Brainstem – spinal systems

Motor System Summary

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

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

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

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

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

Brainstem & its connections to spinal cord are responsible for these postures Forebrain connections removed Decerebrate (all 4 limbs extended – extensor rigidity) Lesions separate forebrain from brainstem HT 24-13, 24-15 Decortitate (UE’s flexed, Le’s extended)

Decerebrate Posture Gamma loop HT 24-10, 24-11 Lesion A Hyper-extension 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 Lesion Gamma loop HT 24-10, 24-11

Decerebrate Posture Lesion B Extensor Hyperactivity due to Gamma Loop Hyper-extension Lesion B Extensor Hyperactivity due to Gamma Loop proven by Lesion B Extensor Rigidity Collapsed as a result Thus above statement proven In tact here with A, since no cortical input Gamma loop Lesion HT 24-10, 24-11

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

Decerebellate Posture Fires at greater rate thus increasing Extensor Rigidity 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 What happens if you take away inhibitory input? Lesion Gamma loop HT 24-10, 24-11

Decerebellate + Posterior Root Fires at greater rate thus increasing Extensor Rigidity Lesion A + C + B Extensor hypertonus persists Alpha motor neurons receive direct vestibulospinal input Alpha rigidity What happens if you take away inhibitory input? Gamma loop HT 24-10, 24-11

Decorticate Posture Lesion D Upper limb flexed Lower limb extended Rubrospinal tract Upper limb flexors Intact due to excitatory cerebellar input Flexors UE somehow overcoming Gamma loop HT 24-10, 24-11

Decorticate Posture Lesion removes influence of cortex over Rubrospinal Tract Rubrospinal tract excited by cerebellar input In humans, rubrospinal tract controls only UE Gamma loop HT 24-12, 24-11

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 Signals lesion is descending into Medulla Decerebrate