Voluntary movements depend on interactions among motor areas of the cerebral cortex, the cerebellum, and the basal ganglia.
17.
Motor areas of the cerebral cortex are arranged as a parallel distributed network, in which each contributes to the various descending motor pathways. The areas primarily involved in body and head movement include the primary motor cortex, the premotor area, the supplementary motor cortex, and the cingulate motor areas. The frontal eye fields are important for eye movement and help initiate voluntary saccades.
18.
Individual corticospinal neurons discharge before voluntary contractions of related muscles occur. The discharges are typically related to contractile force rather than to joint position. However, the activity of an individual neuron may encode different parameters of a movement at different times in relation to the execution of that movement.
19.
The population activity of motor cortex neurons can be used to predict the direction of upcoming movements.
20.
The cerebellum influences the rate, range, force, and direction of movements. It also influences muscle tone and posture, as well as eye movement and balance.
21.
The intrinsic circuitry of the cerebellum is remarkably uniform. Differences in function of different parts of the cerebellum arise largely as a result of differing afferent sources and efferent targets.
22.
Anatomical and physiological techniques have shown that the cerebellar cortex may be divided into many functionally distinct, longitudinally running compartments.
23.
Most of the input to the cerebellum is through pathways that end as mossy fibers. Mossy fibers excite granule cells, which in turn can evoke single action potentials, called simple spikes, in Purkinje cells, whose axons form the only output pathway from the cerebellar cortex.
24.
The projections of the inferior olivary nucleus to the cerebellum end as climbing fibers and are the only source of them. Each Purkinje cell receives massive input from just one climbing fiber. As a result, each climbing fiber discharge produces a high-frequency burst of several action potentials, known as a complex spike, in the Purkinje cell.
25.
Although complex spike activity is relatively rare in comparison to simple spike activity, complex spikes are precisely synchronized across populations of Purkinje cells, and because of the convergence of these cells onto cerebellar nuclear neurons, this synchronization may allow complex spike activity to significantly affect cerebellar output. Synchronization of complex spikes is the result of electrical coupling of inferior olivary neurons by gap junctions.
26.
The basal ganglia include several deep telencephalic nuclei (including the caudate nucleus, putamen, and globus pallidus). The basal ganglia interact with the cerebral cortex, subthalamic nucleus, substantia nigra, and thalamus.
27.
Activity transmitted from the cerebral cortex through the basal ganglia can either facilitate or inhibit the thalamic neurons that project to motor areas of the cortex, depending on the balance between direct and indirect basal ganglia pathways. When there is an imbalance of these two pathways, hyperkinetic or hypokinetic disorders occur.
CHAPTER 9 Organization of Motor Function 28. Some types of eye movement help stabilize the view of the visual world. This is critical because visual acuity drops dramatically when the visual world moves, or slips, across the retina. Vestibuloocular and optokinetic movements help stabilize the visual world on the retina by compensating for movement of the head or external world (or both). Smooth pursuit movements allow tracking of a visual target so that it remains centered on the foveae.
Eccles JC, Ito M, Szentagothai J. The Cerebellum as a Neuronal Machine. New York: Springer; 2013. (Original work published 1967.)
Shadmehr R, Wise SP. The Computational Neurobiology of Reaching and Pointing: A Foundation for Motor Learning. Cambridge, MA: Bradford Books; 2004.