The Motor System 2 Flashcards
What are the two broad types of upper motor neurone systems?
-More direct/ linear system (The Upper motor neurone system)
=Direct cerebral cortex control of LMNs
-Less direct/less linear system
=System organising movements into set actions
What are the names of the two upper motor neurone systems?
Cortico-spinal and Cortico-bulbar system
The Extrapyramidal system
What is the cortico-bulbar system?
- Controls the cranial motor LMNs
- UMN cell bodies in the cerebral cortex
- Axons pass down to control
- Lower motor neurones in the brain stem nuclei
Why is it called bulbar?
Fibres originate in cortex and go to bulb (brainstem)
Can also be called cortico-nuclear as fibres go to brain-stem nuclei
What is the cortico-spinal system?
- Controls the spinal LMNs
- UMN cell bodies in the cerebral cortex
- Axons pass down to control the LMNs (Anterior Horn Cells) in the spinal cord
What are pyramids?
Descending cortico-spinal fibres form prominences on medulla as they cross to supply spinal cord
Can also therefore be called the pyramidal system
Where are the cell bodies of the cortico-spinal and cortico-bulbar systems located mainly?
Primary Motor Cortex (frontal lobe, precentral gyrus)
Describe the primary motor cortex
Cell bodies arranged so body represented upside down
Generally unilateral, individual movements
Describe the Supplementary motor area
Body represented horizontally, head forwards
Generally complicated, bilateral movements (coordinated walking movement) so actions
What are the cortico-spinal and cortico-bulbar systems responsible for?
More precise
Non-stereotyped
Voluntary movements
More with movements or components of actions than actions
What does the corticospinal system control?
Motor cortex control of trunk and limb musculature
Where do axons in the cortex run through?
The internal capsule
What is the Decussation of the Pyramidal Tracts in the Medulla
Axons run down the internal capsule down to the medulla and then most axons cross sides in the medulla
Axons from the right side of the motor cortex cross to the left side of the spinal cord and vice versa
How many fibres cross in the pyramids and where are the rest of the fibres?
85% fibres cross in the pyramids (contra-lateral side)
15% remain ipsilateral at the pyramid level most of these cross lower down
Some control is bilateral
Once the axons are in the cord, how do the axons continue down the spinal cord?
Lateral corticospinal tracts (biggest so most of fibres)
Ventral corticospinal tracts
Where do the cortico-spinal tract fibres terminate in the spinal cord?
Ventral= ventral grey matter of the cervical and upper thoracic cord
Lateral= ventral grey matter of all the cord (end of sacral)
The descending cortico-spinal fibres usually terminate on interneurons in the grey matter (few synapse directly with LMNs)
What effects do the descending fibres have on the LMN?
Excitatory and inhibitory, mediated by interneurons
What is ipsilateral and bilateral control most associated with?
Neck and trunk muscles
What does the corticobulbar system control?
Motor cortex control of cranial musculature
Which cranial nerves do not have nuclei in the brain stem?
1, 2 and 11
Describe the cranial nerves
- Generally mixed sensory-motor nerves (not all)
- Motor fibres are the LMN supply to muscles around head and neck
- Facial movements, mouth and tongue movements, speech and swallowing, neck movements, eye movements, eyelids, pupillary movements
Describe UMN control of the 5th cranial nerve (trigeminal nerve)
UMN control of LMNs supplying jaw musculature is ipsilateral and contralateral on a 50:50 basis
Jaw muscle innervation therefore bilateral
What is the clinical implication of bilateral innervation of the jaw musculature?
A stroke in one hemisphere rarely results in significant weakness of jaw muscles
Describe UMN control of the 7th cranial nerve (facial nerve)
- UMN fibres that control LMNs supplying forehead and eye closure terminate ipsilaterally and contralaterally on a 50:50 basis= bilateral innervation
- UMN fibres that control LMNs supplying mouth muscles terminate on a strongly contralateral basis so unilateral innervation
What are the movements of the upper face?
Eye closure
Eyebrow elevation
Frowning
What are the movements of the lower face?
Elevation of angles of mouth
Lip closure
Lip pursing
What is the clinical implication of LMN lesion in the facial nerve?
Lesion of 7th nerve nucleus or nerve= weakness of all ipsilateral face
What is the clinical implication of a unilateral UMN lesion?
Contralateral lower face only
What does the accessory nerve control?
Motor control around the neck
Junction of head (controlled by brainstem/ cranial nerves)
Trunk (spinal cord/ spinal roots and peripheral nerves)
Where corticospinal and corticobulbar systems meet
Describe the UMN control of the 11th cranial nerve (accessory nerve and sternocleidomastoid muscle)
- Motor fibres originate in the nucleus ambiguous as the cranial root of the accessory nerve (mastoid process)
- Motor fibres also originate in the cervical cord grey matter (anterior horn cells) (Sternocleido)
- These exit the cord as rootlets forming the spinal root of the accessory nerve. This ascends upwards alongside the spinal cord, through the foreamen magnum to unite with the cranial root of the accessory nerve
What muscle is supplied by the accessory nerve?
Sternocleidomastoid
What does the sternocleidomastoid muscle do?
Attached posteriorly to head and anteriorly to trunk so turns head
Right muscle turns head to left and vice versa
Describe sternocleidomastoid motor control
Left hemisphere UMN controls Left SCM and vice versa
What are the clinical implications of ipsilateral control of the sternocleidomastoid?
-In focal epileptic seizures originating in the left frontal region
Right limbs are stimulated, Left SCL is stimulated
The right limbs jerk, the head jerks to the right
-In a left hemisphere stroke= loss of control of right limbs + Left SCM
Weakness of right limbs and left SCL= head turned to left as unopposed right SCM
If there are lesions in the UMN how does this affect muscle?
Excitatory effect on LMN= weakness
Inhibitory effect on LMN= hypertonia/ spasticity
Which regions in the spinal cord contain LMN cell bodies for parts of the body?
-Cervical= upper limbs
-Thoracic= trunk
-Lumbar= leg
The level at which the pyramidal system is affected determines the distribution of weakness
Which artery is occluded to get contralateral hemiplegia?
Middle cerebral artery
Supplies the primary motor cortex
What lesion will lead to contralateral hemiparesis?
Internal capsule lesion= small arteries suppling the central brain
