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Muscle Microanatomy
LECOM Yr 1
46
Anatomy
Graduate
08/05/2011

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Term
what are the three types of muscle?
Definition
skeletal, cardiac, and smooth
Term
describe skeletal muscle
Definition
striated, long parallel arrangement, and multiple peripheral nuclei
Term
describe cardiac muscle
Definition
striated, branched cells, central nucleus, and intercalated discs
Term
describe smooth muscle
Definition
fusiform, central "cork screw nucleus"
Term
the fusion of ______ forms skeletal muscles
Definition
myeloblasts
Term
what are satellite cells?
Definition
myeloblasts that remain as stem cells
Term
True or false: under different conditions satellite cells can change to muscle cells.
Definition
True
Term
what is the sarcolemma?
Definition
the muscle fiber
Term
what is the sarcoplasm?
Definition
the muscle fiber cytoplasm
Term
what is the sarcoplasmic reticulum?
Definition
specialized muscle endoplasmic reticulum
Term
what is the endomysium?
Definition
connective tissue surrounding individual muscle cells, composed of reticular fiber and external basal lamina
Term
what is a perimysium?
Definition
thicker connective tissue that surrounds and defines fascicles (functional bundles of muscle fibers)
Term
what is the epimysium?
Definition
dense connective tissue that surrounds the entire muscle (a collection of fasicles)
Term
strength of a muscle and the direction of its pull are determined partly by?
Definition
the orientation of its fascicles
Term
what is reflexive muscle contraction?
Definition
not voluntarily controlled
Term
what is tonic muscle contraction?
Definition
slight contraction that gives muscle firmness, assisting stability of joints and posture
Term
what are the 2 types of phasic muscle contraction?
Definition
isometric and isotonic
Term
what is isometric muscle contraction?
Definition
muscle length does not change
Term
what is isotonic muscle contraction?
Definition
muscle length changes
Term
how are skeletal muscles characterized?
Definition
by the speed of contraction and metabolic activity
Term
describe type I skeletal muscle fibers
Definition
red, slow twitch, not easily fatigued, high myoglobin content, many mitochondria and high in oxidative enzymes, slow myosin ATPase reaction velocity; they need to be able to be active for long periods of time, they are aerobic
Term
where do type I skeletal muscle fibers predominate?
Definition
deep back muscles and other postural muscles to maintain upright posture, soleus of the calf
Term
describe type IIb skeletal muscle fibers
Definition
white, fast twitch, power and rapid contraction but easily fatigued, low myoglobin content, few mitochondria and low in oxidative enzymes, very fast myosin ATPase reaction velocity
Term
describe type IIa skeletal muscle fibers
Definition
intermediate, fast oxidative, they make up fast twitch fatigue resistant motor units that have intermediate characteristics from those described above
Term
where does TnT bind?
Definition
binds to tropomyosin
Term
where does TnC bind?
Definition
binds to calcium
Term
what does TnI do?
Definition
inhibits actin-myosin binding
Term
what is myosin composed of?
Definition
2 identical heavy chains and 2 pairs of light chains
Term
what is a sarcomere?
Definition
the region between two successive Z lines; the sarcomere is the functional unit of striated muscle
Term
describe the sliding filament model
Definition
thin filaments slide past thick filaments, I and H bands shorten, sarcomere shortens, Z discs are drawn close, A band does not change in length
Term
mutations in the dystrophin gene cause?
Definition
muscular dystrophies
Term
absence of dystrophin causes?
Definition
Duchenne's muscular dystrophy; causes progressive muscle weakness in boys
Term
what is a sarcoplasmic reticulum?
Definition
specialized network of endoplasmic reticulum around the myofibrils. Acts as a calcium sink
Term
where is the 'triad' located in skeletal muscle?
Definition
at the A-I junction
Term
what do t-tubules do?
Definition
act to rapidly spread depolarization throughout the muscle fiber so that there is widespread release of calcium from the sarcoplasmic reticulum allowing for uniform contraction of the muscle fibers
Term
axon terminals contain synaptic vesicles filled with what neurotransmitter?
Definition
ACh
Term
what is a motor unit?
Definition
a single motor axon and all the muscle fibers it innervates; can be large for muscles that require course movements
Term
what is the autoimmune disease in which antibodies are made to the ACh receptor?
Definition
Myesthenia Gravis
Term
what is the most common motor neuron disease?
Definition
ALS (Lou Gehrig's disease)
Term
what type of receptor is the muscle spindle?
Definition
stretch receptor
Term
describe cardiac muscle
Definition
centrally positioned nuclei, the fibers are branched, have intercalated discs, t tubules are larger than in skeletal muscle and are located at a Z disc, have large mitochondria
Term
which type of muscle has the 'diad' format?
Definition
cardiac muscle
Term
what is found in the intercalated disc?
Definition
macula adherens, gap junctions and fascia adherens
Term
when there is a death of cardiac muscle due to prolonged ischemia (lack of blood) what occurs?
Definition
myocardial infarction
Term
describe smooth muscle cells
Definition
elongated, spindle shaped cells with a single centrally located nucleus, found in the walls of hollow organs and blood vessels
Term
what are cytoplasmic densities/dense bodies?
Definition
proteins which anchor thin filaments and intermediate filaments, analogous to z lines in striated muscle
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