VPH

• What is released when acyl-carnitine is converted back to acyl-CoA?

  Carnitine
• What is the end product of beta-oxidation in the mitochondrial matrix?

  A 2-carbon Acetyl-CoA product
• What cycle does newly formed Acetyl-CoA enter to produce ATP?

  The Krebs cycle
• What are the two types of muscle contractions?

  • Isometric contraction: generates force without significant shortening (e.g., pushing a heavy object without moving it).
  • Isotonic contraction: muscle fibers shorten while developing force (e.g., pushing a heavy object moves it).

  
• What is an example of isotonic contraction?


  Pushing on a heavy object that moves it
• What happens to the sarcomere during isometric contraction?

  There is slight shortening of the sarcomere, tautening elastic elements in muscle and connective tissue.
• What precedes isotonic contraction during muscle activity?

  A period of isometric contraction
• What are the two types of isotonic contractions?

  • Concentric contraction: muscles shorten while generating force (e.g., upward phase of a bicep curl).
  • Eccentric contraction: muscles elongate while generating force (e.g., downward phase of a bicep curl).

  
• What determines the maximum shortening of a muscle fiber?

  The number of sarcomeres in individual myofibrils.
• What is the optimal length of a muscle for maximum force production?

  It is the length at which there is a high degree of overlap between filaments.
• What happens when the sarcomere is overly contracted at rest?

  Further muscular contraction is inhibited, and tension decreases.
• What occurs when there is little overlap between filaments in a muscle fiber?

  Little cross-bridge formation occurs, resulting in less tension produced.
• What is the optimal resting length of a sarcomere?

  It is the length at which more cross-bridge cycling occurs, resulting in increased tension.
• What is a single twitch in muscle contraction?

  • A single isometric contraction-relaxation cycle in a muscle fiber.
  • Brief contraction due to an action potential (AP) followed by relaxation.
  • Latent period due to time taken for AP to reach t-tubules until cytosolic Ca2+ concentration reaches threshold.

  
• What is a tetanic contraction?

  • Persistent contraction of muscle fiber due to a series of action potentials in rapid succession.
  • New AP can be induced before the previous twitch subsides, leading to fused contractions and increased tension.
  • Can be incomplete (low frequency of stimulation) or complete (high frequency of stimulation).

  
• What is the difference between incomplete and complete tetanic contraction?

  Incomplete tetanic contraction has fluctuating fused contractile forces, while complete tetanic contraction develops sustained constant force with no relaxation.

  
• What are the different types of skeletal muscle fibers?

  • Slow-oxidative fibers (type I): low myosin-ATPase activity, high oxidative capacity.
  • Fast-oxidative fibers (type IIa): high myosin-ATPase activity, high oxidative capacity.
  • Fast-glycolytic fibers (type IIb): high myosin-ATPase activity, high glycolytic capacity.
  • Intermediate type (type IIx).
• What characterizes type I muscle fibers?

  They have small motor units, weak muscle contractions, and prevent muscle fatigue due to oxidative metabolism.
• What characterizes type IIb muscle fibers?

  They have large motor units, are last to be recruited, and are used for brief powerful work.
• How do different muscle types vary among species or breeds?

  Muscles for body posture have more slow fibers, while propulsive muscles have more fast fibers.
• What are the characteristics of motor units in skeletal muscle?

  • Whole muscles are made up of many muscle fibers organized into motor units.
  • All muscle fibers in a single motor unit are of the same fiber type.
  • Recruitment increases the number of active motor units, making contractions stronger.

  
• What is the structure of smooth muscle?

  • Spindle-shaped cells arranged in bundles.
  • Poorly developed sarcoplasmic reticulum (SR) and no t-tubules.
  • Actin and myosin filaments arranged in bundles with different orientations.

  
• How does the arrangement of myofilaments in smooth muscle affect contraction?

  Irregular arrangement allows for maximum contractile force over a greater length span.
• What is the role of calmodulin in smooth muscle contraction?

  Calmodulin binds to Ca2+ to activate myosin light chain kinase, leading to phosphorylation of myosin heads.
• What are the two types of smooth muscle?

  • Multi-unit: independent units that must be stimulated by nerves separately.
  • Single unit: self-excitable, contraction can occur in absence of action potentials.

  
• What determines the degree of smooth muscle contraction?

  Cytosolic Ca2+ concentration.
• What is the stress-relaxation response in smooth muscle?

  Initial contraction after smooth muscle stretch increases tension but tension decreases within a minute.
• What influences smooth muscle activity?

  • Nerves (autonomic nervous system)
  • Hormones (e.g., norepinephrine, epinephrine)
  • Paracrine substances (e.g., histamine, prostaglandins)
  • Stretch (mechanical stress)
  • Local tissue conditions (e.g., pH, oxygen concentration)

  
• What is the process of excitation-contraction coupling in smooth muscle?

  1. Increased cytosolic Ca2+ concentration due to Ca2+ influx and release from SR.
  2. Ca2+ binds calmodulin, activating myosin kinase.
  3. Myosin heads are phosphorylated, allowing cross-bridge cycling.
  4. Muscle contraction continues as long as myosin heads are phosphorylated.
  5. When stimulation ceases, Ca2+ is pumped out, leading to relaxation.
• What happens when stimulation ceases in smooth muscle contraction?

  Ca2+ pumps remove cytosolic Ca2+, leading to relaxation as myosin heads lose ATPase activity.