Skeletal Muscle Contraction

Question 1

What is the epimysium?

Answer 1

connective tissue surrounding the entire muscle

Question 2

What is the muscle made up of?

Answer 2

multiple fascicles.

Question 3

What is the perimysium?

Answer 3

tissue surrounding multiple fascicles.

Question 4

what is the endomysium?

Answer 4

tissue surrounding each myofiber

Question 5

what is the sarcolemma?

Answer 5

cell membrane of muscle fiber

Question 6

what is a myofiber?

Answer 6

muscle cell; an indivudali multinucleated muscle cell

Question 7

what is the myofibril?

Answer 7

a chain of sarcomeres within a myofiber; it contains actin and myosin necessary for a muscle contraction.

Question 8

What is a myofilament?

Answer 8

actin and myosin filaments that make up a sarcomere.

Question 9

What are T-tubues

Answer 9

invaginations of the sarcolemma that lie close to cisternae of the sarcolasmic reticulum.

Question 10

What does the sarcoplasmic reticulum do?

Answer 10

regulates calcium storage and reuptake; important for muscle contraction.

Question 11

What does the sarcomere lie inbetween?

Answer 11

two Z-disks.

Question 12

Where are the Z discs, and what do they do?

Answer 12

at the end of the sarcomere; they anchor the actin filaments.

Question 13

What are I bands composed of?

Answer 13

actin; their width changes during contraction.

Question 14

What are A bands composed of?

Answer 14

myosin and actin; they do not change during contraction

Question 15

What are H bands composed of?

Answer 15

myosin; the width changes during contaction.

Question 16

What does Titin do?

Answer 16

holds actin and myosin in place and acts as a framework. It is springy and allows for contraction of the sarcomere.

Question 17

What enters a nerve fiber’s terminal buttons after an action potential has been fired?

Answer 17

calcium

Question 18

What neurotransmitter does the nerve fiber release?

Answer 18

acetylcholine

Question 19

What kind of sodium channels are opened when Ach binds?

Answer 19

ligand-gated

Question 20

What kind of channels are open once sodium enters through the ligand-gated channel?

Answer 20

voltage-gated

Question 21

What do DHP channels on T-tubules interact with once an action potential has been initiated on the sarcolemma?

Answer 21

ryanodine receptors

Question 22

What are ryanodine receptors sensitive to?

Answer 22

calcium

Question 23

Where are ryanodine receptors located?

Answer 23

sarcoplasmic reticulum membrane

Question 24

What is released after the opening of ryanodine receptors on the SR membrane?

Answer 24

calcium

Question 25

What do calcium ions from the SR bind to?

Answer 25

troponin

Question 26

What is deactivated (and allows binding of actin to myosin) once calcium binds to troponin?

Answer 26

tropomyosin

Question 27

What molecule do the ATPase heads of myosin use before binding to actin?

Answer 27

ATP

Question 28

What does myosin have to use to break away from actin?

Answer 28

ATP

Question 29

When does contraction stop?

Answer 29

When ATP-dependent calcium pumps moves calcium ions back into the sarcoplasmic reticulum.

Question 30

What is DHP?

Answer 30

Dihydropyridine receptor; it is on the membrane of the sarcolemma (T-tubules) and changes conformation of ryanopyridine if an action potential is initiated.

Question 31

What is SERCA?

Answer 31

ATP dependent pump that moves calcium back into the SR

Question 32

What is calsequestrin?

Answer 32

molecule in the SR that maintains optimum calcium concentration gradients.

Question 33

When does a sarcomere have the least tension?

Answer 33

When the actin filaments do not overlap.

Question 34

When does a sarcomere have the most tension?

Answer 34

When the actin filaments either touch or overlap all of the cross bridges.

Question 35

Does velocity increase or decrease with the amount of contraction?

Answer 35

decrease

Question 36

When is ATP required for muscle contraction?

Answer 36

pumping calcium ions into SR, maintaining Na/K concentration after action potentials, binding/release of myosin heads from actin filaments.

Question 37

What is phosphocreatine?

Answer 37

a molecule that contains a high-energy phosphate; it releases it to make ATP for 5 - 8 seconds of contraction.

Question 38

How long can glycolysis sustain muscle contractions?

Answer 38

1 minute

Question 39

What metabolic pathway provides the most energy needed for long-term contraction?

Answer 39

oxidative metabolism

Question 40

What are isometric contractions?

Answer 40

Increase in tension, but not length

Question 41

What are isotonic contractions?

Answer 41

Change in muscle length. Is either eccentric or concentric.

Question 42

What is an eccentric contraction?

Answer 42

isotonic contraction in which the muscle length lengthens

Question 43

What is an concentric contraction?

Answer 43

isotonic contraction in which the muscle length shortens

Question 44

What are characteristics of fast, white fibers?

Answer 44

are muscles that react rapidly; they have fast twitch fibers, few mitocondria, high levels of ATPase, and use anaerobic respiration

Question 45

What are characteristics of slow, red fibers?

Answer 45

are muscles that contract slowly, but have endurance. They have high mitochondria and myoglobin and small ATPase; they use aerobic respiration.

Question 46

What muscle component can be increased after birth?

Answer 46

myofibrils; lost muscle tissue is replaced by scar tissue.

Question 47

Which muscle is composed predominantly of dark fibers?

Answer 47

soleus

Question 48

Which muscle is composed predominantly of light fibers?

Answer 48

gastrocnemius

Question 49

What is a motor unit?

Answer 49

a single nerve cell (neuron) that innervates myofibers. When a neuron fires, all the myofibers in the motor unit contract.

Question 50

What is summation?

Answer 50

Addition of individual twitch contractions to the increase the overall intensity of a muscle contraction. It increases muscle tension and adds to the effects of the previous spikes.

Question 51

How is summation caused?

Answer 51

When electrical event soccur before the previous calcium ions enter the SER again; the amount of Ca ions ourside the SER increases.

Question 52

What is tetany?

Answer 52

When a muscle rmains at maximal contraction from summation; little ability to use the muscle for a perio dof time.