NS31 Brainstem – spinal systems. Motor System Summary.
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Transcript of NS31 Brainstem – spinal systems. Motor System Summary.
![Page 1: NS31 Brainstem – spinal systems. Motor System Summary.](https://reader036.fdocuments.in/reader036/viewer/2022062511/551b719c550346a10a8b49bb/html5/thumbnails/1.jpg)
NS31
Brainstem – spinal systems
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Motor System Summary
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Brainstem Spinal Systems• Flexors
– Rubrospinal
• Extensors– Medial reticulospinal (-)– Pontine reticulospinal (+)– Lateral vestibulospinal– MLF (medial vestibulospinal)
• descending
Opposing Effects
HT 24-1
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• Ipsilateral (primarily)
• Throughout spinal cord
• Extensors (primarily)
• Pontine RF medial (+)– Excitatory input to excitatory
interneurons
• Medullary RF lateral (-)– Excitatory input to inhibitory
interneurons
• RF has cortical input
• Pontine RF has pain input from ALS
HT 2-9
Blue-from PontineRed-from Medulla(dashed – some projectContralateral – we’ll ignore)
Reticulospinal System
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Vestibulospinal System• Medial Vestibulospinal Tract
– Medial & inferior vestibular nuclei– Ipsilateral pathway (ignore
contralateral part)– Descends bilaterally as MLF– Reaches lower cervicals / upper
thoracic levels• Primarily related to neck
– Extensors muscles– No cortical input– Input from CN VIII & (+) (-) cerebellar
input – (both components Purkinje)
HT 24-8, 24-7
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Vestibulospinal System• Lateral Vestibulospinal Tract
– Lateral vestibular nucleus– Ipsilateral– Entire length of spinal cord– Extensors– No cortical input– Input from CN VIII & (+) (-)
cerebellar input
HT 24-8, 24-7
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Rubrospinal System• Red nucleus
• Crosses in midbrain– The ONLY one of these that is
contralateral
• Extends ONLY to low cervical or upper thoracic levels
• Flexors of upper limb– The ONLY one of these that controls
flexors
• Cerebral cortical input
• (+) cerebellar nuclear input
• Somatotopic organizn/anterior horn– Flexors– Extensors HT 24-9
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• Brainstem & its connections to spinal cord are responsible for these postures
Decerebrate (all 4 limbs extended – extensor rigidity)
Decortitate (UE’s flexed, Le’s extended)HT 24-13, 24-15
Forebrain connectionsremoved
Lesions separate forebrain from brainstem
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Decerebrate Posture
Gamma loop
HT 24-10, 24-11
• Lesion A– Intercollicular section – (between sup & inferior)– Upper limbs extended– Lower limbs extended– Vestibulospinal system unaffected by lesion
• no cortical input– Flexor inactivated
• Flexor motor neuron receives input from rubrospinal tract
• BUT, that tract has been cut• Same true for corticospinal tract
– Posture must be result of reticulospinal system
• Excitatory part is being driven but inhibitory is not
– Alpha motor neurons are indeed activated by gamma motor neurons via gamma loop
Hyper-extension
Lesion
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Decerebrate Posture
Gamma loop
HT 24-10, 24-11
• Lesion B– Extensor Hyperactivity due
to Gamma Loop • proven by Lesion B
– Extensor Rigidity Collapsed as a result
• Thus above statement proven
Hyper-extension
In tact here with A, since no cortical input
Lesion
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Decerebrate + Posterior Root Section
• Lesion A + B– Loss of
Extensor Hyperactivity
• Gamma rigidityGamma loop
HT 24-10, 24-11
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Decerebellate Posture• Lesion A + C
• Extensor hypertonus enhanced in all 4 limbs
• Is gamma loop involved or is it just due to alpha motor neuron activity ??
• Vestibulospinal fires faster resulting in increase in rigidity– All cerebellar output is excitatory
Gamma loop
HT 24-10, 24-11
Lesion
What happens if you take away inhibitory input?
Fires at greater rate thus increasing Extensor Rigidity
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Decerebellate + Posterior Root• Lesion A + C + B
• Extensor hypertonus persists
• Alpha motor neurons receive direct vestibulospinal input
• Alpha rigidityGamma loop
HT 24-10, 24-11
Fires at greater rate thus increasing Extensor RigidityWhat happens if you
take away inhibitory input?
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Decorticate Posture• Lesion D• Upper limb flexed• Lower limb extended• Rubrospinal tract
– Upper limb flexors– Intact due to excitatory
cerebellar input
Gamma loop
HT 24-10, 24-11
Flexors UEsomehowovercoming
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Decorticate Posture
Gamma loop
HT 24-12, 24-11
• Lesion removes influence of cortex over Rubrospinal Tract– Rubrospinal tract excited
by cerebellar input– In humans, rubrospinal
tract controls only UE
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Decorticate to Decerebrate Posture• Brainstem spinal systems
released from cortical control
• Extensors in UE & LE are activated by Ascending Somatosensory
– might involve CV & respiratory systems – patient may need respiratory & CV support
Some Patients will convert……
Decorticate
Decerebrate
Signals lesion isdescending into Medulla