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KNPE 254 > Term Test 2: Muscle Mechanics > Flashcards

Term Test 2: Muscle Mechanics Flashcards

1
Q

Muscle fibres

A
  • Single muscle cells
  • Multi-nucleated, long thread-like cells
  • Each muscle fibre is encased in a connective tissue
    sheath called the endomysium
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2
Q

Fascicles

A
  • Bundles of muscle fibres (each containing 10-100
    muscle fibres)
  • Encased in a connective tissue sheath called the
    perimysium
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3
Q

Whole muscles

A
  • Are bundles of muscle fascicles (can vary widely).
  • Encased in a connective tissue sheath called the
    epimysium
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4
Q

Tendons

A

Cord-like and aponeuroses (sheet-like) are woven connective tissues that extend beyond the muscle and connect to bone

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5
Q

Myofibrils

A
  • Threadlike structures that lie parallel to each other
    and run the full length of the muscle fibre.
  • Transverse light and dark bands appear across each
    myofibril and align with the same bands on adjacent
    myofibrils
  • Bands of light and dark repeat every 2.5 um, giving
    skeletal muscle its striated appearance
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6
Q

Sarcomere

A

Is the basic contractile unit of the muscle. It is the repeating unit of the myofibril between the stripes

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7
Q

Myofilaments

A

Are protein filaments that overlap within the sarcomere

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8
Q

Thin filaments contain

A
  • Actin
  • Troponin C
  • Tropomyosin proteins
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9
Q

Thick filaments contain

A

Myosin proteins

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10
Q

I-band

A

Region that contains only actin and Z-line (no overlapping myosin), appears as light band

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11
Q

A-band

A
  • Region that contains myosin
  • Overlapping actin, appears as dark band
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12
Q

H-zone

A
  • Region of the A band
  • Contains only myosin and M-line (no overlapping
    actin)
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13
Q

M-line

A

Transverse band that anchors myosin to each other

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14
Q

Z-line

A

Transverse band that anchors actin to each other (Z-line to Z-line defines sarcomere)

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15
Q

Sliding filament theory

A

Proposes that muscle force arises from cyclic binding between thin actin and thick myosin filaments of the sarcomere
- Absence of calcium, tropomyosin prevents
myosin from attaching to actin
- During AP, calcium is released from the
sarcoplasmic reticulum and binds to troponin
C
- This induces a conformal change in
tropomyosin, giving myosin head access to
actin
- Myosin head binds actin and a power stroke
causes muscle contraction
- ATP binds allowing the release of actin

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16
Q

Electron micrographs

A
  • Confirms the existence of thick myosin and thin
    actin filaments
  • Stretching the muscle does not cause a change
    in the length of the thick and thin filaments,
    but only a change in the length of the I-band
    and H-zone
17
Q

Factors affecting muscle force development

A
  • Length of muscle
  • Velocity
  • Physiological cross-sectional areas of the
    muscle
  • Muscle geometry
  • Level of activation
18
Q

If you have ever done a hamstring curl on a flat bench, you may have noticed that your hamstrings feel very weak when in a fully flexed position. Why do you think that is? Why might assuming some hip flexion may make the exercise easier?

A
  • Flexing the hip makes the length of the
    hamstring longer
  • Making exercise easier
  • You are on the ascending limb
  • You can generate more force
19
Q

Contractile element

A

Represents force development via cross-bridge attachments in the sarcomeres

20
Q

Series elastic element

A

Represents force-deflection properties of tendon

21
Q

Parallel elastic element

A

Represents force-deflection properties of the sarcolemma, epimysium, perimysium and endomysium

22
Q

Shortening does not equal short

A
  • The force-length relationship tells us that the
    maximum force a muscle can generate
    depends on whether it is short or long
  • The force-velocity relationship tells us that the
    maximum force a muscle can generate
    depends on whether it is shortening or
    lengthening
23
Q

Short and long

A
  • Short does not equal shortening
  • Long does not equal lengthening
  • Short and long refer to the muscle length
  • Short muscles can be shortening or lengthening
24
Q

Shortening and lengthening

A
  • Short does not equal shortening
  • Long does not equal lengthening
  • Shortening and lengthening refers to the muscle velocity
25
Q

Muscle force-velocity relationship

A
  • The greater the shortening velocity of the
    muscle, the smaller the force that can be
    produced (we cannot lift heavy objects quickly)
  • A muscle contracting eccentrically or
    isometrically is capable of producing more
    force than a muscle contracting concentrically
26
Q

Muscle force-length relationship

A

In a whole muscle, Total = active (muscle contraction) + passive (connective tissue) tension

27
Q

Activation

A

Number (or proportion of) muscle fibres that are stimulated to contract at any given time

28
Q

Motor unit

A

Composed of a single motor neuron and all of the muscle fibres with which it synapses
- Electrical stimulation causes muscle to contract through the release of Ca2+

29
Q

How do we increase activation?

A
  1. Increase the firing frequency of any given
    motor unit
  2. Recruit more motor units to produce greater
    force (tension), you also recruit more motor
    units to increase the proportion of fibres
    running
30
Q

Heneman’s size principal

A

Motor units are recruited from smallest (slow twitch) to largest (fast twitch)

31
Q

Physiological cross-sectional area I

A
  • Increasing the number of sarcomeres lined up
    end to end = increasing number of cross-
    bridges = increasing the length of the myofibril
  • If adding the sarcomeres in parallel by
    increasing the number of myofibrils, the
    number of possible attachments of cross
    bridges have increased
32
Q

Physiological cross-sectional area II

A

Adding sarcomeres in parallel makes a muscle stronger, but not faster. Strength is thus proportional to muscle cross-sectional area because it is proportional to the number of parallel-acting sarcomeres

KNPE 254 (3 decks)

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