Skeletal Muscle Physiology (Exam 3) Flashcards
What are the characteristics of skeletal muscle?
-long fibers
-striated
-cylindrical
-multinucleated fibers
-under voluntary control
What are the 2 types of skeletal muscle tissue?
1) intrafusal
2) extrafusal
Which type of skeletal muscle tissue forms sensory receptors?
intrafusal
Which type of skeletal muscle tissue contracts muscle spindles only?
intrafusal
Which type of skeletal muscle tissue contracts entire muscle fibers?
extrafusal
Which part of the muscle cell stores calcium?
sarcoplasmic reticulum (SR)
Which part of the muscle cell forms triad with T tubules?
SR
Which part of the muscle cell has voltage gated calcium channels?
SR
What runs the length of the muscle fiber and is segmented by sarcomeres?
myofibrils
What is the smallest contractile unit of a muscle fiber/cell that runs from Z disc to Z disc and contains actin and myosin myofilaments?
sarcomeres
What are the 2 types of myofilaments?
actin and myosin
Which myofilament is thick with head on opposite sites?
myosin
Which myofilament is thin with a double helix and myosin binding sites?
actin
In a relaxed muscle cell, myosin binding sites are covered by….
tropomyosin
note: myosin head is in the high energy upright cocked position (bound to ADP)
In a relaxed muscle cell, tropomyosin is held in place by….
troponin
What is in the center of an I band?
Z disc
What secures actin to the sarcolemma?
dystrophin
Sarcomeres are made up of different bands and zones bound by…
Z discs on either side
What is located on either side of the Z line?
I band
Which band contains only actin (light zone)?
I band
What is located between the I bands?
A band
Which band contains both actin and myosin (darkest zone)?
A band
What is located in the center of the sarcomere?
H band
Which band only contains myosin (dark zone)?
H band
What is located in the center of the H zone?
M line
What identifies the exact center of the sarcomere?
M line
Myosin and actin filaments are anchored to each other and the z disc by a protein called ___________, which acts as a molecular spring giving passive elasticity to the muscle and helps recoil after stretch
titin
Actin are anchored/attached to each other within the Z disc by….
actinin
Skeletal muscle contraction requires 2 APs from where?
LMN and skeletal muscle cell
T/F: typically, each AP at the NMJ is strong enough to facilitate a muscle cell contraction
true
What are the events at the NMJ?
1) AP reaches the axon terminal
2) AP causes voltage gated calcium channels to open and calcium enters the axon terminal
3) calcium causes the release of ACh
4) ACh diffuses across the synaptic cleft and binds to ACh receptors in sarcolemma
5) ion channels open, sodium enters the muscle fiber depolarizing the motor endplate (endplate potential) and AP spreads away from the NMJ in both directions
6) ACh is removed from synaptic cleft and is broken down by AChE to make choline and acetate. Choline is taken up by axon terminal of LMN. Removal of the ACh closes ion channels terminating its effect (note: this does not cause the muscle cell to relax)
Once the motor endplate depolarizes, an AP is generated. The AP will propagate across the sarcolemma by:
1)
2)
3)
4)
APs are all or none once initiated, it cannot be stopped
1) opening voltage gated sodium channels (depolarization)
2) closing voltage gated sodium channels (peak)
3) opening voltage gated potassium channels (repolarization)
4) closing voltage gated potassium channels (back to RMP)
What are the events of a muscle fiber contraction?
ordering test question!
1) an AP propagates along the sarcolemma and down the T tubules and causes voltage gated calcium channels to open on the SR aka ryanodine channels (RyR)
2) calcium is released from the SR
3) calcium binds to troponin exposing myosin binding sites in actin filaments
4) myosin head attaches to exposed binding site on the actin forming cross bridges and contraction begins
5) ATP quickly binds to the free site on the myosin head causing detachment from actin
6) myosin head to return to the cocked position (this cycle repeats as long as calcium levels are maintained and there is sufficient ATP)
The SR stores calcium. Calcium binds to a protein called ______________ inside the SR. AP down the T tubule depolarizes the membrane and opens _____________ calcium receptors on the SR. Muscle cell contraction continues as long as intracellular calcium remains high. The SR has a calcium pump that actively pumps calcium back into SR. Relaxation of a muscle fiber requires removal of calcium from the cytoplasm
calsequestrin, ryanodine
What is the sliding filament theory?
boards q
during a contraction, actin and myosin filaments slide across each other to shorten the sarcomere. Actin and myosin DO NOT shorten
