Muscle Physiology

Question 1

Which troponin..

• Binds Calcium
• Anchors to Actin
• Anchors to Troponin

Answer 1

• Troponin C
• Troponin I
• Troponin T

Question 2

What occurs when ATP binds to Myosin in the crossbridge cycle of skeletal muscle contraction?

Answer 2

The Myosin releases the troponin chain. Myosin-ATP complex has a LOW affinity for actin.

Question 3

What events occur during the Power-stroke of the cross-bridge cycle?

Answer 3

ADP and Pi are released, the myosin head swivels and Z-discs are drawn closer as troponin fibers are dragged along the myosin fibers.

Question 4

What occurs when ATP is hydrolyzed on the myosin head (crossbridge cycle)?

Answer 4

ATP hydrolysis forms ADP and Pi that enables myosin-actin binding. Myosin/(ADP+Pi) complex has a HIGH affinity for actin.

Question 5

The healthy heart mainly uses ________ to generate ATP. It uses the process of _________ when under stress such as exercise.

Answer 5

Fatty Acid Oxidation;

Glycolysis

Question 6

After the potential is relayed from the motor neuron to the motor end plate. What events occur to relay the action potential to the muscle fiber?

Answer 6

1. Newly induced AP in motor end plate travels down T-tubules.
2. APs from T-tubules activate DHRP receptors
3. This activates RyR receptors on the sarcoplasmic reticulum
4. Activated RyR receptors cause a Ca2+ efflux from the SR

Question 7

After Calcium from the SR is released, what has to occur to enable the cross-bridge cycle (for skeletal muscle contraction)?

Answer 7

1. Elevated Ca2+ levels in SR bind to Troponin C
2. Troponin C-Ca2+ complex reveals tropomyosin
3. ADP+Pi on myosin allows for Myosin-actin binding.
4. Power-stroke begins with the release of Pi

Question 8

What are the bands or features in the myofibril and what do they represent?

Answer 8

Z-Line: a band that separates sarcomere units
I-Band: actin filaments attached to the Z-line (Light section)
H-Band: myosin filaments in the center of the sarcomere (DARK)
A-Band: overlap of actin and myosin filaments at rest (length changes with contraction)

Question 9

What occurs to the myofilaments in the sarcomeres during skeletal muscle contraction?

Answer 9

Myosin pulls the Actin towards the center of the sarcomere.

I-bands (actin) shrink, A-bands (myosin and actin overlap) expand