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82 Cards in this Set

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What is "The Motor System"?
The parts of the nervous system that contribute to movements of the body.
What BEGINS motor processing?
An internal representation of the desired movement.
What is "achieved" by motor processing?
Neural signals are transformed into contractile force in muscles.
What are 3 important general principles of motor systems to keep in mind?
1. Motor system is like somato sensory system turned backward.
2. Motor control is hierarchical
3. Motor control occurs in parallel pathways that are somewhat redundant.
What does it mean to say motor systems are hierarchical?
Smaller/simpler elements of motor control at the SC level are integrated into more complex patterns at higher levels of NS.
So where would each originate:
-Complex motor programs
-Simple reflexes
Complex = higher cortex
Reflex = lower spinal cord
What is the Final Common Pathway?
The motor neuron that innervates the skeletal muscle to cause movement.
What do we call the motor neurons that influence skeletal muscle directly?
LOWER MOTOR NEURONS
3 Major components and levels of control in motor systems:
1. Spinal cord
2. Brain stem
3. Cerebral cortex
2 ways that motor cortex can influence the spinal cord:
1. Directly
2. Indirectly
What are the 3 areas of cortex involved in motor systems?
1. Primary motor cortex
2. Premotor cortex
3. Supplementary cortex
Where do LMNs originate?
In the ventral horn of the spinal cord
What 2 independent SUBcortical structures modulate all 3 levels of motor systems?
1. Basal ganglia
2. Cerebellum
What are the 5 nuclei in the basal ganglia?
1. Caudate
2. Putamen
3. Globus pallidus
4. Substantia nigra
5. Subthalamic nuclei
How does the Thalamus function in the motor system?
As a relay station for information from the basal ganglia to the cortex, and the cerebellum to the cortex.
So motor systems are organized in what two general ways?
1. Serially
2. In parallel
Which of the three levels of motor systems (cortex, stem, sc) receive sensory input?
All three.
What is at the bottom of the hierarchy of motor systems?
The spinal neurons that execute movement.
What are the 2 general types of spinal cord neurons in the motor systems?
1. Motor neurons
2. Interneurons
Where are motor neurons?
In the ventral horn - these are LOWER MOTOR NEURONS.
And what do we all the lower motor neurons?
Final common pathway
What do Medial LMNs innervate?
Proximal muscles that control balance, posture, and trunk movement.
What do Lateral LMNs innervate?
Distal muscles that control limbs and digits.
Where in the ventral horn are interneurons found?
In intermediate zones
2 types of Interneurons:
-Segmental
-Propriospinal
Where do Segmental interneurons project?
Within a single spinal cord level, to either ipsilateral or contralateral areas.
Where do propionspinal interneurons project?
To motor neurons in multiple SC levels - because they are longer.
What is the function of interneurons?
To form circuits that coordinate motor neurons responsible for groups of muscles that perform specific tasks.
So the main function of SC neurons is to execute movement; what is the function of BRAINSTEM neurons?
To modulate the action of spinal motor circuits.
2 general types of neurons in the brainstem:
1. Those that innervate facial muscles (LMNs)
2. Those that project to neurons in SC gray matter (UMNs)
2 specific examples of LMN nuclei in the brainstem:
1. Facial nucleus - controls muscles of facial expression
2. Hypoglossal nucleus - controls tongue movements
What do the brainstem UMN nuclei give rise to?
Medial and lateral descending Brainstem pathways
What are the 3 Medial brainstem pathways?
1. Reticulospinal
2. Vestibulospinal
3. Tectospinal
What is the Lateral brainstem pathway to know?
Rubrospinal
What do the medial brainstem pathways influence?
Axial proximal muscles - because they terminate on medial areas of the spinal cord ventral horn.
What is achieved by medial brainstem pathways?
Basic postural control upon which higher cortical motor areas can organize more highly differentiated movement.
Where do Medial tracts descend?
Where do lateral tracts descend?
Medial = in ventromedial white matter
Lateral = in dorsolateral white matter
What feature of the Rubrospinal tract makes it very different from medial tracts?
It crosses to the contralateral side while descending the SC.
What does the lateral Rubrospinal tract influence?
Motor neurons that control distal muscles of limbs.
What is achieved by the Rubrospinal tract?
Modulation of goal-directed limb movements like reaching and manipulating.
What is the role of CEREBRAL CORTEX in motor systems?
To modulate action of motor neurons in the brainstem and spinal cord.
Where LMNs originate from SC, and UMNs originate in brainstem, what originates in the cortex?
Also Upper Motor Neurons (UMNs)
3 major areas of cerebral cortex involved in motor control:
1. Primary motor cortex
2. Premotor cortex
3. Supplementary motor area
How are the 3 areas of cerebral cortex involved in motor control related?
Premotor and supplementary motor area are HIGHER than primary motor cortex.
What is the Primary motor cortex function?
To execute commands to motor neurons.
How is the primary motor cortex arranged?
Somatotopically
What is the function of the premotor cortex?
To integrate motor movements with sensory input - mainly visual. Also coordinates motor learning.
What is the function of the supplementary motor area?
Formulation of intentions to make a movement - internally driven, will-driven movements.
What is the Posterior Parietal cortex's involvement in motor cerebral cortex functions?
Localization of an object with respect to the body.
Where will cerebral bloodflow increase if you only mentally rehearse a complex movement?
Bilaterally in the supplementary motor area.
Where will cerebral bloodflow increase if you both mentally rehearse a complex movement of the left hand, AND perform it?
-Right primary motor cortex
-Bilateral supplementary motor areas
-Right postcentral somatosensory areas (because of sensation too)
Where will cerebral bloodflow increase if you perform a SIMPLE movement of the left hand, without thinking about it?
Increase to RIGHT primary motor cortex and somatosensory areas.
What are the 2 descending tracts by which the Cerebral cortex acts on the spinal cord? What is the system they make up called?
PYRAMIDAL SYSTEM:
1. Ventral corticospinal tract
2. Lateral corticospinal tract
What does the ventral corticospinal tract control?
Neck and trunk muscles (proximal)
What does the lateral corticospinal tract control?
Limb and digit muscles (distal)
By which tract does the Cerebral cortex act on brainstem motor neurons?
Corticobulbar tract
What is the bundle of axons that pass from the cortex down to the brainstem and spinal cord?
Internal capsule
Main difference in how the ventral and lateral corticospinal tracts descend?
Lateral crosses to contralateral side. Ventral doesn't.
Where does the lateral corticospinal tract cross?
At the pyramidal decussation.
What 2 subcortical structures influence motor control?
-Cerebellum
-Basal ganglia
What are the main functions of the Cerebellum and Basal Ganglia?
-Regulation of movement planning and execution
-Providing feedback circuits that regulate cortical and brainstem motor areas.
What is achieved by the Cerebellum and Basal Ganglia?
Smooth movements and posture
How does input from the cerebellum and basal ganglia get to the cortex?
Via the thalamus - NOT directly
How does input from the cerebellum and basal ganglia get to the spinal cord?
Via the Brainstem tracts - NOT directly.
How much of all neurons in the brain are in the cerebellum?
50%
What does the Cerebellum receive input from?
-Motor cortex
-Somatosensory cortex
How does the cerebellum improve accuracy and coordination of limb movements?
By comparing intentions from the cortex, with somatosensory info from the actual movement.
So three things the cerebellum coordinates:
-Direction
-Timing
-Force of movement
How do the Basal Ganglia modulate movement?
-By reinforcing selected motor programs
-By inhibiting the motor cortex to restrict available motor outputs to only those needed.
What exactly do the Basal Ganglia give negative feedback inhibition to?
Conflicting motor programs to the desired motor program.
So the idea to pick up a pencil is formed in the:
Supplementary motor area
Sensory information about the pencil location, and propriocept info relative to pencil is taken in by:
The Posterior Parietal Cortex
Where are postural adjustments to balance the impending reach for the pencil initiated?
In the premotor cortex
What does the Primary motor cortex do?
Uses the information from steps 1-3 to generate a specific plan for muscle movement - sends the info to LMNs in spinal cord.
What happens during the movement of picking up a pencil?
The cerebellum and basal ganglia monitor sensory info and make adjustments to smooth out the movement.
So what are the 4 steps of the motor system hierarchy, top to bottom?
1. Cortex
2. Brainstem
3. Spinal cord
4. Muscles
What are lower neural structures concerned with?
More simple tasks (reflexes, withdrawals from painful stimuli)
Where is somatotopic organization found in the hierarchy of motor systems?
At every level
What are the 3 general types of movement?
1. Reflex
2. Automatic Posture adjustments
3. Voluntary movements
What is the highest level that can be reached by reflex movements?
Brainstem nuclei
What are some reflex movement examples?
-Withdrawal from painful stimulus
-Repetitive rhythmic motor patterns like chewing/swallowing
How do automatic postural adjustments compare to reflexes?
-Slightly more complex
-More flexible