Physiology of Muscle

Posted by e-Medical PPT Wednesday, July 13, 2011
Characteristics of muscle:    * excitability - responds to stimuli (e.g., nervous impulses)
    * contractility - able to shorten in length
    * extensibility - stretches when pulled
    * elasticity - tends to return to original shape & length after contraction or extension

Functions of muscle:
    * motion
    * maintenance of posture
    * heat production

Types of muscle:
    * skeletal:
          o attached to bones & moves skeleton
          o also called striated muscle (because of its appearance under the microscope, as shown in the photo to the left)
          o voluntary muscle
    *   smooth (photo on the right)
          o involuntary muscle
          o muscle of the viscera (e.g., in walls of blood vessels, intestine, & other 'hollow' structures and organs in the body)
    * cardiac:
          o muscle of the heart
          o involuntary

Muscle Contraction Summary
  • Nerve impulse reaches myoneural junction
  • Acetylcholine is released from motor neuron
  • Ach binds with receptors in the muscle membrane to allow sodium to enter
  • Sodium influx will generate an action potential in the sarcolemma
  • Action potential travels down T tubule
  • Sarcoplamic reticulum releases calcium
  • Calcium binds with troponin to move the troponin, tropomyosin complex
  • Binding sites in the actin filament are exposed
  • Myosin head attach to binding sites and create a power stroke
  • ATP detaches myosin heads and energizes them for another contaction
  • When action potentials cease the muscle stop contracting

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