Lecture 4-Skeletal Muscle Contraction Flashcards

1
Q

A?

A

I-band

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

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2
Q

B?

A

h-band

Contains both

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3
Q

C?

A

z-band

Anchors myosin (via titin)

Anchors actin filaments

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4
Q

D?

A

M-line: center of myosin filaments

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5
Q

E?

A

H-band: Myosin chain only

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

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6
Q

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

A

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

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7
Q

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

A

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

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8
Q

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

A

T-tubule (invagination of the sarcolemma)

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9
Q

What occurs after depolarization of the DHP-R?

A

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

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10
Q

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

A

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

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11
Q

What “activates” the mysoin head?

A

ATP

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12
Q

ADP+Pi (after ATP hydrolysis) causes _______.

A

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

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13
Q

When does the “powerstroke” occur?

A

With the loss of ADP from myosin head

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14
Q

What releases the myosin head from the actin active site?

A

Binding of ATP to myosin head

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15
Q

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

A

0.1 microMolar to 1 microMolar

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16
Q

How is the cytosolic [Ca2+] reduced?

A

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

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17
Q

What is the conformation of DHP-R?

A

Voltage-gated L-type channel in quadruplets

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18
Q

What is the mechanism behind calsequestrin?

A

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

19
Q

How is myosin “reactivated?”

A

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

20
Q

Define “pre-load”

A

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

21
Q

Define “afterload”

A

The load the muscle must work against

22
Q

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

A

more

23
Q

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

A

less

24
Q

Type of tension produced by preload

A

Passive

25
Q

Type of tension produced by cross-bridge cycling

A

Active tension

26
Q

What produces maximum tension in a muscle

A

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

27
Q

What is the relation between muscle load and contractile speed

A

Inverse (load proportional to 1/contractile speed)

28
Q

3 places ATP required

A
  • CROSS-bridge cycle
  • pump Na/K out/in to reset RMP on SR
  • pump Ca2+ back into SR
29
Q

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

A

Phosphocreatine

30
Q

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

A
  • ATP (1-2 sec)
  • Phosphocreatine (5-8 sec)
  • glycolysis (1 minute)
  • oxidative phosphorylation (long term contraction)
31
Q

Isotonic contraction where the muscle lengthens is ______ contraction.

A

eccentric

32
Q

Isotonic contraction where the muscle shortens is _____ contraction.

A

concentric

33
Q

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

A
34
Q

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

A

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.

35
Q

Fast, white fibers utilize what for energy?

A

Glycolytic reactions (rapidly depletes energy stores)

36
Q

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

A

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

37
Q

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

A

motor unit

38
Q

Describe the mechanism behind “tetany.”

A

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.”

39
Q

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

A

fulcrum

40
Q

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

A

resistance (‘load’)

41
Q

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

A

effort (‘in force’)

42
Q
A

Type: 1st

A: out-lever

B: in-lever

43
Q
A

Type: 2

A: out-lever

B: in-lever

44
Q
A

Type: 3rd

A: in-lever

B: out-lever