Motor systems overview anatomy and functions

Motor systems overview anatomy and functions

1. Motor Systems By: Pragnya N Chair: Ms. Samyukta Vaidyanathan

2. Sensorimotor system Sensory vs Motor General model Classical model Principles of Motor systems: Sequential Hierarchical Parallel processing Cortical areas Association area Secondary motor cortex Primary motor cortex Subcortical motor processing Basal Ganglia Cerebellum Pathways Corticobulbar tracts Corticospinal tracts Lateral corticospinal tract Medial corticospinal tract Disorders of Motor systems References Contents

3. Sensorimotor System 01

4. 1. The sensory systems provide a window to the world, and the motor systems, in turn, provide the means of acting on the world. 2. Whereas control of sensory systems occurs in posterior brain regions, the cortical control of movement is mainly anterior. 3. Movement takes several forms, including reflex actions, automatic repetitive actions such as walking, semi-voluntary actions such as yawning, and voluntary actions such as deciding to pick up an object Sensory and Motor vs Sensorimotor

5. Voluntary Inhibiting involuntary response Feedback correction Complex movements Cortical involvement Pyramidal tracts Involuntary Reflexes Ballistic movements Motor program Spinal involvement Extrapyramidal tracts

6. 2. Principles of the Motor System

7. Principle of Motor Sequences Lashley Principle of Hierarchy John Hughlings Jackson Principle of Parallel Processing Miller, etc

8. Serial vs sequence Feedback Time-sensitive Principle of Motor Sequences

9. Evolutionary perspective Less complex vs more complex activities Higher levels vs lower levels of functioning Forebrain, brainstem and spinal cord Dissolution Functional independence Principle of Hierarchy

10. Automatism through leaning Cognitive leads to associative leading to autonomous (Fitts and Posner model) Pairing less-demanding with more-demanding actions Principle of Parallel Processing

11. 03 Cortical Motor areas

12. Notice its hierarchical structure, functional segregation, parallel descending pathways, and feedback circuits. General Model of Sensorimotor System Function

13. Posterior Parietal Association Cortex The posterior parietal association cortex (the portion of the parietal neocortex posterior to the primary somatosensory cortex) plays an important role, in: directing behaviour by providing spatial information, in directing attention,

14. Posterior Parietal Association Cortex

15. Dorsolateral Prefrontal Association Cortex D orsolateral prefrontal association cortex receives projections from the posterior parietal cortex. It sends projections to areas of the: secondary motor cortex , to the primary motor cortex , and to the frontal eye field .

16. Dorsolateral Prefrontal Association Cortex

17. Connects the associations and the secondary motor areas Neurons in an area of secondary motor cortex become more active just prior to the initiation of a voluntary movement and continue to be active throughout the movement. programming of specific patterns of movements after taking general instructions from dorsolateral prefrontal cortex Secondary Motor Cortex

18. Supplementary motor area Functions in organization and sequential timing of movement . Receives input from the parietal lobes the somatosensory strip, the secondary somatosensory areas, and subcortically from the basal ganglia and the cerebellum. outputs to the primary motor cortex in both the ipsilateral and contralateral hemisphere, Feedback to the basal ganglia and the cerebellum. Planner of motor sequences. Microstimulation vs stimulation

19. Premotor cortex The premotor cortex works in conjunction with the primary motor cortex and the supplemental motor area to help control voluntary movement in humans. The premotor cortex specifically utilizes external cues to help determine the specific muscles needed for an action to take place. the premotor cortex helps to decide upon the specific sequence of neuronal stimulation and muscles needed to carry out the movement based on visual stimuli

20. Cingulate motor area The Cingulate motor area lies next to the cingulate gyrus. The CMA is organized somatopically in relation to the spinal cord. It projects both to the spinal cord and to the primary motor area. Damage to the CMA results in a lack of spontaneous motor activity

21. Responsible for voluntary movements Cells in the premotor cortex and supplementary motor cortex are active during the planning of movements, even if the movements are never actually executed. The posterior parietal cortex keeps track of the position of the body relative to the world. The primary somatosensory cortex is the main receiving area for touch and other body information Primary motor cortex

22. Voluntary Movements The prefrontal cortex, The premotor cortex (Brodmann’s area 6), The supplementary motor cortex (Brodmann’s area 6), The primary motor cortex (Brodmann’s area 4), The posterior sensory regions of the cortex.

23. Blood flow in the cerebral cortex

24. Subcortical Motor Areas 4.

25. The Basal Ganglia Collection of nuclei in the forebrain Connections with the motor cortex and with the midbrain. Inputs from: all areas of the neocortex and limbic cortex Dopaminergic projection to the basal ganglia from the substantia nigra, Send projections back to both the motor cortex and the substantia nigra.

26. Divided into 3 parts Vestibulocerebellum : Equilibirium movements Spinocerebellum : hands and fingers Cerebrocerebellum : planning and relaying information Ipsilateral side The Cerebellum

27. 5. The Pathways

28. The Pathways Franz Gall and Johann Spurzheim Pathways that extended to the motor cortex to: The Lower brain stem: corticobulbar tracts The spinal cord: corticospinal tracts Lateral corticospinal tract Medial corticospinal tract

29. Corticobulbar tracts It originates from the lateral aspect of the primary motor cortex The upper motor neurons that project to the lower motor neurons of the brainstem innervate some of the cranial nerves to control the facial, mouth and tongue muscles The upper part of the face tends to be bilateral lower face and mouth contralateral central facial palsy . pseudobulbar palsy .

30. Corticobulbar tracts

31. Corticospinal Pathway Its purpose of it is to serve as a sensory filtering mechanism. Fibre bundles from primary motor cortex the supplementary and premotor cortices fibre bundles that arise from primary somatosensory cortex that project to the dorsal column nuclei and dorsal horn of the spinal cord.

32. Corticospinal Pathway The third component consists of two functionally distinct tracts: The lateral tract helps to control distal muscles (in the forearm, lower-limb hand and fingers) mainly on the opposite side of the body. Damage will compromise skilled movement involving hands or fingers. The ventral tract controls more medial muscles (in the trunk, upper limbs, etc.) on both sides. Damage will affect posture and ambulation.

33. Movement Disorders 6.

34. Huntington’s Disease Disorders result from basal ganglia damage Caudate putamen damaged: unwanted choreiform (writhing and twitching) movements result Involuntary and exaggerated movements.

35. Tourette’s syndrome Hyperkinetic movements unwanted tics and vocalizations such as head twists or sudden movements of a hand or arm or will often utter a cry. P hasic activity changes throughout the sensorimotor loop of the cortico-basal ganglia- thalamo -cortical network

36. Parkinson’s disease hypokinetic symptoms. loss of dopamine cells in the substantia nigra muscular rigidity impairments in posture and balance rhythmic tremors of the hands, legs, and body.

37. Some disorders of spinal column

38. Summary Vertebrates have smooth, skeletal, and cardiac muscles. All nerve-muscle junctions rely on acetylcholine as their neurotransmitter. Skeletal muscles range from slow muscles that do not fatigue to fast muscles that fatigue quickly. We rely on the slow muscles most of the time, but we recruit the fast muscles for brief periods of strenuous activity. Proprioceptors are receptors sensitive to the position and movement of a part of the body. Two kinds of proprioceptors, muscle spindles and Golgi tendon organs, help regulate muscle movements. Children and some adults have trouble shifting their attention away from a moving object toward an unmoving one. Some movements, especially reflexes, proceed as a unit, with little if any guidance from sensory feedback. Other movements, such as threading a needle, are guided and redirected by sensory feedback.

39. Summary The primary motor cortex is the main source of brain input to the spinal cord. The spinal cord contains central pattern generators that actually control the muscles. The primary motor cortex produces patterns representing the intended outcome, not just the muscle contractions. Areas near the primary motor cortex—including the prefrontal, premotor, and supplementary motor cortices—are active in detecting stimuli for movement and preparing for a movement. Mirror neurons in various brain areas respond to both a self-produced movement and an observation of a similar movement by another individual. Although some neurons may have built-in mirror properties, at least some of them acquire these properties by learning. Their role in imitation and social behaviour is potentially important but as yet speculative. When people identify the instant when they formed a conscious intention to move, their time precedes the actual movement by about 200 ms but follows the start of motor cortex activity by about 300 ms . These results suggest that what we call a conscious decision is our perception of a process already underway, not really the cause of it.

40. Summary People with damage to part of the parietal cortex fail to perceive any intention before starting their own movements. The lateral tract, which controls movements in the body's periphery, has axons that cross from one side of the brain to the opposite side of the spinal cord. The medial tract controls bilateral movements near the midline of the body. The cerebellum is critical for rapid movements that require accurate aim and timing. It has multiple roles in behaviour, including sensory functions related to the perception of the timing or rhythm of stimuli. The cells of the cerebellum are arranged in a regular pattern that enables them to produce outputs of precisely controlled duration. The basal ganglia are a group of large subcortical structures that are important for selecting and inhibiting particular movements. Damage to the output from the basal ganglia leads to jerky, involuntary movements. The learning of a motor skill depends on changes occurring in both the cerebral cortex and the basal ganglia.

41. Summary Parkinson’s disease is characterised by impaired initiation of activity, slow and inaccurate movements, tremors, rigidity, depression, and cognitive deficits. Parkinson’s disease is associated with degenerating dopamine-containing axons from the substantia nigra to the caudate nucleus and putamen. A gene has been identified that is responsible for early-onset Parkinson’s disease. Heredity plays a minor role in the more common form of Parkinson’s disease, with onset after age 50. The chemical MPTP selectively damages neurons in the substantia nigra and leads to the symptoms of Parkinson’s disease. Some cases of Parkinson’s disease may partly result from exposure to toxins. The most common treatment for Parkinson’s disease is L-dopa, which crosses the blood-brain barrier and enters neurons that convert it into dopamine. However, the effectiveness of L-dopa varies, producing unwelcome side effects.

42. Summary Many other treatments are in use or at least in the experimental stage. The transfer of immature neurons into a damaged brain area seems to offer great potential, but so far, it has provided little practical benefit. Huntington’s disease is a hereditary condition marked by deterioration of motor control as well as depression, memory impairment, and other cognitive disorders. By examining chromosome 4, physicians can determine whether someone will likely develop Huntington’s disease later in life. The more C-A-G repeats in the gene, the earlier the likely onset of symptoms. The gene responsible for Huntington’s disease alters the protein structure, known as huntingtin. The altered protein interferes with the functioning of the mitochondria.

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