BHow the muscle spindle works see Figure

- Muscle spindle reflexes oppose (correct for) increases in muscle length (stretch).

(1) Sensory information about muscle length is received by group la (velocity) and group II (static) afferent fibers.

(2) When a muscle is stretched (lengthened), the muscle spindle is also stretched, stimulating group la and group II afferent fibers.

(3) Stimulation of group la afferents stimulates a-motoneurons in the spinal cord. This stimulation in turn causes contraction and shortening of the muscle. Thus, the original stretch is opposed and muscle length is maintained.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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