Muscle contraction

Question 1

What molecule is liberated into the synaptic cleft by synaptic vesicles?

Answer 1

Acetylcholine

Question 2

What occurs when Ach binds to receptors on the post-synaptic membrane?

Answer 2

1. Na+ ions enter the cell
2. K+ ions leave the cell
3. Sarcolemma depolorizes

Question 3

What protein is contained within the sarcoplasmic reticulum?

Answer 3

Calsequestrin

Question 4

Where is calsequestrin located?

Answer 4

Sarcoplasmic reticulum

Question 5

What is the role of calsequestrin?

Answer 5

Stores calcium ions and liberates them into the cytoplasm, in the region overlapping thick and thin filaments (goes from SR and into cytoplasm)

Question 6

What subunit of troponin do calcium ions bind to?

Answer 6

TnC

Question 7

What happens when TnC binds calcium ions?

Answer 7

1. TnT pushes tropomyosin filaments to move deeper into the spiral groove of actin, exposing actin active sites
2. Myosin head associates with actin monomer (ATP expended)
3. Head and neck of myosin bend
4. Myosin pulls the actin filament over the myosin filament, resulting in sliding of thin filament toward midline of sarcomere

Question 8

What happens to the length of thin filaments during contraction?

Answer 8

Remains the same!

Question 9

What happens to the length of thick filaments during conraction?

Answer 9

Remains the same!

Question 10

During contraction, what happens to the A band?

Answer 10

Remains the same size

Question 11

During contraction, what happens to the H band?

Answer 11

Almost disappears

Question 12

During contraction, what happens to the I band?

Answer 12

Becomes smaller

Question 13

During contraction, what happens to the Z discs?

Answer 13

Approaches midline

Question 14

What happens during rigor mortis?

Answer 14

Actin-myosin complexes cannot dissociate since ATP is not available - muscles stiffen