Muscular System Lecture - 14

Muscular System Lecture - 14

• Learning Outcomes:

  • Describe the mechanism of contraction and relaxation of skeletal muscle fibers.
  • Describe the neuromuscular junction (NMJ).

• Muscle Contraction:

  • Physiology of Muscle Contraction:
    • Muscle fiber contraction is "all or none".
    • Not all skeletal muscle fibers are stimulated at the same time.
    • Different combinations of muscle fiber contractions result in varied responses.
    • Graded responses result in different degrees of skeletal muscle shortening.
    • Rapid stimulus results in constant contraction (tetanus).
  • Force of Muscle Contraction:
    • Force depends on the number of fibers activated.
    • More fibers contracting result in greater muscle tension
    • Muscle contraction continues until ATP is depleted or Ca2+ is unavailable.
    • One ATP molecule supplies energy for one actin-myosin cross-bridge.

Energy for Muscle Contraction

• ATP Utilization:
  • Muscles use stored ATP for energy.
  • ATP bonds are broken to release energy.
  • Only 4-6 seconds worth of ATP is stored in muscles
  • Three ways for muscle to create ATP:

Methods of ATP Production

• Creatine Phosphate:

  • A high-energy compound used for rapid ATP production.
  • Fastest way to make ATP available for muscles.
  • Ideal for activities lasting less than 15 seconds.
  • Anaerobic (no oxygen required)
  • Made during muscle rest.

• Cellular Respiration:

  • Mitochondria use glucose, in the presence of oxygen, to produce ATP.
  • Provides most of a muscle's ATP
  • Aerobic (requires oxygen).
  • Ideal for activities lasting hours.

• Fermentation/Anaerobic Respiration:

  • Breaks down glucose without oxygen.
  • Used for activities lasting from 30-60 seconds.
  • Anaerobic.
  • Produces lactic acid, contributing to muscle soreness.

Oxygen Deficiency

• Heavy breathing after exercise: Indicates oxygen deficiency.
• Marathon runner exhaustion: Caused by depleted glucose and oxygen reserves.
• Recovery time: Replenishment of muscle glycogen and liver glycogen takes up to two days.

Muscles and Body Movement

• Movement: Happens when a muscle moves an attached bone.
• Attachment Points: Muscles attach to at least two points.
  • Origin: Attachment to an immovable bone.
  • Insertion: Attachment to a movable bone.
  • Tendon: Connects muscle to bone

Types of Body Movements

• Flexion: Decreases the angle of a joint, bringing bones closer together.
• Extension: Increases the angle of a joint
• Rotation: Bone movement along its longitudinal axis.
• Abduction: Movement away from the midline.
• Adduction: Movement towards the midline.
• Circumduction: Cone-shaped movement, distal end moves in a circle, while the proximal end remains relatively stationary.

Types of Muscles

• Muscles in Opposing Pairs: Work in opposing pairs (e.g., biceps and triceps).
• Prime Mover: Muscle primarily responsible for a movement.
• Synergist: Muscles that assist the prime mover.
• Antagonist: Muscles that oppose or reverse the prime mover.

Naming of Skeletal Muscles

• Muscles are named based on various factors:
  • Direction of muscle fibers
  • Relative size of the muscle
  • Location of the muscle
  • Number of origins
  • Location of origins or insertion
  • Shape of the muscle
  • Action of the muscle

Effects of Aging on Muscles

• Muscle Atrophy: Unused muscles are replaced by connective tissue and fat.
• Mitochondrial Degeneration: Degeneration due to oxygen exposure and free radicals.
• System Changes: Changes in nervous and endocrine systems affect muscle structure and function.
• Muscle Weakness: Muscles weaken over time, but exercise can stimulate muscle building.

Disorders of the Muscular System

• Muscular Dystrophy: Inherited disorder, muscle enlarge due to increased fat and connective tissue. Muscle fibers degenerate and atrophy.
  • Duchenne Muscular Dystrophy (DMD): Inability to produce a protein to maintain the sarcolemma.
• Myasthenia Gravis: Progressive muscle weakness due to a shortage of acetylcholine receptors.

Sprain vs. Strain

• Strain: Overstretching of a muscle near a joint.
• Sprain: Twisting of a joint, leading to damage to ligaments, tendons, blood vessels, and nerves.

Myalgia and Tendinitis

• Myalgia: Inflammation of muscle tissue.
• Tendinitis: Inflammation of tendon due to strain from repeated activity.

Explore the intricacies of muscle contraction and relaxation in this comprehensive lecture. Understand the mechanisms behind skeletal muscle fibers, the role of the neuromuscular junction, and the factors affecting muscle force and energy supply. Ideal for students studying anatomy or physiology.