6 The Motor System physiology slides.pptx

motor system

1. THE MOTOR SYSTEM INTRODUCTION, ORGANISATION AND RELATION TO THE BRAIN STEM.

2. June 26, 2024 motor system 2 Motor System Motor system of brain exist to translate Thought, sensation, emotions into Movements Movement is the end product of Number of control systems Extensive interactions

3. June 26, 2024 motor system 3 Nature of Movements In most forms of movements Motion occurs at joints Where two or more bones come together To form a near frictionless pivot Muscles are arranged so that Ends are attached on opposite sides of joint which acts as a fulcrum

4. June 26, 2024 motor system 4 Nature of Movements Usually movement of one joint Require fixation of next joint By other muscles Example Movement of forearm Muscles of shoulder Contract to fix the humerus

5. June 26, 2024 motor system 5 Motor cortex Basal ganglia Brain Stem Cerebellum Spinal Cord Skeletal muscles Neural centers for control of movements

6. THE MOTOR SYSTEM

7. June 26, 2024 motor system 7 Spinal Cord A series of interconnections Has developed in spinal cord Link motor neurons of muscles that Commonly work together All the motor pathways ultimately Converge on a series of simple circuits Link each skeletal muscle with spinal cord From H.T. Sherrief Book of Physiology

8. June 26, 2024 motor system 8 Spinal Cord Sensory neurons Carry impulses from muscles Connect to motor neurons Transmit impulses back to muscles This forms a closed loop For regulation of each muscle These circuits May function autonomously In simple reflexes From H.T. Sherrief Book of Physiology

9. June 26, 2024 motor system 9 Spinal Cord However, their activities Controlled by centers at higher levels From these centers Tracts descend to spinal cord Giving off fibers at all levels From H.T. Sherrief Book of Physiology

10. June 26, 2024 motor system 11 Brain Stem Composed of Midbrain, pons & medulla oblongata Pre spinal integrating center Receive signals from all higher centers Processes them for Transmission to spinal cord

11. THE BRAINSTEM

12. June 26, 2024 motor system 14 Basal Ganglia Superimposed on The upper end of brain stem Receives signals from Sensory-motor cortex Processes this information Discharges it into brain stem Provide motor pattern necessary To maintain postural support

13. June 26, 2024 motor system 17 Sensory-motor Cortex Highest level in the motor command system Origin of Corticospinal tracts Corticobulbar pathways

14. THE CORTICOSPINAL TRACT

15. June 26, 2024 motor system 21 Cerebellum Interconnected with all levels Acts as an overall Coordinator of motor activity Receives signals from Cerebral cortex Muscles, tendons, joints, skin Visual, auditory, vestibular organs

16. June 26, 2024 motor system 22 Cerebellum All this enormous influx Analyzed and integrated by cerebella cortex Efferent fibers pass to Thalamus, red nucleus, vestibular nucleus, reticular formation Cerebellum coordinates Activity of motor circuits at all levels

17. MOTOR UNIT A motor unit is defined as a single motoneuron and the muscle fibers that it innervates. The number of muscle fibers innervated can vary from a few fibers to thousands of fibers , depending on the nature of the motor activity.

18. June 26, 2024 motor system 24 Alpha motor nerve, Axon, muscle fibres Number of muscle fibre per one nerve varies Motor Unit

19. June 26, 2024 motor system 25 Types of Motor Units Type I (slow twitch) Small in diameter High capillary density Low glycolytic enzymes

20. June 26, 2024 motor system 26 Type I Motor Units High mitochondria content High oxidative enzyme content Resistant to fatigue Suited for weak sustained contractions

21. June 26, 2024 motor system 27 Type II Motor Units Type II a (fast twitch oxidative) Small in diameter High capillary density High mitochondria content High oxidative enzyme content Has high glycolytic enzymes as well Resistant to fatigue

22. June 26, 2024 motor system 28 Type II b Motor Units Fast twitch glycolytic Larger diameter High content of glycogen & glycolytic enzymes Few mitochondria Fatigue easily Suited for brief powerful contractions

23. motor cortex 30 26-Jun-24 Motor Cortex Localization of functions Experimental stimulation in monkeys & man Cause contraction of groups of muscles on opposite side All parts of the body - represented on the motor cortex Hand, fingers, thumb Have the largest representation

24. motor cortex 32 26-Jun-24 Motor Cortex Motor cortex not uniformly spread in proportion to muscle size Muscles controlling thumb Are used in many skilled movement Have large representation

25. motor cortex 33 26-Jun-24 Motor Cortex Muscles controlling tongue, larynx Used for talking and singing Also have large representation That is; It is skill and finesse That is reflected in the cortical representation

26. motor cortex 34 26-Jun-24 I Molecular layer II outer granular layer III outer pyramidal IV inner granular V inner pyramidal VI polymorphic fusiform Layers of Cerebral Cortex

27. motor cortex 36 26-Jun-24 Layers of Cortex (I) Molecular layer Dentrites of pyramidal and fusiform cells, axons of stellate cell (II) Small pyramidal cells and stellate cells (III) Pyramidal cells

28. motor cortex 37 26-Jun-24 Layers of Cortex (IV) closely packed stellate cells (V) stellate cells, giant cells of Betz (VI) Fusiform cells, pyramidal cells

29. motor cortex 38 26-Jun-24 Afferents to Motor Cortex Somatic sensory inputs Skin, joints,muscles Relayed to cortex Via ventrobasal nucleus of thalamus Provide the cortical cells the sensory cues required to guide and direct movements

30. motor cortex 39 26-Jun-24 Afferents to Motor Cortex From opposite cerebral cortex Via corpus callossum Coordination of motor activities on two side of the body

31. motor cortex 41 26-Jun-24 Afferents to Motor Cortex From cerebellum Through red nucleus, thalamus, Closed loop linking cerebellum and motor cortex Provide signals necessary for coordination between Motor cortex, basal ganglia & cerebellum

32. motor cortex 43 26-Jun-24 Afferents to Motor Cortex From Ipsilateral cortical area Cortico-cortical association fibres Indirectly via sub cortical center Though the basal ganglia

33. motor cortex 44 26-Jun-24 Afferents to Motor Cortex Other area Visual cortex Important for visually guided movements

34. motor cortex 45 26-Jun-24 Afferents to Motor Cortex Distributed to layers I to IV From somatic sensory Relay in thalamus End in layer IV Cerebellar inputs also end in layer IV Non specific fibers from thalamus end in layer I Give collaterals to other layers

35. motor cortex 48 26-Jun-24 Afferents to Motor Cortex The 2 deepest layer of cerebral cortex receive little direct sensory inputs Influenced by the discharges from the other 4 layers

36. motor cortex 49 26-Jun-24 Output From Motor Cortex Pyramidal (direct cortico spinal tract) Consist of neurons whose cell bodies are in cerebral cortex Axon pass through pyramid - medulla - spinal cord 1 million fibres in each tract

37. motor cortex 50 26-Jun-24 20% of fibers leaving cortex project as far as spinal cord corticospinal 80% project to sub-cortical nucleus brain stem Corticobulbar Output From Motor Cortex

38. motor cortex 51 26-Jun-24 Origin of Corticospinal Tracts Corticospinal and corticobulbar tracts Originate in all areas of motor – sensory cortex 30% of fibers come from area 4 30% from area 6 (pre-motor area) 40% from parietal lobe SI, SII (area 3, 1, 2)

39. motor cortex 52 26-Jun-24 Origin of Corticospinal Tracts On the way to spinal cord axons give collaterals Thalamus, red nucleus, brain stem, basal ganglia

40. motor cortex 53 26-Jun-24 Pyramidal Decussation 75 - 90% of fibers Cross over to opposite side Run in dorsolateral quadrant of spinal cord Lateral corticospinal tract 10 - 25% of fibers Run uncrossed anteromedially This as a rule end in cervical & thoracic area

41. motor cortex 55 26-Jun-24 Axonal Ending CST axons make Synaptic contacts with inter-neurons Which the synapse with motor neuron Flexors + Extensors - CST

42. motor cortex 56 26-Jun-24 Axonal Ending Monosynaptic connections with alpha motoneurons Man & primates Corticospinal tract Excitatory to flexors Inhibitory to extensors Flexors + Extensors - CST

43. motor cortex 57 26-Jun-24 Other Output Fibers The motor cortex gives other output fibers Axons from the giant cells of Betz Send short collaterals to Deep regions of cerebrum Midbrain These provide lateral inhibition Sharpen boundaries of excitatory signals

44. motor cortex 59 26-Jun-24 To Basal Ganglia Fibers from motor cortex Pass to basal ganglia Caudate nucleus Putamen Motor cortex Brain stem Spinal cord Basal ganglia Thalamus

45. motor cortex 60 26-Jun-24 To Basal Ganglia From the BG Feedback to motor cortex Relayed to brain stem Relay to spinal cord Motor cortex Brain stem Spinal cord Basal ganglia Thalamus

46. motor cortex 61 26-Jun-24 To Red Nucleus Fibers from motor cortex Collaterals to red nucleus Then transmitted to Spinal cord Rubrospinal tract

47. motor cortex 62 26-Jun-24 To Cerebellum Fibers from motor cortex Give collaterals to cerebellum Pontocerebella Olivocerebella Motor cortex Cerebellum Spinal cord

48. Brain Stem

49. June 26, 2024 brain stem 64 Functional Anatomy Brain stem in the physiological sense is comprised of Medulla, Pons, Mesencephalon (midbrain) Neuronal circuits within this area control many physiological functions BP, respiration, body temp, sleep & wakefulness, GIT

50. June 26, 2024 brain stem 65 Functional Anatomy Control of physiological functions Stereotyped movements of the body Equilibrium and balance Eye movement In addition Reticular formation (RF) and Vestibular Nuclei Important components of motor control system

51. June 26, 2024 brain stem 67 Functional Anatomy Serves as a way station for Command signals from higher neural centres that command the brain stem to Initiate, modify specific control functions throughout the body

52. June 26, 2024 brain stem 68 Brain Stem Motor centres Red nucleus Lateral vestibular nucleus (Deiter’s nucleus) Certain parts of reticular formation in pons and medulla oblongata

53. June 26, 2024 brain stem 69 Motor centres Have efferent fibres that influence motor pathways in Spinal cord Cranial motor nerves Form part of efferent pathways from higher motor centres

54. June 26, 2024 brain stem 70 The Red Nucleus Lie in the midbrain Receive signals from the Motor cortex, Cerebellum Project signals to the spinal cord: Rubro-Spinal Tract (RUST) Stimulation of the system Excitation of Flexors Inhibition of extensors

55. June 26, 2024 brain stem 71 Red Nucleus RUST crosses over the opposite side Runs through the spinal cord close to CST Connect to MN Inhibit extensors Excite flexors Extensors + Flexors Red nucleus RUST

56. June 26, 2024 brain stem 72 Reticular Formation Brain stem reticular formation Two areas with motor control activity Pontine reticular nucleus Medullar reticular nucleus Give rise to reticulospinal tracts

57. June 26, 2024 brain stem 73 Reticular formation The two sets of nuclei Function antagonistically to each other Pontine exciting the Antigravity muscles Medullary inhibiting them

58. June 26, 2024 brain stem 74 Pontine Reticular Nucleus Located in the pons, extends to midbrain Transmit excitatory signals down the spinal cord Pontine (medial) Reticulospinal tract (M-REST) Terminate on MN Excite extensors (antigravity) Inhibit flexors + Extensors - Flexors Pontine reticular Nucleus M-REST

59. June 26, 2024 brain stem 75 Pontine Reticular Nucleus Pontine (medial) Reticulospinal tract (M-REST) Also excite Axial muscles which support body against gravity Muscle of the vertebral Extensor muscles of limbs + Extensors - Flexors Pontine reticular Nucleus M-REST

60. June 26, 2024 brain stem 76 Pontine Reticular Nucleus Cells of the Pontine R.N have High degree of excitability (inherent) Excitability is held in check by Inhibitory signals Cerebral cortex Basal ganglia Cerebellum Cerebral cortex, basal ganglia, cerebellum Inhibitory signals Pontine R.N Vestibular N., Cerebellum Excitatory signals ++ α MN, γ MN excitability increases - - + + Muscle spaciticity

61. June 26, 2024 brain stem 77 Pontine Reticular Nucleus Receive excitatory signals from Vest. Nucleus Cerebellum (deep nucleus) If unopposed by medullary syst Causes powerful excitation of antigravity muscles SPACITICITY Cerebral cortex, basal ganglia, cerebellum Inhibitory signals Pontine R.N Vestibular N., Cerebellum Excitatory signals ++ α MN, γ MN excitability increases - - + + Muscle spaciticity

62. June 26, 2024 brain stem 78 Medullary Reticular Nucleus Located in the reticular area of medulla Transmit inhibitory signals down the spinal cord Medullar (lateral) Reticulospinal tract (L-REST) Connect to MN Inhibit extensors Excite flexors Extensors + Flexors Medullar reticular Nucleus L-REST

63. June 26, 2024 brain stem 79 Medullar Reticular System Receive strong imputes by way of collaterals from CST, RUST, other motor pathways These normally activate the medullar inhibitory system This counteracts the excitatory effects of Pontine reticular system Pontine R.N Medullar R.N CST, RUST, other motor pathways ++ - - ++ α MN, γ MN

64. June 26, 2024 brain stem 80 Medullar Reticular System Can also receive inhibitory imputes by way of collaterals from CST, RUST, cerebellum These normally inhibit medullar inhibitory system When the brain wishes to cause excitation of Pontine reticular system, to facilitate standing Pontine R.N Medullar R.N CST, RUST, other motor pathways ++ ++ α MN,  MN CST, RUST cerebella - -

65. June 26, 2024 brain stem 81 Vestibular Nucleus Located in the pons and medullar Project to spinal cord Vestibulospinal tract (VEST) Connect to MN Excite extensors Inhibit flexors + Extensors - Flexors Vestibular Nucleus VEST

66. June 26, 2024 brain stem 82 Vestibular Nucleus Provide strong excitatory signals to antigravity muscles Selectively control the excitation of different antigravity muscles To maintain equilibrium and balance in response to vestibular apparatus + Extensors - Flexors Vestibular Nucleus VEST

67. June 27, 2024 brain stem 83 Brain Stem Motor Effects CST RUST L - REST Flexors excited Extensors inhibited Flexors inhibited Extensors excited VEST M- REST

68. LESIONS.

69. Lesions Lesion above midbrain [ A ] Loss of cortical area that inhibit gamma efferent discharge via reticular formation Causes decorticate rigidity Arms flexed and adducted Legs extended

70. Lesion of mid-level of midbrain [ B ] Leave the pontine, medullary RF as well as the Vestibular nuclei intact Interrupt descending tracts from Cerebral cortex, red nucleus, basal ganglia Medullary inhibitory system non functional Allow full over activity of pontine excitatory system

71. Development of Decerebrate rigidity (rigidity of antigravity muscles) Muscles of neck, trunk, and extensors of the legs If the brain stem is severed from spinal cord [ C ] Spinal shock develops