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17DescendingMotorControl

17DescendingMotorControl - Figure 17.1 Overview of...

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Figure 17.1 Overview of descending motor control (Part 2)
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Figure 17.1 Overview of descending motor control (Part 1)
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Overview Upper Motor Neurons that Maintain Posture and Balance Vestibular nuclei (image to follow) Reticular formation (image to follow) Superior colliculus (image to follow) Red Nucleus (no image following)
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Figure 17.2 Descending projections from the brainstem to the spinal cord
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Vestibular nucleus Receives input from vestibular neurons Projects to medial motor neurons and to medial intermediate zone (where LCNs are) to control posture Other targets as related to vestibular reflexes Axial musculature - snapping the head back during a fall proximal musculature - forelimb extension during a fall ocular musculature - vestibulo- ocular reflex
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Vestibular nucleus also exerts direct control over lower motor neurons Reticular formation Diffuse structure, structurally and functionally similar to the intermediate grey matter of the spinal cord projects to medial motor neurons and to medial intermediate zone to control axial and proximal musculature
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Figure 17.3 The location of the reticular formation (Part 1)
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Figure 17.3 The location of the reticular formation (Part 2)
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Figure 17.3 The location of the reticular formation (Part 3)
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Reticular formation cont’d Plays role in spatial and temporal coordination of movements Largely controlled by other motor centers in the cortex or brainstem Feedforward mechanisms E.g. contraction of gastrocnemius during forelimb movement
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Figure 17.4 Anticipatory maintenance of body posture
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Figure 17.5 Feedforward and feedback mechanisms of postural control
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Reticular formation experiments done in cats Lifting forepaw evoked postural adjustments in other limbs, regardless of whether movement was response to training or to exogenous electrical stimulation of motor cortex Pharmacological inactivation of reticular formation spared forepaw, but inhibited postural adjustments.
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Superior colliculus Projects to medial cervical spinal cord
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