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NS31 Brainstem – spinal systems. Motor System Summary.

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Presentation on theme: "NS31 Brainstem – spinal systems. Motor System Summary."— Presentation transcript:

1 NS31 Brainstem – spinal systems

2 Motor System Summary

3 Brainstem Spinal Systems Flexors –Rubrospinal Extensors –Medial reticulospinal (-) –Pontine reticulospinal (+) –Lateral vestibulospinal –MLF (medial vestibulospinal) descending Opposing Effects HT 24-1

4 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 Pontine Red-from Medulla (dashed – some project Contralateral – we’ll ignore) Reticulospinal System

5 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

6 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

7 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

8 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, Forebrain connections removed Lesions separate forebrain from brainstem

9 Decerebrate Posture Gamma loop HT 24-10, 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

10 Decerebrate Posture Gamma loop HT 24-10, 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

11 Decerebrate + Posterior Root Section Lesion A + B –Loss of Extensor Hyperactivity Gamma rigidity Gamma loop HT 24-10, 24-11

12 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, Lesion What happens if you take away inhibitory input? Fires at greater rate thus increasing Extensor Rigidity

13 Decerebellate + Posterior Root Lesion A + C + B Extensor hypertonus persists Alpha motor neurons receive direct vestibulospinal input Alpha rigidity Gamma loop HT 24-10, Fires at greater rate thus increasing Extensor Rigidity What happens if you take away inhibitory input?

14 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, Flexors UE somehow overcoming

15 Decorticate Posture Gamma loop HT 24-12, Lesion removes influence of cortex over Rubrospinal Tract –Rubrospinal tract excited by cerebellar input –In humans, rubrospinal tract controls only UE

16 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 is descending into Medulla


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