Skeletal Muscle Physiology (Exam 3)

Question 1

What are the characteristics of skeletal muscle?

Answer 1

-long fibers
-striated
-cylindrical
-multinucleated fibers
-under voluntary control

Question 2

What are the 2 types of skeletal muscle tissue?

Answer 2

1) intrafusal
2) extrafusal

Question 3

Which type of skeletal muscle tissue forms sensory receptors?

Answer 3

intrafusal

Question 4

Which type of skeletal muscle tissue contracts muscle spindles only?

Answer 4

intrafusal

Question 5

Which type of skeletal muscle tissue contracts entire muscle fibers?

Answer 5

extrafusal

Question 6

Which part of the muscle cell stores calcium?

Answer 6

sarcoplasmic reticulum (SR)

Question 7

Which part of the muscle cell forms triad with T tubules?

Answer 7

SR

Question 8

Which part of the muscle cell has voltage gated calcium channels?

Answer 8

SR

Question 9

What runs the length of the muscle fiber and is segmented by sarcomeres?

Answer 9

myofibrils

Question 10

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?

Answer 10

sarcomeres

Question 11

What are the 2 types of myofilaments?

Answer 11

actin and myosin

Question 12

Which myofilament is thick with head on opposite sites?

Answer 12

myosin

Question 13

Which myofilament is thin with a double helix and myosin binding sites?

Answer 13

actin

Question 14

In a relaxed muscle cell, myosin binding sites are covered by….

Answer 14

tropomyosin

note: myosin head is in the high energy upright cocked position (bound to ADP)

Question 15

In a relaxed muscle cell, tropomyosin is held in place by….

Answer 15

troponin

Question 16

What is in the center of an I band?

Answer 16

Z disc

Question 17

What secures actin to the sarcolemma?

Answer 17

dystrophin

Question 18

Sarcomeres are made up of different bands and zones bound by…

Answer 18

Z discs on either side

Question 19

What is located on either side of the Z line?

Answer 19

I band

Question 20

Which band contains only actin (light zone)?

Answer 20

I band

Question 21

What is located between the I bands?

Answer 21

A band

Question 22

Which band contains both actin and myosin (darkest zone)?

Answer 22

A band

Question 23

What is located in the center of the sarcomere?

Answer 23

H band

Question 24

Which band only contains myosin (dark zone)?

Answer 24

H band

Question 25

What is located in the center of the H zone?

Answer 25

M line

Question 26

What identifies the exact center of the sarcomere?

Answer 26

M line

Question 27

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

Answer 27

titin

Question 28

Actin are anchored/attached to each other within the Z disc by….

Answer 28

actinin

Question 29

Skeletal muscle contraction requires 2 APs from where?

Answer 29

LMN and skeletal muscle cell

Question 30

T/F: typically, each AP at the NMJ is strong enough to facilitate a muscle cell contraction

Answer 30

true

Question 31

What are the events at the NMJ?

Answer 31

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)

Question 32

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

Answer 32

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)

Question 33

What are the events of a muscle fiber contraction?

ordering test question!

Answer 33

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)

Question 34

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

Answer 34

calsequestrin, ryanodine

Question 35

What is the sliding filament theory?

boards q

Answer 35

during a contraction, actin and myosin filaments slide across each other to shorten the sarcomere. Actin and myosin DO NOT shorten