Skeletal Muscle Physiology 1 Flashcards
our skeletal muscles are composed of ?
bundles of fascicles
each fascicle is composed of linearly aligned ?
muscle fibers (myofiber)
T or F: Muscle fiber is a single, multi-mucleated, elongated cell
true
each muscle fibre is composed of many ?
myofibril
myofibrils have many ?
sacromere
what is a sacromere?
structural units of myofibrils that facilitate contraction and relaxation
what is the epimysium
the connective tissue sheath surrounding the whole muscle and extending from the tendons
what is the sheath surrounding each fascicle?
perimysium
what is the sheath that surround each individual muscle fiber?
endomysium
what is the cell membrane of the muscle cell?
sarcolemma
each myofibril composed of many ?
myofilaments
what are the contractile proteins of the muscle?
actin and myosin
what are the regulatory proteins of the muscle?
tropomyosin and troponin
sacromeres consist of interdigitating myofilaments called
thin filaments and thick filaments
thin filaments are made of ?
actin
thick filaments are made of?
myosin
the striated appearance of skeletal muscle is due to ?
the overlapping of thick and thin filaments
each sarcomere is bound by the ?
Z-disk
thin filament attaches to the
Z-disk
at the center of the sarcomere is the ?
M-line
thick filaments lie between the
thin filaments
what are light bands (I bands)
regions of thin filaments that do not overlap with thick filaments
what is at the center of the light bands?
the Z-disk
what are dark bands (A bands)
the region where the thick and thin filaments do overlap
during muscle contraction, the I band ?, while the A band ?
- shortens
- does not change in length
what is the monomer of Actin?
G-actin
what is the polymer of actin?
F-actin
thin filaments are composed of 2 strands of ?
F-actin
each G-actin monomer has a?
binding site for myosin
what is the major constituent of the thin filament?
F-actin
what is the thick filament composed of?
myosin
myosin head region, has 3 important biochemical features:
- ATPase activity
- actin-binding region
- ATP binding region
what is the regulatory protein that associates with actin?
tropomyosin
what are the 3 subunits of troponin?
- troponin C
- troponin T
- troponin I
which troponin binds to calcium?
troponin C
which troponin binds to tropomyosin
troponin T
which tropinin binds to actin and inhibits contraction
troponin I
how do cross-bridge formation occur
when calcium binds to tropinin C, the troponin complex undergoes a conformational change and troponin T “pulls” tropomyosin and troponin I off of the myosin-binding site of G-actin subunits
what is the plasma membrane of the muscle fiber called?
sarcolemma
the sarcolemma contains invaginations called?
transverse tubules (aka T-tubules)
what allows the action potential to be carried deep into the muscle fiber?
transverse tubules
what is the sarcoplasmic reticulum
a specialized endoplasmic reticulum containing high concentrations of calcium
what are the terminal cisternae of the sarcoplasmic reticulum
specialized regions that associate with the T-tubules
what is the junction between T-tubules and sarcoplasmic reticulum cisterna called?
muscle triad
a motor nerve axon contacts each muscle fiber near the middle of the fiber, foriming a synapse called the ?
neuromuscular junction
what is the region of the sarcolemma in closest contact with the presynaptic nerve terminal called?
motor end plate
what does the motor nerve terminal release?
acetylcholine
what bind to the nicotinic receptor on the sarcolemma?
acetylcholine
what happens when the acetylcholine binds to the nicotinic receptor?
it activates voltage-gated sodium channels
what happens when voltage-gated sodium channels are activated?
triggering an action potential that propagates along the sarcolemma
the action potential propagates along the surface of the skeletal muscle fiber and penetrate deeper into the muscle fiber via what?
T-tubules
what is the purpose of T-tubule
to “bring” the action potential deep within the very large muscle fibres
action potential propage along the T-tubules and activate what? in the sarcolemma
L-type Ca2+ channels
activation of the L-type Ca2+ channels also triggers mechanical activation of what? on the surface of the SR terminal cisterna within the cell
Ryanodine receptors (RYR) which release calcium into the cytosol of the muscle fiber
opening of L-type Ca2+ channels and RYR allows what?
Ca2+ to flow down its concentration gradient into the cytosol of the muscle fiber
what happens to the calcium released by L-tyoe Ca2+ channels and RYR?
it bins to troponin C subunit to expose the binding sites for myosin
T or F: most of the calcium that activates the skeletal muscle sarcomere is from the SR, NOT the extracellular fluid
true
what is a motor unit?
all the muscle fibers innervated by a single nerve fiber
what is a tetany?
development of force (tension) in a muscle fiber due to many action potentials
what is fused tetany?
maximal force development in the muscle fibres of a motor unit
