NS31 Brainstem – spinal systems. Motor System Summary.

NS31

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

• 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

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

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

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

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

Decerebrate + Posterior Root Section

• Lesion A + B– Loss of

Extensor Hyperactivity

• Gamma rigidityGamma loop

HT 24-10, 24-11

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

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?

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

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

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