Lecture 5 Flashcards
What are the three types of muscle found in vertebrates?
Skeletal (striated, voluntary), Cardiac (striated, involuntary), and Smooth (non-striated, involuntary)
What is the Sliding Filament Theory?
Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.
What are the two main types of myofilaments in a sarcomere?
Thin filaments (actin, troponin, tropomyosin) and Thick filaments (myosin).
What is a motor unit?
A motor neuron and all the muscle fibers it innervates.
How does calcium regulate muscle contraction?
Calcium binds to troponin, causing tropomyosin to shift, exposing myosin-binding sites on actin.
What are the differences between fast-twitch and slow-twitch muscle fibers?
Slow-twitch (Type I): Aerobic, high endurance, many mitochondria, red color.
Fast-twitch (Type II): Anaerobic, high force, fatigue quickly, white color.
What is the role of mitochondria in muscle cells?
Mitochondria generate ATP through aerobic respiration, supporting sustained muscle activity.
How do muscles contribute to locomotion in water, land, and air?
Water: Myomeres enable undulatory movement.
Land: Appendicular muscles enable limb-based movement.
Air: Wing muscles create lift and thrust.
What are the primary functions of muscles? (5)
Movement, force generation, posture maintenance, heat production, and organ function.
What is the fundamental contractile unit of a muscle?
The sarcomere, which shortens during contraction.
What is required for muscle contraction to occur?
ATP and calcium (Ca²⁺).
Where is calcium stored in muscle cells?
sarcoplasmic reticulum (SR).
How is calcium released from the sarcoplasmic reticulum?
Through ryanodine receptors (RyR), triggered by depolarization of the T-tubules.
What is the role of ATP in muscle contraction?
ATP is required for cross-bridge cycling, detaching myosin from actin, and re-sequestering Ca²⁺ into the SR.
What are the two primary types of muscle fibers?
Slow-twitch (Type I) and Fast-twitch (Type II) fibers.
What are tonic fibers?
Found in amphibians, birds, and some mammalian eye muscles; contract gradually and do not fire action potentials.
What are twitch fibers?
The most common type, contract in response to a single action potential.
What are the three metabolic classifications of muscle fibers?
Slow oxidative (SO, Type I) – High endurance, aerobic metabolism.
Fast oxidative-glycolytic (FOG, Type IIA) – Intermediate properties.
Fast glycolytic (FG, Type IIB/X) – High power, anaerobic metabolism.
What cellular organelle is responsible for aerobic metabolism in muscle cells?
Mitochondria, which produce ATP through oxidative phosphorylation.
Why do fast glycolytic fibers fatigue more quickly?
They rely on anaerobic metabolism, producing lactic acid, which leads to muscle fatigue.
How does motor unit recruitment affect force production?
More motor units activated = greater force production.
What neurotransmitter is released at the neuromuscular junction (NMJ)?
Acetylcholine (ACh)
What is the role of the T-tubules in muscle contraction?
They conduct action potentials into the muscle fiber, triggering Ca²⁺ release from the SR.
How do fish muscles differ from tetrapod muscles?
Fish muscles are arranged in myomeres, allowing undulatory swimming.
Tetrapods have appendicular muscles for limb-based locomotion.
What are myomeres?
Segmented trunk muscles in fish that contract in a wave-like motion for swimming.
What are red muscle fibers in fish?
Used for sustained swimming, high endurance, aerobic.
What are white muscle fibres?
Used for burst swimming, powerful but fatigues quickly.
How do birds minimize energy use during flight?
By using aerofoil-shaped wings, tendon locking mechanisms, and soaring on air currents.
What is elastic energy storage, and why is it important for running animals?
Tendons and muscles store and release energy to improve efficiency, reducing metabolic cost.
What is cost of transport (COT)
The energy required to move a given distance.
Why is COT lower in water than on land?
Water reduces the effects of gravity, requiring less energy for movement.
How do gaits affect the cost of transport?
Different gaits (walking, running, galloping) optimize energy use at different speeds.
How does posture affect locomotion efficiency?
Sprawling posture: Used by amphibians, requires trunk bending for movement.
Upright posture: More efficient, used by mammals and birds.
Why do large animals have a lower cost of transport than small animals?
They have greater stride length and use elastic energy storage more effectively.
