SKELETAL PT 2 Flashcards
describe how muscle fiber type shifts
with loading (exercise training), IIX goes down and with unloading (like a space flight or spinal cord injury), IIX amount goes up
why do IIX fibers increase with inactivity
because I and IIA use a lot of oxygen, so it’s a lot of work to keep them up
describe aerobic training and muscle fiber type
less IIA, more I
describe motor units
vary in size; consists of a motor neuron and all muscle fibers they supply
how are muscle fibers dispersed through a muscle
muscle fibers from a motor unit spread throughout the whole muscle, so stimulation of a single motor unit causes only weak contraction of muscle
what principle so motor units follow
all or none principle
what are the three types of muscle fibers
type I (slow), type IIA (fast fatigue-resistant), type IIX (fast fatiguable)
describe type IIX motor fibers
fast fatiguable, large motor units with high innervation ratio, fast twitch
describe IIA motor fibers
large motor units, more sustained but less dramatic twitch; more fatigue resistant but still fatiguable
describe type I fibers
small motor neurons, low innervation ratio, slow twitch and fatigue resistant
what is excitation-contraction coupling
process of pairing electrical events (motor neuron AP) to mechanical events (muscle contraction); aka events that occur between excitation and coupling
where does EC coupling occur
synapse of junction of motor neuron axon terminal with muscle fiber motor end plate (very excitable region of muscle fiber plasma membrane)
what neurotransmitter is released at neuromuscular junction
acetylcholine
describe the first step of EC coupling process
have signal that sent do somatic motor neuron,
which is a depolaorizing event
describe the second step in EC process
at neuromuscular junction, we release Ach, which binds
to receptors on skeletal muscle membrane, which allows for depolairzation
of skeletal muscle membrane
describe the third step in EC process
opening of Na channels, which causes influx of Na which causes depolirzation
describe the fourth step in the EC process
depolariization goes down t-tubules; along t-tubules on either side is a bunched up
part of the sarcoplasmic reticulum
describe the 5th step in the EC coupling process
ca binds to tropnin, which tells tropomyosin to move from actin
describe the sixth step of EC process
myosin can bind to actin and allow for contraction
whats the cross bridge
binding site of ATP on each molecule
what is cross bridge formation triggered by
Ca2+ cycle
whats the first step in cross bridge formation
active site on actin is exposed as Ca binds to troponin
whats the second step in cross bridge formation
myosin head forms a cross-bridge with actin
whats the third step of cross bridge formation
during power stroke, myosin head bends and ADP and phosphate are released
whats the fourth step in cross bridge formation
a new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach
whats the fifth step in crossbirdge formation
ATP hydrolyzes to ADP and phosphate, which returns myosin to cocked position
describe the skeletal muscle length-tension relationship
describes the amount of tension that is produced by a muscle as a feature of it’s length
what are skeletal muscle satellite cells
skeletal muscle stem cells, that are multipotent and give rise to more satellite cells, differtnited skeletal muscle cells, myonuclei
how much nuclear material belongs to true myonuclei
85 - 95% (i.e. located inside plasma membrane)
how much of nuclear material are satellite cells
5 - 15%; located between basement membrane and plasma membrane
how many nuclei per fiber length do satellite cells have
approx. 200 - 300 nuclei per mm of fiber length (contrast to many other cells in our body which are usually single nucleus)
why are satellite cells/myonuclei important
growth + development of muscle
adaptive capacity of skeletal muscle
recovery from injury or neuromuscular disease
where is nuclear material located
between myofiber basement and plasma membrane
describe satellite cell role in myofiber hypertrophy
not completely known; but as fiber grows, there is need for new myonuclei to maintain myonuclear domains
whats the myonuclear domain theory
every nuclei within the muscle fiber
is responsible for a specific amount
of volume within the cell, so we can only
make muscle grow if we get more nuceli
involved
so satellite cells donate
describe the first step in myonuclear donoation
untrained muscle fiber
describe the second step in myofiber donation
training muscle fiber increases in size; each myonuclei is near its domain ceiling
describe the third step in myonuclei donation
satellite cells fuse to the muscle fiber, donating nuclei
describe the fourth step of myofiber / myonuclear donation
muscle fiber now has more nuclei; therefore, it’s growth capacity has increased
different between the two possible response to fiber stress
hypertrophy (fibers grow in size - humans); hyperplasia (fibers grow in number)
describe regenerating normall musclle fiber
myonuclei + satellite cell
describe regenerating damaged muscle fiber
activated + proliferating satellite cells
describe regenerating repairing muscle fibers
muscle precursors cells derive from satellite cells have fused
describe generating regenerated muscle fibers
with new satellite cell and centrally-placed, newly-generated myonuclei
describe the calcium/tropnonin/tropomyosin relationship
Ca connects to troponon,
which tells tropomyosin to get off binding sites so myosin can attach
where is calcium stored and what happens when that thing is depolarized
Ca stores in sarcoplasmic reticulum;
when depolaorized, Ca ion channels open up and let Ca into sarcoplasm which lets
everything happen
what are the three parts of the power stroke
- adp and P on myosin = myosin can grab actin
- adp and P leave myosin, nothing on myosin and can pull in
- atp on myosin, myosin releases actin
