CHAPTER 8: SKELETAL MUSCLE - STRUCTURE AND FUNCTION

Question 2

What percentage of total body weight do muscles account for?

Answer 2

40-50%

This highlights the significant mass and role of muscles in the human body.

Question 3

Name three functions of skeletal muscle.

Answer 3

• Force production for locomotion and breathing
• Force production for postural support
• Heat production during cold stress

Question 4

What surrounds a muscle?

Answer 4

Epimysium

Epimysium is the connective tissue that encapsulates the entire muscle.

Question 5

What is the structure that surrounds fascicles?

Answer 5

Perimysium

Perimysium is the connective tissue that groups muscle fibers into fascicles.

Question 6

What surrounds individual muscle fibers (cells)?

Answer 6

Endomysium

Endomysium is the connective tissue that surrounds each muscle fiber.

Question 7

What is the muscle cell membrane called?

Answer 7

Sarcolemma

Sarcolemma is crucial for muscle fiber function and action potential conduction.

Question 8

What connects muscle to bone?

Answer 8

Tendons

Tendons are essential for transmitting the force generated by muscles to the skeletal system.

Question 9

What are myofibrils?

Answer 9

Further differentiation of muscle fibers

Myofibrils are the contractile units within muscle fibers.

Question 10

What are the two types of contractile proteins in muscle?

Answer 10

• Myosin (thick filament)
• Actin (thin filament)

Question 11

What role does troponin play in muscle contraction?

Answer 11

Regulates the interaction between actin and myosin

Troponin binds calcium ions, leading to muscle contraction.

Question 12

What is a sarcomere?

Answer 12

Individual segments of myofibrils

Sarcomeres are the basic functional units of muscle contraction.

Question 13

What divides sarcomeres?

Answer 13

Z line

The Z line is a key structural component that defines the boundaries of each sarcomere.

Question 14

What is the I band in a sarcomere?

Answer 14

Light band (primarily actin)

The I band appears light under a microscope and contains only thin filaments.

Question 15

What is the A band in a sarcomere?

Answer 15

Dark band (primarily myosin)

The A band contains thick filaments and overlaps with thin filaments.

Question 16

What is the H zone?

Answer 16

Center with no actin-myosin overlap

The H zone appears lighter within the A band, where only myosin is present.

Question 17

What is the function of the sarcoplasmic reticulum?

Answer 17

Ca2+ storage

The sarcoplasmic reticulum is crucial for muscle contraction and relaxation.

Question 18

What do T-tubules do?

Answer 18

Extend from sarcolemma into muscle fibers

T-tubules help transmit action potentials deep into the muscle fiber.

Question 19

What is the neuromuscular junction?

Answer 19

Junction between motor unit and muscle fiber

This is where nerve impulses trigger muscle contractions.

Question 20

What happens when an action potential reaches the synaptic cleft?

Answer 20

• Acetylcholine (ACh) released
• Binds to receptors on motor end plate
• Causes sarcolemma depolarization
• Initiates muscle contraction

Question 21

What is the Sliding Filament Theory?

Answer 21

Muscle fibers contract by actin sliding over myosin

This theory explains the mechanism of muscle contraction at the molecular level.

Question 22

Name the ATP sources in muscle.

Answer 22

• Phosphocreatine
• Glycolysis
• Oxidative phosphorylation

Question 23

What is the role of ATP in muscle contraction?

Answer 23

Provides energy for myosin cross-bridges (‘power-stroke’)

ATP is essential for muscle contraction and relaxation processes.

Question 24

What occurs during excitation-contraction coupling?

Answer 24

• Action potential arrives at neuromuscular junction
• ACh released into synaptic cleft
• ACh binds to receptors, depolarizing muscle cell
• Depolarization conducted down T-tubules
• Ca2+ released from sarcoplasmic reticulum
• Ca2+ binds to troponin
• Tropomyosin changes position, exposing actin’s active sites
• Myosin forms cross-bridge with actin
• Cross-bridge binding releases energy, myosin pulls actin (‘power-stroke’)
• Fresh ATP binds to myosin, breaking cross-bridge

Question 25

What leads to muscular relaxation?

Answer 25

* Action potential ends, ACh no longer released * Muscle fiber repolarizes * Ca2+ no longer binds to troponin * Tropomyosin returns to block actin's binding sites

Question 26

What is muscle fatigue?

Answer 26

Decline in muscle power output during activity ## Footnote Fatigue can result from various physiological factors.

Question 27

What are the causes of muscle fatigue during severe exercise (1-10 min)?

Answer 27

* Decreased Ca2+ release * Metabolite accumulation

Question 28

What are the causes of muscle fatigue during heavy exercise (>60 min)?

Answer 28

* Increased radical production * Glycogen depletion

Question 29

What are exercise-associated muscle cramps?

Answer 29

Spasmodic, involuntary muscle contractions ## Footnote Cramps can be caused by various factors, including dehydration.

Question 30

What are the theories behind exercise-associated muscle cramps?

Answer 30

* Dehydration and electrolyte imbalance * Excitability of motor neurons (leading theory) * Hyperexcitation of motor neurons * Dysfunction of Golgi Tendon Organs/Muscle Spindles

Question 31

What are the characteristics of Slow, Type I muscle fibers?

Answer 31

* High endurance capacity * High mitochondrial volume * High capillary density * High myoglobin concentration * Low myosin ATPase activity * High efficiency * Moderate specific tension

Question 32

What are the characteristics of Fast, Type IIa muscle fibers?

Answer 32

* Intermediate characteristics * High/moderate mitochondrial volume * High/moderate fatigue resistance * High ATPase activity * High specific tension

Question 33

What are the characteristics of Fast, Type IIx muscle fibers?

Answer 33

* High-intensity performance * Low mitochondrial volume * Low capillary density * Low myoglobin concentration * Highest myosin ATPase activity * Low efficiency * High specific tension

Question 34

What is a concentric muscle action?

Answer 34

Muscle shortens under tension ## Footnote Concentric actions are common in lifting movements.

Question 35

What is an eccentric muscle action?

Answer 35

Muscle lengthens under tension ## Footnote Eccentric actions occur during lowering movements.

Question 36

What is an isometric muscle action?

Answer 36

Muscle length doesn't change under tension ## Footnote Isometric actions are often used in stabilization.

Question 37

What factors influence force regulation in muscles?

Answer 37

* Number/types of motor units recruited * Initial muscle length (Length-Tension Relationship) * Firing rate of motor neurons * Contractile history

Question 38

What is the relationship between force and velocity in muscle contractions?

Answer 38

Inverse relationship between force and velocity ## Footnote Muscles move fastest when the force is low.

Question 39

What adaptations occur in resistance training during the first 2-8 weeks?

Answer 39

Neural adaptations ## Footnote Strength increases before muscle size changes.

Question 40

What is hypertrophy in muscle training?

Answer 40

Increase in contractile proteins ## Footnote Hypertrophy is greater in Type II fibers.

Question 41

What is hyperplasia in muscle training?

Answer 41

Increase in muscle fiber number ## Footnote Not believed to occur significantly in humans.