Skeletal Muscle

Question 1

What is each muscle myofibril divided into?

Answer 1

Sarcomere

Question 2

What is the sarcomere?

Answer 2

The contractile unit of skeletal muscle

Question 3

What are the proteins in the sarcomere?

Answer 3

Actin
Myosin
Titin

Question 4

What is the role of the T-Tubules?

Answer 4

Allows rapid spread of the muscle action potential

Question 5

What are essential for muscle contraction?

Answer 5

ATP and calcium

Question 6

What are the components of the thin filament?

Answer 6

Troponin
Tropomyosin
Globular actin

Question 7

What are the properties of slow twitch/red/type I muscle fibers?

Answer 7

Postural muscles
Myoglobin
Mitochondria
Oxidative metabolism
Fatigue resistant

Question 8

What are the properties of fast twitch/white/type II muscle fibers?

Answer 8

Less myoglobin
Less mitochondria
Fatigue prone
Glycolytic metabolism

Question 9

Define a motor unit.

Answer 9

A somatic motor neurone and all the muscle fibers innervated by that neurone

Question 10

Where do alpha motor neurones originate?

Answer 10

Ventral horn of the spinal cord

Question 11

What does the muscle action potential do?

Answer 11

Triggers release of Ca++ from the SR through the ryanodine receptor

Question 12

What does the muscle action potential do?

Answer 12

Triggers release of Ca++ from the SR through the ryanodine receptor

Question 13

What does Ca++ bind to on the thin filament?

Answer 13

Troponin C

Question 14

What happens when actin-myosin interaction cause?

Answer 14

Sarcomere shortens

Question 15

What is muscle relaxation associated with?

Answer 15

Ca++ pumped back into SR

Question 16

Where are DHPR receptors found?

Answer 16

Embedded in the T-tubules

Question 17

What is DHPR?

Answer 17

A voltage sensor that senses the arrival of a muscle AP as it tracks along the t-tubule signalling the RYR receptors to open releasing Ca++ from the SR

Question 18

What is the shuttle protein for calcium in skeletal muscle?

Answer 18

Calsequestrin

Question 19

What is sarcalumenin?

Answer 19

Facilitates moving calcium from areas where its taken up by SERCA to areas for release in the cisternae region

Question 20

What does SERCA stand for?

Answer 20

Sarcoplasmic Endoplasmic Reticulum Calcium ATPase

Question 21

What does the binding of troponin C to calcium result in?

Answer 21

Uncovers myosin binding sites so that myosin binds to actin and a cross-bridge can now form

Question 22

How does the cross-bridge cycle work?

Answer 22

At rest, myosin and actin are detached and myosin is in energised state
AP triggers release of Ca++ from SR binding to troponin C allowing interaction
Inorganic phosphate detaches from myosin head allowing the sliding of the 2 filaments and pulls the actin filament towards the centre of sarcomere (power stroke)
ATP attaches to myosin, detaching it from actin
Muscle relaxes and Ca++ pumped into SR
ATP hydrolysed

Question 23

Explain isotonic muscle contraction.

Answer 23

Constant force
Muscle shortens and can move the load
Muscle length can be measured

Question 24

Explain isometric muscle contraction.

Answer 24

Constant length
Muscle unable to shorten
Force generated is measured

Question 25

What is the optimal resting length for the sarcomere in order to achieve maximum strength of contraction?

Answer 25

2.25 microns

Question 26

What is the relationship between velocity of muscle contraction and the load on the muscle?

Answer 26

Varies inversely with each other

Question 27

How do we modulate the force of skeletal muscle contraction?

Answer 27

Spatial summation
tetany

Question 28

What is tetany?

Answer 28

Sustained contraction of the muscle at high levels of stimulation

Question 29

In spatial summation, what type of muscle fibres tend to be recruited first?

Answer 29

Slow twitch muscle fibers

Question 30

What is muscle fatigue?

Answer 30

Reduced ability of muscle to generate power