Muscle Physiology Quiz

Normal Skeletal Muscle Physiology: Contraction-Relaxation Steps

• Skeletal muscle contraction is a complex process involving multiple steps.
• Contraction and relaxation rely on the interaction of actin and myosin filaments, regulated by calcium.

Muscle Structure

• Muscle tissue is organized into hierarchical structures:
  • Epimysium surrounds the entire muscle.
  • Perimysium surrounds fascicles (bundles of muscle fibers).
  • Endomysium surrounds individual muscle fibers.
• Muscle fibers contain myofibrils, composed of repeating units called sarcomeres.
• Sarcomeres are the functional units of muscle contraction.
• Myofibrils are composed of actin and myosin filaments.
• Sarcolemma is the muscle cell membrane.
• The sarcoplasmic reticulum (SR) stores and releases calcium ions.
• T-tubules are invaginations of the sarcolemma that transmit action potentials into the muscle fiber.
• A triad is a combination of a T-tubule and two terminal cisternae of the SR.

Proteins of Myofibrils

• Contractile proteins: Myosin (thick filament) and Actin (thin filament)
• Regulatory proteins: Tropomyosin (covers actin active site) and Troponin complex (Ca2+ binding)
• Structural proteins: Titin and Nebulin

Myotonia Congenita

• Inherited disorder characterized by muscle membrane hyperexcitability
• Muscle stiffness
• Genetic defect in chloride channel CLCN1

Duchenne Muscular Dystrophy

• Progressive muscle weakness caused by dystrophin deficiency.
• Results in early death

Other Structural Proteins

• Dystrophin : Important for structural integrity of muscle cells.
• Dystroglycan complex : Important for anchoring the muscle cell to its surroundings.

Excitation-Contraction Coupling

• Neuromuscular Junction: ACh release from motor neuron triggers muscle fiber excitation.
• Depolarization travels along sarcolemma and into T-tubules.
• Release of Ca2+ from the sarcoplasmic reticulum.
• Sliding Filament Theory: Increases overlap between actin and myosin, leading to muscle shortening.
• Contraction/Relaxation Cycle: The cycle of events involved in the sliding-filament theory.

Protein Interactions During Muscle Contraction

• ATP binding to myosin causes myosin head to detach from actin.
• ATP hydrolysis "cocks" the myosin head.
• Myosin head binds to a new position on actin filaments.
• Release of inorganic phosphate causes power stroke.
• Release of ADP causes myosin head to return to resting conformation.

Rigor Mortis

• Muscle stiffness after death due to lack of ATP.
• Myosin heads remain bound to actin, preventing muscle relaxation.

Energy Requirements for Skeletal Muscle Contraction

• ATP hydrolysis provides energy for the power stroke.
• Ca-ATPase pumps and Na-K pumps are essential for relaxation and maintaining resting membrane potential.

Twitch and Tetanus

• Twitch: A single contraction-relaxation cycle in a muscle fiber.
• Tetanus: Sustained muscle contraction due to rapid stimulation, characterized by incomplete and complete tetanus.

Motor Units

• A motor unit consists of a motor neuron and all the muscle fibers it innervates.
• Motor units are categorized by their properties into fiber types.

Somatic Reflexes

• Reflexes based on somatic efferent pathways.
• Reflexes are categorized by the effector, integrating region, time of development, and number of neurons involved.
• Classified as monosynaptic (two neurons involved) and polysynaptic (three or more neurons involved).

Muscle Spindles

• Sensory receptors that monitor muscle length changes.
• Consist of intrafusal fibers located within extrafusal fibers.
• Provide feedback to the CNS regarding muscle length.
• Primary afferent endings : Rapidly adapt to changes in muscle length.
• Secondary afferent endings : Slowly adapt to changes in muscle length.

Golgi Tendon Organs (GTOs)

• Located in the tendons of muscles, monitoring tendon tension.
• Consist of specialized sensory endings wrapped around collagen fibers within tendons and responding to muscle tensions.
• Provides information regarding tension produced by muscles, providing feedback to the CNS about tension in the muscle-tendon complex.

Alpha-Gamma Coactivation

• Simultaneous activation of alpha and gamma motor neurons.
• Ensures that spindle receptors continue to provide feedback to CNS.
• Maintains optimal sensitivity of the muscle spindle during muscle shortening.

Flexor Reflex

• A reflex movement of a limb away from a painful stimulus.

Crossed Extensor Reflex

• Reciprocal inhibition reflex, supporting body weight as weight shifts to the opposite limb.
• Compensatory action to maintain balance.

Review of Normal Physiology Somatic Reflexes and Sensory Receptors

• Includes a comprehensive overview of the somatic reflexes and sensory receptors.
• Muscle spindles and Golgi tendon organs are key sensory components to report muscle tension.

Test your knowledge on the role of calcium in muscle contraction and relaxation cycles. This quiz covers key concepts like excitation-contraction coupling, the function of the neuromuscular junction, and categorization of motor units. Perfect for students of physiology or anatomy.