RT Book, Section A1 Aminoff, Michael J. A2 Jameson, J. Larry A2 Fauci, Anthony S. A2 Kasper, Dennis L. A2 Hauser, Stephen L. A2 Longo, Dan L. A2 Loscalzo, Joseph SR Print(0) ID 1155941987 T1 Neurologic Causes of Weakness and Paralysis T2 Harrison's Principles of Internal Medicine, 20e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259644016 LK accessmedicine.mhmedical.com/content.aspx?aid=1155941987 RD 2024/03/28 AB Normal motor function involves integrated muscle activity that is modulated by the activity of the cerebral cortex, basal ganglia, cerebellum, red nucleus, brainstem reticular formation, lateral vestibular nucleus, and spinal cord. Motor system dysfunction leads to weakness or paralysis, discussed in this chapter, or to ataxia (Chap. 431) or abnormal movements (Chap. 428). Weakness is a reduction in the power that can be exerted by one or more muscles. It must be distinguished from increased fatigability (i.e., the inability to sustain the performance of an activity that should be normal for a person of the same age, sex, and size), limitation in function due to pain or articular stiffness, or impaired motor activity because severe proprioceptive sensory loss prevents adequate feedback information about the direction and power of movements. It is also distinct from bradykinesia (in which increased time is required for full power to be exerted) and apraxia, a disorder of planning and initiating a skilled or learned movement unrelated to a significant motor or sensory deficit (Chap. 26).