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66 Cards in this Set
- Front
- Back
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What does the motor system do? |
Allows us to maintain balance and posture, move our body, limbs, and eyes, and to communicate through speech and gesture |
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What are the three classes of movement? |
Voluntary movements, reflex responses, and rhythmic motor patterns |
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Describe voluntary movements. |
Most complex Purposeful Goal directed Largely learned Performance increases with practice |
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Describe reflex responses. |
Simplest Least affected by voluntary controls Rapid, somewhat stereotyped, involuntary Controlled in graded way by eliciting stimulus |
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Describe rhythmic motor patterns. |
Combine features of voluntary and reflex acts Only the initiation and termination of sequence are voluntary Relatively stereotyped once initiated |
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Can individual muscles push? Pull? |
They can only pull |
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What are the tasks carried out by the motor system? |
Contracting and relaxing Timed commands to many groups Postural adjustments Motor plant: mechanical arrangement of the muscles, bones, and joints |
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Why must motor system constantly adjust commands? |
Compensate for the inertia of the limbs |
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What are the two important organizational features of motor systems? |
1) Motor systems have available to them a continuous flow of sensory information about events in the environment, the position and orientation fo the body and limbs, and the degree of contraction of the muscles 2) Hierarchy of control levels and each level is provided with that sensory information that is relevant for the functions it controls |
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What are the sensory mechanisms that contribute to motor control? |
1) Vision, hearing, and body surface receptors inform us about where objects are in space and our own position relative to them 2) Proprioceptors in muscle, joints, and the vestibular apparaturs inform the motor systems about the length and tension of muscles |
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What is sensory information used for? |
To correct errors through feedback and feed-forward mechanism |
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What is a feedback signal? |
Compared to a reference signal that indicates the desired output value |
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What is negative feedback? |
Feedback signal is subtracted from the reference signal by a comparator, and the resultant error signal acts on a controller to increase or decrease the output of the controlled system |
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What is regulation? |
When the variable is to be maintained around a set value, the reference signal remains constant through this process |
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What type of movements is feedback limited to? |
Slow movements |
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What is high gain? |
When the feedback loop is very powerful Long time delays System can be driven into an undesirable state of oscillation |
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How can sensory events control motor action more effectively? |
By providing advance rather than feedback information |
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What is feed-forward control? |
Advance information that requires dynamic representations or internal models |
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What types of processes is feedback responsible for? |
Maintain posture Regulate slow movements Operates continuously |
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What types of processes is feed-forward responsible for? |
Operate more quickly Triggered intermittently |
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What can compensate for the loss of proprioceptive sensation through feed-forward as well as through feedback? |
Vision |
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What are the three levels in the hierarchy of motor control? |
Spinal cord, brain stem, and cortical motor areas |
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What three mechanisms are involved in the hierarchy? |
Feedback Feed-forward Adaptive mechanisms |
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What is a benefit of the hierarchical organization? |
Higher orders give general commands while lower levels can generate complex spatiotemporal patterns |
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What does the corticospinal tract do? |
Controls pathways descending form the brain stem but also controls spatial interneurons and motor neurons directly |
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What is the lowest level of the hierarchy? |
Spinal cord mediates autonomic and stereotyped reflexes |
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What is the final common path? |
Motor neurons |
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What is the middle level of the motor hierarchy? |
Brain stem |
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What are the three neuronal systems of the brain stem? |
Medial Lateral Aminergic |
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What does the brain stem do? |
Integrates visual and vestibular information Posture Controls eye and head movements |
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What is the highest level of motor control? |
Motor cortex |
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What are the three areas of motor cortex? |
Primary motor cortex Lateral premotor area Supplementary motor area |
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Which areas project to primary motor cortex? |
Lateral premotor area and supplementary motor area |
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What do the lateral premotor area and supplementary motor area do? |
Coordinate and plan complex sequences of movement Receive information from the posterior parietal and prefrontal association cortices |
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What are three organization features of the motor hierarchy? |
1) Each component contains somatotopic maps (spatial relations are preserved so that neurons that influence adjacent body parts are adjacent to each other) 2) Each level of control receives information from the periphery 3) Higher levels can control information by facilitating or suppressing the transmission of afferent input in sensory relay nuclei |
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What two other parts of the brain regulates motor function? |
Cerebellum and basal ganglia |
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What does the cerebellum do? |
Improves the accuracy of movement by comparing descending motor commands with information about the resulting motor action By acting on the brain stem and on cortical motor areas, monitoring both their activity and the sensory feedback signals they receive from the periphery |
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What does the basal ganglia do? |
Receives input from all cortical areas and projects principally to areas of frontal cortex that are concerned with motor planning |
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What do the medial and lateral groups of spinal motor neurons do? |
Innervate proximal and distal muscles |
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Describe motor nuclei. |
Motor neuron pools Form longitudinal columns extending over one to four spinal segments |
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What are two important anatomical and functional rules of the spinal cord? |
1) Proximal-distal rule 2) Flexor-extensor rule |
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Describe the proximal-distal rule. |
Motor neurons innervating most proximal muscles located most medially |
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Describe the flexor-extensor rule. |
Motor neurons that innervate extensor muscles lie ventral to those of flexor muscles (proximal = equilibrium and posture) |
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Which interneurons project to both sides? |
More medial interneurons |
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Where does the brain stem project? |
Spinal gray matter |
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What are the two main pathways from the brain stem to the spinal gray matter? |
1) Medial pathways: terminate in ventromedial part that influence axial and proximal muscles 2) Lateral pathways: terminate in dorsolateral part that control distal muscles 3) Aminergic pathways: originates in nuclei of brain stem and branches diffusely throughout the spinal cord |
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What are the three major components of the medial pathways? |
1) Vestibulospinal tracts 2) Reticulospinal tracts 3) Tectospinal tract |
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Where do the medial pathways descend? |
Ipsilateral ventral columns terminate on interneurons, some directly on motor neurons |
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What information is carried in the vestibulospinal tracts? |
Reflex control of balance and posture |
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What information is carried in the reticulospinal tracts? |
Maintenance of postures Integrate information from variety of inputs |
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What does the tectospinal tract do? |
Coordinates head and eye movements |
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What is the main lateral descending pathway from the brain stem? |
Rubrospinal tract |
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What are the two sets of aminergic pathways and where do they send their axons? |
All over the spinal cord Ceruleospinal system: noradrenergic Raphe-spinal system: serotonergic |
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What does the raphe-spinal system do? |
Modulates transmission of painful stimuli |
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What do the corticobulbar fibers do? |
Control the cranial motor nerve nuclei (facial muscles) |
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What do the corticospinal fibers do? |
Control the motor neurons innervating the spinal segments |
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What do CST fibers act on? |
Directly on motor neurons and interneurons |
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What is the largest descending fiber tract from the brain? |
CST |
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Where do CST fibers originate? |
1/3: Primary motor cortex 1/3: Premotor motor areas 1/3: Somatic sensory cortex |
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What is the pathway of CST? |
Through posterior limb of internal capsule to ventral portion of midbrainthrough pons between pontine nuclei, to medulla form medullary pyramid on ventral surface (3/4 decussate) to dorsal part of lateral columns terminate in gray matter on motor nuclei and interneurons |
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What are common causes of damage to the CST? |
Tumor, trauma, and demyelinating disease |
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What are positive signs of damaged motor fucntion? |
Stereotyped abnormal responses: release phenomena (extensor plantar reflex) |
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What can cause muscle weakness? |
Disturbances in descending motor pathways (upper motor neurons) or in spinal motor neurons themselves (lower motor neurons) |
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How do you determine whether the disturbance is to the descending pathway or the motor neuron? |
Lower motor: poliomyelitis, weakness of small groups of muscles while nearby muscles remain normal; fasciculation; atrophy; decreased tone; reduced tendon reflexes Upper motor: groups of muscles are all affected; atrophy rare; no fasciculations; spasticity (muscle tone and reflexes increased) |
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What is the ability to control individual muscles independently called? |
Fractionation of movement, requires CST of medullary pyramid |
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Where does the CST originate? |
Frontal and parietal cortex |
