18. Excitation Contraction Coupling

Question 1

Where is the myosin when the ATP is hydrolyzed?

Answer 1

Cocked and ready to interact with actin and contract

Question 2

What happens after the myosin head attaches to the actin?

Answer 2

Pi dissociates and the power stroke contracts the sarcomere.

Question 3

What enzyme breaks down acetylcholine in the synaptic gap?

Answer 3

Acetylcholine Esterase

Question 4

What small structures are made in the sarcolemma of the neuromuscular junction to increase the action potential going into the muscle?

Answer 4

Subneural Clefts

Question 5

What receptors have to change confirmation to allow calcium to release into the sarcoplasm?

Which one is located in the membrane of the T Tubule?

Answer 5

DHP and RYR

DHP

Question 6

Where is the myosin head after ATP binds, but before ATP is hydrolyzed?

Answer 6

Released from the actin, but not yet cocked.

Question 7

What are the three members of the troponin complex, and what do they bind to?

Answer 7

Troponin I: Actin

Troponin C: Calcium

Troponin T: Tropomyosin

Question 8

Besides the muscle cell hypertrophy, what changes in the muscles of a trained athelete vs someone like me (a nerd)?

Answer 8

More mitochondrial enzymes

More glycogen

More phosphocreatine

More stored fat

Question 9

Which type of muscle fibers are larger?

Answer 9

Type II

Question 10

When we strength train, do we get more muscle fibers, or just bigger muscle fibers?

Answer 10

Just bigger muscle fibers

(more myofibrils per muscle fibers)

Question 11

How do we induce a smooth, continuous muscle movement within a single motor unit when our neurons can only produce all or nothing responses?

Answer 11

Summation and tetanization

Increasing frequencies of stimulation increases the rate of contraction

Question 12

What receptors are responsible for initiating a local potential at the neuromuscular junction?

Answer 12

Ligand gated acetylcholine receptors

Question 13

How do we make a muscle contract with more or less force?

Answer 13

Recruitment - activate more or fewer muscle units

Question 14

How long can we use phosphocreatine for muscle contraction?

Answer 14

8-10 seconds

Question 15

How long does Rigor Mortis last?

Answer 15

15-25 hours

Question 16

Where are the two hinges in a myosin molecule?

Answer 16

Hinge 1: Separating the two heads

Hinge 2: One on each of the myosin heads, allowing independent movement

Question 17

What allows the sarcoplasmic reticulum to hold up to 40x more calcium than it otherwise would?

Answer 17

Calsequestrin

Question 18

What enzyme is used to shuttle calcium from the sarcoplasm into the sarcoplasmic reticulum after a contraction occurs?

Answer 18

Calcium ATPase

Question 19

When is a sarcomere able to produce the maximum amount of force?

Answer 19

When there is no overlap in actin, and every myosin head is able to access a binding site.

Question 20

Which type of muscle fiber has more glycogen?

Answer 20

Type II

Question 21

Which type of muscle fibers have more phosphocreatine?

Answer 21

Type II

Question 22

Would smaller, more precise muscles have more or less muscle fibers?

Answer 22

More muscle fibers

This allows them to regulate the force of their contraction more precisely.

Question 23

Which type of muscle fiber has more mitochondria and myoglobin?

Answer 23

Type I

Question 24

How long can we use stored ATP for a muscle contraction?

Answer 24

Two seconds

Question 25

How long can we use Glycolysis for a muscle contraction?

Answer 25

1.3 - 1.6 minutes

Question 26

Where is the myosin head after a contraction, but before it binds a new ATP?

Answer 26

Still stuck to its binding site on the actin.

Question 27

What is a motor unit?

Answer 27

All the muscle fibers innervated by a single nerve fiber.

Question 28

How long can we use oxidative phosphorylation to sustain a muscle contraction?

Answer 28

Until the muscle runs out of things to throw into the TCA cycle.