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63 Cards in this Set
- Front
- Back
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How is the motor system organized?
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Hierarchically
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Are reflex controls and the rhythmic pattern generator found in lower or higher levels of the motor system?
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Lower levels
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Do lower levels of the motor system have the capacity to generate complex patterns of muscle activation?
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Yes
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What is the function of higher levels of the motor system?
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They provide relatively general commands without specifying details of motor action
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What do parallel pathways do?
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They allow higher centers to act directly on lower centers
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How do parallel pathways allow higher centers to act on lower center?
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-Adjust reflex circuits
-Control individual motor neurons (fine control of hand and finger movement) |
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Where are motor neurons located in the spinal cord?
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In the medial and lateral portion of the ventral horn
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Where do motor neurons in the medial portion of the ventral horn innervate?
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Muscles of the neck and back (axial muscles)
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Where do motor neurons in the lateral portion of the ventral horn innervate?
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Muscles of the extremities
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Where do medial motor neurons in the lateral portion of the dorsal horn innervate?
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Proximal muscles
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Where do lateral motor neurons of the lateral portion of the ventral horn innervate?
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Distal muscles
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Where do dorsal motor neurons of the lateral portion of the ventral horn innervate?
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Flexor muscles
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Where do ventral motor neurons of the lateral portion of the ventral horn innervate?
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Extensor muscles
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What do motor neuron pools for a single muscle look like?
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They are long, slender nuclei
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How far do motor neuron pools travel? Why is this an advantage?
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3 or 4 segments; a lesion at one segment results in weakness not paralysis
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Where are long propriospinal interneurons located?
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Medially in the gray matter
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Where do the axons of long propriospinal interneurons travel? Where do they terminate?
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They transcend many segments of the spinal cord and terminate on ipsilateral and contralateral medial motor neurons
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What is the function of long propriospinal interneurons?
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They help coordinate axial and postural muscles
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Where are short propriospinal neurons located?
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Laterally in the gray matter
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Where do the axons of short propriospinal neurons travel? Where do they terminate?
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The transcend only a few segments of the spinal cord and terminate only on lateral ipsilateral motor neurons
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What is the function of short propriospinal neurons?
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They help coordinate limb movement
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What are the two main descending pathways that allow the cortex and brainstem to control movement?
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1. Medial pathways
2. Lateral pathways |
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What do medial descending pathways control?
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Axial and proximal muscles
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What do lateral descending pathways control?
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Distal extremity muscles
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Where do the medial descending pathways originate?
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Three originate in the brainstem, one originates in the cerebral cortex
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Where do the medial descending pathways descend?
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In the ventral funiculus of the spinal cord
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Where do the medial descending pathways terminate?
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-Ipsilaterally and contralaterally
-Onto long propriospinal neurons -Onto motor neurons that control axial and postural muscles |
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Where do collaterals of the medial descending pathways go? How many are there?
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Many spinal segments
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Where does the vestibulospinal tract originate?
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In the lateral and medial vestibular nucleus
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Where does the vestibulospinal tract descend? Where does it terminate?
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In the ventral funiculus; terminates ipsilaterally and contralaterally
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What is the vestibulospinal tract involved in?
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Controlling posture and balance
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What muscles do fibers from the vestibulospinal tract innervate?
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Primarily excitatory to extensor muscles of the trunk and proximal anti-gravity muscles
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Where does the tectospinal tract originate?
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In the superior colliculus
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Where does the tectospinal tract cross?
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As it descends the brainstem
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Where do fibers in the tectospinal tract travel? Where do they terminate?
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They travel in the ventral funiculus; they terminate ipsilaterally and contralaterally
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What is the function of the tectospinal tract?
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It is important for conjugating eye movements and helps direct eyes and head toward objects in the visual field
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Where does the reticulospinal tract originate?
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In the reticular formation of the brainstem
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Where do fibers from the reticulospinal tract travel? Where do they terminate?
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They travel in the ventral funiculus; terminate ipsilaterally and contralaterally
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What is the function of the reticulospinal tract?
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It is important in maintaining upright posture; controls crude, stereotypical movements
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Where does the ventral corticospinal tract originate?
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In areas 4 and 6 of the cerebral cortex
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Where do collaterals of the ventral corticospinal tract travel?
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To the brainstem nuclei
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Do fiber tracts from the ventral corticospinal tract cross in the pyramidal decussation?
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No
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Where do fibers of the ventral corticospinal tract travel? Where do they terminate?
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In the ventral funiculus of the spinal cord on the ipsilateral side; terminate ipsilaterally and contralaterally
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What is the function of the ventral corticospinal tract?
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Controls axial muscles of the neck and trunk
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Where do the lateral descending pathways originate?
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One originates in the cerebral cortex and one originates in the brainstem
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Where do lateral descending pathways descend?
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In the lateral funiculus of the spinal cord
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Where do lateral descending pathways terminate?
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Contralaterally from origin onto motor neurons that control muscles of the extremities
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Where do lateral descending pathways send collaterals?
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To only a few spinal cord segments
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What are the medial descending pathways?
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1. Vestibulospinal tract
2. Tectospinal tract 3. Reticulospinal tract 4. Ventral corticospinal tract |
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Where does the rubrospinal tract originate?
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In the red nucleus
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Where do fibers from the rubrospinal tract cross over?
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In the midbrain
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Where do fibers from the rubrospinal tract descend?
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Near the lateral corticospinal tract in the lateral funiculus
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Where do fibers from the rubrospinal tract terminate?
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Onto motor neurons that control distal muscles of the extremities (flexors more than extensors)
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Where does the lateral corticospinal tract originate?
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In the cerebral cortex from cells in areas 4, 6 and in the somatosensory cortex
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Where do fibers from the lateral corticospinal tract cross over?
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In the pyramidal decussation
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Where do fibers from the lateral corticospinal tract synapse?
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-Onto motor neurons that control muscles of the extremities
-Monosynaptic connections to distal muscles of UE -Some fibers synapse on dorsal column nuclei to influence somatosensory system |
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What are the lateral descending pathways?
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1. Rubrospinal tract
2. Lateral corticospinal tract |
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Where are corticospinal fibers found?
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-Posterior limb of internal capsule
-Middle portion of crus cerebri (cerebral peduncles) -Pyramids of medulla -Lateral funiculus and ventral funiculus of spinal cord |
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Do lesions of the motor cortex and corticospinal pathways result in positive or negative signs?
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Both
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What are some positive signs of lesions of the motor cortex and corticospinal pathways?
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-Stereotypical movements
-Associated reactions -Spasticity (increased resistance to passive stretch) -Hyperactive tendon reflexes (DTR) -Clonus (repetitive contraction of the plantarflexors) -Positive Babinski reflex |
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What is a positive sign?
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Stereotypical abnormal responses that emerge after a lesion
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What are negative signs associated with lesions of the motor cortex and corticospinal pathways?
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-Weakness
-Loss of fractionated movement (inability to control isolated finger movement) -Increased time to generate muscle force, which may result in slowness of movement |
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What is a negative sign?
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The loss of specific capacities that are normally controlled by the damaged motor system
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