Physiology of Skeletal Muscles 1

Question 1

Skeletal muscles are composed of bundles of _______.

Answer 1

Fascicles

Question 2

Each fascicle is composed of _______.

Answer 2

Linearly aligned muscle fibers

Question 3

What kind of cell is a muscle fiber?

Answer 3

A single multi-nucleated, elongated cell

Question 4

Each muscle fiber is composed of many _______, arranged linearly

Answer 4

Sarcomeres

Question 5

Connective tissue surrounding the whole muscle?

Answer 5

Epimysium

Question 6

Sheath surrounding each fascicle?

Answer 6

Perimysium

Question 7

Sheath surrounding the individual muscle fibers?

Answer 7

Endomysium

Question 8

What is below the endomysium?

Answer 8

Sarcolemma = cell membrane of the muscle cell

Question 9

Each myofibril is composed of many ________.

Answer 9

Myofilaments

Question 10

Myofilaments are composed of what?

Answer 10

• Contractile proteins
• Regulatory proteins
• Additional accessory proteins

Question 11

Contractile proteins?

Answer 11

• Actin
• Myosin

Question 12

Regulatory proteins?

Answer 12

• Tropomyosin
• Troponin

Question 13

What forms the contractile unit of skeletal muscle?

Answer 13

Sarcomeres

Question 14

Sarcomeres are composed of interdigitating myofilaments made up of what?

Answer 14

• Thin filaments (actin)
• Thick filaments (myosin)

Question 15

What are the bounds of each sarcomere?

Answer 15

Z-disk

Question 16

What structures attach to the Z disk?

Answer 16

• Thin filaments
• Proteins involved in stretch sensing and signal communication

Question 17

What is at the center of the sarcomere?

Answer 17

M-line

Question 18

Regions of thin filament that don’t overlap with thick filament?

Answer 18

Light I bands

Question 19

Regions of thick filament that don’t overlap thin filament?

Answer 19

H-zone

Question 20

Region where the thick and thin filaments do overlap?

Answer 20

Dark A bands

Question 21

What shortens during muscle contraction? What stays the same?

Answer 21

Shorten = I band and H-zone
Same = A band

Question 22

Actin monomer? Polymer?

Answer 22

Monomer = G-actin
Polymer = F-actin

Question 23

What are thin filaments composed of?

Answer 23

Two strands of F-actin wound together

Question 24

Each G-actin has a binding site for _______

Answer 24

myosin

Question 25

Head region of myosin forms _________ that interact with adjacent actin filaments

Answer 25

Cross-bridges

Question 26

Many myosin units are arranged in staggered positions to form what?

Answer 26

Thick filament

Question 27

Important biochemical features of myosin head

Answer 27

- ATPase activity - Actin-binding region - ATP binding region

Question 28

regulatory molecule that prevents cross-bridge formation between myosin and actin in a relaxed muscle

Answer 28

Tropomyosin

Question 29

Troponin complex subunits? What do they bind to?

Answer 29

- Troponin C - binds calcium - Troponin T - binds tropomyosin - Troponin I - binds actin and inhibits contraction

Question 30

When Ca binds to Troponin C, this causes ________ to pull ______ and _______ off of myosin-binding site of G-actin subunits

Answer 30

Troponin T; Tropomyosin and Troponin I

Question 31

Sarcolemma contains invaginations called ______

Answer 31

Transverse tubules (T-tubules)

Question 32

What is the purpose of T-tubules?

Answer 32

Allows the action potential to be carried deep into the muscle fiber

Question 33

What do the sarcolemma and T-tubules associate closely with? What is it?

Answer 33

Sarcoplasmic reticulum = specialized ER that has high [Ca]

Question 34

What is the terminal cisternae?

Answer 34

Specialized regions of the SR that associate with T-tubules

Question 35

Junction between T-tubules and SR cisterna?

Answer 35

Muscle triad

Question 36

What is the neuromuscular junction?

Answer 36

Synapse where a motor nerve axon contacts each muscle fiber near the middle of the fiber

Question 37

The region of the sarcolemma in closest contact with the presynaptic nerve terminal is called the...?

Answer 37

Motor end plate

Question 38

The motor nerve terminal releases ______ which binds to the _______ receptor on the sarcolemma

Answer 38

Acetylcholine; nicotinic

Question 39

Action potential propagate along the T tubules and activate ________ channels in the sarcolemma

Answer 39

L-type Ca2+ channels

Question 39

What is the purpose of the T-tubule in action potential propagation?

Answer 39

It brings the action potential deep within very large muscle fibers

Question 40

Activation of the L-type Ca2+ channels triggers ______ activation of what kind of receptors?

Answer 40

Mechanical activation of Ryanodine receptors

Question 41

Most of the Ca2+ that activates the skeletal muscle sarcomere is from what?

Answer 41

Sarcoplasmic reticulum

Question 42

A single action potential for a motor neuron that barely causes any force development in the muscle fiber group?

Answer 42

Twitch

Question 43

Development of force (tension) in a muscle due to many action potentials that causes a greater release of Ca from the SR?

Answer 43

Tetany

Question 44

What is fused tetany?

Answer 44

Maximal force development in the muscle fibers of a motor unit = no individual "twitches" visible