Lecture 14 - Muscle Tissue Flashcards

1
Q

What are the different classifications of muscle tissues?

A
  • skeletal (voluntary/striated)
  • cardiac
  • smooth (involuntary)
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2
Q

What are the histological characteristics of skeletal muscle?

A
  • multinulceated syncytium formed by fusion of embryonic myotubes
  • peripheral nuclei
  • sarcomeric arrangement
  • innervated by a single motor axon
  • contains troponin C
  • “all-or-none” contraction
  • 50-60μm
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3
Q

What are the characteristics of Type I myofibers?

A
  • intense staining for oxidative enzymes
  • rich in NADH transferase and myoglobin
  • many mitochondria
  • primarily uses oxidative phosphorylation
  • slow, continuous contractions
  • “red” or “dark” fibers
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4
Q

What are the characteristics of Type IIA myofibers?

A
  • intermediate staining for oxidative enzymes
  • uses aerobic and anaerobic respiration
  • contract more rapidly than Type I but slower than Type IIB
  • resistant to fatigue
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5
Q

What are the characteristics of a Type IIB myofiber?

A
  • light staining for oxidative enzymes
  • utilize anaerobic respiration primarily
  • rich in ATPase
  • contract most rapidly
  • fatigue quickly
  • “white” or “light” fibers
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6
Q

What are the histological characteristics of smooth muscle?

A
  • single, mononucleated cells
  • no sarcomeric arrangement
  • innervated by ANS
  • no “all-or-none” response
  • connected via gap junctions
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7
Q

What are the histological characteristics of cardiac muscle?

A
  • single, mononucleated cells
  • centrally located nuclei
  • often branched
  • sarcomeric arrangement
  • connected via gap junctions (intercalated discs)
  • not directly innervated
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10
Q

Describe the hierarchal structure of skeletal muscle (include connective tissue).

A

Myofilament (actin/myosin filaments that make up a sacromere) -> myofibril (chain of sarcomeres) -> myofiber (muscle cell containing many myofibrils) -> sarcolemma (cell membrane of myofiber) -> endomysium (connective tissue surrounding each myofiber) -> fascicle (bundle of myofibers) -> perimysium (connective tissue surrounding each fascicle) -> muscle (multiple fascicles) -> epimysium (connective tissue around each muscle

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11
Q

What are Z disks?

A
  • separates adjacent sarcomeres

- anchor actin filaments

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12
Q

What are A bands?

A
  • consist of both actin and myosin
  • represents the length of myosin filaments
  • flanked by I bands and contains H band
  • does not change length
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13
Q

What is the I band?

A
  • portion of actin filaments not overlapping with myosin
  • in between A band and Z disc
  • changes length
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14
Q

What is the H band?

A
  • portion of myosin not overlapped by actin
  • in the middle of the A band
  • changes length
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15
Q

Describe thick myofilaments.

A

Myosin:
-dimeric protein with long tails and two heads
-two pairs of light chains
—essential light chains (stability of head?)
—regulatory (stability of myosin II and sites for PO4+ binding)

Heads contain:

  • actin binding region
  • ATP-binding region
  • light-chain binding site
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16
Q

Describe thin myofilaments.

A

F actin:

  • polymer of G actin
  • two polymers wound in an alpha helix
  • plus end inserts into Z-disk
Actin-associated molecules:
-troponin
—troponin I (inhibits binding of actin and myosin)
—troponin C (binds calcium)
—troponin T (binds tropomyosin)
-tropomyosin
—sits in groove of actin strands
—spans 7 actin monomers
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17
Q

Where are T tubules located in the sarcomere in skeletal muscle?

A

-A-I junctions (two per sarcomere)

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18
Q

What is αβ-crystalline?

A

-heat shock protein that protects desmin from mechanical stress

19
Q

What is dystrophin?

A
  • links α-actinin/desmin complex to sarcolemma
  • anchors actin to sarcolemma
  • reinforces sarcolemma
20
Q

What is the dystroglycan complex?

A

-links dystrophin (intracellular) to laminin-2 (extracellular)

21
Q

What is α-actinin?

A

-attaches thin filaments to Z line

22
Q

What is nebulin?

A
  • extends from Z disc to end of actin filaments

- regulates length of actin filament

23
Q

What is titin?

A
  • large, fibrous protein
  • extends from Z-disk to middle of H-band and connects ends of thick filaments to Z-line
  • provides myosin elasticity
  • centers thick filaments in the sarcomere
24
Q

What is desmin?

A
  • intermediate filaments
  • framework of desmin filaments which surrounds Z disc
  • links myofibrils laterally and to the sarcolemma
25
Q

What is plectin?

A

-binds desmin filaments

26
Q

What is muscular dystrophy?

A
  • X-linked genetic disease resulting in progressive degeneration of skeletal muscles
  • result of the absence of or abnormal dystrophin which anchors actin to the sarcolemma and stabilizes muscles during contraction
27
Q

What are satellite cells?

A

-reserve “stem” cells found in muscle tissue

28
Q

What are the contents of a neuromuscular spindle?

A
  • extrafusal fibers (muscle fiber)
  • intrafusal fibers (nuclear bag, sensory)
  • alpha motor neurons (supply extrafusal fibers)
  • gamma motor fibers (supply intrafusal fibers)
  • primary and secondary afferent fibers
29
Q

What are the histological characteristics of cardiac muscle tissue? (6)

A
  • single, mononucleated cells
  • central nuclei
  • sarcomeric (striated)
  • communicate via gap junctions (intercalated discs)
  • not innervated
  • one T-tubule per cisterna (diad)
30
Q

What is the composition of an intercalated disc?

A

Macula adherentes (desomsomes)

  • link intermediate filaments (desmin)
  • transverse component

Fascia adeherentes

  • anchor actin filaments
  • transverse component

Gap junctions
-longitudinal component

31
Q

Where does ANP come from and what does it do?

A

Atrial natriuretic peptide

-secreted as prohormone by cardiac muscle cells in atria when the atria stretches

  • regulates fluid electrolytes
  • relaxes vascular smooth muscle
32
Q

What are the histological characteristics of smooth muscle tissue?

A
  • singe, mononucleated cells
  • central nuclei
  • no sarcomeric arrangement
  • innervated by ANS or enteric system
  • not “all-or-none”
  • actin/myosin bundles in meshwork arrangement
  • dense bodies
  • no T-tubules
  • no extensive SR
  • pinocytic vesicles transporting Ca++
  • caveolae and lipid rafts
33
Q

What is the function of dense bodies in smooth muscle tissues?

A
  • anchors actin bundles

- communicate force of contraction to cytoskeleton and cell membrane

34
Q

What is the function of pinocytic vesicles in smooth muscle cells?

A
  • source of Ca++ in absence of T-tumble system and extensive SR
  • Ca++ is extracellular
35
Q

What are the caveolae and lipid rafts?

A
  • depressions in cell membrane involved in electrolyte transfer
  • forms vesicles