The Motor System Flashcards
Where is the primary motor cortex?
In the pre central gyrus which is within the frontal lobe.
What is the structure called in which a fan of motor fibres slowly converge onto the internal capsule?
The corona radiata
Which motor fibres are represented in the genu of the internal capsule?
The facial fibres
Which fibres are represented in the proximal part of the posterior limb of the internal capsule?
The motor fibres controlling the upper limb
Which large mid brain structure connecting the cerebellar hemispheres and the brainstem do motor fibres pass through in the mid brain?
The cerebral peduncles
What is the motor pathway called that controls the upper limbs and lower limbs (i.e not face)
The corticospinal tract
What motor pathway controls the face?
The corticobulbar tract
Where do motor fibres dessucate?
In the medullary pyramids
How many neurones are there in the corticospinal pathway?
2- an upper motor neurone and a lower motor neurone. They synapse at the spinal level at which the fibre leaves.
Where can the cell body of the lower motor neurone be found?
In the ventral horn of the spinal cord
What are the cardinal signs of LMN damage?
Weakness Areflexia Wasting Fasciculation Hypotonia
Why do patients develop hyperreflexia in an UMN lesion?
The net effect of a upper motor neurone lesion is inhibitory; the fibre splits and has one fibre which synapses with an inhibitory interneurone which then inhibits the LMN (this is stronger), the other fibre provides weak excitation.
Why does an upper motor neurone lesion of the facial nerve cause forehead sparing?
The facial nerve nucleus has a dual innervation to the upper half of the face coming from both sides of the brain so even if one UMN is damaged the contralateral UMN can still provide innervation to the upper half of that nerve nucleus.
What are the cardinal signs of upper motor neurone lesions?
Weakness
Hypertonia
Hyper reflexia
Extensor plantar reflex
Why might an UMN lesion initially look like a LMN lesion?
Due to spinal shock.
