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Chapter 6 The Sensorimotor System  How You Do What You Do <ul><li>This multimedia product and its contents are protected u...
3 Principles of Sensorimotor Function <ul><li>Hierarchical organization </li></ul><ul><ul><li>Association cortex at the hi...
 
2 Major Areas of Sensorimotor Association Cortex <ul><li>Each composed of several different areas with different functions...
Posterior Parietal Association Cortex <ul><li>Integrates information about </li></ul><ul><ul><li>Body part location </li><...
What affect does damage to the posterior parietal area have? <ul><li>Apraxia  – disorder of voluntary movement – problem o...
Dorsolateral Prefrontal Association Cortex <ul><li>Input from posterior parietal cortex </li></ul><ul><li>Output to second...
 
Secondary Motor Cortex <ul><li>Input mainly from association cortex </li></ul><ul><li>Output mainly to primary motor corte...
Secondary Motor Cortex <ul><li>Subject of ongoing research </li></ul><ul><li>May be involved in programming movements in r...
Primary Motor Cortex <ul><li>Precentral gyrus of the frontal lobe </li></ul><ul><li>Major point of convergence of cortical...
Motor homunculus
The Motor Homunculus <ul><li>Control of hands involves a network of widely distributed neurons </li></ul><ul><li>Stereogno...
Cerebellum and Basal Ganglia <ul><li>Interact with different levels of the sensorimotor hierarchy </li></ul><ul><li>Coordi...
Cerebellum <ul><li>10% of brain mass, > 50% of its neurons </li></ul><ul><li>Input from 1 °  and 2 °  motor cortex </li></...
Basal Ganglia  <ul><li>A collection of nuclei </li></ul><ul><li>Part of neural loops that receive cortical input and send ...
4 Descending Motor Pathways <ul><li>2 dorsolateral </li></ul><ul><ul><li>Corticospinal  </li></ul></ul><ul><ul><li>Cortico...
Dorsolateral Tracts <ul><li>Most synapse on interneurons of spinal gray matter </li></ul><ul><li>Corticospinal - descend t...
 
Ventromedial Tracts <ul><li>Corticospinal </li></ul><ul><ul><li>Descends ipsilaterally </li></ul></ul><ul><ul><li>Axons br...
 
Dorsolateral Vs Ventromedial Motor Pathways <ul><li>Dorsolateral </li></ul><ul><li>one direct tract, one that synapses in ...
Motor Units and Muscles <ul><li>Motor units – a motor neuron + muscle fibers, all fibers contract when motor neuron fires ...
Muscles <ul><li>Acetylcholine released by motor neurons at the neuromuscular junction causes contraction </li></ul><ul><li...
Muscles <ul><li>Flexors  – bend or flex a joint </li></ul><ul><li>Extensors  – straighten or extend </li></ul><ul><li>Syne...
Receptor Organs of Tendons and Muscles <ul><li>Golgi tendon organs </li></ul><ul><ul><li>Embedded in tendons </li></ul></u...
 
Knee-jerk (patellar tendon) reflex
Reflexes <ul><li>Stretch reflex – monosynaptic, serves to maintain limb stability </li></ul><ul><li>Withdrawal reflex – mu...
 
Central Sensorimotor Programs <ul><li>Perhaps all but the highest levels of the sensorimotor system have patterns of activ...
Motor equivalence <ul><li>A given movement can be accomplished various ways, using different muscles </li></ul><ul><li>Cen...
The Development of Central Sensorimotor Programs <ul><li>Programs for many species-specific behaviors established without ...
The Development of Central Sensorimotor Programs <ul><li>Response chunking </li></ul><ul><ul><li>Practice combines the cen...
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Pinel basics ch06

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Pinel basics ch06

  1. 1. Chapter 6 The Sensorimotor System How You Do What You Do <ul><li>This multimedia product and its contents are protected under copyright law. The following are prohibited by law: </li></ul><ul><li>any public performance or display, including transmission of any image over a network; </li></ul><ul><li>preparation of any derivative work, including the extraction, in whole or in part, of any images; </li></ul><ul><li>any rental, lease, or lending of the program. </li></ul>
  2. 2. 3 Principles of Sensorimotor Function <ul><li>Hierarchical organization </li></ul><ul><ul><li>Association cortex at the highest level, muscles at the lowest </li></ul></ul><ul><ul><li>Parallel structure – signals flow between levels over multiple paths </li></ul></ul><ul><li>Motor output guided by sensory input </li></ul><ul><li>Learning (experience) changes the nature and locus of sensorimotor control </li></ul><ul><ul><li>Conscious to automatic, for example </li></ul></ul>
  3. 4. 2 Major Areas of Sensorimotor Association Cortex <ul><li>Each composed of several different areas with different functions </li></ul><ul><li>Some disagreement exists about how to divide the areas up </li></ul><ul><li>Posterior parietal association cortex </li></ul><ul><li>Dorsolateral prefrontal association cortex </li></ul>
  4. 5. Posterior Parietal Association Cortex <ul><li>Integrates information about </li></ul><ul><ul><li>Body part location </li></ul></ul><ul><ul><li>External objects </li></ul></ul><ul><li>Receives visual, auditory, and somatosensory information </li></ul><ul><li>Outputs to motor cortex </li></ul>
  5. 6. What affect does damage to the posterior parietal area have? <ul><li>Apraxia – disorder of voluntary movement – problem only evident when instructed to perform an action – usually a consequence of damage to the area on the left </li></ul><ul><li>Contralateral neglect – unable to respond to stimuli contralateral to the side of the lesion - usually seen with large lesions on the right </li></ul>
  6. 7. Dorsolateral Prefrontal Association Cortex <ul><li>Input from posterior parietal cortex </li></ul><ul><li>Output to secondary motor cortex, primary motor cortex, and frontal eye field </li></ul><ul><li>Evaluates external stimuli and initiates voluntary reactions – supported by neuronal responses </li></ul>
  7. 9. Secondary Motor Cortex <ul><li>Input mainly from association cortex </li></ul><ul><li>Output mainly to primary motor cortex </li></ul><ul><li>At least 7 different areas </li></ul><ul><ul><li>2 supplementary motor areas </li></ul></ul><ul><ul><ul><li>SMA and preSMA </li></ul></ul></ul><ul><ul><li>2 premotor areas </li></ul></ul><ul><ul><ul><li>dorsal and ventral </li></ul></ul></ul><ul><ul><li>3 cingulate motor areas </li></ul></ul>
  8. 10. Secondary Motor Cortex <ul><li>Subject of ongoing research </li></ul><ul><li>May be involved in programming movements in response to input from dorsolateral prefrontal cortex </li></ul><ul><li>Many premotor neurons are bimodal – responding to 2 different types of stimuli </li></ul>
  9. 11. Primary Motor Cortex <ul><li>Precentral gyrus of the frontal lobe </li></ul><ul><li>Major point of convergence of cortical sensorimotor signals </li></ul><ul><li>Major point of departure of signals from cortex </li></ul><ul><li>Somatotopic – more cortex devoted to body parts which make many movements </li></ul>
  10. 12. Motor homunculus
  11. 13. The Motor Homunculus <ul><li>Control of hands involves a network of widely distributed neurons </li></ul><ul><li>Stereognosis – recognizing by touch – requires interplay of sensory and motor systems </li></ul><ul><li>Some neurons are direction specific – firing maximally when movement is made in one direction </li></ul>
  12. 14. Cerebellum and Basal Ganglia <ul><li>Interact with different levels of the sensorimotor hierarchy </li></ul><ul><li>Coordinate and modulate </li></ul><ul><li>May permit maintenance of visually guided responses despite cortical damage </li></ul>
  13. 15. Cerebellum <ul><li>10% of brain mass, > 50% of its neurons </li></ul><ul><li>Input from 1 ° and 2 ° motor cortex </li></ul><ul><li>Input from brain stem motor nuclei </li></ul><ul><li>Feedback from motor responses </li></ul><ul><li>Involved in fine-tuning and motor learning </li></ul><ul><li>May also do the same for cognitive responses </li></ul>
  14. 16. Basal Ganglia <ul><li>A collection of nuclei </li></ul><ul><li>Part of neural loops that receive cortical input and send output back via the thalamus </li></ul><ul><li>Modulate motor output and cognitive functions </li></ul>
  15. 17. 4 Descending Motor Pathways <ul><li>2 dorsolateral </li></ul><ul><ul><li>Corticospinal </li></ul></ul><ul><ul><li>Corticorubrospinal </li></ul></ul><ul><li>2 ventromedial </li></ul><ul><ul><li>Corticospinal </li></ul></ul><ul><ul><li>Cortico-brainstem-spinal tract </li></ul></ul><ul><li>Both corticospinal tracts are direct </li></ul>
  16. 18. Dorsolateral Tracts <ul><li>Most synapse on interneurons of spinal gray matter </li></ul><ul><li>Corticospinal - descend through the medullary pyramids, then cross </li></ul><ul><ul><li>Betz cells – synapse on motor neurons projecting to leg muscles </li></ul></ul><ul><ul><li>Wrist, hands, fingers, toes </li></ul></ul><ul><li>Corticorubrospinal – synapse at red nucleus and cross before the medulla </li></ul><ul><ul><li>Some control muscles of the face </li></ul></ul><ul><ul><li>Distal muscles of arms and legs </li></ul></ul>
  17. 20. Ventromedial Tracts <ul><li>Corticospinal </li></ul><ul><ul><li>Descends ipsilaterally </li></ul></ul><ul><ul><li>Axons branch and innervate interneuron circuits bilaterally in multiple spinal segments </li></ul></ul><ul><li>Cortico-brainstem-spinal </li></ul><ul><ul><li>Interacts with various brain stem structures and descends bilaterally carrying information from both hemispheres </li></ul></ul><ul><ul><li>Synapse on interneurons of multiple spinal segments controlling proximal trunk and limb muscles </li></ul></ul>
  18. 22. Dorsolateral Vs Ventromedial Motor Pathways <ul><li>Dorsolateral </li></ul><ul><li>one direct tract, one that synapses in the brain stem </li></ul><ul><li>Terminate in one contralateral spinal segment </li></ul><ul><li>Distal muscles </li></ul><ul><li>Limb movements </li></ul><ul><li>Ventromedial </li></ul><ul><li>one direct tract, one that synapses in the brain stem </li></ul><ul><li>More diffuse </li></ul><ul><li>Bilateral innervation </li></ul><ul><li>Proximal muscles </li></ul><ul><li>Posture and whole body movement </li></ul>
  19. 23. Motor Units and Muscles <ul><li>Motor units – a motor neuron + muscle fibers, all fibers contract when motor neuron fires </li></ul><ul><li>Number of fibers per unit varies – fine control, fewer fibers/neuron </li></ul><ul><li>Muscle – muscle fibers bound together by a tendon </li></ul>
  20. 24. Muscles <ul><li>Acetylcholine released by motor neurons at the neuromuscular junction causes contraction </li></ul><ul><li>Motor pool – all motor neurons innervating the fibers of a single muscle </li></ul><ul><li>Fast muscle fibers – fatigue quickly </li></ul><ul><li>Slow muscle fibers – capable of sustained contraction due to vascularization </li></ul><ul><li>Muscles are a mix of slow and fast </li></ul>
  21. 25. Muscles <ul><li>Flexors – bend or flex a joint </li></ul><ul><li>Extensors – straighten or extend </li></ul><ul><li>Synergistic muscles – any 2 muscles whose contraction produces the same movement </li></ul><ul><li>Antagonistic muscles – any 2 muscles that act in opposition </li></ul>
  22. 26. Receptor Organs of Tendons and Muscles <ul><li>Golgi tendon organs </li></ul><ul><ul><li>Embedded in tendons </li></ul></ul><ul><ul><li>Tendons connect muscle to bone </li></ul></ul><ul><ul><li>Detect muscle tension </li></ul></ul><ul><li>Muscle spindles </li></ul><ul><ul><li>Embedded in muscle tissue </li></ul></ul><ul><ul><li>Detect changes in muscle length </li></ul></ul>
  23. 28. Knee-jerk (patellar tendon) reflex
  24. 29. Reflexes <ul><li>Stretch reflex – monosynaptic, serves to maintain limb stability </li></ul><ul><li>Withdrawal reflex – multisynaptic </li></ul><ul><li>Reciprocal innervation – antagonistic muscles interact so that movements are smooth – flexors are excited while extensors are inhibited, etc. </li></ul>
  25. 31. Central Sensorimotor Programs <ul><li>Perhaps all but the highest levels of the sensorimotor system have patterns of activity programmed into them and complex movements are produced by activating these programs </li></ul><ul><li>Cerebellum and basal ganglia then serve to coordinate the various programs </li></ul>
  26. 32. Motor equivalence <ul><li>A given movement can be accomplished various ways, using different muscles </li></ul><ul><li>Central sensorimotor programs must be stored at a level higher than the muscle (as different muscles can do the same task) </li></ul><ul><li>Sensorimotor programs may be stored in 2 ° motor cortex </li></ul>
  27. 33. The Development of Central Sensorimotor Programs <ul><li>Programs for many species-specific behaviors established without practice </li></ul><ul><li>Fentress (1973) – mice without forelimbs still make coordinated grooming motions </li></ul><ul><li>Practice can also generate and modify programs </li></ul><ul><ul><li>Response chunking </li></ul></ul><ul><ul><li>Shifting control to lower levels </li></ul></ul>
  28. 34. The Development of Central Sensorimotor Programs <ul><li>Response chunking </li></ul><ul><ul><li>Practice combines the central programs controlling individual response </li></ul></ul><ul><li>Shifting control to lower levels </li></ul><ul><ul><li>Frees up higher levels to do more complex tasks </li></ul></ul><ul><ul><li>Permits greater speed </li></ul></ul>

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