MOTOR SYSTEMS

1. MOTOR SYSTEMS • Muscles and Joints • Muscles • Moving • The Spinal Cord • Spinal Reflexes • Reciprocal Control of Opposing Muscles • Polysynaptic Adaptations and Reflexes • The Motor Cortex • The Basal Ganglia • Limbic System • The Cerebellum • Cranial Nerves

2. Muscle groups are complex; attach bone to bone via tendons and ligaments

3. A muscle group has many fibers

4. The Neuromuscular junction (NMJ): The receptive portion of muscle-the motor end-plate

5. The NMJ ( sometimes called the motor end-plate)

7. nACHr

8. End-plate potential • Larger • Longer • Leads to Ca+ influx in sarcolema of muscle • Ca+ causes muscle contraction

9. Disease of the NMJ? MG

10. MG

11. muscle fibers encase myofibrils. The casing is called the sarcolema Muscle group myofibril Muscle fiber

12. End-plate potential causes ca+ influx into sarcolemma

13. Myofibrils in turn contain “Actin and Myosin” filaments

14. When the NMJ is activated Actin-myosin interact to shorten the length of a muscle fiber

15. Sliding filament model of muscular contraction

16. Muscle shortens=work

17. Goal-directed Complex Higher levels of control Plastic Numerous reflexive behaviors are involved Reflexive Simple Automatic inplastic Cortical vs Spinal control of behavior

18. Spinal reflex ARCs • Monosynaptic • stretch • Polysynaptic • Withdrawal • Antagonist muscle groups • Synergistic muscle groups • Polysegmental relexes • Cross-spinal reflexes

19. A “monosynaptic” spinal reflex arc- the Stretch reflex

20. The stretch reflex involves neuromuscular “spindles”

21. Stretch reflex regulates muscle tension in every muscle group

22. The polysynaptic part of stretch reflexes: inhibition of Antagonist muscles

23. Spinal inhibition of antagonist muscles require inhibitory interneurons

25. The “withdrawal reflex arc” a polysynaptic spinal reflex

26. Also involves interneurons

27. And may involve more than one spinal cord segment

28. And/or Cross spinal reflex arcs

30. The Goli tendon organ (GTO) reflex

31. Neural activity of spinal neurons related to whole muscle group activity

34. Lower motor neurons “the final common pathway”

35. Goal-Directed Behavior and Reflexive Behavior

36. Goal-Directed Behaviors Require: • Goal selection and prioritization • Resistance to distracters -Cross-modal Sensory integration • Perception of target • Awareness of location of movable body part • Ability to aim movement of body part • Ability to detect errors and re-adjust, (use feedback) • Ability to use feedback to control movement of body part

37. Sensory-Motor Integration in the frontal lobes

38. THE DLPFC: “The conductor” Integrates cross modal input- may initiate goal-directed behaviors Lesions of the dorsolateral frontal areas results in a number of “executive” motor impairments. These include perseveration, incoordination, motor impersistence, apraxias and hypokinesia.

39. The premotor and supplementary motor ctx: “The sections” Stimulation= complex sequences of behavior (aimless behavior)

40. Damage to the secondary Motor Cortex? • Ideomotor Apraxia • This apraxia is associated with great difficulty in the sequencing and execution of movements. A common test of apraxia is to request the patient to demonstrate the use of a tool or household implement (e.g., "Show me how to cut with scissors"). Difficulties are apparent when the patient moves the hand randomly in space or uses the hand as the object itself, such as using the forefinger and middle finger as blades of the scissors. They have additional trouble sequencing the correct series of movements and make errors in orienting their limbs in space consistent with the desired action. Imitation of the movements of others will usually improve performance but it is still usually defective. • Memories for skilled acts are probably stored in the angular gyrus of the parietal lobe in the left hemisphere.

41. The primary motor cortex; “the instrument” Stimulation = relatively simple fragments of behavior

42. TWO MAJOR DESCENDING PATHWAYS FROM THE PRIMARY MOTOR CORTEX: The Dorsolateral pathway

43. And the VM Path. • The VM pathway does not discretely decussate, but does branch and innervate contra lateral segments in the spinal cord.

44. Dorsolateral Decussates at medullary pyramids Distal muscle groups More direct More volitional control Higher resolution of control Ventromedial Does not cross Medial muscle groups Gives off spinal collaterals Yoking Lower resolution of control DL vs VM descending motor paths

45. Other Motor Pathways • In addition there are other motor paths that have relays in the brainstem • These other paths innervate nuclei of the RAS, cranial nerve nuclei, etc…

46. Descending paths get additional inputs

47. Both pathways terminate in spinal cord segments

48. According to part of the body they control

50. On lower motor neurons (alpha motor neurons)