Physiology Lab 7 Homework Quiz

Muscle Contraction and Mechanisms

• Tension produced by skeletal muscle is proportional to the number of motor units activated.
• During the latent period, no force is generated; this is the time before contraction begins.
• The threshold voltage is the minimum voltage required to initiate active force in skeletal muscle.
• A motor unit consists of a single motor neuron and all the muscle fibers it stimulates.
• An action potential's arrival at the T tubule leads to the release of calcium from the terminal cisternae of the sarcoplasmic reticulum.

Calcium and Muscle Contraction

• Calcium binds to troponin, leading to a shape change that exposes myosin binding sites on actin.
• Myosin heads form cross bridges by binding to actin.
• The release of ATP from myosin causes the myosin head to disconnect from actin.
• The power stroke is caused by the release of ADP and inorganic phosphate after the binding of calcium.

Graded Muscle Contraction

• Muscle contractions are graded by increasing stimulus strength and frequency.
• Excitation-contraction coupling involves action potentials propagating along the sarcolemma, which prompts calcium release and subsequent muscle contraction.

Structural Components

• A triad consists of a T-tubule and two adjacent terminal cisternae.
• T-tubules are the infoldings of the sarcolemma that allow excitation to penetrate the muscle fiber.
• Calcium ions are crucial for the coupling of excitation to contraction in muscle fibers.

Cross Bridge Cycle

• The cross bridge is defined as myosin binding to actin.
• The binding of ATP to the myosin head causes cross bridge detachment.
• ATP hydrolysis occurs during the cocking of the myosin head, storing energy for the next cycle.
• Myosin heads will remain attached to actin if they cannot detach due to factors like the inhibition of ATP hydrolysis.

Regulation of Muscle Fiber Activity

• Tropomyosin covers active sites on actin; its displacement allows cross bridge formation.
• The role of troponin is to regulate tropomyosin positioning, enabling myosin heads to bind to active sites.
• During contraction, always having some myosin heads attached prevents actin from sliding backward.

Effects of Inhibitors

• BMD (2,3-butanedione 2-monoxime) inhibits myosin's ability to hydrolyze bound ATP, preventing myosin heads from cocking and affecting the cross bridge cycle's progression.

These notes summarize the essential aspects of skeletal muscle contraction, detailing the roles of ions, proteins, and mechanical processes involved in the cross bridge cycle and overall muscle functionality.

Test your understanding of skeletal muscle tension and muscle twitch dynamics with this Lab 7 homework quiz. Assess your knowledge of terms like latency and motor unit activation. Ideal for students revising for physiology exams.