• BIO 461 Principles of Physiology
  • Module 1.0. Homeostasis, Membranes, Electrophysiology and ANS
  • Module 2.0. Skeletal Muscle and Special Senses
  • Module 3.0. Cardiovascular System
  • Module 4.0. Urinary and Respiratory Systems
  • Module 5.0. Digestive, Endocrine and Reproductive Systems
  • Appendix A. Gender
  • Appendix B. The Placebo Effect
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  • Translations
  • 2.3.1

    Motor Units

    image048.jpg
    Motor Neurons
    Image drawn by BYU-Idaho student Nate Shoemaker Spring 2017

    2.3.1 - Motor Units

    The motor neurons that innervate skeletal muscle fibers are called alpha motor neurons. As the alpha motor neuron enters a muscle, it divides into several branches, each innervating a muscle fiber (note this in the image above). One alpha motor neuron, along with all of the muscle fibers it innervates, is a motor unit. The size of the motor unit correlates with the function of the muscle. In muscles involved with fine, coordinated control, the motor units are very small with 3–5 muscle fibers per motor neuron. Muscles that control eye movement and muscles in our hands have relatively small motor units. On the other hand, in muscles involved with more powerful but less coordinated actions, like the muscles of the legs and back, the motor units are large with thousands of muscle fibers per motor neuron.

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