Muscle Flashcards
epimysium
dense connective tissue that surrounds muscle
perimysium
surround muscle fiber bundles (fascicles)
muscle fiber bundles consist of…
individual multinucleate muscle fibers (cells)
surrounds muscle cells and contain capillaries that supply blood to muscle fiber (cell)
endomysium
what are the components of the endomysium?
basal lamina and reticular fibers
in a cross section where would you find nuclei in skeletal muscle?
nuclei lie in a peripheral location just beneath the sarcolemma
satellite cells
infrequent small cells found between the sarcolemma and basal lamina. Stem cells that may proliferate after trauma to form new myoblasts
muscle cells are the same as
muscle fibers
At the light microscope level, H and E stained muscle fibers have
dark A bands and light I bands.
functional unit of muscle contraction
sarcomere
skeletal muscle has a well developed _____ system
triad
The inner portion of skeletal muscle triad is…
an infolding of the plasma membrane (T-tubule)
The 2 side portions of skeletal muscle triad are
modified smooth endoplasmic reticulum (sarcoplasmic reticulum)
Where is the skeletal muscle T tubule system located?
at the junction of the A and I bands
interaction site between nerve axon and muscle
motor end plate (myoneural junction)
As axons get close to muscle cell, what happens to myelin sheath and Schwann cells?
axon loses myelin sheath near the muscle cell, but Schwann cells still cover the axon
interactions at the motor end plate
At the motor end plate the axon and Schwann cells basal lamina fuse with the muscle fiber
What are Schwann cells called in the region of the motor end plate?
teloglia
Axon terminals contain__________ which diffuses across synaptic cleft and binds ______________ located in the __________ ________ of the sarcolemma.
Axon terminals contain acetylcholine which diffuses across synaptic cleft and binds to Ach receptors located in the junctional folds of the sarcolemma.
Triad
T tubule flanked on both sides by dilations of sarcoplasmic reticule,
how many muscle fibers may a single axon innervate?
a single axon may innervate one or more muscle fibers
A nerve and the muscles it innervates is called a
motor unit
Myasthenia gravis
autoantibodies against acetylcholine receptors. Antibodies block acetylcholine which leads to progressive muscle weakness
Action potentials generated at the motor end plate is propagated along….
the sarcolemma and is carried into the myofibrils by the transverse T tubule system continuous with the myofibril sarcolemma
depolarization of the T tubule system causes
the release of Ca++ from the terminal cisternae of the sarcoplasmic reticulum
the release of Ca++ from the terminal cisternae of the sarcoplasmic reticulum causes…
conformational changes in molecules (troponin-C) that mediate the interaction of actin and myosin and results in muscle contraction
Red fibers
Type I, slow twitch. High myoglobin, numeRous mitochondRia, and fatigue Resistant
White fibers
Type II, fast twitch. Lower myoglobin and mitochondria than Red fibers. More stored glycogen. Higher myosin-ATPase activity than Type I
Intermediate fibers
characteristics between Type I and II
What controls fiber type differentiation?
innervation. a red fiber may be changed to a white fiber by denervating and replacing with nerve from white fiber
Stain strongly for mitochondrial enzymes i.e succinate dehydrogenase
Red fibers (Type I)
Where can you find muscle spindles?
muscle spindles run parallel with the main muscle fibers
Spindles sense…
Spindles sense changes in muscle length (stretch receptor)
contents within muscle spindle
contain modified muscle fibers (intrafusal fibers) and neuron terminals in a fluid filled connective tissue capsule
As the sensory ending is stretched the nerve terminal discharge rate increases or decreases?
increases
Nerve terminal has an _____________ ending
annulospiral (wraps around fiber in spiral configuration)
2 types of intrafusal fibers?
nuclear bag (cluster of nuclei) and nuclear chain
Muscle spindles may receive afferent sensory nerve fibers with what 3 types of endings?
1)annulospiral 2)flower spray 3)γ-efferents(fusimotor)
annulospiral nerve ending
wind around intrafusal fibers
flower spray nerve ending
terminate in clusters
γ-efferents (fusimotor)
motor end plates formed near spindle poles
After muscle injury, myoD and HGF induces
proliferation of satellite cells (quiescent myoblasts)
Rigor mortis
Upon death, muscle cell membranes become more permeable to Ca++. The Ca ions promote the cross-bridge attachment between actin and myosin. The muscle fibers contract while acetylcholine and ATP are present or until fully contracted. Muscles use ATP to pump calcium out of the cells and once the ATP is used up, the actin and myosin proteins will stay linked until decomposition
muscle atrophy
atrophy due to disuse is caused by a reduction in muscle fiber size
Does the number of muscle fibers change with muscle atrophy?
NO.NO.NO.
4 main proteins found in myofilaments and associated size
actin(thin), tropomyosin(thin), troponin (thin), and myosin (thick)
Myofibrils are composed of
myofilaments
Z-disk
attachment point for thin filaments. Alpha actinin
Z disk bisects
I band
I band (isotopic band)
Thin myofilaments attach to Z disk and extend into A band
Elastin protein that connects myosin to Z disc
Titin
Inelastic protein attached to Z disc (runs parallel to actin)
Nebulin
Desmin
intermediate filament that helps bind myofibrils to each other. Also encircles Z-disk
What protein links Desmin to each other?
Plectin
a filament of actin (F-actin) is made of
globular actin monomers (G-actin)
Actin filaments are made up of __ strings of monomers wound around each other in a right handed helix
2
Elongated protein dimer which lies in grooves of the actin helix
tropomyosin
tropomyosin molecule binds these three troponin peptides
Tn-T, Tn-I, Tn-C
Binds the Tn complex to tropomyosin
Tn-T
this peptide in conjunction with tropomyosin inhibits the binding of actin to myosin
Tn-I
Tn-C
calcium binding subunit- binding of Ca to this subunit releases the Tn-I tropomyosin inhibition of actin activation of myosin ATPase
Desmin encircles the ______ of each sarcomere
Z-Disk
______ links desmin together
Plectin
Duchenne’s muscular dystrophy
X linked mutation in dystrophin gene
Function of dystrophin
Dystrophin reinforces and stabilizes sarcolemma during contraction by linking the cytoskeleton with the ECM
how does a lack of dystrophin impact muscle
defective or no dystrophin disrupts sarcolemma and Ca entrance into the cell = muscle fiber necrosis
Sarcoglycanopathies
mutations in genes for sarcoglycans. disrupts interaction with other proteins and association of sarcolemma with ECM
both a globular enzyme and a fibrous structural protein
myosin
Basic components of a myosin molecule
2 identical heavy chains and 2 pairs of light chains
Each myosin head binds how many molecules of light chains
Each myosin head binds 2 molecules of light chains
Mechanism for muscle contraction
membrane depolarized and Ca released from the sarcoplasmic reticulum. Calcium ions then bind to the Tn-C subunit of troponin
Ca ions binding to the Tn-C subunit of troponin results in
spatial configuration shift of troponin and moves the tropomyosin molecule deeper into the actin helix groove and exposes the myosin binding site on actin
myosin binds to
actin
when myosin head binds to actin- energy yielding breakdown of ATP to ADP + Pi ….
flexes the myosin head and the actin thin filaments are pulled into the A band
Banding of cardiac muscle is similar to
skeletal muscle
nucleus of cardiac muscle cells
single nucleus per cell, centrally located
cardiac muscle fibers are composed of several cardiac muscle cells joined end to end by junctional zones called
intercalated disks
transverse portion of intercalated disks contain
fasciae adherens (actin filaments anchor site) and macula adherens (desmosomes) to bind adjacent cells together
lateral portion of intercalated disks have
gap junctions which ionically couple adjacent cells
cardiac muscle in relation to skeletal muscle
cardiac muscle has more mitochondria and extra fibrillar sarcoplasm than skeletal muscle. Larger T tubules in cardiac. triads are less common in cardiac muscle
how does cardiac muscle respond to injury
cardiac muscle responds to injury by forming a fibrous connective tissue scar.
how does cardiac muscle make new cells
under normal circumstances cardiac muscle does not regenerate
Phospholamban
controls active transport of Ca++ into sarcoplasmic reticulum lumen.
amount and activity of phospholamban is controlled by what hormone
thyroid hormone
how is smooth muscle controlled?
smooth muscle is under involuntary control of sympathetic or parasympathetic nervous system
appearance of smooth muscle cells
spindle shaped, but may branch. single central oval nucleus with one or more nucleoli. surround by a basal lamina
smooth muscle cells may secrete
collagen and elastin
2 smooth muscle cells may form
gap junctions and interdigitations that facilitate electrical conduction
Plasma membrane on smooth muscle cells has numerous _______ on the surface and cytoplasmic _______ ______ that contain alpha actinin
caveolae
dense bodies
arranged of cells in smooth muscles can be described as
“staggered”
single smooth muscle cells can be found
around sweat, salivary, lacrimal, and mammary glands
mammary glands contract in response to
oxytocin
lacrimal glands contract in response to
acetylcholine
smooth muscle of mesodermal origin can be found in what body systems/areas
respiratory, circulatory, digestive and reproductive tracts
smooth muscle of ectodermal origin can be found…
in the iris and ciliary body of the eye
smooth muscle does not contain
sarcomeres
If smooth muscle is dephosphorylated
completely soluble
Components of smooth muscle myosin (chains)
smooth muscle has 2 heavy chains and 4 light chains like striated muscle
when smooth muscle is stimulated, Ca++ increases in cytoplasm and complexes with
calmodulin (Ca++ binding protein)
the Ca++-calmodulin complex activates
myosin light chain kinase
myosin light chain kinase phosphorylates myosin which causes
myosin to unfold and form filaments and this allows myosin to interact with actin
other than Ca-calmoduin complex what else may activate myosin light chain kinase
cAMP
H band contains
myosin (no heads) and creatine kinase
creatine kinase, which is located in the H band, catalyzes
ATP formation from ADP and phosphocreatine
A band
(anisotropic band)- thick myofilaments found only A band + thin myofilaments
