CH 8: The Sensorimotor System Flashcards
WRT the Sensorimotor System, explain what’s meant by ‘HIERARCHICALLY ORGANIZED” & “FUNCTIONAL SEGREGATION”
- Sensorimotor sys directed by commands cascading down levels of hierarchy from the association cortex = hierarchically organized
- Hierarchy characterized by FUNCTIONAL SEGREGATION = each level composed of diff units that perform diff functions
Describe the ASSOCIATION CORTEX
- Top of the sensorimotor hierarchy
- Specifies general goals rather than specific plans of advantage
Name an advantage of higher levels of hierarchy?
Higher levels of hierarchy are free to perform & complex functions
What’s the primary difference b/w the flow of info in SENSORY systems vs. SENSORIMOTOR systems?
- The primary direct of info flow
- Sensory sys: info mainly flows UP through hierarchy
- Sensorimotor sys: info flows DOWN
Describe SENSORY FEEDBACK and its important role of sensory input for motor output.
- Sensory signals that are prod by a response & are used to guide the continuation of the response
- Eyes, organs of balance, skin receptors, muscles & joints monitor body’s responses
- -> Feed info back into sensorimotor circuits
- Motor output adjustments that occur IRT sensory feedback = unconsciously controlled via lower levels of sensorimotor hierarchy
Describe how learning changes the nature & locus of sensorimotor control.
- Initial motor learning stages = each individual response performed under CONSCIOUS control
- -> practice
- -> individual responses organized into cont. integrated sequences of action
- -> smoothly flows & adjusted via sensory feedback
- -> transfer control to lower levels of CNS
- ie) typing, knitting, dancing, etc.
Explain the role of the POSTERIOR PARIETAL ASSOCIATION CORTEX in sensorimotor function.
Its input & output?
Posterior Parietal Association Cortex:
= Area of association cortex
- Receives input from visual, auditory & somatosensory systems
- **Involved in perception of spatial location & guidance of voluntary behaviour
- INPUT from sensory sys that play role in localization of body & external objects in space
- OUTPUT from posterior parietal cortex goes to MOTOR CORTEX (located in frontal cortex
List the deficits that occur as a result of damage to the Posterior Parietal Association Cortex (4).
DAMAGE –> deficits in:
- perception & memory of spacial relations
- accurate reaching & grasping
- eye movement control
- attention
List the 2 largest consequences of damage to the Posterior Parietal Association Cortex.
- Apraxia
2. Contralateral Neglect
Describe APRAXIA
- Disorder of voluntary movement that’s not attributable to simple motor deficit (ie. not to paralysis or weakness)
- Difficulty making specific movements when requested
- -> Can do same movements naturally when not thinking
Describe CONTRALATERAL NEGLECT
- Disturbance of ability to respond to stimuli on side of body OPPOSITE to side of brain lesion in absence of simple sensory or motor deficits
- -> Behave as if (L) side of their world doesn’t exist
- ie) Does makeup on only (R) side of face
- ie) Doesn’t notice food on (L) side of plate
- ie) Only turns right
Explain the role of the DORSOLATERAL PREFRONTAL ASSOCIATION CORTEX in sensorimotor function.
Where does it receive its inputs from?
Dorsolateral Prefrontal Association Cortex:
= Area of prefrontal association cortex
- **Plays role in evaluation of external stimuli & initiation of voluntary motor responses
- Receives input from POSTERIOR PARIETAL ASS. CORTEX
- -> Sends input to areas of secondary motor cortex, primary motor cortex, & Frontal eye field
Describe the response properties of neurons in the Dorsolateral Prefrontal Association Cortex.
- Activity of dorsolateral prefrontal neurons are related to RESPONSE rather than object
- -> Begins to fire before response & continues to fire until response complete
- Decisions to initiate voluntary movements depends on critical interactions w/ posterior parietal cortex & other areas of frontal cortex
Explain the general role of areas of SECONDARY MOTOR CORTEX (aka what are its neurons responsible for (2)?
Secondary Motor Cortex:
= supplementary motor area + premotor cortex
- Neurons in this area:
1. Become ^active just prior to initiating voluntary movement, & continue being active throughout the movement
2. Are involved in programming specific patterns of movement after taking general instructions from Dorsolateral Prefrontal Cortex.
Input & output of the secondary motor cortex?
- Receives input from association cortex & sends output to primary cortex
Association cortex = _________ + ________.
- Posterior Parietal Cortex + Dorsolateral Prefrontal Cortex
When do MIRROR NEURONS fire?
- Fires when an individual performs a particular goal-directed hand movement, or when they observe the same goal directed performed by another
Explain why Mirror Neurons have received so much attention from neuroscientists.
- **Provides possible mech for SOCIAL COGNITION = knowledge of the perceptions, ideas & intentions of others
- Mapping actions of others onto own action repertoire = social understanding, cooperation & imitation
- Mirror neurons responds to the understanding of the purpose of an action
Describe the PRIMARY MOTOR CORTEX.
- Cortex of the pre-central gyrus (in frontal lobe)
- Major point of departure for motor signals descending from cerebral cortex into lower levels of the sensorimotor system
Describe the CONVENTIONAL view of primary motor cortex function & the evidence up which it was based.
- Motor cortex organized via SOMATOTOPIC LAYOUT = organized, like the primary somatosensory system, to a map of the surface of the body
- Each site in primary motor cortex receives sensory feedback from receptors in the muscles that the site influences
- Each primary motor cortex neuron thought to encode the direction of movement
- Learned by stimulating parts of body & seeing which parts of brain are active
- -> via brief pulses of current just above threshold to produce a reaction
**Many primary motor cortex neurons are tuned to movement in a particular direction
Describe the CURRENT view of primary motor cortex function & the evidence up which it was based.
- Map primary motor cortex via longer bursts of currents
- Rather than eliciting individual muscle contractions, currents elicit complex natural-looking response sequences
- **Signals from every site in primary motor cortex greatly diverge
- -> So each particular site has ability to get a body part to a target location regardless of starting position
**Primary motor cortex neurons play MAJOR role in initiating body movements
Describe the structure of the CEREBELLUM (2).
Cerebellum:
- Organized systematically in lobes, columns & layers
- Contains >1/2 of brain’s neurons
Describe the 3 types of info the cerebellum receives & explain the current view of cerebellar function.
- Info from primary & secondary motor cortex
- Info about descending motor signals from brain stem motor nuclei
- Feedback from motor responses via somatosensory & vestibular systems
- -> Compares these 3 sources of input & corrects ongoing movement that deviate from intended course
- -> Thus plays major role in MOTOR LEARNING
Describe the consequence of cerebellar damage.
- Disrupts motor function via balance, gait, speech & eye movement control
Describe the anatomy of the BASAL GANGLIA.
- Not as many neurons as cerebellum, but is more complex
- Organized via complex heterogeneous collection of interconnected nuclei
Explain the current view of the function of the Basal Ganglia (4).
- Part of neural loops that receive cortical input from various cortical areas
- -> Transmits it back to cortex via thalamus - Plays role in modulation of motor output (like cerebellum)
- Involved in variety of cognitive functions
- Play role in habit learning = motor learning
