anatomy and physiology of motor systems n.
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  1. ANATOMY AND PHYSIOLOGY OF MOTOR SYSTEMS CHAPTER V

  2. Motor pathways

  3. Somatotopic organization of the motor cortex

  4. Cortical motor areas The central sulcus divides motor and sensory areas SUPPLEMENTARY CORTICAL AREAS PROVIDE INPUT TO MOTOR CORTEX

  5. LATERAL DESCENDING SYSTEM • CORTICOSPINAL TRACT • CONNECT DIRECTLY TO ALPHA MOTONEURONS, OR THROUGH PROPRIOSPINAL INTERNEURONS • RUBROSPINAL TRACT • FROM NUCLEUS RUBER TO PROPRIOSPINAL INTERNEURONS

  6. Descending motor pathways Lateral system

  7. The medial descending motor pathways

  8. Motor pathways from the brainstem

  9. Projections from motor cortex (MI) to the spinal cord Projection of dorsal horn to the somatosensory cortex

  10. Connections between the basal ganglia and the primary motor cortex (MI)

  11. INFORMATION FROM THE MOTOR CORTEX IS PROCESSED IN THE BASAL GANGLIA AND RETURNED TO THE MOTOR CORTEX THE THALAMUS CONDUCT THE INFORMATION BACK TO THE MOTOR CORTEX THE DISTINCTION BETWEEN PYRAMIDAL AND EXTRAPYRAMIDAL SYSTEMS THEREBY BECOMES IRRELEVANT

  12. Motor systems are complex

  13. Two descending motor tracts The alpha-motoneuron is the final common pathway

  14. Anatomical localization of basal ganglia and motor thalamus

  15. Connections between the cerebral cortex and the cerebellum

  16. The alpha-motoneuron innervates muscles

  17. The alpha-motoneurons (common final pathway) receive many inputs Some are facilitating and some are inhibitory

  18. The anatomical basis for the stretch reflex

  19. Motoneurons receive excitatory input from muscle spindles (length), and inhibitory input from tendon organs (tension)

  20. Recording from the exposed spinal cord D and I waves

  21. Blood supply to the spinal cord • Mainly two sources: • The anterior spinal artery • Posterior spinal artery • Segmental arteries • Dorsal and ventral portions of the spinal cord have mostly different blood supplies • Large degree of individual variability

  22. Blood supply to the spinal cord

  23. Anterior spinal artery Number of feeder arteries varies

  24. Two posterior spinal arteries Number of feeder arteries varies

  25. Activation of motor tracts • Transcranial magnetic stimulation of the motor cortex • Transcranial electrical stimulation of the motor cortex • Electrical stimulation of the spinal cord

  26. Magnetic stimulation of the motor cortex • Non-invasive • Technically difficult to apply • Need trains of stimulation, which is difficult to achieve

  27. Transcranial electrical stimulation of the motor cortex • Non-invasive • Can easily produce trains of impulses • High voltage may seem a risk

  28. Electrical stimulation of the spinal cord • Produces effective stimulation of spinal cord • Invasive • Not clear if only motor pathways are stimulated

  29. Recording of responses • Electromyographic potentials • Compound action potentials from motor nerves

  30. Electromyographic potentials • Large potentials • Cannot be done with muscle relaxation

  31. Compound action potentials • Can be recorded with muscle relaxation • Amplitude is small

  32. Recording from the exposed spinal cord D and I waves

  33. Recordings from the surface of the spinal cord in a monkey in response to stimulation of the cerebral cortex Transcranial electrical stimulation Transcranial magnetic stimulation Direct electrical stimulation D I1

  34. Recordings from the surface of the spinal cord in a 14 year old patient Undergoing a scoliosis operation. Transcranial electrical stimulation at different strengths (100%=750V at Cz and 6 cm anterior)

  35. Effect of placement of stimulating electrodes Deletis and Shils 2002

  36. Comparison between transcranial and direct stimulation of the motor cortex Deletis and Shils 2002

  37. Techniques for recording motor evoked potentials Deletis and Shils 2002

  38. Repeating trains can increase the EMG responses from the right abductor hallucis brevis in response to trains of five electrical impulses to scalp (C3-C4). Deletis and Shils 2002

  39. Deletis and Shils 2002

  40. Using BSM, surgeon can get anatomical guidance to enter the brainstem safely. From Morota N, Deletis V, Epstein FJ, et al: Brain stem mapping: neurophysiological localization of motor nuclei on the floor of the fourth ventricle. Neurosurgery 37: 922-930, 1995

  41. Corticobulbar MEPs - Recordings in IV Ventricle Mapping - Recordings

  42. Modulation of the monosynaptic stretch reflex

  43. The Hoffmann reflex Amplitude of Hoffmann (H) Response, and the direct muscle (M) response.

  44. DESCENDING MOTOR ACTIVITY IS AFFECTED BY ATTENTION