Animal Phys Ch.12

Muscles

What are the three main muscle types?

Skeletal, cardiac, and smooth muscle

Which muscle type is voluntary?

Skeletal muscle

Which nervous system innervates skeletal muscle?

Somatic nervous system

What is the function of skeletal muscle?

Body movement and maintenance of posture

What is the function of cardiac muscle?

Pumps blood through pulmonary and systemic circulation

What is the function of smooth muscle?

Moves contents through organs and regulates organ diameter

How are skeletal muscle fibers formed?

Fusion of many myoblasts during embryonic development

What is a sarcomere?

The repeating contractile unit of striated muscle

What is the main protein of thin filaments?

Actin

What is the main protein of thick filaments?

Myosin

What does myosin do?

Interacts with actin to produce contraction

What is titin?

A giant elastic protein connecting myosin to the Z-disc

What does titin do?

Centers thick filaments and provides passive elasticity

What happens to the sarcomere during contraction?

It shortens as thin filaments slide past thick filaments

Do actin and myosin filaments shorten during contraction?

No; they slide past one another

What happens to the H zone during contraction?

It narrows

What happens to the I band during contraction?

It narrows

What happens to the A band during contraction?

Its length stays constant

What happens to Z-discs during contraction?

They move closer together

What is the cross-bridge cycle?

Repeated myosin binding, pulling, detaching, and re-cocking

What allows myosin to bind to actin?

Calcium binds troponin, moving tropomyosin

What does troponin bind?

Calcium ions

What does tropomyosin do in relaxed muscle?

Blocks myosin-binding sites on actin

What is MyBP-C?

Myosin-binding protein C, which helps regulate thick-filament function

What is excitation-contraction coupling?

Link between electrical excitation and muscle contraction

What does DHPR detect in skeletal muscle?

T-tubule membrane depolarization

What does RyR do?

Releases calcium from the sarcoplasmic reticulum

What does SR stand for?

Sarcoplasmic reticulum

What is the SR's role?

Stores and releases calcium for contraction

What returns calcium to the SR?

ATP-dependent calcium pumps

What is a muscle twitch?

One contraction and relaxation after a single action potential

What are the three phases of a muscle twitch?

Latent, contraction, and relaxation

What occurs during the latent period?

Excitation-contraction coupling before measurable tension

What happens during the contraction phase?

Tension develops as cross-bridges cycle

What happens during the relaxation phase?

Calcium returns to SR and tension falls

What is an isometric contraction?

Muscle produces force without changing overall length

What is a concentric contraction?

Muscle shortens while producing force

What is an eccentric contraction?

Muscle lengthens while resisting a load

What do flexors do?

Bend a limb

What do extensors do?

Straighten a limb

What are antagonistic muscle pairs?

Muscles producing opposing movements

What is the length-tension relationship?

Muscle force depends on its length when stimulated

What is a motor unit?

One motor neuron and all muscle fibers it innervates

What is motor unit recruitment?

Activating additional motor units to increase force

Which motor units are recruited first?

Those with lower firing thresholds

What are small motor units best for?

Precise movements and weaker contractions

What are large motor units best for?

Gross movements and stronger contractions

What is twitch summation?

A new twitch adds tension before the previous twitch relaxes

What is tetanus in muscle physiology?

Sustained contraction from rapid repeated stimulation

What molecule provides energy for muscle activity?

ATP

Name three processes requiring ATP in muscle.

Cross-bridge cycling, calcium pumping, and Na+/K+ pumping

What are the three major ATP-producing pathways?

Phosphagens, anaerobic glycolysis, and aerobic catabolism

How much ATP does anaerobic glycolysis yield per glucose in the slides?

2–3 ATP

What aerobic ATP yield is listed in the slides?

32–36 ATP per glucose

What is muscle fatigue?

Reduced contractile response despite stimulation

Name two contributors to muscle fatigue.

ADP/Pi buildup and impaired SR calcium release

What are Type I fibers?

Slow oxidative fibers with high fatigue resistance

What are Type IIa fibers?

Fast oxidative fibers with intermediate fatigue resistance

What are Type IIx/IIb fibers?

Fast glycolytic fibers with low fatigue resistance

What is sarcopenia?

Age-associated muscle loss