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What does the learning:

This text explores the organization and function of the spinal cord, brainstem, and forebrain in motor control and learning. It discusses the divisions and pathways within the spinal cord and brainstem, as well as the role of the cerebellum and basal ganglia in motor control. The text also highlights the importance of the motor cortex, posterior parietal cortex, and thalamus in reaching and pointing movements.

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What does the learning:

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  1. What does the learning: I) Spinal cord and brainstemII) Forebrain

  2. Spinal cord and brainstem Spinal cord organization: • four major divisions • Cervical (8) • Thoracic (12) • Lumbar (5) • Sacral (5) • Each spinal segment controls a set of muscles

  3. Spinal cord organization dorsal White matters (nerve fibres) Sensory inflow Dorsal horn lateral medial Ventral horn Motor commands Grey matters (cell bodies) ventral

  4. Spinal cord organization Dorsal root Sensory neuron Interneuron Motor neuron Ventral root

  5. Spinal cord organization Some interneurons project within their own spinal segments, while others relay information to other spinal segments and/or the brain.

  6. Proprioceptive pathways to the brain • Dorsal column-medial lemniscal pathway  major pathway by which proprioceptive and touch information ascend to the cerebral cortex • Spinocerebellar tract  ascend to the cerebellum

  7. Brainstem organization • like the spinal cord, the brainstem contain motor neurons who axons make up the cranial nerves that innervate the muscles of the tongue, face and eyes etc. • some neurons in the brainstem also project to interneurons and motor neurons in the spinal cord

  8. Medial brain stem pathways Basic postural control Tectum Tectospinal tract Vestibular nucleus Reticulospinal tract Vestibulospinal tract Influence axial & proximal muscles

  9. Medial brain stem pathways Basic postural control Phylogenetically oldest descending motor pathway Individual axons project widely, coordinating different regions of spinal cord In ventromedial cord, contact interneurons, long propriospinal cells, & some MNs Influence axial & proximal muscles

  10. Reticulospinal adjustments • maintaining balance during limb movements • voluntary movements of our arm can have postural consequences, ex. lifting an object • to counter this, leg muscles need to increase their activity just before you pick up the object

  11. Reticulospinal adjustments • Cordo & Nashner, 1982 • found activity of the legs precedes the activity of the biceps • depends on the context (sitting vs standing)

  12. Reticulospinal adjustments

  13. Lateral brain stem pathways Main path is rubrospinal Goal-directed limb movements, e.g. reaching, manipulation From red nucleus Crosses midline in brain stem Influence distal muscles

  14. Red nucleus • receives input from the deep cerebellar nuclei, as well as the motor cortex • sends majority of its neurons down the spinal cord (rubrospinal tract) and to the cerebellum through the inferior olive nucleus (source for climbing fibres)

  15. Cerebellum • contains ~70% of all the brain's neurons; contributes to timing, coordination, and the learning of motor skills. • only approx. 10% of the volume • complete removal produces no muscle weakness or loss of perception

  16. flocculus Cerebellum: divisions Anterior Lobe Anterior Lobe Posterior Lobe Posterior Lobe vermis nodulus Side View Front View • cerebellar cortex (gray matter), white matter • 2 hemispheres, vermis – ridge in centre • 3 lobes – anterior, posterior, flocculonodular

  17. Cerebellum: divisions Vermis & intermediate zone: mainly controls posture  I/O spinal cord Lateral zone: participates more directly in reaching and pointing  I/O cerebral cortex (via pons) Intermediate zone Vermis Lateral zone nodulus flocculus

  18. Parallel fibre Purkinje cell Granule cell Inferior olive fibre Climbing fibre Mossy INPUT OUTPUT Intrinsic architecture • Main inputs: • Mossy fibres (via parallel fibres from Granule cells) • Climbing fibres Climbing fibres • Main output: • Purkinje cells Mossy fibres Deep nuclei

  19. Cerebellum: inputs Climbing fibres (CF) arise from neurons in the inferior olive and terminate of Purkinje cells and the cells in the deep cerebellar nuclei Inputs from CF cause complex spikes – supposed to signal motor errors (teaching signal) or loss of coordination

  20. Cerebellum: inputs Mossy fibres also terminate on the deep cere-bellar nuclei as well as granule cells (whose axons make the parallel fibres) Parallel fibres supply a huge & continuous supply of sensory information to the Purkinje cells which cause simple spikes.

  21. Cerebellum: outputs Purkinje cells inhibits neurons in the deep cerebellar nuclei. These deep nuclei send excitatory outputs to a variety of structures, e.g. thalamus, reticulo-spinal system, ION, spinal cord, superior colliculus. Fastigial nuclei Dentate nuclei Interpositus nuclei

  22. Cerebellum

  23. What does the learning: I) Spinal cord and brainstemII) Forebrain

  24. Forebrain Forebrain comprises the diencephalon & telence-phalon Basal ganglia plays an enigmatic, role in motor control and learning, including reaching & pointing Thalamus acts as a key node in recurrent, loops which integrate the cerebral cortex & subcortical motor-control systems. The motor cortex and the posterior parietal cortex make important contributions to reaching and pointing.

  25. Anatomy review: Basal ganglia Basal ganglia consists of a group of subcortical nuclei: caudate, putamen, globus pallidus.

  26. Anatomy review: Basal ganglia Clinically includes subthalamic nucleus & substantia nigra These structures are highly interconnected anatomically.

  27. Anatomy review: Basal ganglia { Input: striatum Output: globus pallidus & substantia nigra

  28. Basal ganglia Major inputs to the striatum come from the cerebral cortex & the thalamus Globus pallidus sends GABAergic, inhibitory projections to the brainstem and thalamus. Subthalamic nucleus plays an important role in control of the basal ganglia’s output.

  29. Circuitry of the basal ganglia

  30. Circuitry of basal ganglia The cerebral cortex (and thalamus) projects to the striatum: excitatory. Striatum also receives dopaminergic projections from the SN pars compacta (SNc). The striatum inhibits the globus pallidus (GP) and substantia nigra pars reticulata (SN pr). STN sends excitatory projections to the GPi, GPe & SN pr. GPi or SN pr inhibits (GABAergic) the thalamus. Thalamus projects to the cortex: excitatory.

  31. Circuitry of basal ganglia Direct path: striatum ¢GPi (internal) ¢thalamus ¢cortex Indirect path: striatum ¢GPe (external) ¢STN ¢GPi ¢thalamus ¢cortex

  32. Circuitry of basal ganglia • Direct path: • Leads to less inhibition of the thalamus, i.e. striatum inhibits GPi which in turn inhibits its normal (inhibitory) action on the thalamus, thus leading to greater excitation from the thalamus to the cortex. • Allows for sustain actions or initiation of action • Indirect path: • Excites the GPi thereby increasing its inhibition of the thalamus • Suppresses unwanted movements.

  33. Parkinson disease: Basal ganglia circuitry Abnormal functioning

  34. Circuitry of the basal ganglia

  35. Context switching & Basal ganglia - activity of the legs precede the activity of the biceps  depends on the context (sitting vs standing) • but patients who had Parkinson’s disease – couldn’t use their body’s state for predicting the consequences to minimize them

  36. Thalamus • Dorsal thalamus sends its largest outputs to the cerebral cortex and basal ganglia • Ventral thalamus has a diverse pattern of connections, including direct projections to the spinal cord • Thalamus: relay station for all sensory information; maintains two loops (recurrent modules) between 1) the cerebellum and the cerebral cortex & 2) the basal ganglia and the cerebral cortex, on the other hand.

  37. Thalamus loops Cerebellar cortex STN gran GPe Deep Cb Nuclei GPi Pons Striatum Thalamus Thalamus Cortex Cortex

  38. Thalamus SMA M1 X VApc VLo VLc VPlo Cb GPi

  39. Cortical organization • Cerebrum • Allocortex – includes hippocampus & piriform • Neocortex – cerebral cortex

  40. Cortical organization • Neocortex has 6 layers of neurons (sheets of cells parallel to the surface of the cortex)

  41. Cortical organization

  42. Cortical organization

  43. Lateral corticospinal tracts Largest descending tract, ~750,000 fibres from each hemisphere Originates from primary motor, premotor,& somatosensory cortex. Descends through brain in internal capsule; strokes here causes contralateral weakness Crosses at pyramidal decussation In lateral ventral horn, contacts Ins and MNs of distal muscles.

  44. Ventral corticospinal tracts ~ 250,000 fibres from each hemisphere Originates from premotor and primary motor cortex Remains uncrossed until spinal cord Bilaterally activates MNs of axial muscles

  45. Primary & Non-primary motor cortex SMA M1 M1 SMA PMA Premotor area (PMA)

  46. PPC

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