Chapter 15: Disorders of Motor Function

Muscular dystrophy, particularly Duchenne muscular dystrophy, represents a group of inherited myopathies characterized by progressive muscle fiber death and replacement with fibrous and fatty tissue, leading to functional decline. Myasthenia gravis exemplifies an autoimmune condition targeting the neuromuscular junction, where antibodies against acetylcholine receptors reduce the capacity for neuromuscular transmission and muscle activation. Upper motor neuron disorders include amyotrophic lateral sclerosis, a devastating condition affecting both upper and lower motor neurons simultaneously, resulting in progressive paralysis and neuronal death. The chapter addresses demyelinating diseases of the central nervous system, with multiple sclerosis serving as a primary example. Multiple sclerosis involves immune-mediated destruction of myelin sheaths and formation of inflammatory plaques, typically affecting young adults and progressing through distinct clinical patterns including relapsing-remitting, secondary progressive, primary progressive, and progressive-relapsing courses. Parkinson disease illustrates basal ganglia dysfunction through the selective loss of dopamine-producing neurons in the substantia nigra, producing characteristic motor signs including tremor at rest, muscular rigidity, and postural abnormalities. The chapter emphasizes how various parkinsonism syndromes share common pathological features with Parkinson disease. Contemporary diagnostic approaches employing genomic sequencing and proteomic profiling are increasingly important for precise disease identification, differentiation of similar conditions, and understanding the molecular mechanisms underlying these motor disorders. This comprehensive overview enables students to understand how dysfunction at different points along the motor pathway produces distinct clinical presentations and disease progressions.