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MSK Week 2 > 2.2.5. Muscle Tissue > Flashcards

2.2.5. Muscle Tissue Flashcards

1
Q

What are the major contractile proteins involved in muscle contraction? (2 of them)

A

Actin

Myosin

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2
Q

What are the three major classifications of muscle tissue in the human body?

A

Skeletal

Smooth

Cardiac

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3
Q

What are some functions of skeletal muscle?

Name 3

A

Movement

Regulation of Body Temperature (Shivering when cold)

Protecting body entrances (swallowin, defecating)

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4
Q

Describe the formation of skeletal muscle

A

Myoblasts aggregate in an area, fuse together and form myotubes, which then increase their production of sarcomeric proteins, leading to mature myofibers once innervated.

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5
Q

What is the name of the tissue that surrounds skeletal muscles?

A

Epimysium

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6
Q

What is the name of the tissue that surrounds muscle fascicles?

A

Perimysium

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7
Q

What is the name of the tissue that surroundsmuscle fibers?

A

Endomysium

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8
Q

Name the indicated regions/structures.

A
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9
Q

Sarcoplasmic Reticulum surrounds which structural portion of skeletal muscles?

A

Myofibrils

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10
Q

What are some distinguishing histological features of myofibrils?

A

Elongated cells

Striated formation

Multi-nucleated, nuclei at periphery

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11
Q

In what pattern do thin filaments surround the thick filaments?

A

Hexagonal pattern

Thin outnumber thick by about 6:1

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12
Q

How do the thick filaments surround the thin?

A

In a triangular pattern

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13
Q

What protein makes up the thin filaments?

A

Actin

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14
Q

What protein makes up the thick filaments?

A

Myosin

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15
Q

What is the sliding filament theory?

A

It’s a theory explaining the mechanics of how muscle cells generate force

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16
Q

What does the sliding filament theory state?

A

It states the muscle is composed of sarcomeres, where thin filaments, anchored to the Z line, “attach” to thick filaments and these filaments pull each other to shorten the sarcomere.

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17
Q

What composes a thin filament?

A

Actin

Troponin (3 parts: I, T, and C)

Tropomyosin

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18
Q

What do each of the troponins do (Troponin I, T, and C)?

A

I - binds actin

T - binds tropomyosin

C - binds calcium

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19
Q

What does tropomyosin do?

A

Tropomyosin binds the cross-bridging site of actin, preventing it from binding myosin during times of non-contraction

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20
Q

What is the purpose of titin?

Bonus: Why is it called titin?

A

Titin serves as a spring, stabilizing the location of myosin chains in the sarcomere by linking them to the Z line.

Bonus: It is called titin because it is a massive protein (each one has a Molecular Weight of 3 million :O)

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21
Q

What is the purpose of troponin?

A

Troponin lies on actin and tropomyosin, and serves to move tropomyosin when exposed to calcium. This movement opens the cross-bridging sites of actin to myosin

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22
Q

During a contraction what happens to the length of the sarcomere and each of the filaments?

A

The sarcomere gets shortened.

The filaments never change their length (in a healthy cell).

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23
Q

Velocity of sliding is dependent upon which of the fibers?

A

The myosin

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24
Q

Each skeletal muscle fiber is innervated by how many neurons?

A

Typically, just one

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25
Q

How many different types of skeletal muscle fibers are there?

A

Two: named I and II

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26
Q

Describe Type I Muscle Fibers:

Type of Metabolism

Speed of Fatigue

Speed of myosin hydrolysis

Main function

A

Red Fibers

Type of Metabolism: Oxidative Glycolytic (Mitochondria)

Speed of Fatigue: Slow

Speed of myosin hydrolysis: Slow

Main function: Posture

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27
Q

Describe Type IIb Muscle Fibers:

Type of Metabolism

Speed of Fatigue

Speed of myosin hydrolysis

Main function

A

White Fibers

Type of Metabolism: Glycolytic (not many mitochodria)

Speed of Fatigue: Fast

Speed of myosin hydrolysis: Fast

Main function: Force Generation (Sprinting, Lifting, Fighting)

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28
Q

What are satellite cells in skeletal muscle?

A

These are cells that function in skeletal muscle repair, and give us the basis of lifting weights to make our muscles stronger.

When activated, they become mature muscle cellsin order to replace those damaged or lost

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29
Q

What is the skeletal muscle triad?

A

The triad refers to the structure of sarcoplasmic reticulum “split” by the transverse tubule (T tubule) on histological examination

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30
Q

What is the name of cardiac muscle cells?

A

Myocytes

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31
Q

Where is cardiac muscle found? Is it voluntary or involuntary?

A

Only found in the heart

Involuntary muscle fiber

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32
Q

What are some key structural features of cardiac muscle?

Name 5

A

1) Cross striations (similar to those in skeletal muscle, but more stair-like)
2) Intercalated discs: Zonula adherens and Macula adherens (desmosome) hold cells together in a “stair and riser arrangement”
3) Intermittent Mitochondria
4) Centrally located spherical nuclei
5) Gap Junctions between cells

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33
Q

How is the contraction of heart muscle controlled?

A

Cardiac muscle contracts due to electrical stimulation originating from the Sino-Atrial Node in the heart itself

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34
Q

What specialized groups of cells are responsible for the electrical stimulus generated at the Sino Atrial (SA) node?

A

The pacemaker cells generate signals without specific instructions from nerves (though their activity may be modulated by nerves).

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35
Q

What is the purpose of Purkinje fibers?

A

Purkinje fibers help to spread electrical stimulation throughout the heart extremely quickly.

They allow our ventricles and atria to contract in synchronicity.

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36
Q

Purkinje fibers are rich in what two things?

A

Mitochondria

Glycogen granules

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37
Q

Purkinje fibers are a modified version of what other fiber?

A

Cardiac Myofibers!

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38
Q

Identify the indicated structure

A
39
Q

Identify the indicated structures

A
40
Q

What is the bundle of His?

A

A section of conducting fibers (like Purkinje Fibers) that carry the electric stimulus from the Atrio-Ventricular (AV) Node to the Ventricles

41
Q

What is the Atrio-Ventricular Node (AV Node)?

A

It is an area filled with specialized conducting cells similar to the Sino-Atrial Node.

42
Q

What is the function of the AV Node?

A

It serves to delay the impulses from the SA node so that the atria have time to squeeze blood into the ventricles before the ventricles contract.

43
Q

How does the heart respond to injury/stress?

Think two processes

A

Hypertrophy (cells here do not replicate, they just get larger)

Injured tissue is replaced by fibrotic scars (preserves ability to contract)

44
Q

What is the function of cardiac muscle?

A

To contract in a rhythmic manner to pump blood throughout our body

45
Q

What is the main function of smooth muscles?

What are some examples?

A

Involuntary control of organ shape:

Blood vessels

Respiratory Passages

Bladder

etc

46
Q

From which embryonic layer do smooth muscle cells originate?

A

Mesoderm

47
Q

Through what process are smooth muscle cells created?

A

Myogenesis

48
Q

How are smooth muscles typically organized as a whole?

A

In sheets or bundles

49
Q

What is the organization of the contractile unit of smooth muscle cells?

A

Still actin-myosin unit, but there are no Z lines or sarcomeres.

Instead, actin is bound to the plasma membrane at structures called dense bodies

50
Q

What are the two types of smooth muscles?

A

Multi-unit

Single-unit (Unitary)

51
Q

Why are multi-unit muscles called multi-unit?

A

NOT structural

These muscle fibers have many motor units that are each innervated separately from one another and contract INDEPENDENTLY from each other

Thus there are many units within one “muscle”

52
Q

Why are single-unit muscles called single-unit?

A

NOT structural

These muscles have many units that are interconnected to each other through gap junctions, and therefore contract as one large unit

53
Q

What muscle type is similar to unitary smooth muscle?

A

Cardiac muscle

54
Q

Where might one find multi-unit smooth muscles within the human body?

A

In arteries, iris, pulmonary air passages, and arrector pili muscles

55
Q

Where might one find unitary smooth muscle in the human body?

A

In blood vessels and viscera as circular/longitudinal muscle layers

56
Q

What are some distinguishing structural characteristics of smooth muscle?

Name 3

A
  1. Cells are spindle-shaped
  2. One nucleus per cell, located in the center of the cell. “Corkscrewed” nucleus indicates a cell that is contracted
  3. NO STRIATIONS
57
Q

Through what structure are skeletal muscles innervated?

What about smooth muscles?

A

Skeletal: Neuromuscular Junction (NMJ)

Smooth: Varicosities of innervating nerves

58
Q

How does smooth muscle respond to stress?

A

Both hypertrophy AND hyperplasia

59
Q

Identify the muscle types and some characterisitics:

A
60
Q

What is Excitation-Contraction (EC) Coupling?

A

It is the process by which a nerve’s excitation of a muscle cell leads to its contraction

61
Q

What happens when a nerve excites a muscle cell?

(Up to Ca release from SR)

A

1) At NMJ, action potential leads to acetylcholine release from synaptic bouton
2) acetylcholine binds acetylcholine-gated channels, allowing Na to flow into and K to flow out of the muscle cell
3) muscle cell becomes depolarized, leading to opening of voltage gated Na and K channels
4) as the depolarization spreads throughout the muscle cell, it dives into the cell through the transverse tubule to cause Ca release from the sarcoplasmic reticulum

62
Q

What happens once Ca is released from the SR?

Go to end of Myosin cycling

A

1) Calcium binds to troponin, opening cross-bridge sites on Actin
2) Actin forms cross-bridge with Myosin-ADP-P
3) Myosin ratchets, pulling actin towards the M line, ADP and P released
4) ATP binds Myosin, causing release of Actin
5) Myosin hydrolyzes ATP, cocking itself back to the start

This is the process of Myosin hydrolysis, or “cycling”

63
Q

What happens once nerve excitation of a muscle cell ends?

A

1) Calcium channels in SR (sarcoplasmic reticulum) close
2) Ca is rapidly taken into the SR by Ca ATPase pump
3) once Ca levels are low (happens very quickly), troponin C no longer binds Ca
4) tropomyosin is moved back into its place, covering the cross-bridging sites of actin
5) Contraction ceases

64
Q

What two things (1 molecule, 1 ion) are directly critical for skeletal muscle contraction?

A

Calcium

ATP

65
Q

The muscle cell’s plasma membrane s also known as …

A

The sarcolemma

66
Q

The channel which releases the calcium from the SR is known as the…

A

Ryanodine Receptor

67
Q

What is the name of the protein that reaches from the T-tubule to interact with the Ryanodine Receptor?

A

The Dihydropyridine Receptor

68
Q

What is the source of Ca for muscle cell contraction?

Is it intracellular, or extracellular?

A

The Sarcoplasmic Reticulum (SR), which is intracellular

69
Q

How can you increase the force generated by a muscle contraction?

A

Increase the frequency of muscle cell excitation

Increase the number of motor units recruited

70
Q

What are two major difference between cardiac muscle and skeletal muscle in regards to generating a muscle contraction?

A

No NMJ (neuromuscular junction) for cardiac muscle

Calcium Induced Calcium Release (via voltage gated calcium channels in the T-tubules)

71
Q

What is the function of Calcium Induced Calcium Release (CICR)?

A

It is the mechanism by which cardiac myocytes release calcium from the SR for muscle contraction.

72
Q

What is different about the role of Calcium in smooth muscle contraction versus skeletal muscle contraction?

A

In smooth muscle, calcium binds Calmodulin to change myosin activity

In skeletal muscle, calcium binds troponin C to change actin activity.

73
Q

How does calcium activate contraction in smooth muscles?

A

1) Calcium binds calmodulin (forming Ca-Calmodulin)
2) Ca-Calmodulin binds to and activates Myosin Light Chain Kinase (MLCK)
3) Ca-MLCK phosphorylates a regulatory myosin light chain head, allowing associated myosin heads to form a cross-bridge with Actin
4) Muscle contraction occurs

74
Q

How does smooth muscle contraction halt?

A

This is completed by two separate events, causing increased phosphatase activity, and decreased kinase activity:

1) A Myosin Light Chain Phosphatase (MLCP) removes the Phosphate from the regulatory myosin head
2) Ca levels are reduced due to the cessation of excitation, leading to lowered levels of Ca-calmodulin, and ultimately reduced levels of Ca-MLCK.

75
Q

What does curare do to skeletal muscle?

A

Curare blacks acetylcholine from reaching the acetylcholine-gated ion channels, halting the E-C process at the NMJ. This causes loose muscle paralysis

Bonus: Curare is a poison derived from plants in Central and South America used for arrow tip poisoning.

76
Q

What is an autoimmune condition affecting skeletal muscle at the NMJ?

A

Myasthenia Gravis

Antibodies block acetlycholine receptors

77
Q

What happens when you change the excitability of the sarcolemma?

Increase:

Decrease:

A

Increase: spontaneous voltage sensor activation leading to hypercontractility/stiffness

Ex: Congenital Myotonia

Decrease: Reduced membrane excitability leading to loose paralysis or weakness

ex: Periodic Paralysis

78
Q

What happens when you have an uncontrolled release of calcium from the sarcoplasmic reticulum?

Name a condition where this occurs and its cause.

A

Hypercontractility/stiffness

Condition: Malignant Hyperthermia

Cause: Mutations in the Ryanodine Receptor leading to decreased activation thresholds (easier to release Ca) and increased deactivation thresholds (harder to close Ca release channel)

79
Q

What happens when the myofilaments cannot bind calcium well?

A

You get fatigue which causes weakness

80
Q

What is dermatomyositis?

A

An inflammatory isorder of the skin and skeletal muscle

81
Q

What are the clinical features of dermatomyositis?

A

1) Bilateral, proximal muscle weakness (distal later in disease)
2) Heliotrope rash (upper eyelids), maybe malar rash (upper jaw)
3) Red papules on elbows, knuckles, and knees (flexor surfaces)

82
Q

What lab findings come with dermatomyositis?

A
  1. increased creatine kinase
  2. positive ANA and anti-Jo-1 antibody
  3. perimysial inflammation (CD4 T cells) w/perifascicular atrophy on biopsy
83
Q

What is the treatment for dermatomyositis?

A

Corticosteroids

84
Q

What is polymyositis?

A

Inflammatory disorder of skeletal muscle

85
Q

What is a clinical difference between polymyositis and dermatomyositis?

A

The skin is not involved in polymyositis

86
Q

What lab finding do we have with polymyositis?

A

endomysial (CD8 T cells) w/necrotic muscle fibers seen on biopsy

87
Q

What happens in patients with x-linked muscular dystrophy?

A

muscle wasting and replacement of skeletal muscle by adipose tissue, degenrative disorder

88
Q

What is the defect found in x-linked muscular dystrophy?

A

Mutation in the dystrophin gene

Often mutations are spontaneous due to the large size of the dystrophin gene

89
Q

What is the function of dystrophin?

A

Anchors muscle cell cytoskeletons to the ECM

90
Q

What are two examples of x-linked muscular dystrophy?

A

Duchenne Muscular Dystrophy

Becker Muscular Dystrophy

91
Q

What is the difference between Becker and Duchenne muscular dystrophy

A

Duchenne is a DELETION of the dystrophin gene, whereas Becker is simply a mutation in that gene

Same issues between the diseases, but Becker is a milder version of Duchenne

92
Q

What are the clinical signs of Duchenne muscular dystrophy?

A
  1. presents as proximal muscle weakness at ~1 year of age; progresses to distal muscles
    1. characteristic finding: calf pseudohypertrophy (enlargement of the calf)
  2. serum creatine kinase is elevated
  3. Death results from cardiac or respiratory failure; myocardium is commonly involved (average life expectancy = 25)
93
Q

Describe Type IIa Muscle Fibers

Type of Metabolism

Speed of Fatigue

Speed of myosin hydrolysis

A

Intermediate Fibers

Fast Oxidative Glycolysis

Do not fatigue easily (slow)

Intermediate

MSK Week 2 (28 decks)

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