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UMN Motor Pathways (neuromotor control)

Terms in this set (13)

1. Corticospinal tract
2. Corticobulbar tract


Both tracts' axons called pyramidal tract before differentiating at brainstem
2 descending UMN pathways that originate in cerebral cortex
1. Primary motor cortex - initiates movement
2. Premotor complex - plans, selects, and facilitates execution of motor plan
3. Primary somatosensory cortex - facilitates proprioceptive input to LMN

(cortical origins of each tract relate to their target LMN)
descending UMN pathways cortex origins (3)
neck-up CN motor neuron targets

o Similarly for primary somatosensory cortex origins
Corticobulbar origins of primary motor cortex relate to...
neck-down SN motor neuron targets

o Similarly for primary somatosensory cortex origins
Corticospinal origins of primary motor cortex relate to...
corticobulbar tract pathway to brainstem
· From cortical origins, corticobulbar tract passes thru internal capsule
· Then synapse with target CN motor neurons at various levels of brainstem
o Including CN motor neurons: III, IV, V, VI, VII, IX, X, and XII
corticobulbar tract brainstem connections
· Most UMN corticobulbar axons have bilateral connections with LMN cranial motor neurons
· Bilateral innervation believed to be related to CN motor functions with symmetrical movements
o Examples: Biting, chewing, swallowing, vocal fold movement
~ Notable exception is CN VII Facial - motor branch
Corticobulbar UMN tract's interaction with both CN LMN and LCM
· influence on CN LMN allows fine motor control over individual motor movements, such as tongue, during speech and swallowing
o Whereas, UMN interactions with LCN of reticular formation allow coordination of multiple motor movements simultaneously during speech and swallowing

· Throughout speech and swallowing, basal ganglia and cerebellum continually influence UMN
corticospinal tract pathways to spinal cord
· From cortical origins, corticospinal tract passes thru internal capsule
o Then passes thru brainstem
~ As it passes thru medulla, axons become "visible" as pyramids at medulla
· Just before leaving medulla, corticospinal tract splits into: lateral and anterior corticospinal tracts
Anterior corticospinal tract
smaller of the 2 corticospinal tracts (10% of axons)
o And consists of axons related to trunk, shoulders, and hips
Lateral corticospinal tract
larger of the 2 corticospinal tracts (90% of axons)
o And consists of axons related to fingers and feet
lateral corticospinal tract
· decussates to contralateral side, just before it leaves medulla and enters spinal cord
o Crossover is called "decussation of pyramids"
· After decussation, tract descends spinal cord via lateral funiculus
· Its axons synapse in lateral cluster of LMN cell bodies in anterior horns of spinal cord
· Targets are distal muscles associated with fine motor control
o And in most cases interact directly on LMNs allowing fine motor control of hands, fingers, toes
· Also provides muscular force required for speech breathing and hand gestures
anterior corticospinal tract
· enters spinal cord on ipsilateral side
· Descends spinal cord via anterior funiculus
o As tract descends some axons decussate, some do not
· Its axons synapse in medial cluster of LMN cell bodies in anterior horns of spinal cord
· Targets are proximal muscles associated with shoulder and hip control
o Allows for voluntary control of trunk, shoulder, and hip related muscles
o Some of these movements likely contribute to speech gestures
corticospinal tracts interactions with both SN LMN and LCN
· Lateral corticospinal UMN influence on SN LMN allows fine motor control over individual hand movements that contribute to gestural communication
o Whereas, both corticospinal tracts UMN interactions with LCN of spinal cord allowing coordination of multiple motor movements contributing to speech breathing and gestures
· Throughout these various motor acts, basal ganglia and cerebellum continually influence UMN
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