Block III - Muscle

Question 1

What is the function of the ryanodine receptors?

Answer 1

To release Ca into cytosol from SR in skeletal muscle cells

Question 2

What happens in myosin/actin/s location during an active skeletal muscle contraction?

Answer 2

Actin filaments slide past myosin filaments shortening the distance between Z discs

Question 3

Tetanic skeletal muscle tension is resulted from the sustained elevation of which molecule’s concentration in myocytes?

Answer 3

Ca

Question 4

What does the pre-stimulation length of the muscle (%Lo) represent for in terms of myosin-actin interaction?

Answer 4

Number of myosin cross-bridges interacting with actin

Question 5

What are the differences between Type I (slow, red) human skeletal muscle fibers and the Type II (fast, white) muscle fibers?

Answer 5

Type 1 has (slow, red)

• more mitochondria
• smaller diameter
• more myoglobins
• harder to fatigue
• lower glycolytic enzyme activity

Question 6

What is the primary function of gap junctions between smooth muscle cells?

Answer 6

Allow neighboring SMCs to communicate electrically

Question 7

What is the physiological result if the level of myosin light chain phosphorylation increases in smooth muscle?

Answer 7

The rate of actin-myosin cross-bridge cycle increases. The maximum contraction force increases.

Question 8

Which of the following structures in SM motor unit releases neurotransmitters as neuromuscular junction does in skeletal muscle?

Answer 8

Varicosity

Question 9

What is the latch state in smooth muscle?

Answer 9

The cross bridge cycle is slowed down due to the myosin light chain dephosphorylation, but not completely stopped

Question 10

What are the similarities between smooth muscle and skeletal muscle contraction?

Answer 10

They both involve voltage dependent Ca channels, ATP consumption, myosin-actin interaction, and Ca release from SR

Question 11

What factors modulate smooth muscle contraction?

Answer 11

Autonomic nerves, circulating hormones, local signals from other cells, electrical signals from other SMCs

Question 12

Why does the force of smooth muscle in the BV continually increase after (longer than) the optimal length?

Answer 12

Because the passive stress from other tissues continually increases

Question 13

What are the sequential events during SMC contraction?

Answer 13

1. Rising intracellular Ca
2. Binding of Ca to calmodulin
3. Activation of MLCK by Ca/calmodulin complex
4. Phosphorylation of myosin light chain
5. Activation of myosin ATPase

Question 14

What factors regulate intracellular calcium of skeletal muscle?

Answer 14

L-type Ca channel, Ca pump, ryanodine receptor and Na-Ca exchanger

Question 15

What are the differences among skeletal, cardiac, and smooth muscle in terms of nuclei?

Answer 15

Skeletal: multinuclei structure
Smooth: Mononuclear
Cardiac: mixture

Question 16

What are the differences among skeletal, cardiac, and smooth muscle in terms of performing automatic phase contraction?

Answer 16

Only smooth muscle has automatic phase contraction

Question 17

What are the differences among skeletal, cardiac, and smooth muscle in terms of fatigue?

Answer 17

Only white fiber (type 2) of skeletal muscle get fatigued

Question 18

Is skeletal muscle innervated by sympathetic nervous system?

Answer 18

No. Skeletal muscle innervated by motor neurons

Question 19

Does skeletal muscle always attach to bones without exception?

Answer 19

No. Diaphragm and facial muscles are exceptions

Question 20

What type of contraction is when myosin heads bind to the same F-actin monomer during cross-bridge cycling?

Answer 20

Isometric contraction

Question 21

Why can airway allergy be treated with epinephrine?

Answer 21

Epi activates Beta-2 adrenergic receptor, which in turn activates cAMP signaling pathway, causes airway smooth muscle relaxation

Question 22

Can nerve stimulation induce smooth muscle relaxation?

Answer 22

Yes, smooth muscle innervation regulates both contraction and relaxation

Question 23

In a single stimulated isotonic contraction, what changes in the shortness-time relationship curve when the load is increasing?

Answer 23

1. latency of contraction increase
2. total shorten duration decrease
3. speed of contraction decrease
4. max shorten distance decrease

Question 24

*Is ATP depletion responsible for skeletal muscle fatigue?

Answer 24

No

*what is?