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
