Chapter 11 Summary & Outline
The Behavioral View
- There are two broad categories of motor activity: movements and acts. Reflexes are simple movements; more-complex motor behaviors are acts. Complex acts indicate the existence of a motor plan.
- Reflexes are patterns of relatively simple and stereotyped movements elicited by the stimulation of sensory receptors.
Study questions: 1 | 2 | 3 | 4
The Control Systems View
- In closed-loop control, movements may be corrected while they are being produced on the basis of feedback from sensory systems. Some behaviors are so rapid, however, that they are controlled by open-loop systems; that is, the pattern is preset and not modified by feedback once it has started. Review Figure 11.3
Study questions: 5 | 6
The Neuroscience View
- Motor control systems are organized into a hierarchy that consists of the skeletal system and associated muscles, the spinal cord, the brainstem, and various parts of the brain, including the primary and nonprimary motor cortices, the cerebellum, and the basal ganglia.
- Muscles around a joint work in pairs. Antagonists work in opposition; synergists work together. Review Figure 11.6
- Smooth muscles, such as those in the stomach, are under involuntary control; striated muscles are under voluntary control.
- Action potentials travel over motor nerve fibers (axons from motoneurons) and reach muscle fibers at the neuromuscular junction, releasing acetylcholine to trigger muscle contraction. Review Figure 11.7, Web Activity 11.1
- The final common pathway for action potentials to skeletal muscles consists of motoneurons whose cell bodies in vertebrates are located in the ventral horn of the spinal cord and within the brainstem. The motoneurons receive information from a variety of sources, including sensory input from the dorsal spinal roots, other spinal cord neurons, and descending fibers from the brain. Review Figure 11.8
- Muscle spindles and Golgi tendon organs—sensory receptors in the muscles and tendons, respectively—transmit crucial information about muscle activities to the central nervous system. The sensitivity of the muscle spindle can be adjusted by efferent impulses that control the length of the spindle. This adjustment enables flexible control of posture and movement. Review Figure 11.9
Study questions: 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23
Movements Are Controlled at Several Nervous Systems Levels
- When a muscle is stretched, a reflex circuit often causes contraction, which works to restore the muscle to its original length; this response is called the stretch reflex. The stretch of the muscle is detected by muscle spindles. Review Figure 11.10, Web Activity 11.2
- The fibers of the pyramidal (corticospinal) tract originate mainly in the primary motor cortex (M1) and adjacent regions, and they run directly to spinal motoneurons or to interneurons in the spinal cord. Nonprimary motor cortex helps control the sequence of movements. Premotor cortex contains mirror neurons that are active when an individual is moving an object in a particular fashion, or when the individual sees someone else moving an object in that manner. Review Figures 11.2 and 11.17
- Although the primary motor cortex (M1) is organized in the form of a map of the body, the subregional organization is broadly distributed and highly overlapping, in order to efficiently control the multiple muscles that make up a movement. M1 is involved in learning motor responses and is a highly plastic region; the cortical map is continually remodeled as a consequence of motor learning. Review Figure 11.15
Study questions: 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38
Extrapyramidal Systems Also Modulate Motor Commands
Study questions: 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46
Disorders of Muscle, Spinal Cord, or Brain Can Disrupt Movement
- Movement disorders, such as muscular dystrophy, amyotrophic lateral sclerosis (ALS), Parkinson’s and Huntington’s diseases, and others, can result from impairment at any of several levels of the motor system: muscles, neuromuscular junctions, motoneurons, spinal cord, brainstem, cerebral cortex, basal ganglia, or cerebellum. The characteristics of these disorders depend on and permit diagnosis of the locus of impairment.
- The cerebellum is made up of three major functional divisions: spinocerebellum, cerebrocerebellum, and vestibulocerebellum. Damage in each division is associated with specific motor impairments. Review Figure 11.24
Study questions: 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64
