Muscular System

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Muscular System
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3 types of muscle fibers

• Skeletal
• Cardiac
• smooth

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Fascia

• Dense connective tissue that separates an
  individual muscle
• Surrounds each muscle
• May extend to form a tendon

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Fascicles bundles of skeletal muscle
fibersSkeletal muscle fiber

• Single cells that contracts in response to
  stimulation, and then relaxes when stimulation
  ends
• Thin, long cylinder with ends

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• Myofibrils threadlike substances that lie
  parallel to each other
• 2 kinds
• Actin thin
• Myosin thick
• these lying together form striations (bands of
  skeletal muscle fibers)
• Together these striations form a pattern called a
  sarcomere

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-goes from one z-line to another z-line

1. I-bands (light) thin actin attached to z-lines
2. A-bands (dark) thick myosin overlapping actin

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Motor neuron a nerve cell that connects to each
skeletal fiber

• Muscle fiber contracts only when motor neuron
  stimulates it
• This is why a person can be parlyzed, but there
  is nothing wrong with their actual muscles!!
• Neuromuscular junction the connection between
  the motor neuron and the muscle fiber
• Neurotransmitters chemicals that help stimulate
  muscle fibers to contract

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• Acetylcholine the neurotransmitter that motor
  neurons use to control skeletal muscle
  contractions
• Motor unit a muscle neuron the muscle fibers
  that it controls

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What happens during a muscle impulse?

• A charge passes in all directions over the
  surface of the muscle fiber
• This causes a contraction

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Hemoglobin vs. Myoglobin

• Hemoglobin red pigment responsible for the
  color of blood
• Myoglobin the reddish-brown pigment responsible
  for the color of skeletal muscle

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• Oxygen debt the amount of oxygen that must be
  repaid to the liver, so that the lactic acid can
  be converted into glucose
• Muscle fatigue the inability of a muscle to
  contract
• -usually due to muscle being exercise
  strenuously for a long period of time
• Heat production muscles are a major heat source
  for the human body over ½ of the energy released
  from cellular respiration becomes heat

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• Threshold stimulus the minimal strength
  required to cause a contraction

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• Twitch a single contraction that lasts only a
  fraction of a second
• -one single muscle fiber
• -can be either slow-twitch of fast-twitch
• Tetanic contraction a forceful, sustained
  contraction that lacks even partial relaxation
• Eg muscle cramp/ charlie horse
• Muscle tone the amount of sustained contraction
  that is occurring in its fibers

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• Origin the less movable end of the muscle (near
  to the head of the muscle)
• Insertion the movable end of the muscle

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• Prime mover the muscle that provides most of
  the movement
• aka agonist
• Synergists muscle that contract and assist the
  prime mover
• Antagonists the muscle that resist a prime
  movers action
• -causes movement in opposite direction

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3 Types of Muscle cells

• Skeletal
• Found in muscles attached to bones
• Controlled by conscious effort
• Voluntary muscle tissue
• Have alternating light/dark markings called
  striations
• Each fiber has many nuclei just below cell
  membrane
• Muscles with these types of fibers are
  responsible for movement of head, trunk, limbs,
  talking, singing, breathing, etc.

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• Cardiac
• Located only in heart
• Striated cells join end to end
• Intercalated disks between cells
• Each has single nucleus
• Fibers are branched and interconnected into
  networks
• Involuntary muscle
• Responsible for pumping blood through chambers
  and vessels

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• Smooth
• Lacks striations
• Each cell has single, centralized nucleus
• Usually cannot be stimulated by conscious effort
  (aka involuntary)
• Found in walls of hollow organs (stomach,
  intestines, bladder, uterus, blood vessels)
• Responsible for moving food through digestive
  tube, constricting blood vessels, and emptying
  the urinary bladder