Descending motor pathway

Question 1

What is a upper motor neurone?

Answer 1

A neurone from the cortex to either the cranial nerve nuclei or ventral grey horn in the CNS

Question 2

What is the route of LMN and what nerves do they run in?

Answer 2

Axons of LMNs pass from the ventral grey horn of the spinal cord (CNS) and cranial nerve motor nuclei of the brain stem (CNS) to muscles. From the spinal cord they will run in spinal nerves and from the brain stem they will run in cranial nerves.

Question 3

Neurons that originate from the brain stem & spinal cord

Answer 3

Ventral grey horn
Ventral roots
Periphery nerves to motor end plates and neuromuscular junction

Question 4

What is the cause of a LMN lesion?

Answer 4

Periphery nerve injury ( cut or crush) or poliomyelitis

Question 5

What is poliomyelitis?

Answer 5

It is acute viral infection of the neurones–> result in muscle weakness, parlysis, asympetrical but recoverable

Question 6

What is the consequence of LMN lesion?

Answer 6

Muscle weakness/reduce power
Muscle wasting
Fisculation/fibrillation 
Hypotonia --> reduced based line tone 
Absent tendon reflex

Question 7

What is the function of upper motor neurones?

Answer 7

They influence the LMN activity
They modify local reflex activity
They superimpose more complex pattern of movement
There are 4 different descending pathways relating to the origion

Question 8

What part of the brain stem do corticospinal tract and cotricobulbar tracts run through?

Answer 8

The pyramids

Question 9

What is the consequence of damaging the corticospinal tracts only?

Answer 9

flaccid paralysis of opposite limbs
Loss of tendon reflexes

After several days to a week motor function recovers but hypertonia

Long term
Spasticity
Hyperreflexia

Left with permanent inability to carry out fine movements of hands and feet

Other pathways appear to take over most “corticospinal” functions

Question 10

What is internal capsule?

Answer 10

Deep bundle of white matter between deep nuclei

Question 11

What part of the internal capsule does the corticospinal/bulbar tract pass through?

Answer 11

Corticospinal tract pass through the posterior limb of the internal capsule

The Corticobulbar tract pass through the genu

Question 12

What is the somatotopic representation of the internal capsule anterior to posterior?

Answer 12

Strarting at the Genu is face, arm, trunk and then legs

Question 13

What is the route of the corticospinal tracts?

Answer 13

Post central gyrus ( Cerebral hemisphere) –> Internal capsule posterior limb –> cerebral peduncle (mid brain) –> Pons –> Pyramids ( open medulla) –> pyramid decussation ( closed medulla) –> lateral corticospinal tract –> spinal cord

Question 14

What percentage of corticospinal tract cross over at the closed medulla and run down the lateral corticospinal tract?

Answer 14

85%

Question 15

What is the somatotopic representation of the midbrain?

Answer 15

From lateral to medial:

Legs –> trunk –> arm –> face

Question 16

What is the route of the corticospinal tract down the spinal cord ?

Answer 16

85% of UMNs descend cord contralaterally –> via lateral corticalspinal tract
15% of UMNs descend cord ipsilaterally (cross at appropriate SC level) -> via anterior/ventral corticospinal tract

Question 17

Where is the cell body of the lower motor neurones? How do LMN leave the spinal cord

Answer 17

All the UMN synapse with the cell bodies of the LMN in the contralateral ventral grey horn.

The LMN leaves the spinal cord as ventral rootlets to form spinal nerves

Question 18

Where do the fibers of the corticobulbar pathway originate from?

Answer 18

The lateral part of the pre central gyrus

Question 19

Where are cranial nerve nuclei found?

Answer 19

Found in the floor of the 4th ventricle

Question 20

How do the UMN of the corticobulbar pathway distribute?

Answer 20

They distribute bilaterally

Question 21

From what side doe sthe UMN innervate the hypoglossal cranial nerve nuclei?

Answer 21

From the contralateral side

Question 22

If you get damage to the UMN of the hypoglossal nerve nuclei what is the result?

Answer 22

Atrophy of the contralateral tongue muscles and deviation to the contralateral side of the face.

Question 23

What two cranial nerves are exception to the rule of bilateral corticobulbar input?

Answer 23

Facial and hypoglossal cranial nerve nuclei

Question 24

What is the route of the facial nerve?

Answer 24

Facial nerve goes from the cerebellopontine angle, pass through the internal acoustic meatus, course through the facial canal and existing at the styloid mastoid foramen and then split into 5 at the parotid gland

Question 25

What is the facial cranial nerve nuclei structure?

Answer 25

It has a upper and lower face on either side

Question 26

Where do the UMN for the facial nerve originate from the PCG?

Answer 26

There is a upper face and lower face part of the PCG

Question 27

What is the input to the facial cranial nerve nuclei form the UMN?

Answer 27

THe UMN suppleis bilaterally to both sides of the upper face of the facial cranial nerve nuclei but only contralaterally to the lower face of the facial carnial nerve nuclei

Question 28

What is the consequence of the distrubution if there is a lesion in the UMN of the facial cranial nerve?

Answer 28

There is still movement of the upper face as there is still innervation of the upper face from the other side, however there is paralysis on the lower face as there is no input from the other side. It is contralateral input

Question 29

What happens if there is a LMN lesion to the facial cranial nerve?

Answer 29

There is complete paralysis of the ipsilateral side as there is no more crossing over of fibers

Question 30

What can cause LMN lesion of the facial nerve?

Answer 30

Infranuclear lesions can be a rseult of Bell’s palsy, tumours of cerebellopontine angle, middle ear disease, parotid tumour.

Question 31

What is the consequence of a supranucleur lesion?

Answer 31

Deprives the lower half of the opposite facial
motor nucleus of corticobulbar input

Results in paralysis of the lower half of the
face on the opposite side to the lesion

Question 32

What does paralysis of the whole ipsilateral side indicate?

Answer 32

Complete damage of the facial neve –> infranucleur lesion

Question 33

What is the cause of a supranucleur lesion?

Answer 33

Usually a vascular stroke

Question 34

What is the type of lesion if If on one side of the face the corner of the mouth fails to rise whilst the eyebrows are raised on that same side it would indicate a supranuclear lesion when you ask the patient to smile or raise there eyebrow?

Answer 34

Supranucleur lesion

Question 35

What type of lesion is it when upon asking to smile and raise eyebrow there was complete in ability to raise corner of mouth or eyebrows on one side?

Answer 35

Infranucleur lesion/ facial neve is damaged