ca2+ channels. 2. Neurotransmitters open Ca2+ channels = influx. 3. Ca2+ binds to calmodulin which binds to and activate myosin-light-chain kinase. 4. MLCK phosphorylates myosin light chain increasing ATPase for cross bridge coupling. 5. Calponin and caldesmon inhibit/excite myosin ATPase. 6. When [Ca2+] decreases to low enough levels, relaxation occurs by either hyperpolarization, direct inhibition of Ca2+ channels, or decreased release of Ca2+ from SR.

Question 27

What is a sustained contraction of muscle twitch due to insufficient tome for SR to accumulate Ca2+?

Answer 27

Tetanus

Question 28

What is the relationship between the length and tension of a muscle?

Answer 28

A full length, there is zero tension. As length decreases, produces overlap, producing tension

Question 29

What is the relationship between force and velocity of a muscle contraction?

Answer 29

At initial length, as contraction occurs, velocity slows. (An isometric contraction initially @ 3 lengths has 0 velocity until added force.

Question 30

What type of muscle fiber has rapid cross bridge cycling and rapid rate of shortening?

Answer 30

Fast twitch (Type II)

Question 31

What type of muscle Fibers have slow cross bridge cycling and slow rate of shortening?

Answer 31

Slow Twitch (Type I)

Question 32

What type of fibers withstand better fatigue?

Answer 32

Slow twitch (Type I) due to oxidative nature vs glycolytic nature of Type II

Question 33

True/False: Fibers can be different within a given motor unit.

Answer 33

False, thy are all the same.

Question 34

What is the relationship between control and size of fibers?

Answer 34

Small fibers have better control over large fibers

Question 35

What is the relationship between reaction and size of fibers?

Answer 35

Small fibers are rapid reacting while large fibers are slower reacting

Question 36

Hypertrophy (increase in size) does what to the stimulation of a muscle?

Answer 36

Increase force but not speed

Question 37

Hyperplasia (increase in # of fibers) does what to the stimulation of a muscle?

Answer 37

Increase force but no change in velocity

Question 38

Lengthening a fiber has what effect on the stimulation of a muscle?

Answer 38

No change in force but increase speed of contraction

Question 39

Atrophy (decrease in size) does what to the stimulation of a muscle?

Answer 39

Decreases load, decreasing size, decreasing force