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Human Physiology 1 -- Zach H. > Skeletal Muscle Contraction (Lecture 4) > Flashcards

Skeletal Muscle Contraction (Lecture 4) Flashcards

1
Q

Fill in the Blank:

_______is made up of multiple fascicles?

A

Muscle is made up of multiple fascicles.

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2
Q

True or False:

The connective tissue surrounding individual fascicle is called the perimysium.

A

True

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3
Q

What is a fascicle made up of?

A

A bundle of myofibers.

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4
Q

What is the connective tissue covering that is around each myofiber?

A

Endomysium

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5
Q

What is another name for the cell membrane of a muscle fiber?

A

Sarcolemma (=plasmalemma)

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6
Q

What is another name for an individual multinucleated muscle cell?

A

Myofiber (= muscle cell)

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7
Q

What is a myofibril?

A

A chain of sarcomeres within a myofiber.

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8
Q

What is a myofilament?

A

Actin and myosin filaments that make up a sarcomere.

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9
Q

How many T-tubules are there per sarcolemma?

A

2 per sarcomere

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10
Q

What is a t-tubule and what structure does it lie close to?

A

T-tubule is an invagination of the sarcolemma and it lies close to the cisternae of the sarcoplasmic reticulum.

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11
Q

What band is replaced by the M-line at full muscle contraction?

A

H Bands

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12
Q

What two bands have a width that changes with muscle contraction?

A

H Band and I Band

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13
Q

What band is entirely composed of actin, entirely composed of myosin, and which is composed of both actin and myosin?

A

I Band –> composed entirely of actin
A Band –> composed of actin and myosin
H Band –> composed entirely of myosin

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14
Q

Which band length does not change during muscle contraction?

A

A Band

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15
Q

What is the main function of the Z discs?

A

To anchor the actin filaments at both ends of the sarcomere.

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16
Q

Which molecule is the thick filament and which is the thin filament?

A

Thin Filament –> actin

Thick Filament –> myosin

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17
Q

What type of receptor is the dihydropyridine (DHP) receptor?

A

Voltage-sensitive L-type calcium channel

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18
Q

Where is the dihydropyridine (DHP) receptor primarily located?

A

DHP receptor is located on the sarcolemma t-tubules.

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19
Q

What does the DHP receptor do to the ryanodine receptor?

A

Causes a conformational change in the ryanodine receptor.

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20
Q

Does a large or small amount of calcium flow in to the cytosol through DHP receptors?

A

NO, a minute amount of calcium flows into the cytosol through the DHP receptor.

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21
Q

What is the epimysium?

A

The connective tissue surrounding the entire muscle.

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22
Q

What are the two types of muscle contraction?

A

Isometric and Isotonic

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23
Q

What are the two different forms of isotonic muscle contraction?

A

Eccentric and concentric

  • eccentric –> contraction occurs when the muscle lengthens
  • concentric –> contraction occurs when the muscle shortens
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24
Q

What is the difference between isometric and isotonic muscle contraction?

A
  • Isometric contraction -> occurs when there is an increase in tension but not in length (cross-bridges are still formed and that is what builds tension, but no muscle length change).
  • Isotonic contraction -> the muscle length changes. Either it shortens (concentric) or lengthens (eccentric.
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25
Q

What determines the myofiber type of a muscle?

A

The innervating neuron.

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26
Q

What are the two types of myofibers?

A
  • Dark, slow fibers (red fibers)

* Light, fast fibers (white fibers)

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27
Q

How are fiber types classified, mainly?

A

On endurance (resistance or fatigue) and speed of contraction.

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28
Q

What are the four characteristics that fast (white; light) fibers?

A

1) fewer mitochondria
2) little myoglobin
3) larger concentration of ATPase
4) primarily use anaerobic respiration resulting in a buildup of pyruvic and lactic acids (glycolysis)

29
Q

Fill in the blank:

____twitch fibers contract rapidly but have less endurance.

A

FAST

30
Q

Fill in the blank:

Slow twitch fibers _____ more slowly than fast twitch fibers, but have more endurance.

A

CONTRACT

31
Q

What are the 4 characteristics of slow (red, dark) twitch fibers?

A

1) more myoglobin than fast twitch muscle fibers
2) more mitochondria than fast twitch muscle fibers
3) smaller concentration of ATPase than fast twitch muscle fibers
4) primarily use aerobic respiration

32
Q

True or False:

After birth, the number of myofibers can be increased.

A

False -> after birth, the number of myofibers cannot be increased.

33
Q

What can be increased within the myofiber that will increase the mass of it, thus, increasing the mass of the muscle?

A

The number of myofibrils.

**remember: the number of myofibers cannot be increased after birth, just the number of myofibrils within the myofiber.

34
Q

What is lost muscle tissue replaced with?

A

Scar Tissue (fibrous connective tissue)

35
Q

What type of myofiber is the soleus mostly composed of?

A

Dark Fibers (slow twitch; red fibers)

36
Q

What type of myofiber is the gastrocnemius mainly composed of?

A

Light Fibers (white fibers; fast twitch)

37
Q

True or False:

A single nerve cell (neuron) may innervate from a few to several hundred myofibers.

A

TRUE

38
Q

What makes up a motor unit?

A

A neuron and the myofibers it innervates constitute a motor unit.

39
Q

Does all of the myofibers in a motor unit contract when the neuron of that motor unit fires?

A

YES, the all-or-none really refers to a motor unit.

40
Q

Discuss the process of summation in a specific muscle as it builds up to tetany of that muscle.

A

electrical events occur faster than mechanical events –> an additional spike can occur before the previous calcium ions have been returned to the sarcoplasmic reticulum (SR) –> this increases the total amount of calcium ion in the cytosol and increases the rate of cycling between the myosin and actin cross-bridges –> this increases muscle tension –> each additional spike adds to the effects of the previous spikes –> if the frequency of spikes is fast enough, there is no time for relaxation between spikes –> muscle remains at maximal contraction (tetany is reached)

41
Q

What happens to the muscle when tetany is reached?

A

The muscle remains at maximal contraction.

42
Q

Fill in the blank:

______transmit forces from one place to another?

A

machines (consider bone-muscle systems as machines)

43
Q

What two forces do machines involve?

A

1) force applied to the machine (in-force (Fi) or effort)

2) force derived from the machine (out-force (Fo) or resistance)

44
Q

What is a lever?

A

A lever is a rigid body (bone) that rotates around a pivot (joint) or fulcrum.

45
Q

What is the distance from the in-force (muscle attachment) to the fulcrum (joint)?

A

The in-lever arm

46
Q

What is the distance from the out-force to the fulcrum (joint)?

A

The out-lever arm.

47
Q

True or False:

A functional lever must have at least two moments.

A

True

48
Q

How do you calculate Mi?
How do you calculate Mo?
What is the formula at equilibrium?

A
  • Mi = FiLi
  • Mo = FoLo
  • equilibrium = FiLi = FoLo
49
Q

What is a first-class lever and example of one?

A
  • the fulcrum is in the middle
  • the in-force and out-force move in opposite directions

*Example: raising chin using sternocleidomastoids or similar muscles (fulcrum = atlas/axis complex)
Also, a sea-saw or a pry bar.

50
Q

What is a second-class lever system and an example?

A
  • resistance (out-force) is in the middle
  • fulcrum = ball of foot
  • both in and out forces are on the same side of the fulcrum

*Example: raising the body on the ball of the foot

51
Q

What is a third-class lever and an example?

A
  • effort (in-force) is in the middle
  • both in and out forces are on the same side of the fulcrum
  • both forces move in same direction

*Example: lifting a weight in the palm of your hand

52
Q

How are lever systems classified?

A

Lever systems are classified according to the position of the fulcrum in relation to the in-force and the out-force.

53
Q

Where is ATP required for muscle contraction?

A

1) most is used for sliding filament mechanism
2) pumping calcium ions from sarcoplasm back into sarcoplasmic reticulum
3) pumping sodium and potassium ions through the sarcolemma to reestablish resting potential

54
Q

What is the concentration of ATP in muscle fiber?

A

about 4 mmol (at least enough to maintain contraction for 1-2 seconds)

55
Q

What are the 3 main things that provide the energy for rephosphorylation?

A

1) Phosphocreatine
2) Glycolysis
3) Oxidative Metabolism

56
Q

What provides more than 95% of all energy needed for the long-term contraction of muscle?

A

oxidative metabolism

57
Q

What does phosphocreatine do to provide energy for rephosphorylation?

A
  • it releases energy rapidly
  • it reconstitutes ATP
  • ATP + phosphocreatine provides enough energy for 5-8 seconds of contraction
58
Q

How does glycolysis provide energy for rephosphorlyation?

A
  • by lactic acid build-up

* can sustain contraction for 1 minute

59
Q

What is the definition of preload?

A

The load on a muscle in the relaxed state (before it contracts).

60
Q

What is directly proportional to the preload in muscle?

A

The passive tension.

***The greater the preload, the greater the passive tension in the muscle.

61
Q

What is passive tension in the muscle?

A

How the force of the resistance is measured.

**Thus, the preload stretches the muscle which stretches the sacromere. This preload generates passive tension in the muscle, in which the muscle resists this tension applied to it. This force of the resistance is then measured as passive tension.

62
Q

What is the definition of the afterload in a muscle?

A

The load the muscle works against.

63
Q

What kind of muscle contraction would occur if the muscle generates more force than the afterload?

A

An isotonic contraction.

64
Q

Using the term “afterload”, construct a sentence that describes an isometric muscle contraction.

A

If the muscle generates less force than the afterload placed on it, then isometric contraction will occur.

65
Q

What are the 3 types of tension?

A

1) passive: produced by the preload
2) active: produced by cross-bridge cycling
3) total: sum of active and passive tension

66
Q

When does the cross-bridge cycling start, physiologically?

A

When free calcium is available and attaches to troponin.

67
Q

True or False:

Contraction is the continuous cycling of cross-bridges.

A

True

68
Q

True or False:

ATP is required to form the cross-bridge linking to actin but is required to break the link with actin but is required to break the link with actin.

A

False, ATP is NOT required to form the cross-bridge linking to actin but is required to break the link with actin.

69
Q

What are the two situations that will stop cross-bridge cycling?

A

1) withdrawal of calcium ion

2) ATP is depleted

Human Physiology 1 -- Zach H. (12 decks)

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