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PHYSL212 > MUSCLES > Flashcards

MUSCLES Flashcards

1
Q

What is a Muscle?

A

A biological machine that converts chemical energy (ATP) into work.

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2
Q

What do contractile muscles do?

A

Convert energy stored in ATP into a sliding of protein filaments and hence muscle shortening.

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3
Q

Muscle is specialized for _____ because it contains a large amount of _____ proteins.

A

Contraction, contractile

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4
Q

What are the three types of muscles?

A

Skeletal, smooth, cardiac.

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5
Q

What muscles are striated?

A

Skeletal, cardiac

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6
Q

What muscles are unstriated?

A

smooth

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7
Q

What muscles are voluntary?

A

Skeletal

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8
Q

What muscles are involuntary??

A

Smooth, cardiac.

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9
Q

What are the 4 functions of muscles?

A

Movement, manipulation of external objects, propulsion of contents through hollow internal organs, emptying contents to the external environment.

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10
Q

What is a myocyte?

A

A muscle cell

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11
Q

What is a sarcolemma?

A

The plasma membrane of a muscle cell

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12
Q

What is sarcoplasm?

A

The cytoplasm of the muscle cell

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13
Q

What is a sarcomere?

A

The contractile or functional unit of muscle.

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14
Q

What makes up muscle fibre?

A

Many muscle cells

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15
Q

What does each fibre cell end in?

A

Tendons made of fibrous inelastic tissue composed of collagen.

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16
Q

What are the muscle cell subunits called

A

Rods or myofibrils

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17
Q

What are the functional units of muscle fibres?

A

Motor units

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18
Q

How many muscle fibers can one motor nerve innervate?

A

One motor unit (1:1)

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19
Q

What is the number of muscle fibres controlled by a single motor axon determined by?

A

The dexterity of the movement (size of motor unit)

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20
Q

What is required for the contraction of skeletal muscle cells?

A

Each cell must be stimulated by a process of a motor neuron.

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21
Q

What is the A band?

A

Dark with the slightly lighter region in the center

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22
Q

What is the H Zone?

A

Light region in the middle of the A band

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23
Q

What is the M Line?

A

Transverse line in the middle of the H zone.

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24
Q

What is the I band?

A

Light regions of the muscle

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25
Q

What is the Z line (disk)?

A

The narrow dark line in the middle of the I band.

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26
Q

What is the length of the sarcomere?

A

The distance from Z line to repeated Z line (all are identical)

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27
Q

What is the thin filament I band protein?

A

Actin

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28
Q

What is the thick filament A band protein?

A

Myosin

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29
Q

What molecules are required for muscle contraction? (7)

A

Actin, myosin, troponin (TnT, TnC, TnI), tropomyosin, ATP, Trace of MG2+, and CA2+.

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30
Q

If all necessary molecules are present for muscle contraction, what will occur?

A

Cross-bridge cycling

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31
Q

What is the thin filament composed of?

A

Actin which is double stranded alpha helical polymers of F actin.

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32
Q

What is F actin associated with?

A

Tropomyosin and troponin

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33
Q

Where are the thin filaments tethered?

A

One end of the Z disk

34
Q

What is tropomyosin?

A

Two identical alpha helices, shadow the actin double helix

35
Q

What is troponin?

A

Heterotrimer: TnT, TnC, TnI

36
Q

What does TnT bind to?

A

Tropomyosin

37
Q

What is nebulin?

A

Contained in the thin filaments, an inelastic protein that anchors the thin filaments to the Z disc

38
Q

What are the thick filaments?

A

Polymers of proteins (myosin II), each myosin molecule is a double trimer of: two intertwined heavy chains, two regulatory light chains, and two essential (alkali) light chains.

39
Q

What are the heavy chains of the thick filaments composed of?

A

Three regions: rod, hinge, and head. Rods are alpha helices, hinge regions flare into two globular heads, heads are cross bridges, contain binding sites for actin. and contain site for binding and hydrolyzing ATP.

40
Q

What is a cross-bridge?

A

Interaction of thick and thin filaments; ATP is split in the region where actin and myosin heads can make contact and this energy is converted into a small movement.

41
Q

What is titin?

A

large elastic accessory protein which anchors the thick myosin filament to the Z disk to provide elastic recoil.

42
Q

What are C proteins and myomesin?

A

Accessory proteins that hold the thick filament in precise alignment at the M line.

43
Q

What is alpha actinin?

A

Accessory protein that aids with the attachment of actin filament to Z disk.

44
Q

Describe the contraction steps of the sliding filament theory

A
  1. A band remains constant
  2. I band shortens
  3. Z lines move closer together
  4. H zone gets smaller or disappears
    Actin filaments must slide between the myosin and the sarcomere changes length
45
Q

What is the cross-bridge cycle?

A
  1. ATP binds to myosin head, causing dissociation of actin-myosin complex.
  2. ATP is hydrolyzed, causing myosin heads to return to their resting contraction.
  3. Cross-bridge is formed and the myosin head binds to a new position on actin.
  4. P is released, myosin heads change conformation resulting in power stroke. Filaments side past each other.
  5. ADP is released.
46
Q

What occurs when ATP binds to the myosin head?

A

Reduction in affinity of myosin for actin. Myosin head is released from actin.

47
Q

What is the actin-myosin complex known as?

A

The rigor complex

48
Q

What concentration of calcium is needed to contract muscles?

A

Greater than 1x10-7 M

49
Q

How is calcium increased past 1x10-7 M

A

Action potential near contractile proteins

50
Q

Why can myosin and actin not bind at low calcium concentrations?

A

Tropomyosin is in the may of the complex.

51
Q

Where does calcium bind in skeletal muscles when [Ca]>10-7?

A

TnC, four Ca2+ bind to the four binding sites of troponin complex. This causes a conformational change which removes steric hinderance. This allows myosin and actin to bind.

52
Q

Sarcoplasmic reticulum:

A

Storage for intracellular calcium; releases it and removes it to allow relaxation.
Surrounds myofribrils

53
Q

Transverse tubules (T-tubules):

A

Synchronizes calcium release from sarcoplasmic reticulum.

54
Q

Where are dyads present?

A

Cardiac muscle

55
Q

Where are triads present?

A

Skeletal muscles

56
Q

Where are caveolae present?

A

Smooth muscle

57
Q

What does the triad do?

A

Couples excitation to contraction; (SR cisternae, transverse tubule, SR cisternae)

58
Q

Excitation-contraction coupling in skeletal muscle

A
  1. AP surface membrane depolarizes t-tubule system
  2. Activation of L-type calcium channels on t-tubule system, induces release of calcium from the SR via ryanodine receptors (foot process).
  3. Calcium binds to troponin
  4. Conformational change in troponin moves tropomyosin out of the way.
  5. Actin binds and inorganic phosphorous is released. Contraction
  6. Calcium less than 10-7M because of calcium pump in SR.
  7. Troponin assumes normal shape, tropomyosin returns to complex and actin binding is blocked.
59
Q

How is calcium removed from the cytoplasm?

A

Sodium/Calcium exchanger
Surface calcium pump
SR calcium pump
Calsequestrin (skeletal/cardiac), Calreticulin (smooth)

60
Q

Creatine kinase reaction

A

CrP and ADP –> ATP and Cr

61
Q

White muscle ATP synthesis

A

Glucose hydrolyzes into 2 ATP and lactic acid

62
Q

What are the two types of muscle contractions

A

Isometric: length of the muscle is held constant.
Isotonic: constant tension, shortening occurs.

63
Q

What is a twitch?

A

transient contraction phase followed by a relaxation phase.

64
Q

What is summation?

A

Increase in muscle tension or shortening in response to a rigid, repetitive stimulation.

65
Q

How does tetanus occur?

A

Free calcium remains high, allowing maximal force to be developed. Calcium pumps cannot cause up and allow relaxation.

66
Q

Motor units during voluntary contraction are activated on the basis of ___

A

size. Small first.

67
Q

Desmosomes

A

Mechanically couple muscle cells.

68
Q

Gap junctions

A

electrically couple muscle cells

69
Q

How is cardiac muscle contraction initiated?

A

By a pacemaker which is myogenic in origin.

70
Q

How does cardiac muscle vary from skeletal muscle?

A

Contains receptors for epinephrine and norepinephrin

71
Q

Cardiac monocytes are dependent on ______-cellular calcium

72
Q

Calcium-induced calcium release (CICR)

A
  1. Musclec cell AP
  2. Calcium enters L-type channels
  3. calcium binds to ryanodine receptors
  4. Calcium released from SR
73
Q

How is relaxation caused in cardiac muscles?

A

Calcium sodium exchanger, calcium pump in SR, SERCA2A regulated by phospholambin

74
Q

Dense bodies

A

actin filaments joined at electron-dense regions.

75
Q

What does smooth muscle NOT contain that cardiac/skeletal do??

76
Q

Varicosity

A

ANS Neuron expansion in smooth muscle.

77
Q

Location of multiunit smooth cell

A

blood vessels, iris, piloerector muscle of skin

78
Q

How are unitary smooth muscle units connected?

A

Via gap junctions

79
Q

Unitary smooth muscle location

A

GI tract, bladder, uterus, blood vessels

80
Q

How does cross bridge cycling occur in smooth muscle

A

Calcium binds to calmodulin in myosin, activating MLCK enzyme. MLCK phosphorylates regulatory light chain on myosin II head, increasing ATPase activity and allowing binding to actin.

81
Q

Calsequestrin

A

Calcium binding protein in the SR

PHYSL212 (7 decks)

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