Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

BN09 sensorimotor - movement.ppt by shitingting

VIEWS: 1 PAGES: 42

									  Sensorimotor
Control of Behavior:
    Movement
        Lecture 9
            Motor Systems
 Functions
   movement

   posture & balance

   communication

 Guided by sensory systems
   internal representation of world & self

   detect changes in environment

    external & internal ~
         Movement & Muscles
 Movement occurs at joints
 Contraction & relaxation of of
  opposing muscles
   agonists

        prime movers
       antagonists
        counterbalance agonists
        decelerate movement ~
Dorsal     Upper Motor
            Neurons




      +


  -                      +
            Alpha            +
           Motor neurons
 Ventral
         Movement & Muscles
   Movement control more than contraction
    & relaxation
     Accurately time control of many

      muscles
     Make postural adjustment during

      movement
     Adjust for mechanical properties of

      joints & muscles
      inertia, changing positions ~
      3 Classes of Movement
   Voluntary
     complex actions

       reading, writing, playing piano
     purposeful, goal-oriented

     learned

       improve with practice ~
        3 Classes of Movement
   Reflexes
     involuntary, rapid, stereotyped

       eye-blink, coughing, knee jerk
     graded control by eliciting stimulus ~
         3 Classes of Movement
   Rhythmic motor patterns
     combines voluntary & reflexive acts

       chewing, walking, running
     initiation & termination voluntary

     once initiated, repetitive & reflexive ~
    Organization of Motor Control
 Hierarchical & Parallel
 Parallel
   pathways active simultaneously

   e.g. moving arm

     1. muscles producing movement
     2. postural adjustments during
        movement
 Recovery of function after lesion
   overlapping functions ~
Hierarchical Control of Movement
  3 levels of control
     Cortex

     Brainstem

     Spinal cord (SC)

  Division of responsibility
     higher levels: general commands

     spinal cord: complex & specific

  Each receives sensory input
     relevant to levels function ~
Hierarchical Control of Movement
 Association cortices & Basal Ganglia
   strategy : goals & planning

   based on integration of sensory info

 Motor cortex & cerebellum
   tactics: activation of motor programs

 Spinal cord
   execution: activates a motor neurons

   reflexes

   rhythmic pattern generators ~
Sensorimotor Cortical System
 Integration of sensory information
      and directed movements
 Anatomy
 Descending spinal tracts
    Lateral pathway

        Pyramidal Motor System
       Ventromedial pathway
       Extrapyramidal pathway ~
       Cortical Anatomy
 S1 - postcentral gyrus
 PPC - Posterior Parietal Cortex
 M1 - Precentral Gyrus
   Frontal Lobe

   somatotopic organization
 M2 - Secondary Motor Cortex
     SMA - Supplementary Motor Area
     PM - Premotor Cortex
SMA



      M1 S1   PPC


PM
The Descending Spinal Tracts
       Brain to Spinal Cord
 Upper motor neurons
   communication with lower (a) motor

    neurons
 Lateral pathway
   direct cortical control

 Ventromedial pathway
   brain stem control ~
      The Lateral Pathway
 Voluntary movement
   distal limbs

   2 tracts

 Corticospinal tract
     about 1 million axons
 Rubrospinal tract
     small part of pathway ~
Spinal Cord: Lateral Pathway
     Dorsal       Corticospinal
                      tract




                     Rubrospinal
                        tract
     Ventral
       Corticospinal tract
 Motor cortex ---> spinal cord
   uninterrupted axon

   2/3 of axons from motor cortex

   1/3 from somatosensory cortex

 Decussates at medulla
 Contralateral control movement ~
     The Rubrospinal Tract
 Motor Cortex ---> red nucleus
 Red nucleus ---> spinal cord
   inputs from motor cortex

   bigger role in other mammalian

    species ~
    Lateral Pathway Damage
 Lesion both tracts
   no independent movement of distal

    limbs
   voluntary movements slow & less

    accurate
 Corticospinal only
   same deficits

   recovery over several months

   compensation by rubrospinal tract ~
    The Ventromedial Pathway
 Neurons originate in brainstem
 Vestibulospinal & tectospinal tracts
   head & posture posture

   orienting responses

 Pontine & medullary reticulospinal tracts
   originate in reticular formation

   trunk & antigravity leg muscles

   tracts are antagonistic ~
Spinal Cord: Ventromedial Pathway
                  Dorsal
Vestibulospinal
      tract


                              Tectospinal
                                  tract




  Medullary                   Pontine
Reticulospinal              Reticulospinal
    tract         Ventral       tract
Major Descending Spinal Tracts
              Motor Cortex

    Lateral           Ventromedial



    Red           Reticular   Superior Colliculus
   Nucleus         Nuclei      vestibular nuclei




              Spinal cord
     Cortical Control
      of Movement
     Primary Motor Cortex
 Somatotopic organization
   neurons have preferred direction

    of movement
 Motor homunculus ~
     M1: Coding Movement
 Movement for limbs
 Neuron most active
   Preferred direction

   but active at 45 from preferred

 How is direction determined?
   Populations of M1 neurons

   Net activity of neurons with

    different preferred directions
   vectors ~
M1: Coding Movement
         Implications
        1. Most M1 active for every
          movement
        2. Activity of each neuron
          1 “vote”
        3. direction determined by
          averaging all votes ~
    Motor Association Cortex
 Motor area other than M1
   secondary motor cortex (M2)

 Premotor & Supplemental Motor Areas
 Active during preparation for movement
   Planning of movements

 Stimulation - complex movements
   motor programs ~
Supplementary Motor Area - SMA
  Primarily midline cortex
  Inputs from …
     PPC

     S1

  Bilateral output to M1
     to distal limbs ~
     Premotor Area - PMA
 Anterior to M1
 Input
    primarily from PPC

    reciprocal connections with SMA

 Outputs to M1
    then proximal limbs ~
SMA


      M1   S1     PPC


PMA
           Spinal cord
         Planning Movements
   Targeting vs trigger stimulus
      recording activity of neurons
 active when movement planned
    for specific direction

 Different populations of neurons active
    during planning (targeting)

    & execution (trigger stimulus)

 PM active before movement ~
   Simple finger flexion
     only M1 activation
   Sequence of complex finger movements
     M1 + SMA activation ~
   Mental rehearsal of finger movements
     only SMA activation ~
     Sensorimotor Integration
 Perceptual development
 Active interaction required
   environmental feedback important

 Held & Hein (1950s)
   kittens passively moved

   depth perception deficits

      & related responses, blinking,
      looming ~
        Sensorimotor Integration
   Sensory inputs guide movement
    visual, auditory, tactile
    

       location of objects in space
   Proprioceptive & vestibular

       position of our body
 Critical for planning & refining
  movements ~
     Generation of
Rhythmic Motor Patterns
        Central Pattern Generators
 Half-center Model
   alternating activity in flexor & extensor

 Step-cycle has 2 phases
   swing phase

        foot off ground & flexing forward
       stance phase
        foot planted & leg extending
   Each limb has own pattern generator ~
                            Half-center Model
         Flexor
                            a
         +              +       +

Tonic            +
 input       +

                            a
         +              +       +

             Extensor
Rhythmic Patterns: Sensory Feedback

 Not necessary for locomotion
   but slower, less coordinated

 Stumble correction reaction
   during swing phase

   tactile stimulus on dorsal foot ---> flexion

 Reflex reversal
   override during extension

   flexion would cause collapse ~
    Goal-directed Locomotion
 Requires intact supraspinal systems
 Coordination of antigravity muscles
     Brainstem motor nuclei
 modulation of contraction strength
     Reticulo-, rubro-, corticospinal
 Balance
     Vestibulospinal tract (Ventromedial)
 Also cortical & subcortical areas ~

								
To top