As previously described, upper motor neurons are neurons in the brain that influence the control of skeletal muscle by lower motor neurons (alpha and gamma motoneurons). Neurons in the pre-central gyrus of the cerebral cortex contribute axons that cross to the contralateral sides in the pyramids of the medulla oblongata; these tracts are thus called pyramidal tracts (chapter 8). The pyramidal tracts include the lateral and ventral corticospinal tracts. Neurons in other areas of the brain produce the extrapyramidal tracts. The major extrapyramidal tract is the reticulospinal tract, which originates in the reticular formation of the medulla oblon-gata and pons. Brain areas that influence the activity of extrapyramidal tracts are believed to produce the inhibition of lower motor neurons described in the preceding section.
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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.