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Muscle arrangement

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					     Muscle fiber arrangement
•   Skeletal Muscle fibers arrange in bundles-
    called fascicles.
•   Within a fascicle, all muscle fibers are parallel
    to each other.
•   Fascicular arrangement affects a muscle power
    & range of motion
•   Longer fibers: have greater range of motion &
    cover greater distance
•   Short muscles with higher cross-sectional
    area have more force
               Fascicle arrangement
• There are 5 patterns of fascicle organization. (Arrangement of fibers
  relative to axis of force generation)
• Parallel muscles. The fascicles run parallel to the long axis of the
  muscle.
    e.g. Stylohyoid muscle
• Fusiform or spindle-shaped:muscle tapers toward tendons
  e.g. Digastric muscle

• Triangular (convergent) muscles. The fascicles converge on a
    common tendon. appear fan shaped like pectoralis major.

•   Circular muscles. The fascicles are concentrically arranged around
    an opening.
    These muscles are also called sphincters. When they contract the
    diameter of the opening they surround decreases. Orbicularis oculi
    muscle, & Orbicularis oris of the mouth is an example of a circular
    muscle
      Pennate Fiber architecture

• Pennate means feather which the orientation of these
  fibers resemble.
• pennate fiber arrangement: at an angle to
  the longitudinal axis of the muscle,
   – unipennate: extnesor digitorum longous
   – bipennate: rectus femoris
   – multipennate: deltoid muscle
  Coordination within Muscle group

• Prime mover or agonist: contract to
  initiate an action.
• Antagonist: act against the effect of the
  prime mover
• Synergist: a muscle acts as a synergist when
  it prevents the unwanted action of another
  muscle.
• Fixators: stabilize the origin of the prime mover
Compartment & muscle groups
• In the limbs, a compartment is a group of
  skeletal muscles, along with their blood
  vessels & nerves, that have a common
  function.
• Anterior or flexor compartment
• Posterior or extensor compartment
          NERVE SUPPLY OF MUSCLES

• Muscles have both motor and sensory nerve endings.

• The main motor endings are large myelinated nerves
  that connect to the muscle fibers at motor end plates
  (MEP)
• Motor units – A motor neuron & muscle fibers it
  stimulate is called a motor unit.
• Sensory nerves of muscles
• End in receptors within the muscle or its tendon and
  provide feedback about muscle tension and joint position
  (proprioception). Some participate in reflexes.

• Neuromuscular junction: synapse between muscle &
  motor neuron
             Muscle Tone
• Muscle tone is the continuous and passive
  partial contraction of the muscles. It helps
  maintain posture & keep muscle firm.
• Hypotonia: decreased muscle tone
  (flaccid muscles)
• Hypertonia: increased muscle tone,
  expressed in 2 ways:
1. spasticity- increased tendon reflexes.
 2. rigidity- tendon reflexes are not affected
     Aging & Skeletal Muscle
• Slow progressive loss of skeletal muscle
  mass – at about 30 years of age
• Cause: decline activity
• Slow muscle reflexes
• Aerobic activities

				
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posted:8/27/2012
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