Motor Pathways (UMN and LMN) Flashcards
Where are the cell bodies of the LMN located?
found in the ventral horn of the spinal cord
&
cranial nerve motor nuclei in brain stem
What are the target tissues of the lower motor neurones?
skeletal muscle
What are 5 common symptoms of lower motor neurone lesions?
- Weakness
- Areflexia
- Wasting
- Hypotonia
- Fasiculations
Outline why the following symptoms may occur in patients with a lower motor neurone lesion:
Wasting
Hypotonia
Fasiculation
Wasting
loss of trophic support
Hypotonia
loss of muscle activation
Fasiculation
upregulation of muscle nAChRs to compensate for denervation
What are the two effects of upper motor neurones on lower motor neurones?
Excitation of LMN
Inhibition of LMN via interneurone stimulation
What is the overall NET effect of UMNs on LMNs?
overall effect is inhibitory
(therefore loss of UMN stimulation will cause an increase in LMN activity)
What is the name of the tract carrying descending motor fibres through the spinal cord?
Lateral Corticospinal Tract
At what level do the descending motor pathways decussate?
Medullary Pyramids
(within the medulla of the brainstem)
Outline where the cell bodies and axons of both UMN and LMN are found within the CNS and PNS
UMN
cell bodies in grey (cortex) and axons in white matter of CNS
LMN
cell body grey matter (ventral horn) of CNS/spinal cord, axons located in PNS/spinal nerve
What is a normal plantar reflex response?
normal
great toe plantar flexion/curl downwards
abnormal
(+ve) Babinski Sign
great toe dorsiflexion/curl upwards
Outline the path of an upper motor neurone from the cerebral cortex to medullay pyramids
motor cortex (pre-central gyrus) > corona radiata > internal capsule > midbrain > pons > medullary pyramids (decussation)
Which area of the body is innervated by the most medial aspect of the lateral corticospinal tracts?
Medial: arms
Middle: thorax
Lateral: legs
Which area of the brain is supplied by the lenticulostriate arteries that can lead to pathology affecting the motor system?
Internal Capsule
What area of the body is innervated by the corticonuclear projections of the nervous system?
Facial Muscles
(innervate the facial and neck muscles as they synapse with the lower motor neurones of the cranial nerves)
Where are the corticonuclear/corticobulbar nuclei located?
brainstem
- corresponsing to the level of origin of the cranial nerves*
- (2, 2, 4, 4)*
Why does a patient presenting with a stroke in one of the cerebral hemispheres present with forehead sparing?
facial motor nucleus divided in half
- upper half innervates upper facial muscles*
- lower hald innervates lower facial muscle*
upper motor nucei of facial nerve receive bilateral UMN innervation from the left and right heisphere (homunculus)
therefore loss of innervation from one hemisphere is compensated for by the contralateral innervation
What are 4 common symptoms of upper motor neurone lesions?
- Weakness
- Hypertonia
- Hyper-reflexia
- Extensor Plantar Reflex (Babinski Sign)
Why do patients with an upper motor neurone present with weakness and hypertonia?
Weakness
loss of the few excitatory inputs to LMN
Hypertonia
increased muscle tone due to loss of net inhibition from UMN
How may a patient present initially following a stroke and how can does this change over time?
initially may present with spinal shock
once UMN activity removed the LMN activity decreases - causing weakness and hypotonia
classical symptoms then develop around 7 days later, such as hypertonia and hyper-reflexia
Spinal Tracts Summary
Spinal Tracts Summary
