1-Striated Muscle Skeletal Flashcards

1
Q

basal lamina

purpose

A

important structural element serves as anchor point for proteins than span cell membrane

link endomysium to sarcolemma

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2
Q

T-tubules

definition

A

specialized invaginations in muscle cell membrane conduct AP (depolarization) from cell surface to calcium reservoir (@sarcoplasmic reticulum)

SR surrounds myofilaments

membrane = sarcolemma

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3
Q

muscle development sequence

skeletal muscle

A
  1. pluripotent stem cells diff to myogenic progenitor cells
  2. myoblasts
  3. committed myocytes OR dormant satellite cells to be acitvated later
  4. myocytes aggregate into myotubes
  5. mature fiber w/ nuclei @ periphery
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4
Q

mature muscle organization

A
  1. myofilaments
  2. myofibrils
  3. muscle fiber
  4. muscle fascicle
  5. muscle
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5
Q

layers of CT

A
  1. endomysium: around indiv muscle cells/fibers
  2. perimysium: divides into bundles aka surrounds fascicles
  3. epimysium: attachs directly to bone or tendon aka surrounds entire muscle group
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6
Q

basal lamina/BM composition

A

collagen + proteoglycans + glycoproteins/complex polysaccharides

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7
Q

terminal cisternae of SR

A

swelling at end of reticular network of sarcoplasmic reticulum where Ca stored

2 terminal cisternae + T tubule = triad

SR surrounds fibrils

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8
Q

contractile elements

sarcomere

A
  1. thin filaments (actin)
  2. thick filaments (myosin)
  3. titin
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9
Q

structural elements

A
  1. Z disc (est boundaries of sarcomeres)
  2. M line (center line)
  3. Titin
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10
Q

bands/zones

sarcomere

A
  1. I band (light color) = thin filaments only
  2. A band (dark color, wider) = thin + thick
  3. H zone (middle of A) = thick only
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11
Q

thick filaments

A

bipolar (head and tails, tails medial) structure of a lot of myosin molecules

filaments wrap together in quasi helical fashion

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12
Q

myosin molecule

A

2 heavy chains in alpha-helix + 2 light chains (regulatory and essential) per chain so 4 total

neck of chain allows for hinge to articulate with thin filaments

myosin head has ATPase activity

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13
Q

thin filaments

A

double strand of G actin sub units twisted a helix

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14
Q

regulatory proteins with thin filaments

A
  1. tropomyosin
  2. troponins
    T = bind tropomyosin
    C = bind calcium
    I = inhibitory, changes conformation when C binds Ca and moves T so tropomyosin out of active site on actin
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15
Q

titin

A

gigantic muscle protein that anchors thick filaments to Z discs, spans 1/2 sarcomere

gives structural integrity/elastic stabilization of thick/thin filaments, passive tension

bi-directional spring to help sarcomere return to og

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16
Q

Z disc/Z line

A

lattice like structural element at both ends of sarcomere

anchor point for thin filaments and titin filaments

connect to Z discs of adjacent myofibrils by intermediate filaments (desmin)

17
Q

M line/M disc

A

lattice like structural element at center of sarcomere

anchor for thick filaments and titin
-M protein: stabilized proteins in M line
-obscurin: regulate sarcomere/SR interaction
-myomesin: anchors myosin with titin

18
Q

costameric protein complex

A

aka dystrophin-glycoprotein complex + integrins = costamere

stabilizes muscle cell membrane during contraction

scaffolding for myofibrils by linking cytoskeleton w/ ECM and anchors Z disk (w/ contracticle proteins) to basal lamina

19
Q

outcomes of disease

clinical relevance

A
  1. respiratory insufficiency/failure
  2. inc suscept to respiratory infection
  3. spinal curvature
  4. cardiomyopathy
  5. metabolic abnormalities
  6. reduced mobility/independence
20
Q

muscular dystrophy

A

mutations in genes that encode dystrophin or other components of costamere

results: disorganized costameres
enhanced membrane leak
edema/inapp cytosolic Ca generation
ECM deposition

21
Q

duchenne muscular dystrophy

A

no dystophin protein present

fatal by age 30 via cardio respiratory failure

22
Q

becker muscular dystrophy

A

dystrophin present but reduced in amount

less serious, usually not fatal

23
Q

limb girgle dystrophy

A

mutations for sarcoglycans or other dystrophin-glycoprotein complex

24
Q

motor unit

A

one motor neuron and all the muscle fibers that it innervates

25
neurotransmission at triad
1. depolarization down t tubule 2. conformation change in L type Ca channel (LTCC) 3. 4 LTCC attach to 4 RYR = tetrad, opens 4. termination when Ca sequestered in myoplasm
26
Ca reuptake mechanism
SERCA major way, ATP dependent Calreticulin and Calsequestrin are SR proteins that bind Ca+
27
sliding filament theory
thin filaments slide over thick filaments bc thick pull toward center of sarcomere thin pull Z discs toward each other and sarcomere shortens
28
thin filament regulation
Ca triggers contraction by interacting with troponin C = conformational change tropomyosin shifted deeper into actin groove to expose active site for myosin from thick to bind
29
cross bridge cycle
1. ATP binds to myosin 2. dissociation of AM complex 3. ATP hydrolyzed = conform change aka cocked state 4. cross bridge formed when active site exposed 5. Pi released = conform change and power stroke 6. ADP released and cross bridge detach from myosin if ATP present
30
magnesium | EC coupling
co factor for myosin ATPase mediated ATP hydrolysis deficiency can cause muscle weakness and cramping, common in GI disease, diabetes, alcoholism, aging
31
modulating force
1. recruit more and bigger motor units if inc stimulus intensity 2. frequency summation aka high frequency stimulation = repeated contractions of progressively greater force until reaches sustained maximal force production (fused tetanus) progressive inc in myoplasmic Ca w/ each stimuli until max Ca levels reached
32
type I slow twitch fibers
-aerobic pathway for ATP -resistant to fatigue -low/slow force output | similar to cardiac muscle with diff myosin isoforms
33
type II fast oxidative fibers
aerobic or anaerobic ATP resistant to fatigue moderate/rapid force output
34
type II fast glycolytic
anaerobic pathway for ATP fatigue quickly high/rapid force output