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Chapter 12

Who is this? Chelsey Thomas. What is her problem? Moebius syndrome? A rare disorder which causes paralysis of facial muscles!!!. Chapter 12. Muscular System. Outline. Overview of Muscular System Types and Functions of Muscles Skeletal Muscle Fiber Contraction

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Chapter 12

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  1. Who is this? • Chelsey Thomas. • What is her problem? • Moebius syndrome? • A rare disorder which causes paralysis of facial muscles!!! Chapter 12 Muscular System

  2. Outline • Overview of Muscular System • Types and Functions of Muscles • Skeletal Muscle Fiber Contraction • Whole Muscle Contraction • Muscles Have Motor Units • Energy for Muscle Contraction • Fast-Twitch and Slow-Twitch Fibers • Muscle Disorders • Homeostasis

  3. Types and Functions of Muscles • Smooth muscle is located in the walls of hollow internal organs and contracts involuntarily. (non-striated / involuntary, visceral muscle) • Cardiac muscle forms the heart wall and contracts involuntarily. (striated, involuntary) • Skeletal muscle runs the entire length of the muscle and contracts voluntarily. (striated, voluntary)

  4. Types of Muscle

  5. Functions of Skeletal Muscles • Support body. • Movement of bones. • Maintenance of constant body temperature. • Assist movement in cardiovascular and lymphatic vessels. • Protect internal organs. • Stabilize joints.

  6. SKELETAL MUSCLES Macroscopic View

  7. Skeletal Muscles of the Body • A whole muscle contains bundles of skeletal muscle fibers (= muscle cells), fascicles. • Muscles are covered with fascia (dense connective tissue) that becomes tendons. • Muscles originate on the stationary bone (origin), and insert on the bone that moves (insertion). • Cooperating muscle pairs have prime movers, synergists, and antagonists. • Muscles usually work in antagonistic pairs which work opposite one another to move in opposite directions.

  8. Skeletal Muscles of the Body • Muscles only contract, never push. • Muscle spindles are modified muscle fibers that have a sensory nerve fiber wrapped around the middle of the muscle’s length so as to inform the CNS as to the state of that muscle for coordination with other muscles and for posture and muscle tone.

  9. Names and Actions of Skeletal Muscles • Names based on characteristics. • Size (ie. gluteus maximus). • Also: vastus (huge), longus (long), brevis (short). • Shape (ie. deltoid). • Also: trapezius (trapezoid), latissimus (wide), terres (round). • Location (ie. external obliques) • Also: pectoralis (chest), gluteus (buttock), brachii (arm), sub (beneath).

  10. Names and Actions of Skeletal Muscles • Direction of muscle fibers (ie. rectus, meaning straight, abdominis). • Also: transverse (across), oblique (diagonal). • Attachment (ie. sternocleidomastoid). • Also: brachioradialis (arm, radius). • Number of attachments (ie. Biceps brachii or “two origins, arm”) • Also: quadriceps femoris (“four origins, located on femur”).

  11. Names and Actions of Skeletal Muscles • Action (ie. extensor digitorum). • Also: flexor (to flex or bend), masseter (to chew), levator (to lift).

  12. Science Focus Rigor Mortis

  13. SKELETAL MUSCLES Microscopic View (Skeletal Muscle Fiber Contraction)

  14. Skeletal Muscle Fiber Contraction • “Sliding Filament Model” • When muscle fibers are stimulated to contract, myofilaments (actin – anchored on Z line, myosin – in the middle) slide past one another. • This causes sarcomeres (muscle units) to shorten and the whole muscle fiber shortens. • Thus, when you see the prefixes myo- or sarco-, you will know these refer to muscles.

  15. Skeletal Muscle Fiber Contraction • Myosin filament heads break down ATP and attach to an actin filament, forming cross-bridges that pull the actin filament to the center of the sarcomere. • Contraction continues until nerve impulses cease.

  16. “Sliding Filament Model” Video Clips • Concept 29 - Levels of Muscle Structure • Concept 30 - Sliding Filament Model • Concept 31 - Regulation of Muscle Contraction

  17. Control of Muscle Fiber Contraction • Nerve impulses originate in the brain, travel down motor neurons, and stimulate muscle fibers at neuromuscular junctions and muscle fibers are innervated. . . . . • Stimulated to contract by motor nerve fibers. • Signaled when nerve impulses bring about release of neurotransmitter molecules at a neuromuscular junction.

  18. Whole Muscle Contraction • Method of study: when a muscle (frog’s calf muscle) is attached to a physiograph (machine), a myogram (a recording) will result when muscle is stimulated to contract. • Characteristics of muscle contraction: a muscle fiber, in contrast to a whole muscle, will behave in an all-or-none manner when a threshold stimulus is applied. • The force of contraction of a whole muscle depends upon the number of fibers contracting.

  19. Whole Muscle Contraction (In the Lab) • Muscle Twitch - Single muscle contraction. • Divided into three stages. • Stimulation. • Contraction. • Relaxation. • If a muscle is given a rapid series of threshold stimuli, muscle contraction summates in a sustained contraction, tetanus. . . . • which continues until the muscle fatigues due to depletion of energy reserves.

  20. Physiology of Whole Muscle Contraction

  21. Whole Muscle Contraction (In the Body) • A motor neuron, together with all of the muscle fibers that it innervates, is a motor unit. • As the intensity of nervous stimulation increases, more motor units are activated (recruitment) resulting in stronger and stronger contractions. • Also important are the number of muscle fibers within a motor unit. . . . for example: • innervation ratio of 1 motor neuron / 23 muscle fibers (eye muscles). . . . • 1 motor neuron / 1,000 muscle fibers (calf muscle).

  22. The Effect of Exercise. • A regular exercise program will bring about 1. Increased endurance 2. Increased strength of muscles. • Muscle enlarges, not due to increase in number of muscle fibers, but increased amounts of actin and myosin myofibrils inside each muscle fiber making them bigger and stronger. • “Use it or lose it !” • Benefits include: lower risk of heart attack, increased capacity of heart and lungs, decreased body fat and cholesterol levels.

  23. HEALTH FOCUS Exercise, Exercise, Exercise.

  24. Energy for Muscle Contraction • ATP produced previous to strenuous exercise lasts a few seconds. • Then muscles acquire new ATP in three ways. • Creatine phosphate (phosphocreatine) breakdown. (anaerobic) • Fermentation. (anaerobic) • Cellular respiration. (aerobic)

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