116 Lecture 15.S10 - CBNS 116 Lecture 15 Overview of motor...

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CBNS 116 Lecture 15 - Overview of motor systems and basal ganglia Lecture notes by Todd Fiacco ASSIGNMENT: Read Nolte Chapter 19: “Basal Ganglia”. FOR NEXT LECTURE: Read Nolte Chapter 20: “Cerebellum”. TODAY'S LECTURE: The big picture: Thus far our study of motor control systems has been mostly confined to 2 main motor pathways: the corticospinal tract , one of the four principal pathways, from motor cortex to lower motor neurons to control voluntary movements; and the reticulospinal tracts , controlling complex motor reflexes and rhythmic movements (such as walking, yawning, riding a bike, chewing gum, etc.). These are 2 of several pathways by which upper motor neurons, located in both the cerebral cortex and brainstem, control lower motor neurons in the anterior horn of the spinal cord. In this and the next lecture, we will examine the two primary accessory components of motor control: the basal ganglia and the cerebellum . These two brain areas have no direct input to lower motor neurons; instead, they regulate and modulate movements by influencing the output from the cerebral cortex to the brainstem and spinal cord. Unlike damage to upper or lower motor neurons (which produces symptoms that include muscle weakness), damage to the basal ganglia and cerebellum lead to distinctive movement abnormalities including in voluntary movements, incoordination, and difficulty initiating movements (but no muscle weakness). In addition to their involvement in motor control, through similar loops, it has become clear that the basal ganglia are more generally involved in most cortical functions. Thus the basal ganglia, in addition to playing a role in movement, are also important for normal cognition and personality, as well as affect, emotion and motivation. I. Multiple pathways contribute to upper motor neuron control of lower motor neurons [slides 74 - 76]. A. Corticospinal tract . You guys should know this one by heart at this point. B. Reticulospinal tracts - upper motor neurons from the pontomedullary reticular formation
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to the anterior horn LMNs. Involved in complex motor reflexes and “stereotyped” movements (e.g. yawning, stretching, locomotion, swallowing, righting behavior etc.) C. Vestibulospinal tracts - learned in conjunction with CN VIII and special senses, an important pathway in mediating postural adjustments to head movements. D. Rubrospinal tract - The rubrospinal tract, together with the reticulospinal tract, are the principal alternative routes to the corticospinal tract for mediating voluntary movement. These tracts can together lead to recovery of most voluntary motor function, except for fine motor tasks involving fine movements of the fingers. E. Tectospinal tract - from the superior colliculus to cervical levels of the spinal cord via the anterior funiculus. Involved in reflex orientations to visual and auditory stimuli that may be threatening. (These fibers likely innervate neck musculature). This is a much more prominent pathway in lower vertebrates but is quite small in humans.
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