Muscular System

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Chapter 11

• Muscular System

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Outline

• Types and Functions of Muscles
• Smooth
• Cardiac
• Skeletal
• Muscle Innervation
• Whole Muscle Contraction
• Oxygen Deficit
• Athletics and Muscle Contraction
• Slow and Fast Twitch Fibers
• Muscle Disorders

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Types and Functions of Muscles

• Smooth muscle is located in the walls of hollow
  internal organs and contracts involuntarily.
• Cardiac muscle forms the heart wall and contracts
  involuntarily.
• Skeletal muscle runs the entire length of the
  muscle and contracts voluntarily.

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Functions of Skeletal Muscles

• Body support.
• Bone movement.
• Maintenance of body temperature.
• Assist movement in cardiovascular and lymphatic
  vessels.
• Protect internal organs.
• Stabilize joints.

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Skeletal Muscles of the Body

• A whole muscle contains bundles of skeletal
  muscle fibers, fascicles.
• Muscles are covered with fascia that becomes
  tendons.
• Muscles originate on the stationary bone, and
  insert on the bone that moves.
• Cooperating muscle pairs have prime movers and
  synergists.
• Antagonistic pairs work opposite one another to
  move in opposite directions.

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Skeletal Muscles
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Names and Actions of Skeletal Muscles

• Skeletal muscles are named based on
  characteristics.
• Size gluteus maximus
• Shape deltoid (?, delta, triangular)
• Direction of muscle fibers rectus abdominus
  (straight)
• Attachments sternocleodomastoid
• Number of attachments biceps brachii
• Action extensor digitorum

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Skeletal Muscle Fiber Contraction

• Overview of Muscular Contraction.
• Nerve impulses originate in the brain, travel
  down motor neurons, and stimulate muscle fibers
  at neuromuscular junctions.
• When muscle fibers are stimulated to contract,
  myofilaments slide past one another, causing
  sarcomeres to shorten.

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• Muscle Innervation.
• Stimulated to contract by motor nerve fibers.
• Signaled when nerve impulses bring about release
  of neurotransmitter molecules at a neuromuscular
  junction.

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• Sarcolemma- plasma membrane, forms T tubules
• Sarcoplasm-cytoplasm of muscle, contains
  organelles and myofibrils
• T Tubule- extension of sarcolemma, signal calcium
  release into sarcoplasmic reticulum
• Sarcoplsmic reticulum- smooth ER, stores calcium
• Myofibril- bundle of contractile microfilaments
• Myofilament- actin and myosin filaments,
  striations and contractions
• Sarcomere- contractile unit of a myofibril

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Muscle Innervation and 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.

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Whole Muscle Contraction

• 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.
• Myograms

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Whole Muscle Contraction

• 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.

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Energy for Muscle Contraction

• ATP produced previous to strenuous exercise lasts
  a few seconds, and then muscles acquire new ATP
  in three ways.
• Creatine phosphate breakdown. (anaerobic)
• Fermentation. (anaerobic)
• Cellular respiration. (aerobic)

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Oxygen Deficit

• When a muscle uses the anaerobic means of
  supplying energy, it incurs an oxygen deficit.
• Repaying an oxygen deficit requires replenishing
  creatine phosphate supplies and disposing of
  lactic acid.

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Athletics and Muscle Contraction

• Muscles that are not used, or are used in only
  weak contractions can atrophy.
• Can cause muscle fibers to progressively shorten,
  leaving body parts contracted in contorted
  positions.
• Hypertrophy occurs if the muscle contracts to at
  least 75 of its maximum tension.

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Athletics and Muscle Contraction

• Slow-twitch fibers produce most of their energy
  aerobically and tire only when their fuel supply
  is gone.
• Fast-twitch fibers tend to be anaerobic and seem
  to be designed for strength as their motor units
  contain many fibers.
• Can develop greater, and more rapid, maximum
  tension than slow-twitch fibers.

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Muscle Disorders

• Spasms are sudden, involuntary muscular
  contractions most often accompanied by pain.
• Multiple spasms of skeletal muscles are called a
  seizure or convulsion.
• A strain is an overstretching of a muscle near a
  joint, while a sprain is a twisting of a joint
  leading to swelling and injury.
• Myalgia refers to inflammation of muscle tissue.

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Muscular Disorders

• Muscular dystrophy is a broad term applied to a
  group of disorders characterized by progressive
  muscle degeneration and weakening.
• Myasthenia gravis is an autoimmune disease
  characterized by weakness that especially affects
  the muscles of the eyelids, face, neck, and
  extremities.

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Homeostasis

• Cardiac muscle contraction accounts for the
  heartbeat, delivering blood to the tissues.
• Smooth muscle contraction accounts for
  peristalsis and urination.
• Skeletal muscle contraction returns blood to the
  heart and moves bones, allowing for body movement.