Muscle Flashcards
What is a DNA unit?
volume of cytoplasm controlled by one nucleus
What is a fibril enveloped by?
sarcoplasmic reticulum (loosely)
What is the structural hierarchy of a fascicle?
- endomysium surrounds fibers
- fibers made up of fibrils
- fibrils made up of thin & thickfilaments
What causes tropomyosin to change shape so that actin can bind to myosin?
calcium binding at all 4 sites on TnC
What does TnT do
joins troponin and tropomyosin
Which filaments are longer?
thick
Why doesn’t the A band change length?
it is the length of the myosin filament, which does not change length during contraction
Why does the sarcomere change length?
because the Z lines get pulled toward M plate during contraction
Why does the H band change length?
- it’s the region of myosin filament that does not overlap with actin filament (center of sarcomere)
- the myosin heads bring the actin filaments closer to the M plate which makes region of non-overlap smaller
What is the I band?
region of actin filament that is not overlapping myosin
What binds myosin filaments to z-disks?
titin
Which protein appears to prevent sarcomere from overstretching?
titin
Which protein appears to anchor sarcomeres to adjacent structures and maintains overall structural integrity?
dystrophin
What binds the thin filaments to z-disks and what protein reinforces that attachment?
actinin; nebulin
What protein regulates the length of the thin filaments?
tropomodulin
Which proteins hold thick filaments in register at the M line?
c-proteins and myomesin
What is the cause and manifestation of myasthenia gravis? How is it treated?
- dysfunction of nicotinic receptors at NMJ
- commonly affecting respiration and ocular muscles
- therapy to elevate Ach or immunosuppressants (steroids)
What is meant by isometric contraction?
muscle contracts but does not shorten & fails to move load
What is meant by isotonic contraction?
muscle shortens as tension remains constant (force greater than load)
What is meant by eccentric contraction?
muscle lengthens (extends) as tension remains constant
What is a motor unit?
motor neuron and all the muscle cells innervated by it
What are plaques in smooth muscle?
point at which thin filaments attach to myocyte membrane
Describe single-unit smooth muscle.
- fibers will contract uniformly (due to gap junctions)
- force of contraction varies with calcium concentration
- visceral muscle
How can single-unit muscle be induced to contract?
- a variety of chemicals (e.g. hormones)
- mechanical stimulation (stretch)
What are varacosities?
where neurotransmitter is released through into the wide synaptic cleft
Describe multi-unit smooth muscle.
- fibers are innervated independently of each other
- force of contraction varies with recruitment of fibers
Where can single-unit smooth muscle be found?
- GI tract
- bladder and ureters
- most arteries (not in large, elastic arteries)
Where can multi-unit smooth muscle be found?
- intrinsic muscles of eye
- some portions of reproductive tracts
What are the names of the two voltage-gated calcium channels in skeletal muscle contraction?
- DHP
- ryanodine receptors
