Muscle Physiology - skeletal

Question 1

• What type of muscle is shown in picture?
• Strength?
• Speed?
• Voluntary or involuntary?
• Appearance?

Answer 1

• Skeletal
• Strong
• Quick
• Voluntary
• Striated, large long fibers with many peripheral nuclei

Question 2

• What type of muscle is shown in picture?
• Strength
• Speed
• Voluntary or involuntary?
• Appearance?

Answer 2

• Weak
• Slow
• Involuntary
• No striations, small cells with central nuceli

Question 3

• What type of muscle is this?
• Strength?
• Speed?
• Voluntary or involuntary?
• Appearance?

Answer 3

• Cardiac
• Strong
• Quick
• Involuntary, short, thick fibers with 1-2 central nuclei, striated

Question 4

Answer 4

Question 5

A skeletal muscle fiber (cell) is derived by merging 100s-1000s of […]

Answer 5

Myofibrils

Question 6

• How man nuclei are in skeletal muscle fibers?
• Where are the nuclei located?

Answer 6

• Many
• In periphery of myofibrils

Question 7

Answer 7

Question 8

Do the filaments of the sarcomere shorten during muscle contraction?

Answer 8

NO - neither thick no thin shorten. Rather, the bands of the sarcomere shorten due to increased overlap between the thick and thin filaments.

Question 9

What part(s) of the sarcomere shortens during contraction?

Answer 9

The I-band and the H-zone

Question 10

What part of the sarcomere does not shorten during contraction?

Answer 10

The A band

Question 11

The I-band is primariy […] filaments, aka […].

Answer 11

Thin filaments

Actin

Question 12

The A-band is primarily […] filaments, aka […]

Answer 12

Thick

Myosin

Question 13

What band of the sarcomere is only thick filaments?

Answer 13

H-band

Question 14

The Z-line is the anchor for […] filaments and the M-line is the anchor for […] filaments.

Answer 14

Thin

Thick

Question 15

What is titin? Where is it located in the sarcomere?

Answer 15

Titin is in the I-band with the thin filaments. It helps prevent overstrecthing of the sarcomere

Question 16

Answer 16

Question 17

Is this muscle relaxed or contracted?

Answer 17

Contracted

Question 18

Is this muscle relaxed or contracted?

Answer 18

Relaxed

Question 19

Describe the structure of the thick filaments.

Answer 19

Question 20

Describe the structure of the thin filaments.

Answer 20

Question 21

Describe the structure and function of the troponin complex.

Answer 21

Question 22

Describe the contractile mechanism cross-bridge cycle.

Answer 22

Question 23

In relaxed skeletal muscle, what state of the cross-bridge cycle are muscle fibers in?

Answer 23

The “cocked” and energized position so that they are ready and waiting to bind to actin when Ca2+ moves tropomyosin out of the way

Question 24

What is rigor mortis?

Answer 24

During death, intracellular Ca2+ stores are released, causing exposure of myosin binding sites on actin filaments so energized myosin cross-bridges can bind to actin and perform the power stroke. However, there is not enough ATP in the body to release the myosin from the actin so the muscles remain contracted.

Question 25

What is the role of dystrophin in the sarcomere and why is it clinically relevant?

Answer 25

Dystrophin anchors the thin filaments to the sarcolemma by interacting with both thin filaments and glycoproteins embedded in membrane. It also helps with force generation. Clinically relevant b/c when dystrophin is mutated or dysfunctional muscular dystrophy results.

Question 26

One motor neuron innervates only a single skeletal muscle fiber. True/False.

Answer 26

False - can innervate 10s - 100s

Question 27

Each muscle fiber is innervated by only one motor neuron. True/False

Answer 27

True

Question 28

What is a motor unit?

Answer 28

A motor neuron + the muscle fibers that it innervates.

Question 29

Describe the difference in motor unit size for the quadriceps compared to the extensor digiti minimi.

Answer 29

One axon can innervate either a large number of muscle fibers (quadriceps) and be a large motor unit or a small number of fibers (extensor digiti minimi) and be a small motor unit. This is necessary b/c finer muscle movement does not require activation of as many muscle fibers as gross movement.

Question 30

Much like action potential generation, muscle contraction is an [...] phenomenon.

Answer 30

All or none

Question 31

What is the motor end plate?

Answer 31

The pocket formed around the motor neuron by the sarcolemma.

Question 32

What is the neuromuscular cleft?

Answer 32

The short gap between motor neuron and muscle fiber.

Question 33

Answer 33

Question 34

How is skeletal muscle contraction terminated?

Answer 34

By removal of calcium from troponin and a decrease in the cytosolic Ca2+ concentration. This is accomplished by pumping Ca2+ back into the sarcoplasmic reticulum via Ca2+ ATPase pump. However, it takes longer to return Ca2+ to SR than it does to release.

Question 35

What is this figure showing?

Answer 35

There is a standard amount of Ca2+ that is released with each AP. Therefore, the degree of skeletal muscle contraction is determined by the frequency and number of APs.