Porth's Essentials of Pathophysiology, 4e

ust as our perceptual skills reflect the ability of our sensory systems to detect, analyze, and estimate the significance of our physical environment, the ability to carry out these movements requires skeletal muscles that contract and neural pathways that plan, coordinate, and execute them in a manner that provides for smooth, purposeful, and coordinated movement. In some cases, purposeless and disruptive movements can be almost as disabling as relative or complete absence of movement. This chapter provides an introduction to the organiza- tion and control of motor function, followed by a discus- sion of disorders of motor function, including muscular dystrophy, and disorders of the neuromuscular junction, peripheral nerves, the basal ganglia and cerebellum, and upper motor neurons. Motor function, whether it involves walking, running, or precise finger movements, requires movement and maintenance of posture. Posture can be described as the relative position of the various parts of the body with respect to one another (limb extension, flexion) or to the environment (standing, supine). 1 Posture also can be described as the active muscular resistance to the displacement of the body by gravity or acceleration. The structures that control posture and movement are located throughout the neuromuscular system. The sys- tem consists of the motor unit (motor neuron and the muscle fibers it innervates); the spinal cord, which con- tains the basic reflex circuitry for posture and movement; and the descending pathways from brain stem circuits, the cerebellum, the basal ganglia, and the motor cortex. Organization of Movement As with other parts of the nervous system, the motor systems are organized in a functional hierarchy, each concerned with increased levels of complexity. 2 The Disorders of Neuromuscular Function 36 C h a p t e r Organization and Control of Motor Function J

Organization and Control of Motor Function Organization of Movement The Spinal Cord The Brain Stem The Motor Cortex The Cerebellum and Basal Ganglia The Motor Unit Spinal Reflexes Motor Pathways Assessment of Motor Function Muscle Strength, Bulk, and Tone Spinal Reflex Activity Coordination of Movement Disorders of the Motor Unit Skeletal Muscle Disorders Muscle Atrophy Muscular Dystrophy Disorders of the Neuromuscular Junction Drug- and Toxin-Induced Disorders Myasthenia Gravis Peripheral Nervous System Disorders Peripheral Nerve Injury and Repair Mononeuropathies Polyneuropathies Back Pain and Spinal Nerve Root Disorders Disorders of the Cerebellum and Basal Ganglia Disorders of the Cerebellum Disorders of the Basal Ganglia Functional Properties of the Basal Ganglia Basal Ganglia–Associated Movement Disorders Parkinson Disease Upper Motor Neuron Disorders Amyotrophic Lateral Sclerosis Multiple Sclerosis Pathophysiology Clinical Manifestations Diagnosis and Treatment Vertebral and Spinal Cord Injury Injury to the Vertebral Column Acute Spinal Cord Injury Types and Classification of Spinal Cord Injury Disruption of Somatosensory and Skeletal Muscle Function Disruption of Autonomic Nervous System Function Disruption of Bladder, Bowel, and Sexual Function Disruption of Other Functions Future Directions in Repair of the Injured Spinal Cord

880