PL9 SKELETAL TISSUE Flashcards
(16 cards)
What are the three main types of muscles?
Skeletal Muscle: Striated, attached to bones, and voluntarily controlled.
Cardiac Muscle: Striated, located in the heart, and involuntarily controlled.
Smooth Muscle: Non-striated, located in blood vessels and hollow organs, and involuntarily controlled
What are the layers of connective tissue in skeletal muscles?
Epimysium: Covers all fascicles.
Perimysium: Covers each fascicle containing muscle fibers.
Endomysium: Covers each muscle fiber.
What is a sarcomere, and what does it contain?
A sarcomere is the functional unit of a myofibril, It is located between two ‘Z’ discs and contains:
Actin filaments (1500 thin filaments).
Myosin filaments (3000 thick filaments).
What are the regions of a sarcomere?
Z disc: Anchors actin filaments.
I band: Light band containing only actin.
A band: Dark band containing myosin and overlapping actin.
H zone: Space between actin filaments within the A band.
M line: Middle of the sarcomere.
What proteins are found in actin filaments?
Actin (F): Forms helical chains.
Tropomyosin: Covers actin’s active sites at rest.
Troponin Complex:
Troponin I: Binds to actin.
Troponin T: Binds to tropomyosin.
Troponin C: Binds to calcium ions.
What is the structure of myosin filaments?
Composed of six polypeptide chains: two heavy chains (tail and head) and four light chains.
The head forms cross-bridges with binding sites for ATP and actin.
What are other structural proteins in skeletal muscle?
α-Actinin: Binds actin to Z discs.
Titin: Connects Z discs to M lines.
Nebulin: Involved in muscle development.
Desmin: Binds Z discs to the plasma membrane.
Dystrophin: Connects the cytoskeleton to the extracellular matrix.
What are the key muscular dystrophies?
Duchenne Muscular Dystrophy: X-linked mutation in the dystrophin-glycoprotein complex gene,
Becker Muscular Dystrophy: Dystrophin is altered or reduced.
Limb-Girdle Dystrophy: Mutations in sarcoglycans or the dystrophin-glycoprotein complex.
Titin Mutations: Cause cardiomyopathy or tibialis muscular dystrophy.
Desmin-Related Myopathies: Wasting of distal lower limb muscles.
What are the steps in skeletal muscle contraction?
Motor neuron discharge generates an end-plate potential.
Depolarization spreads along T-tubules.
Calcium is released from the sarcoplasmic reticulum.
Calcium binds to troponin C, uncovering myosin binding sites on actin.
Myosin heads attach to actin, form cross-bridges, and perform a power stroke using ATP.
What changes occur in the sarcomere during contraction?
A band: Remains constant.
I band: Reduces.
H zone: Reduces.
Z lines: Move closer.
What are the differences between red and white muscle fibers?
Red Muscle Fibers: Slow-twitch, endurance muscles, darker in color. Found in antigravity muscles like the back.
White Muscle Fibers: Fast-twitch, skilled movement muscles, pale in color. Found in extraocular and hand muscles.
What are the energy sources for muscle contraction?
ATP from fats, aerobic glycolysis, glycogen, and anaerobic glycolysis.
During exercise: Myoglobin and creatine phosphate provide additional energy.
What is rigor mortis?
Rigid state after death due to the depletion of ATP, causing myosin heads to remain abnormally attached to actin.
What types of heat are produced by skeletal muscles?
Resting Heat: Basal metabolism.
Initial Heat: Excess heat during contraction.
Recovery Heat: Heat produced to restore the muscle state.
Relaxation Heat: Associated with isotonic contractions.
What are the types of smooth muscle?
Visceral (Single-Unit): Spindle-shaped, found in hollow organs, and controlled involuntarily.
Multi-Unit: Resembles skeletal muscle fibers but is involuntary.
What events occur during smooth muscle contraction and relaxation?
Contraction: Binding of acetylcholine to receptors increases calcium influx, activating calmodulin-dependent myosin light chain kinase and myosin binding to actin.
Relaxation: Myosin is dephosphorylated, ceasing actin-myosin interaction.
