1. 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. 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

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
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)

9. 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

10. 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

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

12. 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

13. 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

14. 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

15. 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

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
Signals lesion is
descending into
Medulla
Decerebrate