Muscle and Contractile filaments Flashcards
skeletal muscle surrounded by dense connective tissue
epimysium
skeletal muscle consists of muscle fiber bundles (fascicles) surrounded by
perimysium
skeletal muscle fiber bundles consist of individidual
multinucleated muscle fibers (cells)
skeletal muscle cells surrounded by a basal lamina and reticular fibers
endomysium
skeletal endomysium contains
capillaries that supply blood to the muscle fiber
infrequent small cells found between the sarcolemma and basal lamina of skeletal muscle
satellite cells
satellite cells
stem cells that may proliferate after trauma to form new myoblasts
myofibrils are made up of
myofilaments
another name for a muscle fiber
muscle cell
muscle fibers have dark _ bands and light _ bands
A
I
may see a dark _ line bisecting the I band
Z
functional unit of contraction
sarcomere
T-tubule flanked on both sides by dilations of sarcoplasmic reticulum
triad
triad is located at
the junction of the A and I bands
skeletal muscle interaction site between nerve axon and muscle
motor end plate
axon loses _ near the muscle cell
myelin sheath
a nerve and the muscle it innervates
motor unit
skeletal muscle axon terminals contain _ that diffuses across _ and binds to receptors located in the _ of the sarcolemma
Ach
synaptic cleft
junctional folds
binds to presynaptic membrane and blocks Ach release
botulism toxin
autoantibodies against Ach receptors
myasthenia gravis
antibodies block Ach leading to
progressive muscle weakness
action potential from motor end-plate goes along the sarcolemma and is carried into the myofibrils by the
transverse T tubule system (continuous with the myofibril sacrolemma)
depolarization of the T tubule system causes release of calcium from
terminal cisternae of the sarcoplasmic reticulum
calcium release leads to interaction of actin and myosin leading to
muscle contraction
3 muscle fiber types
red, white, and intermediate
type I, slow twitch: high myoglobin content, numerous mitochondria with succinic dehydrogenase; fatigue resistant
red fibers
type II, fast twitch, lower myoglobin and mitochondria content than type I; have more stored glycogen; higher ATPase activity than Type I
white fibers
characteristics between type I and II
intermediate fibers
_ controls fiber type differentation
innervation
provide information of degree of muscle tension
stretch receptor
contain modified muscle fibers
intrafusal fibers
muscle spindles have
sensory receptors, intrafusal fibers, and neuron terminals in a fluid filled connective tissue capsule
intrafusal fibers may be
nuclear bag fibers (cluster of nuclei) or thin nuclear chain fibers
spindly may receive afferent sensory nerve fibers with 3 types of endings
annulospiral, flower spray, and y-efferents (fusimoter)
wind around intrafusal fibers
annulospiral
terminate in clusters
flower spray
y-efferents (fusimotor)
motor end plates formed near spindle poles
after muscle injury _ transcription factor in combination with HGF induces proliferation of
myoD
satellite cells
rigor mortis
calcium ions enter muscle cells upon death; once the ATP present is used up, the actin and myosin proteins will stay linked until decomposition
muscle atrophy is
decrease in muscle fiber size; the number of muscle fibers does not change
myofilaments have 4 main proteins
actin, tropomyosin, troponin, and myosin (all thin except myosin)
attachment point for thin filaments
Z-disk
thick myofilaments are only found in this band
A
thin myofilaments in this band attach to Z disk and extend into A band
I band
anchors actin filaments to the Z disk
alpha-actinin
helps bind myofibrils to each other; linked to each other by plectin
desmin
absent in Duchenne muscular dystrophy patients
dystrophin
contains myosin (no heads) and creatine kinase
H band
region of myomesin linking with myosin
M line
A filament of _ is made of of globular actin monomers (G-actin)
actin (F-actin)
actin filaments in EM
F-actin
elongated protein dimer that lies in the grooves of the actin helix
tropomyosin
tropomyosin binds 3 tropoinin peptides named
T, I, and C
binds the Tn complex to tropomyosin
Tn-T
together with tropomyosin inhibits the binding of actin to myosin
Tn-I
calcium binding subunit: binding of Ca to this subunit releases the TnI-tropomyosin inhibition of actin activation of myosin ATPase
Tn-C
intermediate filament that encircles Z disk of each sarcomere
desmin
dystrophin
reinforces and stabilizes sarcolemma during contraction by linking cytoskeleton with ECM
mutations in genes for sarcoglycans; disrupts association of sacrolemma with ECM
sarcoglycanopathies (limb-girdle muscular dystrophies)
thick myofilaments of 300-400 _ molecules
myosin
both a globular enzyme and a fibrous structural protein
myosin
when proteolytically digested, each myosin heavy chain produces a globular head called _ and a rodlike alpha-helical tail termed _
heavy meromyosin
light meromyosin
each myosin head binds
2 molecules of light chains
when the membrane is depolarized and calcium released from the SR, calcium binds to the Tn-C leading to
exposes the myosin binding site on actin
when myosin binds to actin and ATP hydrolysis on myosin head occurs,
the myosin head flexes and the actin thin filaments are pulled into the A band
causes the release of the bond between actin and myosin
a new ATP molecule binding to the myosin head
type of muscle with a single nucleus per cell more centrally located
cardiac muscle
cardiac muscle fibers are composed of several cardiac muscle cells joined end to end by junctional zones called
intercalated disks (ID)
ID have a transverse portion containing _ and _ and a lateral portion with _
fasciae adherens and macula adherens (these bind adjacent cells together) gap junction (this ionically couples adjacent cells)
cardiac tissue does not regenerate, but instead it
forms a fibrous connective tissue scar
cardiac muscle is usually a _ instead of a triad
diad
while all calcium comes from SR for skeletal muscle, cardiac muscle gets calcium from the SR and
extracellular calcium
controls active transport of calcium into SR
phospholamban
amount and activity of phospholamban controlled by
thyroid hormone
shape of smooth muscle
spindle shaped
smooth muscle is under involuntary control of
sympathetic and parasympathetic nervous systems
smooth muscle nucleus:
single central oval nucleus
smooth muscle cells are surrounded by a _
basal lamina
2 smooth muscle cells in contact may form
gap junctions
smooth muscle plasma membrane has numerous _ on the surface and cytoplasmic _ that contain alpha actinin
caveolae
dense bodies
single smooth muscle cells found around sweat, salivary, lacrimal, and mammary glands
myoepithelial cells of ectodermal origin
smooth muscle located in respiratory, circulatory, digestive, and reproductive tracts
mesodermal origin
smooth muscle located in the iris and ciliary body of the eye
ectodermal origin
smooth muscle does not contain
sarcomeres
smooth muscle is membrane associated and _ contain _, which is the functional equivalent of Z-disk
cytoplasmic dense bodies
alpha-actinin
smooth muscle cytoplasm has actin and tropomyosin but no
troponin
lots of _ filaments in smooth muscle that function as _
intermediate
links in cytoskeletal network between dense bodies
smooth muscle has _ heavy chains and _ light chains
2
4
if smooth muscle myosin is dephosphorylated it is
completely soluble
for smooth muscle contraction, when stimulated, calcium increases in cytoplasm and complexes with
calmodulin (calcium binding protein)
calcium-calmodulin complex activates
myosin light chain kinase, which phosphorylates myosin and allows it to interact with actin
myosin light chain kinase may be activated by cAMP
estrogen increases cAMP while progesterone decrease cAMP
