Skeletal Muscle part 2

Question 1

What are the thin filaments? Thick?

Answer 1

Thin: Actin, troponin, tropomyosin
Thick: Myosin

Question 2

Give an overview of the sliding filament mechanism.

Answer 2

1. Actin-myosin link is a cross bridge.
2. Attachment, release, hydrolysis & bending, Power stroke
3. Each cycle requires ATP and calcium.

Question 3

Discuss the attachment phase

Answer 3

As a cross bridge, myosin has a high affinity for ATP; Attachment ends when ATP is available for myosin binding. This stage is responsible for rigor mortis in death b/c no ATP.

Question 4

Discuss the Release phase

Answer 4

ATP binds myosin and produces a conformational change on actin binding site of myosin head; Decreases affinity for actin and is released from it.

Question 5

Discuss the Hydrolysis and Bending phase.

Answer 5

1. ATP is hydrolyzed but its products remain bound to myosin
2. Energy from hydrolysis bends the myosin head toward the Z-line.
3. Neither actin or myosin is bound; Muscles are at rest

Question 6

Discuss the Power stroke phase.

Answer 6

1. Intracellular calcium increases
2. Release of Phosphate from myosin increases affinity for actin
3. Myosin returns to original position with actin bound; Pulls filament towards the center of the sarcomere (M-line) causing a power stroke.

Question 7

What do both the cross bridge formation and release require?

Answer 7

1 ATP

Question 8

What is the rate limiting part of a contraction?

Answer 8

The hydrolysis of ATP by myosin; Type 2x fibers are the fastest

Question 9

What are the 5 steps of Excitation and Contraction coupling?

Answer 9

1. AP goes down sarcolemma
2. AP activates voltage sensing channels in T-Tubules
3. Channels change conformation opening SR channels to open; Calcium from SR into cytosol.
4. Calcium binds to Tn-C
5. Actin binds Myosin

Question 10

Describe the T-tubules during excitation.

Answer 10

Contains voltage sensing receptor. SR contains calcium channel protein RyR which links SR to T-tubule

Question 11

Discuss the process of Excitation-Contraction coupling

Answer 11

1. AP goes into T-tubule
2. Voltage sensing receptor changes, opening RyR
3. Calcium is released into cytosol
4. Calcium binds Tn-C, exposing myosin binding sites on actin

Question 12

Where is calcium stored?

Answer 12

In the Sarcoplasmic reticulum.

Question 13

Discuss the reabsorption of calcium

Answer 13

Done by calcium pump on SR; Works immediately after calcium release. Has a higher affinity for calcium than troponin.

Question 14

Describe the calcium pump

Answer 14

Works against the concentration gradient; Uses ATP

Question 15

Describe muscle activation.

Answer 15

All or none response. All fibers in a motor unit contract at the same time.

Question 16

How is ACh removed?

Answer 16

Degraded in the synaptic cleft by AChase. Hyperpolarization of muscle cell ensures only one contraction per AP