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Muscular System

Muscular System. Function Locomotion Posture Protection Heat production. Muscle Classification. Skeletal Muscle Attached to skeleton Striated Muscle fiber = Muscle cell Multinucleate Myofibrils are striated cylinders within myofiber. Skeletal Muscle.

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Muscular System

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  1. Muscular System • Function • Locomotion • Posture • Protection • Heat production

  2. Muscle Classification • Skeletal Muscle • Attached to skeleton • Striated • Muscle fiber = Muscle cell • Multinucleate • Myofibrils are striated cylinders within myofiber

  3. Skeletal Muscle • Myofilaments are proteins within the myofibrils that result in contraction • Actin – thin & has a receptor site for myosin • Myosin – thick & has a receptor site for actin and ATP • Contraction – Myosin heads attach to actin and with ATP perform a Power Stroke

  4. Skeletal Muscle • Sarcomere • The distance from Z line to Z line • The basic unit of contraction • Sarcomere gets smaller as Power Stroke occurs

  5. Key Points • Why is the sarcomere the functional unit of contraction? • Why does the power stroke result in contraction? • What would happen to contraction if you ran out of ATP?

  6. Motor Neurons • Skeletal muscle cannot contract without stimulation from a motor neuron • Motor Unit = The motor neuron plus the myofiber(s) it innervates

  7. Key Points • Why would a spinal cord injury result in paralysis?

  8. Somatic Muscles • All of the body’s skeletal muscles except the branchiomeric muscles • Voluntary • Body wall & Appendage muscles • Trunk and Tail • Hypobranchial • Tongue • Extrinsic Eyeball

  9. Somatic Muscles • Myotome derivatives primarily • Some from hypomere

  10. Key Points • What is a myotome?

  11. Somatic Muscles • Orient the body in the environment

  12. Somatic Muscles • Red Fibers • More blood supply for aerobic metabolism • Myoglobin for oxygen storage • Fatigue resistant • Fish for cruising long distances, tetrapods for posture

  13. Somatic Muscles • White fibers • Less blood supply; geared for anaerobic metabolism • Fatiguable • Fish for spurts of swimming • Tetrapods for sprints

  14. Key Points • Why is the breast meat of the goose dark, but the breast meat of the chicken is white?

  15. Cardiac Muscle • Striated with intercalated disks • Involuntary • Lateral plate mesoderm (hypomere) in origin

  16. Smooth Muscle • Involuntary • Lateral plate mesoderm in origin • Regulates internal environment • Innervated by Autonomic Nervous System • Found in the wall of tubes and hollow organs • Intrinsic Eye muscles • Erectors of feathers and hairs

  17. Key Points • Besides those mentioned, give a specific example of where might you find smooth muscle?

  18. Gross features of skeletal muscle • Origin, insertion • Tendon • Aponeurosis • Fascia

  19. Muscle shapes

  20. Skeletal Muscle Actions • Flex/Extend • Adduct/Abduct • Levator/Depressor • Protract/Retract • Constrictor/Dilator • Rotator

  21. Skeletal Muscle Actions • Supinator/Pronator • Tensor (taut)

  22. Skeletal Muscle Actions • Agonist – primary mover • Antagonist – opposes primary mover • Synergist – helps primary mover

  23. Development & Phylogeny • Position • Embryology • Nerve supply

  24. Development • Dorsal Mesoderm – Epimere – Somite • Myotome • Sclerotome & Dermatome • Lateral plate Mesoderm – Hypomere • Somatic – body wall muscles • Splanchnic – smooth muscle of viscera

  25. AXIAL MUSCLES • Trunk • Tail • Hypobranchial • Tongue • Extrinsic Eye

  26. Axial Muscles • Metamerism as in myomeres

  27. Axial Muscles • Agnathans • Simple • Segments (myomeres) • Myotome derivatives

  28. Axial Muscles – Jawed Fish • Horizontal or Lateral Septum • Epaxial Muscles • From myotomes in embryology • Innervated from dorsal rami of spinal nerves • Extend spine & some lateral bending • Extrinsic eye muscles (innervated by cranial nerves) • Epibranchial muscles

  29. Axial Muscles – Jawed Fish • Hypaxial Muscles • From Myotomes • Innervated by ventral rami of spinal nerves • Ventroflex and lateral bending

  30. Hypaxial Muscles – Jawed fish • Hypobranchial muscles • Located on floor of pharynx, pectoral girdle to jaw • Are hypaxial muscles that migrated forward • Function in respiration & feeding • E.g. Coracomandibularis, Coracohyoid

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