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Histology > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

Muscle tissue

A

Muscle tissue

  • optimize property of contractility
  • actin microfilaments- generate forces necessary for muscle contraction
  • mesodermal origin
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2
Q

3 types of muscle tissue

A

3 types of muscle tissue:

  1. Skeletal muscle
    • long, multinucleated cells with cross striations (muscle fibers)
    • contraction is quick, forceful, & voluntary
    • contraction is caused by the sliding interactions of thick myosin filaments along thin actin filaments
    • embryonic development:
      • Mesenchymal myoblasts fuse->
      • Myotubules with many nuclei
      • Myofilaments->
      • Striated muscle fibers (location of elongated multinuclei- periphery under sarcolemma)
  2. Cardiac muscle
    • has cross-striations, elongated, branched cells bond to intercalated discs
    • contraction is vigorous, rhythmic, & involuntary
    • One or two Centered nuclei with glycogen
  3. Smooth muscle
    • fusiform cells, lack striations
    • contraction is slow & involuntary
    • Single Centered nuclei
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3
Q

Satellite cells

A

Satellite cells

  • inactive reserve myoblasts
  • Progenitor cells produce new muscle fiber following injury
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4
Q

Sarcoplasm, Sarcoplasmic reticulum, Sarcolemma

A

Sarcoplasm- cytoplasm of muscle cell

Sarcoplasmic reticulum- Smooth ER of muscle cell

Sarcolemma- muscle cell membrane & external lamina

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5
Q

Hypertrophy & Hyperplasia

A

Hypertrophy-

  • increased cell volume (BIG TROPHY :)
  • as in exercise that enlarges skeletal musculature by stimulating formation of new myofibrils & growth in the diameter of individual muscle fiber

Hyperplasia-

  • increase in # of cells (I’ve been to MANY PLACES:)
  • Smooth muscles able to renew continually
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6
Q

Identify

A
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7
Q

Organization of skeletal muscle

A

Epimysium

  • surrounds skeletal muscle
  • dense irregular connective tissue
  • present only in skeletal muscle

Perimysium

  • surrounds fascicle
  • functional unit in which fibers work together
  • Present in all muscle types

Endomysium

  • surrounds muscle fibers (has sarcolemma, mitochondria, sarcoplasmic reticulum)
  • with reticular fiber & scattered fibroblast
  • capillaries bring O2 to the muscle fibers
  • Present in all muscle types

Myofibrils-> A bands (dArk bands) & I bands (lIght bands)

Myofilaments (actin & myosin) in sarcomere-> extends from Z disc to Z disc (2.5um resting)

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8
Q

Structure of a myofibril & proteins that make the parts

A

A band- location of thick myosin filament

H band- center of A band, NO actin

M band- ties myosin bundle together

I band- actin without myosin

Z line- ties actin filaments

Force is generated in A but not in H band!

A-actinin

  • protein in Z-discs
  • connectin filaments

Titin

  • protein in I band and Z discs
  • largest protein in the body

Nebulin

  • binds thin myofilaments
  • helps anchor to a-actinin

Creatine kinase

  • found in M line
  • phosphocreatine-> phosphate-> ADP (help supply ATP)

Myomesium

  • found in M line
  • holds thick filaments in place
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9
Q

Myosin and Actin

&

Tropomyosin and Troponin

A

Myosin

  • thick filament
  • has heavy (twisted tails) and light chain (2 heads)
  • heads have actin & ATP binding sites

Actin

  • thIn filament (acTHIN :)
  • 2 regulatory proteins:
    • Tropomyosin
      • 2 polypeptide chains located in the groove between 2 twisted actin strands
      • covers the myosin binding site on actin
    • Troponin
      • 3 subunits: TnT(attaches to tropomyosin), TnC(binds calcium), TnI(regulates actin-myosin interaction)
      • after binding to calcium will change its shape & move tropomyosin to expose myosin-binding active sites
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10
Q

Sarcoplasmic reticulum, Tranverse tubule & Terminal cisternae system of 3 muscle types

A

Sarcoplasmic reticulum

  • contains pumps & other proteins for Ca2+ sequestration
  • well developed in skeletal muscle, less developed in cardiac, & irregular smooth ER without distinctive organization in smooth muscle

Transverse tubule

  • tubular infoldings that penetrate into the sarcoplasm and encircle each myofibril near the aligned A & I bands
  • Ca2+ gets distributed simultaneously to produce uniform contraction of all myofibrils

Terninal cisternae

  • adjacent to T-tubule
  • allows depolarization of sarcolemma in a T-tubule-> release Ca2+-> contraction of sarcomere
  • 2 terminal cisterns per sarcomere in triads with T-tubule in skeletal muscle
  • 1 small terminal cistern per sarcomere in dyad with T-tubule in cardiac muscle
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11
Q

Mechanism of contraction

A

Mechanism of contraction- occurs as the overlapping thin and thick filaments of each sarcomere slide past one another

Action potential at NMJ->

T-tubules->

Terninal cisternae of sarcoplasmic reticulum trigger Ca2+ release->

Ca2+ bind to Troponin->

Troponin changes its shape & moves Tropomyosin on the F-actin to expose the myosin-binding active sites & allow cross bridges to form->

Binding actin produces a pivot in the myosin toward the Z disc. Thin filaments move into the A band (energy through ATP is used)->

Myosin binds another ATP & detaches from actin->

Neural impulse stops & levels of free Ca2+ diminish. Tropomyosin again covers the myosin binding sites on actin->

Filaments passively slide back. Sarcomeres return to relaxed state.

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12
Q

Rigor mortis

A

Rigor mortis

  • absence of ATP
  • actin-myosin cross bridges stabilize
  • skeletal muscle become rigid when mitochondrial activity stops after death
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13
Q

Innervation of action potential

A

At MEP (motor end plate) or NMJ, acetylcholine gets released at synaptic cleft->

ACh binds to the receptors in the junctional folds of sarcolemma. ACh receptors contain a nonselective cation channel->

Muscle action potential->

ACh gets removed by acetylcholinesterase

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14
Q

Motor unit

A

Motor unit

  • 1 axon + all the muscle fibers it innervates
  • finer movements (example: ocular)- innervates few muscles
  • coarser movements (example: gluteus)- innvervates many muscles (100)
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15
Q

Myasthenia gravis

A

Myasthenia gravis

  • autoimmune disorder that involves circulating anitbodies against proteins of ACh receptors
  • skeletal muscle weakness
  • extraocular muscle of eyes are commonly affected first
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16
Q

Muscle spindles and Golgi tendon organs

A

Sensory receptors associated with skeletal muscles:

Muscle spindles

  • stretch detectors in muscle fascicles
  • encapsulated by modified perimysium (cells, fluid, muscle fibers)

Golgi tendon organs

  • enclose sensory axon penetrating among the collagen bundles at the myotendinous junction
  • detect changes in tension
17
Q

Duschenne muscle dystrophy

A

Duschenne muscle dystrophy

  • mutation of dystrophin gene
  • defective linkages between the cytoskeleton & the ECM
  • muscle contractions disrupt weak linkages to atrophy
  • large actin-binding protein inside sarcolemma or skeletal muscle
18
Q

Skeletal muscle fiber types

A

Skeletal muscle fiber types:

  1. Slow oxidative muscle fibers
    • slow contractions over long periods without fatigue
    • red fibers d/t:
      • many mitochondria
      • many surrounding capillaries
      • much myoglobin
  2. Fast glycolytic fibers
    • specialized for rapid short-term contraction
    • white fibers d/t:
      • few mitochondria or capillaries
      • anaerobic metabolism of glucose-derived from stored glycogen
  3. Fast oxidative-glycolytic fibers
    • intermediate
19
Q

Myoglobin

A

Myoglobin

  • globular sarcoplasmic protein similar to hemoglobin which contains iron atoms and allow for O2 storage
20
Q

Cardiac muscle

A

Cardiac muscle

  • embryonic development: mesenchymal cells align in chainlike arrays-> form complex junction between interdigitating process
  • Intercalated discs:
    • abundant of desmosomes & fascia adherens junctions (tranverse)- provide strong intercellular adhesion during the cells’ constant contractile activity
    • gap junction (longitudinal)
    • provide ionic continuity between the cells
    • serve as electrical synapse promoting rapid impulse conduction through many cardiac muscle cells simultaneously & contraction of many adjacent cells as a unit
  • Secretory granules:
    • found near atrial muscle nuclei
    • associated with small golgi complexes
    • release peptide hormone (atrial natriuretic factor ANF)
      • target cells of kidneys to affect Na+ secretion
      • natriuresis and diuresis
  • Fatty acids
    • major fuel of the heart
    • stored in triglycerides in small lipid droplets
  • Also present: glycogen granules, perinuclear lipofucsin pigment granules
  • Ischemia- tissue damage d/t lack of O2
21
Q

Smooth muscle

A

Smooth muscle (visceral muscle)

  • Fibers are enclosed by an external lamina & network of type I & type III collagen fibers comprising the endomysium
  • linked by numerous gap junctions (coordinate contractions)
  • concnetrated near the nucleus are mitochondria, polyribosomes, RER, vesicles of golgi
  • calveolae- contain major ion channels that control Ca2+ release from sarcoplasmic cisternae at myofibrils which initiates contraction
  • myosin phosphorylation by MLCK (myosin light chain kinase) when calmodulin binds Ca2+-> actin-myosin binding
  • Dense bodies
    • contains a-actinin
    • functionally similar to Z disc
  • Intermediate filaments composed of desmin- attach to dense bodies
  • Cadherins of desmosomes (submembranous dense bodies)- links adjacent smooth muscle cells
  • Synaptic vesicles in varicosites release neurotransmitter: ACh or NE
  • Reticulin fibers with the basal lamina of smooth muscle cells help hold the cells together as a functionla unit during the slow rhythmic contraction of this tissue
  • support fibroblast activity synthesizing collagen, elastin, & proteoglycans
  • Leiomyomas
    • benign tumor that develop from smooth muscle fibers- walls of uterus
    • aka fibroids
  • Visceral (single unit):
    • connected by gap junctions
    • visceral organs
    • stress-relaxation-contraction method
  • Multi-unit
    • NOT connected by gap junction but adherens & desmosomes
    • Arteries, airways, eyes
    • nerve or hormones
    • nerve stimulated bu stretching

Histology (9 decks)

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