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MABS Physiology > lecture 6 > Flashcards

lecture 6 Flashcards

muscle contraction and relaxation

1
Q

T/F, skeletal muscle is a voluntary muscle?

A

true

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2
Q

what part of the nervous system controls the skeletal muscle?

A

central nervous system

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3
Q

what is skeletal muscle composed of?

A

bundles of muscle fibers called fasciculus

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4
Q

what are the muscle striations the result of?

A

thick and thin filaments

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5
Q

Z line to Z ine represents what?

A

one sarcomere

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6
Q

the sarcomere is a _______ unit (fill in the blank)

A

contractile

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7
Q

this band contains thin filaments?

A

I band

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8
Q

what are the thin filaments called?

A

actin

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9
Q

what is the area between the two I bands?

A

the A band

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10
Q

what type of filaments comprise the A band and what are these called?

A

thick filaments; myosin

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11
Q

what does the dark area of the A band represent?

A

myosin and actin overlap

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12
Q

this area contains thick filaments (myosin) only?

A

H band

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13
Q

where do the actin fibers extend?

A

from the Z line to the edge of the H band

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14
Q

what do actin filaments over lap with?

A

they overlap with myosin (thick filament) in the A band

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15
Q

what happens to the A bands upon muscle contraction? the I bands? H zone? Z lines?

A

the A bands do not change their length; the I bands and H zone shorten which results in the Z lines coming closer

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16
Q

cardiac muscles have _____ synapses?

T/F, these synapses are used to initiate cardiac function?

A

chemical; F, modulate NOT initiate

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17
Q

what triggers cardiac muscle?

A

electrical signals from the neighbor cells

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18
Q

where are the cardiac electrical signals made?

A

in the SA node

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19
Q

the SA node is the _____ pacemaker of the heart?

A

internal

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20
Q

what carries out the electrical communications between cells?

A

the gap junctions found in the sarcolemma of cardiac muscle to maintain the action potential with neighboring cells

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21
Q

what controls the skeletal muscles?

A

somatic nervous system controlled by the CNS with efferent signals

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22
Q

how many muscle fibers can one nerve innervate?

A

multiple muscle fibers

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23
Q

how many innervations can one muscle fiber have?

A

one innervation

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24
Q

what is the importance of the way the skeletal muscles are innervated?

A

they prevent confusion

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25
Q

describe the tranverse tubules of the skeletal muscles?

A

they are the extensions of the plasma membrane that penetrate the muscle cells at two points in each sarcomere: the junctions of the A and I bands

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26
Q

what is the effect on the muscle cells as the skeleton grows?

A

muscle cells lengthen by forming more sarcomeres at the ends of muscle cells

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27
Q

what happens to the limb with the muscle in a shortened position? the muscle cell?

A

its immobilized; the length of a cell decreased with sarcomeres at the ends eliminated

28
Q

what is the effect of the changes in muscle length?

A

it affects velocity and extent of the shortening but not the amount of force

29
Q

what is muscle hypertrophy?

A

slow increase in strength and diameter of a muscle like working out in the gym

30
Q

what is muscle hyperplasia?

A

skeletal muscles have limited ability to form new muscle fibers, like being immobilized in a cast

31
Q

what is the effect of being immobilized in a cast do to the body?

A

loss of muscle mass (atrophy) and weakness

32
Q

what are the two ways synaptic input to smooth muscle differs from skeletal muscle?

A

1) the neurons are part of the autonomic nervous system rather than the somatic nervous system.
2) the neuron makes multiple contacts with a smooth muscle cell.

also;

1) Smooth muscle cell may get input from more than one neuron (this will never happen in a skeletal muscle cell)
2) No end plate in smooth muscle

33
Q

how is the smooth muscle, unitary? examples?

A

Gap junctions allow electrical communication between the cells → coordinated contraction of many cells as a single unit;
Example: GI tract, uterus, blood vessels

34
Q

what are the invaginations on the smooth muscle called?

A

caveoli

35
Q

what triggers muscle contraction?

A

increase in Ca2+, so the time that Ca2+ remains elevated determines the duration of muscle contraction

36
Q

what is excitation contraction coupling?

A

The process by which “excitation” triggers the increase in [Ca2+] by removing the the inhibition of cross bridge cycling

37
Q

once the calcium comes in, where do they bind?

A

the troponin molecule

38
Q

what comprises the troponin?

A

heterotrimer consisting of Troponin C, Troponin T, Troponin I

39
Q

what does troponin C do?

A

binds to calcium then moves the tropomyosin away from the binding sites, myosin binding can happen and can have the cycle

40
Q

what does troponin T do?

A

binds to a single molecule of tropomyosin

41
Q

what does troponin I do?

A

binds to actin and inhibits contraction

42
Q

why is the “heterotrimeric” troponin molecule important?

A

it contains the key Ca2+ sensitive regulator troponin C.

43
Q

what does the troponin C in the skeletal muscle have that helps in the binding of troponin C to the thin filament?

A

two high affinity Ca2+ binding sites

44
Q

Ca2+ binding to the high affinity Ca2+ binding sites of the troponin C does not change during muscle contraction T/F?

A

T

45
Q

in addition to the high affinity binding sites of the troponin C molecule, there are also two additional low affinity Ca2+ binding sites T/F?

A

T

46
Q

what are the two effects of Ca2+ binding to these low affinity sites besides inducing a conformational change?

A

1) the C terminus of the inhibitory troponin I moves away from the actin/tropomyosin filament, thereby permitting the tropomyosin molecule to move
2) transmitted through troponin T, is to push tropomyosin away from the myosin-binding site on the actin and into the actin groove.

With the steric hindrance removed, the myosin head is able to interact with actin and engage in cross-bridge cycling.

47
Q

Name the 5 steps of Cross Bridge Cycling

A

1) ATP binding
2) ATP hydrolysis
3) Cross Bridge formation
4) release of the Pi from the myosin
5) ADP release

48
Q

describe step 1 of the cross bridge cycle

A
  1. ATP binds to myosin head → dissociation of actin-myosin complex
    ● ATP binds to heavy chain on myosin head → reduces the affinity of myosin for actin
    ● If all cross bridges in a muscle were in this state → muscle is fully relaxed
49
Q

describe step 2 of the cross bridge cycle

A
  1. ATP is hydrolyzed causing myosin heads to return to resting position
    ● Breakdown of ATP occurs in myosin head
    ● After breakdown, myosin head is in “cocked position” → perpendicular to the filaments
    ● The change in position causes the myosin to move 11 nm along the thin filament
50
Q

describe step 3 of the cross bridge cycle

A
  1. Cross-bridge forms and the myosin head binds to a new position on actin
    ● The “cocked” myosin head binds to a new position on the thin filament
    ● This binding shows that there is an increased affinity of the myosin-ADP-Pi complex for actin
51
Q

describe step 4 of the cross bridge cycle

A
  1. P is released. Myosin heads change conformation → power stroke. The filaments slide past each other
    ● P leaves the myosin head → power stroke → myosin head bends 45 degrees → actin filament moves 11 nm towards the tail of myosin → force and motion is generated
52
Q

describe step 5 of the cross bridge cycle

A
  1. ADP is released
    ● ADP leaves myosin head → actomyosin complex is left in a rigid state → myosin is stuck in the 45 degree position
    ● Myosin stays on the actin until another ATP binds to it
53
Q

how far does each cycle move the myosin head?

A

two actin monomers or 11 nm

54
Q

how much ATP do you need for the entire cycle?

A

1 ATP for the entire cycle and another ATP for release

55
Q

the cross bridge cycling is what type of movement?

A

rowing movement

56
Q

why is Rigor Mortis important to note? What happens? what stays attached?

A

■ A dead person can not make ATP → there is no ATP to separate the myosin from the actin → muscle is left in a rigid state

57
Q

how does excitation-contraction coupling happen in smooth muscle?

A

1) Ca2+ enters the cytoplasm through channels located in caveoli
2) Ca2+ release from the sarcoplasmic reticulum can occur either via Ca2+ induced Ca2+ release or more importantly via IP3 activation of SR Ca2+ channels
3) When the SR Ca2+ store become depleted, the SR signals - by an unknown mechanism - a store operated Ca2+ channel to open allowing Ca2+ to enter

58
Q

what is the cause of fatigue?

A

metabolic byproducts are the onset of fatigue

59
Q

***what is not the result of fatigue?

A

depletion of energy stores

60
Q

in terms of onset fatigue, what happens during intense exercise?

A

P and lactic acid buildup → decrease pH → inhibits actin-myosin interactions

61
Q

are ATP levels decreased a lot during intense exercise?

A

not by a lot

62
Q

because its noted that there is a decrease in pH during fatigue, what is this effect?

A

● The decrease in pH reduces the sensitivity of the actin-myosin interaction to Ca by altering Ca binding to Troponin C → decreased the number of actin-myosin interactions

63
Q

Regardless of whether the muscle is fatigued as a consequence of high-intensity exercise or prolonged exercise, the myoplasmic ATP level does not decrease substantially, T/F?

A

T

64
Q

why does fatigue happen?

A

a protective mechanism to minimize the risk of muscle cell injury or death.

65
Q

whats isometric contraction?

A

when there is no change in muscle length and force generated in measured

66
Q

whats isotonic contraction?

A

when there is no change in force and the length of muscle is measured

MABS Physiology (57 decks)

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