muscles Flashcards
Describe the structure of skeletal muscle.
Multnucleated, striated fibres made from myoblasts. Encased in connective tissue sheaths. Skeletal muscle is made of myofibrils. Myofibrils are bundles of protein made from sarcomeres. Sarcomeres are microscopic repeating units that give muscle its strength.
What are sarcomeres made from and how to they change during contraction/relaxation?
Thick myosin filaments and thin actin filaments. Thick filaments are surrounded by thin ones. When muscles contract, actin filaments come closer together. Muscle shortens upon contraction and lengthens upon relaxation.
Define sarcolemma.
The tubular sheath that envelops fibres of skeletal muscles.
Explain the steps of excitation-contraction coupling.
AP is fired. Ca2+ released from SR. Ca2+ ions bind to troponin. Tropomyosin conformational change so actin binding site is exposed. Myosin binds to actin and forms cross-bridges which cause muscle contraction. Ca2+ ions returned to SR via ATP by active transport. Tropomyosin returns to original conformation and cross-bridges are broken.
What is an isotonic twitch?
Contraction with shortening length. Latent period and contraction time longer as muscle is shortening.
What is an isometric twitch?
Contraction with constant length. Contraction time is short as the muscle is staying the same length.
What is the relationship between motor units and load?
As load increases, more motor units are required to carry out the required contraction. Recruitment allows more muscle fibres to be involved in a movement.
What do transverse-tubules do?
Allow depolarisation to reach deep within the core of a muscle and also spread it across the surface.
Define motor unit.
Motor neurons + muscle fibres they innervate. The function of this is redundancy.
Explain the sliding filament theory of muscle contraction.
Thin actin filaments slide past thick myosin filaments during muscle contraction. Both stay a relatively constant length.
Explain the difference between tension and load.
Tension is the force exerted by a muscle. Load is the force exerted on a muscle.
Define tetanus.
Prolonged contraction of a muscle caused by rapidly repeated stimuli. AP’s are fired more frequently to generate more force. Greater than twitch tension as concentration of Ca2+ ions never gets low enough to allow cross-bridge cycle to be broken. Fused? no relaxation. Un-fused? Slight period of relaxation.
Define fatigue.
Caused by repeated muscle stimulation. Prevents using too much ATP to sustain contractions. Depends on fitness of individual, length of contraction and muscle fibres.
What are the different types of skeletal muscle fibres?
Oxidative and glycolytic.
What are oxidative fibres?
Have mitochondria for oxidative phosphorylation. Vascular to allow the delivery of O2 and nutrients. Contain myoglobin for O2 delivery. Red fibres with low diameters. Slow oxidative fibres resist fatigue. Fast oxidative fibres have an intermediate resistance to fatigue.
