880
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.
Organization and Control of
Motor Function
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
J
Disorders of
Neuromuscular
Function
36
C h a p t e r
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
