Sensorimotor system

principles
1. hierarchical organisation
2. motor output guided by sensory input
3. learning changes the nature and locus of sensorimotor control
sensorimotor associaton cortex
1. posterior parietal association cortex
  1. ROLE: knowing the original position of parts of the body that needs to be moved position of external objects directing attention
  2. INPUT: visual system auditory system somatosensory system
  3. OUTPUT: dorsolateral prefrontal association cortex / areas of secondary motor cortex / frontal eye field
  4. DAMAGE - various sensorimotor deficits accurate reaching and grasping control of eye movements APRAXIA CONTRALATERAL (VISUAL) NEGLECT
2. dorsolateral prefrontal association cortex
  1. INPUT: posterior parietal cortex
  2. OUTPUT: areas of secondary motor cortex, primary motor cortex, frontal eye fields
  3. ROLE: evaluation of external stimuli and the initiation of voluntary reactions to them
secondary motor cortex
1. most INPUT - association cortex
2. most OUTPUT primary motor cortex
3. supplementary motor areas (SMA & preSMA)
4. premotor areas
  1. dorsal
  2. ventral
  3. MIRROR NEURONS (found in premotor cortex)
5. small cingulate areas
6. ROLE: areas involved in programming of specific patterns of movements after taking general instructions from dorsolateral prefronral cortex = evidence from Parsons et al (1995)
primary motor cortex
1. ROLE: major point of convergence of cortical sensorimotor signals AND departure of those signals from cerebral cortex
2. organised SOMATOTOPICALLY - according to a map of the body
3. controlling parts of body capable of intricate movements (hands, mouth)
4. feedback from receptors in the muscles and joints
Basal ganglia - heterogenous collection of interconnected stimuli
1. ROLE: inhibiting & initiating movement
2. INPUT motor cortex, prefrontal motor cortex, supplementary areas -> PLAN. prefrontal cortex -> strategy WHEN through BS
3. Relationship with superior colliculus
  1. Evidence: monkeys trained to make specific eye movements. Neurons in the caudate nucleus fire bursts of action potentials just before eye movement initiation. Immediately thereafter neurons in the substantia nigra pars reticulata shut down resulting in a burst of action potentials in the superior colliculus and the production of eye movement
4. components: the striatum (caudate nucleus + putamen), the globus pallidus, the substantia nigra, the nucleus accumbens, subthalamic nucleus
5. damage: movement disorders. Parkinson's disease, Huntington's disease, Tourette
6. substantia nigra is the source of the striatal input of the neurotransmitter dopamine
cerebellum
1. responsible for
  1. online error correction - smoothly coordinated skilled movements
  2. planning - temporal aspects of movement
  3. perceiving short time intervals
  4. judging velocity of moving objects
2. INPUT primary & secondary motor cortex, brainstem motor nuclei, feedback from responses via somatosensory & vestibular systems
3. OUTPUT: cerebellar cortex, thalamus, primary motor and premotor cortices
4. DAMAGE: lost ability to preceisly control direction, force, velocity, amplitude of movements; to adapt patterns of motor outputs to changing conditions, steady postures problems, problems with balance, gait, speech, control of eye movements
  1. lateral cerebellum -> cerebellar ATAXIA - disrupted sensory coordination of limb movements

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Sensorimotor system

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