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HSF Block 1 > Histo - Muscle > Flashcards

Histo - Muscle Flashcards

1
Q

What are the 2 Mechanisms of Connecting Myofibrils to the Sarcolemma?

A
  1. Costameres
    • Desmin surround myofibrils at the Z line
      • muscle-specific intermediate filaments
    • Interconnects multiple myofibrils to the sarcolemma
      • via Plectin
      • alpha/beta crystallin protects desmin
    • Mutations to in this –> damage to myofibrils
  2. Dystrophin-associated protein complex
    • Dystrophin helps to link the sarcolemma & matrix to myofibrils
      • links dystrophin to laminin-2
    • Dystroglycan complex
      • alpha‐dystroglycan binds laminin in BL
      • beta‐dystroglycan is transmembrane and binds dystrophin in the cytoplasm
    • Sarcoglycan complex
      • specific to cardiac & skeletal muscle
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2
Q

What are the 3 Types of Skeletal Muscle Fibers?

A
  • Slow Oxidative (SO)
    • LOTS of mitochondria
    • Resistant to fatigue
    • Lots of myoglobin
    • Appear red
    • Oxidative Phosphorylation
  • Fast Glycolytic (FG)
    • FEW mitochondria
    • Rapid contraction
    • Anaerobic glycolysis
    • Appear white
  • Fast Oxidative-Glycolytic (FOG)
    • Between fast & slow
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3
Q

Explain the Organization of Connective Tissues Layers of Skeletal Muscle

A
  1. Endomysium
    • Around 1 muscle fiber
  2. Perimysium
    • Around a muscle fascicle
  3. Epimysium
    • Around a whole muscle
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4
Q

What type of muscle is this?

A

Basics:

  • Fusiform-shaped cells (like fibroblasts, but bigger)
    • Uni-nucleated
    • No striations
  • Endomysium
    • made by smooth muscle
  • Perimysium
    • has fibroblasts
  • Can proliferates & regenerate

Regulatory Proteins:

  • Calmodulin-myosin light chain kinase
    • (rather than troponin-tropomyosin)
  • Cells linked by gap junctions

TEM Level:

  • Dense bodies
    • like Z line
  • Caveolae
    • like T-tubules
  • Thinner filaments
  • NO myofibrils

Light Level:

  • Eosinophilic tissue
  • XS
    • smaller & larger cell profiles
    • some have nuclei, some don’t
      • Nuclei = round & centered
  • LS
    • cells = fusiform
    • can’t always see nucleus
      • if contracted —> see corkscrew nucleus
    • nuclei = oval & parallel to long axis of myofiber
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5
Q

What is the organization of skeletal muscle?

A
  1. Skeletal Muscle
    • Surrounded: Epimysium
    • Includes: Fascicles
  2. Fascicles (Collection of cells)
    • Surrounded: Perimysium
    • Includes: Myofiber clusters
  3. Skeletal Myofiber (Cells)
    1. Surrounded: Endomysium
    2. Includes: Single skeletal muscle cell
  4. Myofibrils (NOT cells)
    1. Functiton: Contractile apparatus
    2. Includes: Sarcomeres end-to-end
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6
Q

What are Satellite Cells? How can they help with Regeneration?

A

Basics:

  • Muscle cells in Go
    • Proliferation stops
    • Terminal differentiation
  • Satellite cells
    • Muogenic precursor cells
    • present w/in basal lamina
      • quiescent in adult
      • reactive upon injury
    • regenerate muscle w/in basal lamina
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7
Q

Summary of Characteristics of
Muscle Types

A
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8
Q

What is the Myotendinous Junction?

A
  • Tendons
    • Connect skeletal muscle fibers to bone, skin, other muscle
      • Dense Regular CT
  • Continuous w/ CT around the muscle
    • CT around muscle:
      • Epimysium (part of muscle)
      • Deep Fascia (CT outside of epimysium)
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9
Q

Organization of Connective Tissues Layers
of Skeletal Muscle

A
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10
Q

What is this image?

A

Triads

  • 2 cisternae ends of SR + 1 T-tubule
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11
Q

What is this image?

A
  • TEM of Neuromuscular Junction
    • can see the membrane infolding/junctitonal folds
      • where Ach gets released for contraction
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12
Q

What is this image?

A

Muscle Spindle ‐ TEM

  • MF = muscle fibers
  • SC = satellite cells
  • C = capsule
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13
Q

What can cause Muscular Dystrophy?

A

Mutations in the Mechanisms Connecting Myofibrils

  1. Mutation in Sarcoglycan Complex
    • ​causes limb-girdle muscular dystrophies
  2. Loss of dystrophin
    • causes Duchenne’s muscular dystrophy
    • X-linked recessive
      • loss of myofibrils/myofibers
      • increasing amt of adipose tissue instead
  3. Mutation of laminin
    • causes congenital muscular dystrophy
  4. Mutations in desmin, plectin, or crystsallins
    • causes loss of myofibrils
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14
Q

What are Myofibrils?

How are they formed?

A

Basics:

  • Myofibrils = made from Myofilaments
    • Contractile apparatus of muscle
    • Sarcomeres (Z to Z) aligned end-to-end
    • Causes striation in LS
      • aligned myofibrils
    • Appear punctated in XS

How they’re made:

  • Sarcomeres end-to-end
  • Made of 2 kinds of myofilaments:
    • Thick = Myosin molecules
    • Thin = Actin monomers
      • Actin & Myosin interact = contraction & generate force
      • Both have accessory proteins
        • regulate force generation
        • aid in organization of filaments
    • Organized parallel to other myofibrils
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15
Q

How does Smooth Muscle Contract?

A

Basics:

  • Thin filaments attach to dense bodies
    • interact w/ thick filaments —> produce contraction
    • alpha-actin achors thin filaments @ dense bodies
  • Intermediate filaments (desmin or vimentin)
    • also attach to dense bodies
  • Corkscrew nucleus
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16
Q

What is the structure of a Sarcomere?

A

Basics:

  • Z to Z

Relaxed:

  • Light I & H, and dark A band visible
  • Z & M lines visible

Contraction:

  • Dark A band visible only
  • No light I band & No H band
  • Z & M lines visible

Other Proteins:

  • Nebulin
    • Helps anchor to alpha-actin
    • Binds thin filaments laterally
    • May reg. thin filament length
  • Titin (Connectin)
    • Supports & organizes thick filaments
    • Connects M to Z line
    • Scaffold & elastic
      • passive tension during relaxation
17
Q

What are Sensory Receptors in Muscle?

A

Basics:

  • Muscle spindles
  • Golgi tendon organs
    • both interact w/ afferent/sensory nerves

Muscle Spindles:

  • Sensory & Motor
  • Small muscle fibers = intrafusal (ibetween extrafusal fibers)
    • surrounded by a capsule
  • Proprioception
    • senses stretch & tension

Golgi Tendon Organs:

  • Encapsulated bundles of Type I Collagen
    • receive sensory innervation ONLY
    • ​NO motor innervation
  • Contraction of muscle compresses collagen
    • compresses afferent nerve fiber
    • relays info to CNS on muscle tenstion
18
Q

What is a Neuromuscular Junction?

A

Basics:

  • Motor End Plate
    • Where nerve interacts w/ skeletal muscle fibers
  • Nerve vesicles = Acetylcholine
    • Small, clear core vesicles
    • Fuse w/ nerve cell membrane
    • Released into synaptic cleft
      • gap btw muscle & nerve
      • contain acetylcholinesterase
  • Sarcolemma forms junctional folds
    • Acetylcholine receptors
      • Myasthenia Gravis = autoimmune rxn to these receptors
19
Q

How do Sarcoplasmic Reticulum and Transverse Tubules in Skeletal Muscle create a Triad?

A
  • Sarcoplasmic reticulum
    • smooth endoplasmic retriculum (SER)
    • stores calcium
  • Transverse or T-tubules
    • sarcolemma surrounds the muscle fibers
    • dives into cytoplasm to form T-tubules
  • Triad Formation
    • 2 pieces of SER terminal cisternae
      • associated w/ 1 T-tubule
    • In skeletal muscle, trials are at the A-I junction
20
Q

What are the Types of Muscle in these images?

A
  1. Skeletal Muscle
    • Nuclei
    • Striations
    • Muscle fiber
  2. Cardiac Muscle
    • Branching striations
    • Nucleus
    • Glycogen
    • Intercalated disc
  3. Smooth Muscle
    • Nuclei
    • No striations
    • Dense bodies
21
Q

What are Dense Bodies?

A

Basics:

  • Like Z disks
    • dense areas throughout myofiber
  • Myofilaments anchor in them
    • pull against to contract cells
  • “Corkscrew nucleus”
  • Submembranous dense bodies
    • have cadherins
    • link to adjacent cells
22
Q

What is Duchenne’s Muscular Dystrophy?

A
  1. Loss of myofibrils
  2. Loss of myofibers
  3. Increase in amount of adipose tissue
23
Q

Identify the 4 items in this XS photo

A

Skeletal myoblasts

(fuse)

Skeletal Myotubes

(differentiate)

Skeletal Myofibers

Glycogen = Energy source

24
Q

What are the steps of development of Skeletal Myofibers?

A
  1. Skeletal Myoblasts
    • Single nucleated cells
  2. Skeletal Myotube
    • Fused skeletal myoblasts
  3. Skeletal Myofibers
    • Skeletal myotubes make muscle specific proteins & differentiate into myofibers
      • Multiple nuclei in the center of cell
      • Fully formed contractile apparatus
  4. Other: Satellite Cells
    1. Myoblasts that don’t fuse
      1. present w/in the BL (outside the sarcolemma)
      2. Can proliferate (stem-cell-ish)
      3. Produce new muscle fibers after injury
25
Q

What is this?

A

Caveolae

  • Invaginations in the sarcolemma of smooth muscle
    • Like T-tubules
26
Q

What is the different between thick and thin myosin filaments?

A

THICK: MYOSIN

  • 2 heavy + 4 light chains (head)
    • Chains coil together = myosin molecule
    • Molecules = head + tail
  • Head of myosin = 2 binding sites
    • Move along thin filaments during contraction
      • ATPase activity
  • Many myosin = thick filament
    • Associate via tails ANTI-PARALLEL toward center of A band
    • H zone = NO THIN FILAMENTS (hence lighter stain)
      • M line = middle of H zone
      • Contains Myomesin
      • Holds thick filaments together & maintains energy
      • Creatine kinase + ADP for ATP

THIN: ACTIN

  • 2 strands of F-actin coil = thin filament
    • Tropomyosin = found in groove formed by coiling
  • Troponin Complex (Tn-I, Tn-C, Tn-T)
    • interact w/ tropomyosin
    • Troponin causes tropomyosin to shift to expose myosin binding site
    • alpha-actinin achors thin filament = Z line
27
Q

What are the 3 types of muscle?

A
  1. Skeletal
    • Striated
    • Voluntary
  2. Cardiac
    • Striated
    • Involuntary
  3. Smooth
    • Not striated
    • Involuntary
28
Q

Skeletal Muscle Cell Structures w/ Special Names

A
  • Sarcolemma = Plasma Membrane
  • Sarcoplasm = Cytoplasm
  • Sarcoplasmic Reticulum = Smooth ER
29
Q

What are the 4 major characteristics of Skeletal Muscle Cells/Fibers?

A

Characteristics:

  1. Large, elongated
  2. Multinucleated
    • Peripheral nuclei
  3. Striated cells
  4. Fibers interdigitate w/ tendons
    • form myotendinous junctions

HSF Block 1 (19 decks)

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