Lecture 4-Skeletal Muscle Contraction

Question 1

A?

Answer 1

I-band

HI MA -> H-myosin only; I-actin only

Question 2

B?

Answer 2

h-band

Contains both

Question 3

C?

Answer 3

z-band

Anchors myosin (via titin)

Anchors actin filaments

Question 4

D?

Answer 4

M-line: center of myosin filaments

Question 5

E?

Answer 5

H-band: Myosin chain only

HI MA -> H-Myosin only; I-Actin only

Question 6

What occurs (prior to the NMJ) to being contraction?

Answer 6

A.P. arrives at terminal bouton, opening voltage gated Ca2+ channels, Ca2+ influx causes NT vesicle to fuse with P.M.; ACh released into synaptic cleft

Question 7

What is the result of N.T. binding to the motor end plate?

Answer 7

ACh binding to receptor causes ligand gated Na+ channel to open; Na+ influx produces A.P.

Question 8

A.P. arrives at the ____ and opens the dihydropyridine-R (DHP-R)

Answer 8

T-tubule (invagination of the sarcolemma)

Question 9

What occurs after depolarization of the DHP-R?

Answer 9

DHP-R interacts with Ca2+ channel on sarcoplasmic reticulum, prompting efflux of Ca2+ into the muscle cell

Question 10

What is the f(x) of calcium release from the SR in muscle contraction?

Answer 10

Ca2+ binds to troponin-C; this produces a conformational changes to tryopomyosin, uncovering the active sites on actin

Question 11

What “activates” the mysoin head?

Answer 11

ATP

Question 12

ADP+Pi (after ATP hydrolysis) causes _______.

Answer 12

Conformational change to mysoin head; this results in binding of myosin head and A.S. on actin

Question 13

When does the “powerstroke” occur?

Answer 13

With the loss of ADP from myosin head

Question 14

What releases the myosin head from the actin active site?

Answer 14

Binding of ATP to myosin head

Question 15

What is the change to cytosolic Ca2+ with opening of Ca2+ on the SR?

Answer 15

0.1 microMolar to 1 microMolar

Question 16

How is the cytosolic [Ca2+] reduced?

Answer 16

Na/Ca2+ pump uses ATP to cause Ca2+ to be “taken up” into the SR

Question 17

What is the conformation of DHP-R?

Answer 17

Voltage-gated L-type channel in quadruplets

Question 18

What is the mechanism behind calsequestrin?

Answer 18

Binds Ca2+ in the SR, thereby setting up a favorable [Ca2+] gradient, making it easier to return Ca2+ to SR

Question 19

How is myosin “reactivated?”

Answer 19

Hydrolysis of ATP-> ADP+Pi “cocks” the myosin head

Question 20

Define “pre-load”

Answer 20

The load on a muscle while the muscle is relaxed (before contraction)

Question 21

Define “afterload”

Answer 21

The load the muscle must work against

Question 22

Isotonic contraction occurs when the muscle generates ____ force than the afterload

Answer 22

more

Question 23

Isometric contraction occurs when the muscle generates ____ force than the afterload

Answer 23

less

Question 24

Type of tension produced by preload

Answer 24

Passive

Question 25

Type of tension produced by cross-bridge cycling

Answer 25

Active tension

Question 26

What produces maximum tension in a muscle

Answer 26

Maximum overlap of actin/myosin (appx. 1.65-2.2 μm)

Question 27

What is the relation between muscle load and contractile speed

Answer 27

Inverse (load proportional to 1/contractile speed)

Question 28

3 places ATP required

Answer 28

• CROSS-bridge cycle
• pump Na/K out/in to reset RMP on SR
• pump Ca2+ back into SR

Question 29

What molecule reconstituted ATP and can sustain contraction for 5-8 seconds?

Answer 29

Phosphocreatine

Question 30

What E* stores are used in contraction (from shortest to longest duration)

Answer 30

• ATP (1-2 sec)
• Phosphocreatine (5-8 sec)
• glycolysis (1 minute)
• oxidative phosphorylation (long term contraction)

Question 31

Isotonic contraction where the muscle lengthens is ______ contraction.

Answer 31

eccentric

Question 32

Isotonic contraction where the muscle shortens is _____ contraction.

Answer 32

concentric

Question 33

The _____ neuron determines the type of myofiber in the muscle.

Question 34

Explain the mechanism behind the ability of white fibers to contract rapidy and fatigue easily

Answer 34

Fast twitch, or white fibers, lack large numbers of mitochondria. As a result, they are unable to undergo long term, oxidative metabolism. They primarily rely on ATP stores to contract. Because of their inability to undergo oxidative metabolism, they fatigue readily.

Question 35

Fast, white fibers utilize what for energy?

Answer 35

Glycolytic reactions (rapidly depletes energy stores)

Question 36

True or false: Muscle mass is increased by increasing the number of myofibers in the muscle.

Answer 36

False; muscle mass is increased by increasing the number of myofibrils

Question 37

The neuron and the myofibers it innervates is known as a ______.

Answer 37

motor unit

Question 38

Describe the mechanism behind “tetany.”

Answer 38

Prior to a muscle returning to a relaxed state, an additional action potential arrives prior to full Ca2+ sequestration. Additional Ca2+ is released, prompting more cross-bridging, which increases tension. Eventually, new APs arrive so quickly, that no relaxation occurs, resulting in “tetany.”

Question 39

In a first class lever, the ____ is in the middle.

Answer 39

fulcrum

Question 40

In a second class lever, the _____ is in the middle.

Answer 40

resistance (‘load’)

Question 41

In a third class lever, the ____ is in the middle.

Answer 41

effort (‘in force’)

Question 42

Answer 42

Type: 1st

A: out-lever

B: in-lever

Question 43

Answer 43

Type: 2

A: out-lever

B: in-lever

Question 44

Answer 44

Type: 3rd

A: in-lever

B: out-lever