Harrison's Internal Medicine Chapter 23. Weakness and Paralysis Weakness and Paralysis: Introduction Normal motor function involves integrated muscle activity that is modulated by the activity of the cerebral cortex, basal ganglia, cerebellum, and spinal cord. Motor system dysfunction leads to weakness or paralysis, which is discussed in this chapter, or to ataxia (Chap. 368) or abnormal movements (Chap. 367). The mode of onset, distribution, and accompaniments of weakness help to suggest its cause. Weakness is a reduction in the power that can be exerted by one or more muscles. Increased fatigability or limitation in function due to pain or articular. | Chapter 023. Weakness and Paralysis Part 1 Harrison s Internal Medicine Chapter 23. Weakness and Paralysis Weakness and Paralysis Introduction Normal motor function involves integrated muscle activity that is modulated by the activity of the cerebral cortex basal ganglia cerebellum and spinal cord. Motor system dysfunction leads to weakness or paralysis which is discussed in this chapter or to ataxia Chap. 368 or abnormal movements Chap. 367 . The mode of onset distribution and accompaniments of weakness help to suggest its cause. Weakness is a reduction in the power that can be exerted by one or more muscles. Increased fatigability or limitation in function due to pain or articular stiffness is often confused with weakness by patients. Increased fatigability is the inability to sustain the performance of an activity that should be normal for a person of the same age gender and size. Increased time is sometimes required for full power to be exerted and this bradykinesia may be misinterpreted as weakness. Severe proprioceptive sensory loss may also lead to complaints of weakness because adequate feedback information about the direction and power of movements is lacking. Finally apraxia a disorder of planning and initiating a skilled or learned movement unrelated to a significant motor or sensory deficit Chap. 27 is sometimes mistaken for weakness by inexperienced medical staff. Paralysis indicates weakness that is so severe that the muscle cannot be contracted at all whereas paresis refers to weakness that is mild or moderate. The prefix hemi- refers to one half of the body para- to both legs and quadri- to all four limbs. The suffix -plegia signifies severe weakness or paralysis. Weakness or paralysis is typically accompanied by other neurologic abnormalities that help to indicate the site of the responsible lesion. These include changes in tone muscle bulk muscle stretch reflexes and cutaneous reflexes Table 23-1 . Table 23-1 Signs that Distinguish Origin of .
