Descending motor pathway Flashcards
What is a upper motor neurone?
A neurone from the cortex to either the cranial nerve nuclei or ventral grey horn in the CNS
What is the route of LMN and what nerves do they run in?
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.
Neurons that originate from the brain stem & spinal cord
Ventral grey horn
Ventral roots
Periphery nerves to motor end plates and neuromuscular junction
What is the cause of a LMN lesion?
Periphery nerve injury ( cut or crush) or poliomyelitis
What is poliomyelitis?
It is acute viral infection of the neurones–> result in muscle weakness, parlysis, asympetrical but recoverable
What is the consequence of LMN lesion?
Muscle weakness/reduce power Muscle wasting Fisculation/fibrillation Hypotonia --> reduced based line tone Absent tendon reflex
What is the function of upper motor neurones?
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
What part of the brain stem do corticospinal tract and cotricobulbar tracts run through?
The pyramids
What is the consequence of damaging the corticospinal tracts only?
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
What is internal capsule?
Deep bundle of white matter between deep nuclei
What part of the internal capsule does the corticospinal/bulbar tract pass through?
Corticospinal tract pass through the posterior limb of the internal capsule
The Corticobulbar tract pass through the genu
What is the somatotopic representation of the internal capsule anterior to posterior?
Strarting at the Genu is face, arm, trunk and then legs
What is the route of the corticospinal tracts?
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
What percentage of corticospinal tract cross over at the closed medulla and run down the lateral corticospinal tract?
85%
What is the somatotopic representation of the midbrain?
From lateral to medial:
Legs –> trunk –> arm –> face
What is the route of the corticospinal tract down the spinal cord ?
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
Where is the cell body of the lower motor neurones? How do LMN leave the spinal cord
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
Where do the fibers of the corticobulbar pathway originate from?
The lateral part of the pre central gyrus
Where are cranial nerve nuclei found?
Found in the floor of the 4th ventricle
How do the UMN of the corticobulbar pathway distribute?
They distribute bilaterally
From what side doe sthe UMN innervate the hypoglossal cranial nerve nuclei?
From the contralateral side
If you get damage to the UMN of the hypoglossal nerve nuclei what is the result?
Atrophy of the contralateral tongue muscles and deviation to the contralateral side of the face.
What two cranial nerves are exception to the rule of bilateral corticobulbar input?
Facial and hypoglossal cranial nerve nuclei
What is the route of the facial nerve?
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
What is the facial cranial nerve nuclei structure?
It has a upper and lower face on either side
Where do the UMN for the facial nerve originate from the PCG?
There is a upper face and lower face part of the PCG
What is the input to the facial cranial nerve nuclei form the UMN?
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
What is the consequence of the distrubution if there is a lesion in the UMN of the facial cranial nerve?
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
What happens if there is a LMN lesion to the facial cranial nerve?
There is complete paralysis of the ipsilateral side as there is no more crossing over of fibers
What can cause LMN lesion of the facial nerve?
Infranuclear lesions can be a rseult of Bell’s palsy, tumours of cerebellopontine angle, middle ear disease, parotid tumour.
What is the consequence of a supranucleur lesion?
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
What does paralysis of the whole ipsilateral side indicate?
Complete damage of the facial neve –> infranucleur lesion
What is the cause of a supranucleur lesion?
Usually a vascular stroke
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?
Supranucleur lesion
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?
Infranucleur lesion/ facial neve is damaged
