Exam 2 - Muscle Flashcards
epimysium
outermost layer of dense CT surrounding muscle
perimysium
CT surrounding muscle fascicles
contents of muscle fiber bundles
individual multinucleated muscle fibers/cells 10-100 um wide and up to 30 cm long
endomysium
basal lamina and reticular fibers that surround individual muscle cells - contains capillaries that supply blood to fibers
location of nuclei in skeletal muscle cells
in periphery just beneath sarcolemma
satellite cells
infrequent small stem cells found b/w the sarcolemma and basal lamina that may proliferate after trauma to form new myoblasts
triad system
T-tubules + sarcoplasmic reticulum; located at junction of A and I bands
T-tubules
infolding of plasma membrane, forms inner portion of triad
sarcoplasmic reticulum
modified sER, forms two side portions of triad
motor end plate
myoneural jxn - interaction site b/w nerve axon and muscle where basal lamina of axon and teloglia fuse w/ muscle fiber
changes in axon as it nears muscle cell
loses myelin sheath, but Schwann cells remain
teloglia
name for Schwann cells in the motor end plate region
what happens in synaptic cleft?
Ach from axon terminals diffuses across cleft and binds to Ach receptors located in junctional folds/subneural clefts of sarcolemma
number of muscle fibers innervated by one axon?
one or more
motor unit
a nerve and the muscles it innervates
botulism toxin
binds to presynaptic membrane, blocking Ach release
curare
paralytic drug that binds to Ach receptor
myasthenia gravis
autoantibodies against Ach receptors that block Ach binding and lead to progressive muscle weakness
mechanism of contraction
AP along sarcolemma-> T-tubules -> release Ca from terminal cisternae of SR -> Tn-c moves tropomyosin -> ATP on myosin hydrolyzed -> myosin binds actin -> Pi released -> head flexed -> ADP released -> actin pulled into A band -> new ATP binds myosin, releases myosin from actin
red fibers
type I fibers - slow twitch: high Mb, high mitochondria, fatigue resistant (stain strongly b/c mito enzymes)
white fibers
type II fibers - fast twitch: low Mb, low mitochondria, more stored glycogen, higher myosin-ATPase activity
intermediate fibers
characteristics b/w type I and II
control of fiber type differentiation
by innervation - red may become white by denervating and replacing with nerve from white fiber
muscle spindles
stretch receptors in perimysium that regulate muscle tone and tension - run parallel w/ main muscle and contain intrafusal fibers and neuron terminals in a fluid filled CT capsule
muscle spindle nerve terminal discharge rate
discharge rate increases as the sensory ending is stretched
types of intrafusal fibers
nuclear bag (cluster of nuclei) or nuclear chain
types of spindle nerve terminal endings
- annulospiral (wind around intrafusal fibers)
- flower spray (terminate in clusters)
- Gamma-efferents/fusimotor (motor end plats formed near spindle poles)
induction of satellite cell proliferation
after muscle injury, myoD transcription factor and JGF (hepatocyte growth factor) induce proliferatoin of these cells
side-population cells
cells that can differentiate into all major blood cell lineages
where do you find side-population cells?
bone marrow and skeletal muscle
rigor mortis
death -> PM more permeable to Ca -> cross bridge attachment -> muscle fibers contract while Ach and ATP present -> once ATP used up, actin and myosin stay linked until decomposition
muscle atrophy
due to disuse - reduction in muscle fiber size, NOT number
myofilaments
make up myofibrils
thin myofilaments
actin, tropomyosin, troponin
thick myofilaments
myosin
A band
anisotropic band - thick and thin filaments, but only place thick filaments are found
I band
isotropic band - thin filaments only, bisected by Z disk where thin filaments attach
H band
contains myosin w/o heads and creatine kinase
creatine kinase
catalyzes ATP formation from ADP and phosphocreatine
M line
region of myomesin linking w/ myosin
Z disk
attachment point for thin filaments - contains alpha-actinin
sarcomere
functional unit of contraction
myofilament related structural proteins (7)
- titin
- nebulin
- alpha-actinin
- myomesin
- desmin
- dystrophin
- C protein
titin
elastic protein that connects myosin to Z disk - acts like spring to keep myosin filaments centered in sarcomere
nebulin
inelastic protein attached to Z disk that runs parallel to actin
myomesin
myosin binding protein that holds myosin filaments in register at M line
C protein
myosin binding protein similar to myomesin
alpha-actinin
bundles actin filaments into parallel arrays and anchors them to Z disk
desmin
intermediate filament that helps bind myofibrils to each other and encircles Z disk - linked to each other by plectin
dystrophin
actin binding protein that reinforces and stabilizes sarcolemma during contraction by linking cytoskeleton w/ ECM
actin
2 strings (F actin) of monomers (G actin) wrapped around each other in right-handed helix 7 nm in diameter
what regulates polymerization of actin in vivo?
thymosin B4 and profilin
what regulates actin filament length, stability/turnover?
cofilin, severin, gelsolin, villin, CapZ, gCAP39
tropomyosin
elongated protein dimer (35K MW) that lies in groove of actin helix and binds 3 troponin peptides
Tn-T
binds Tn complex to tropomyosin
Tn-I
inhibits binding of actin to myosin w/ help of tropomyosin
Tn-C
binds Ca, releasing Tn-I-tropomyosin inhibition of actin activation of myosin ATPase
alphabeta-crystallin
HSP that protects desmin from stress-induced damage
Duchenne’s muscular dystrophy
X chromosome linked mutation in dystrophin gene that disrupts sarcolemma and Ca entrance into cell, resulting in muscle fiber necrosis
sarcoglycanopathies
limb-girdle muscular dystrophies with mutations in sarcoglycan genes - disrupts interactions w/ other proteins and association of sarcolemma with ECM
myosin
both a globular and fibrous structural protein w/ 2 heavy chains and 4 light chains
how many myosin molecules are thick filaments made of?
300-400
what does proteolytic digestion do to myosin molecules?
cleaves each heavy chain to produce a head and a tail
how many light chains does each head bind?
two light chains
heavy meromyosin
globular head of the heavy chain of myosin that contains an ATP and actin binding region
light meromyosin
rodlike alpha-helical tail of the heavy chain of myosin
cardiac muscle characteristics
banding, single nucleus/cell that is more centrally located, each fiber = many cells joined by intercalated discs, branched fibers
size of cardiac muscle cells
100-150 um long x 10-20 um wide
intercalated discs
transverse portion w/ fasciae adherens (actin filament anchor site) and macula adherens to bind adjacent cells together; lateral portion w/ gap junctions that ionically couple adjacent cells
how is cardiac muscle different from skeletal muscle?
- more mitochondria
- more extrafibrillar sarcoplasm
- larger T tubules
- T tubules at Z disk
- diads instead of triads
- don’t regenerate
- intra and extracellular Ca
- heals w/ fibrous CT that can block conduction
phospholamban
controls active transport of Ca into SR lumen
appearance of cardiocytes after MI
24 hrs: eosinophilic cytoplasm w/ some pyknotic nuclei
3 days: inflammatory cells infiltrate tissue
smooth muscle
muscle under involuntary control of sympathetic or parasympathetic NS
smooth muscle cells
- spindle shaped
- may branch
- 20 um long
- single central oval nucleus w/ 1 or more nucleoli -surrounded by basal lamina
- caveolae on PM
- cytoplasmic dense bodies w/ a-actinin (fxnal = of Z disk)
- staggered arrangement of cells
- no sarcomeres
what might smooth muscle cells secrete?
collagen and elastin
what does smooth muscle cytoplasm contain?
bundles of 5-7 nm thin filaments (actin, tropomyosin ONLY); 8-10 nm intermediate filaments (desmin, vimentin); 12-16 nm thick filaments (myosin)
myoepithelial cells of ectodermal origin
single, basket shaped smooth muscle cells found around sweat, salivary, lacrimal, and mammary glands
what attachments do myoepithelial cells contain?
hemidesmosomes
what do myoepithelial cells in mammary glands and lacrimal glands contract in response to, respectively?
oxytocin and Ach - to help dispel contents of glands
smooth muscle of mesodermal origin
located in respiratory, circulatory, digestive, reproductive tracts
smooth muscle of ectodermal origin
located in iris and ciliary body of eye
smooth muscle intermediate filament expression? why?
at high levels - serve as links in cytoskeletal network b/w dense bodies
smooth muscle myosin
2 heavy and 4 light chains, but filaments form only under certain conditions - dephosphorylation -> completely soluble
smooth muscle contraction
stim -> Ca increase in cytoplasm -> complex w/ calmodulin -> activate MLCK -> phosphorylate myosin -> myoson unfolds, forms filaments -> allows myosin to interact w/ actin
what other small molecule may also activate MLCK?
cAMP
how does estrogen influence smooth muscle?
increases cAMP -> contraction of smooth muscle
how does progesterone influence smooth muscle?
decreases cAMP -> relaxation of smooth muscle
