The Motor System 2

Question 1

What are the two broad types of upper motor neurone systems?

Answer 1

-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

Question 2

What are the names of the two upper motor neurone systems?

Answer 2

Cortico-spinal and Cortico-bulbar system

The Extrapyramidal system

Question 3

What is the cortico-bulbar system?

Answer 3

• 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

Question 4

Why is it called bulbar?

Answer 4

Fibres originate in cortex and go to bulb (brainstem)

Can also be called cortico-nuclear as fibres go to brain-stem nuclei

Question 5

What is the cortico-spinal system?

Answer 5

• 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

Question 6

What are pyramids?

Answer 6

Descending cortico-spinal fibres form prominences on medulla as they cross to supply spinal cord
Can also therefore be called the pyramidal system

Question 7

Where are the cell bodies of the cortico-spinal and cortico-bulbar systems located mainly?

Answer 7

Primary Motor Cortex (frontal lobe, precentral gyrus)

Question 8

Describe the primary motor cortex

Answer 8

Cell bodies arranged so body represented upside down

Generally unilateral, individual movements

Question 9

Describe the Supplementary motor area

Answer 9

Body represented horizontally, head forwards

Generally complicated, bilateral movements (coordinated walking movement) so actions

Question 10

What are the cortico-spinal and cortico-bulbar systems responsible for?

Answer 10

More precise
Non-stereotyped
Voluntary movements
More with movements or components of actions than actions

Question 11

What does the corticospinal system control?

Answer 11

Motor cortex control of trunk and limb musculature

Question 12

Where do axons in the cortex run through?

Answer 12

The internal capsule

Question 13

What is the Decussation of the Pyramidal Tracts in the Medulla

Answer 13

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

Question 14

How many fibres cross in the pyramids and where are the rest of the fibres?

Answer 14

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

Question 15

Once the axons are in the cord, how do the axons continue down the spinal cord?

Answer 15

Lateral corticospinal tracts (biggest so most of fibres)

Ventral corticospinal tracts

Question 16

Where do the cortico-spinal tract fibres terminate in the spinal cord?

Answer 16

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)

Question 17

What effects do the descending fibres have on the LMN?

Answer 17

Excitatory and inhibitory, mediated by interneurons

Question 18

What is ipsilateral and bilateral control most associated with?

Answer 18

Neck and trunk muscles

Question 19

What does the corticobulbar system control?

Answer 19

Motor cortex control of cranial musculature

Question 20

Which cranial nerves do not have nuclei in the brain stem?

Answer 20

1, 2 and 11

Question 21

Describe the cranial nerves

Answer 21

• 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

Question 22

Describe UMN control of the 5th cranial nerve (trigeminal nerve)

Answer 22

UMN control of LMNs supplying jaw musculature is ipsilateral and contralateral on a 50:50 basis
Jaw muscle innervation therefore bilateral

Question 23

What is the clinical implication of bilateral innervation of the jaw musculature?

Answer 23

A stroke in one hemisphere rarely results in significant weakness of jaw muscles

Question 24

Describe UMN control of the 7th cranial nerve (facial nerve)

Answer 24

• 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

Question 25

What are the movements of the upper face?

Answer 25

Eye closure
Eyebrow elevation
Frowning

Question 26

What are the movements of the lower face?

Answer 26

Elevation of angles of mouth
Lip closure
Lip pursing

Question 27

What is the clinical implication of LMN lesion in the facial nerve?

Answer 27

Lesion of 7th nerve nucleus or nerve= weakness of all ipsilateral face

Question 28

What is the clinical implication of a unilateral UMN lesion?

Answer 28

Contralateral lower face only

Question 29

What does the accessory nerve control?

Answer 29

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

Question 30

Describe the UMN control of the 11th cranial nerve (accessory nerve and sternocleidomastoid muscle)

Answer 30

• 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

Question 31

What muscle is supplied by the accessory nerve?

Answer 31

Sternocleidomastoid

Question 32

What does the sternocleidomastoid muscle do?

Answer 32

Attached posteriorly to head and anteriorly to trunk so turns head
Right muscle turns head to left and vice versa

Question 33

Describe sternocleidomastoid motor control

Answer 33

Left hemisphere UMN controls Left SCM and vice versa

Question 34

What are the clinical implications of ipsilateral control of the sternocleidomastoid?

Answer 34

-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

Question 35

If there are lesions in the UMN how does this affect muscle?

Answer 35

Excitatory effect on LMN= weakness

Inhibitory effect on LMN= hypertonia/ spasticity

Question 36

Which regions in the spinal cord contain LMN cell bodies for parts of the body?

Answer 36

-Cervical= upper limbs
-Thoracic= trunk
-Lumbar= leg
The level at which the pyramidal system is affected determines the distribution of weakness

Question 37

Which artery is occluded to get contralateral hemiplegia?

Answer 37

Middle cerebral artery

Supplies the primary motor cortex

Question 38

What lesion will lead to contralateral hemiparesis?

Answer 38

Internal capsule lesion= small arteries suppling the central brain