The Muscular System There are ~650 muscles in the human body.

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The Muscular SystemThere are 650 muscles in the
human body.
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Terminology

• Myology scientific study of muscles
• Striated striped
• Muscle tone firmness of a muscle that results
  from motor units being activated
• Atrophy deterioration of muscle fibers
• Hypertrophy bulking up of muscle fibers
• Oxygen debt the amount of oxygen you owe your
  body after exercise

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3 types of muscle

• Smooth
• Skeletal
• Cardiac

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Muscle Classification

• Striated vs. Nonstriated
• Voluntary vs. Involuntary
• Remember this??

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5 Muscle Functions

• Produce body movement
• Stabilize body positions
• Regulate organ volume
• Movement of substances within body
• Producing heat
• Ever gone to bed hot at night and woke up cold?

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Muscle Characteristics

• Excitability responsiveness to nerve impulses
• Contractility ability to contract
• Extensibility ability to stretch and not tear
• Elasticity ability to return to original shape
  after contraction

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Smooth Muscle

• Nonstriated
• Involuntary
• Found in internal organs and blood vessels
• Spindle-shaped cells with one nucleus

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Cardiac Muscle

• Striated with intercalated discs
• Involuntary
• Found in heart only
• Branched cells with one nucleus

There are LOTS of mitochondria in cardiac muscle.
The average heart beats about 75 times per minute.
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Skeletal Muscle

• Striated
• Voluntary
• Cylindrical cells with many nuclei per cell
• Attached to bones by tendons
• Largest Achilles tendon in heel
• At least 2 attachment sites of each muscle
• Origin stationary site of attachment
• Insertion movable site of attachment

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Histology of muscle tissue

• Muscle cells muscle fibers
• Fibers are held together by fascia
• Superficial fascia under skin/on top of muscle
• Deep fascia holds individual fibers together
• Think about eating roast beef.
• Think about cleaning a chicken breast.
• Bundles of fibers are called fascicles

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More histology

• Actin (thin protein) Myosin (thick protein) ?
  filaments ? myofibril ? muscle fiber ? fascicle
• Where filaments overlap is called the sarcomere
  the basic functioning unit of muscle
• Think of a large rope that can be unraveled.
• Sliding Filament Theory/Mechanism is the
  description of how muscles move when actin and
  myosin move over and past one another at the
  sarcomere, thus allowing the filaments to shorten
  causing contraction

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A look at muscle histology
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Another look
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Muscle contraction

• Occurs after a motor neuron stimulates it
• One motor neuron plus all the muscle fibers it
  stimulates 1 motor unit
• Remember the pathway from chapter 1??

Control Center
Sensory neuron
Motor neuron
Receptor
Effector
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Movement types

• Small precise movements ie. writing, coloring
  (fine motor skills) use many motor units with few
  numbers of muscle fibers
• Large, powerful movements ie. Jumping, lifting
  use few motor units with large numbers of muscle
  fibers.

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Muscles and the Nervous System

• Neuromuscular Junction (NMJ) point where a motor
  neuron excites a muscle fiber
• Neurotransmitters chemicals found within the NMJ
  that trigger contraction
• Acetylcholine is one of the most important
• Certain toxins and drugs can affect NMJ events

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Muscle Contraction

• Requires
• High Calcium
• High ATP
• Aerobic cellular respiration
• Glycolysis
• Creatine phosphate within muscles
• Acetylcholine
• Muscle relaxation requires the opposite.
• Muscles may become fatigued if the above
  mentioned substances are not maintained at proper
  levels.

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Muscle movements

• Nerve impulses must reach a threshold in order
  for there to be a response (movement).
• Twitch brief contraction in response to 1 action
  potential nerve impulse
• Tetanus sustained contraction in response to
  several action potentials
• Can be read with a myogram graphical reading of
  muscle contractions

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Myogram
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Tetanus
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Motor unit recruitment

• Allows for smooth rather than jerky movement.
• Allows for some units to be contracting while
  others are relaxing
• Prevents muscle fatigue

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Types of contractions/exercises

• Isotonic
• Causes movement due to muscle shortening
• Walking, swimming, biking, running
• isometric
• Causes no movement due to muscle shortening
• Wall sits, bar hangs

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Muscle duties

• Movement occurs when several muscles act together
• Most muscles are arranged in opposing pairs
• Ex flexor extensor abductor adductor
• Prime mover muscle causing main movement
• Synergist complements prime mover
• Antagonist opposes prime mover

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Example of muscle duties

• To flex the forearm
• Prime mover biceps brachii
• Synergist brachialis brachioradialis
• Antagonist triceps brachii

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Other helpful hints

• Muscles are named based on
• Origin insertion points
• Ex sternocleidomastoid
• Shape
• Ex trapezius, deltoid
• Number of origins
• Ex bicep, tricep, quadricep
• Size length
• Ex longus, brevis, maximus, minimus
• Direction of fibers
• Ex rectus, oblique, transverse