Structure of Skeletal Muscles

Skeletal Muscle (bigger) -> Myofibrils -> Sarcomeres (smaller)

Sarcomeres

  • Actin : I band, Thin Filaments
  • Myosin : A band, Thick Filaments
  • H zone : Contains only Myosin
  • M line : Centre of the sarcomere, Myosin only
  • Z discs : Boundaries of a sarcomer
    • Sarcomere

    Muscle Contraction

    Key Terms: Sliding Filament Theory, Power Stroke, Cross-Bridge

    Muscle Contraction Steps

    1. 1. Stimulated by nerve impulses, releases a neurotransmitter called acetylcholine.
    2. 2. Calcium ions release from sarcoplasmic reticulum to sarcoplasm.
    3. 3. Troponin bounded by calcium ions.
    4. 4. Troponin moves Tropomyosin away from blocking myosin binding sites.
    5. 5. Binding sites exposed, allowing myosin to bind to actin.
    Muscle Contraction
    1. 6. ATP is required, it binds to myosin head.
    2. 7. This causes myosin to detach from its binding site on actin.
    3. 8. ATP hydrolysed into ADP and Pi.
    4. 9. Myosin head changes position, moving toward the next binding site on actin.
    5. 10. Myosin attaches to the new binding site, forming a CROSS-BRIDGE.
    6. 11. Myosin head pulls actin filament toward the center by a process called POWER STROKE.
    7. 12. The Cycle repeated when ATP binds to myosin head, allowing it to detach from actin.

    Role of Titin in muscle relaxation

  • Large Protein
  • Found inside the sarcomeres, connecting M-line and Z-discs.
  • Support and stabilize to the muscle fibres.
  • Act as a molecular spring, prevent damage from excessive strain.

    • Antagonistic Muscles

  • Work in opposite directions or have opposing effects.
  • ex: Biceps and Triceps
  • ex: Intercostal Muscle and Extercostal Muscle

    • Two Types of Skeletal Systems in Animals

  • Exoskeletons: external skeleton that protects the outer surface.
  • Endoskeletons: internal skeleton composed of hard, mineralized tissue.

    • Movement at a synovial joint

  • Synovial Joint: enclosed in a joint capsule, where bones are separated by a fluid-filled cavity, allowing free movement.
  • Synovial Fluid: Lubricant to reduce friction between bones.
  • Articular Cartilage: Cushsion to absorb shock.
  • Ligaments: Connective tissue, provide stability to the joint.
  • Tendon: Connect muscles to bones.
  • Ligaments, tendons and cartilage all contain collagen (protein).

    • Reasons for locomotion

  • Foraging: find food.
  • Escaping: leave danger.
  • Migration: movement to a new habitat.
  • Searching for a mate: attrack opposite sex.

    • Adaptations for swimming in marine mammals

  • Larger lungs relative to their body size: take in more oxygen
  • Higher Volmes of blood: carry more oxygen
  • Streamlined Bodies: minimize drag, allow efficient movement
  • Thick Layer of Blubber: insulate cold water, provide buoyancy