5: Upper And Lower Motor Neurones Flashcards
(20 cards)
Where is the internal capsule?
Sandwiched between the thalamus and the lentiform nucleus
What is the route of an upper motor neurones descent (pyramidal tracts)?
From the primary motor cortex in the pre central gyrus
Run through the corona radiata
Corona radiata converge through the internal capsule
Pass through medullary pyramid (Hence pyramidal tracts)
In the brainstem the lateral corticotracts dessucate across the midline, anterior corticospinal tracts remains ipsilateral
At the ventral horn, the UMN synapses to a LMN which can then supple the muscle
Is the net effect of an UMN on a LMN excitatory or inhibitory?
Inhibitory
What type of infarcts can occur in the internal capsule?
Lacunae infarcts
Leads to very specific deficits
Where do the corona radiata converge?
At the internal capsule
Upper motor neurones that supply the face are found in which part of the internal capsule?
The genu (“the knee” of the internal capsule)
What are the signs of upper motor neurone damage?
Weakness
HypERtonia (spasticity)
HypERflexia
Extensor plantars (Babinski +ve)
What would cause an UMN lesion?
Stroke
Spinal cord injury
What would cause a LMN injury?
Peripheral neuropathy
Motor neurone Disease
Traumatic injury
What are some signs of LMN lesions?
Weakness
Atrophy (as the LMN provides the muscle with growth factors to maintain muscle bulk)
Hypoflexia/ aflexia
Hypotonia
Fasiculation (uncontrolled muscle twitch)
What is the Babinski sign?
Nociception in the big toe should initiate a spinal reflex which causes the foot plantar flexors to contract and lift the foot away from the stimulus while the dorsiflexors are inhibited
A corticospinal lesion loses the dorsiflexion inhibition so instead there is dorsiflexion of the big toe (Babinski positive)
What would cause a positive Babinski sign?
UMN lesion
For a positive Babinski sign, would the big toe be plantar flexed or dorsiflexed?
Dorsiflexed
Where are LMN cell bodies?
Mostly in the Ventral horn of the spinal cord
Some are in cranial nerve nuclei
The corticobulbar tracts supply the muscles of which region of the body?
Muscle of head and neck
Where do UMN of the corticobulbar tracts synapse with LMN?
On the motor nuclei of the cranial nerves
Outline the knee jerk reflex.
Tapping patellar quadriceps tendon
Sends signal down afferent neurone which synapses onto LMN that supples the quadriceps tendon
Sends signal down efferent motor neurone that supplies the quadriceps muscle
Causes the quadriceps to contract and swing forwards
An interneuron inhibits the hamstring muscle so the hamstring remains relaxed (reciprocal inhibition)
What is the reciprocal inhibition of the patella reflex?
As the quadriceps is stimulated to contract, an inhibitory neurone relaxes the hamstring muscle (the antagonist muscle)
How does the innervation differ between the upper and lower half of the facial nucleus?
Upper half is supplied by both the contralateral and ipsilateral motor cortex
Lower half is supplied only by the contralateral motor cortex
How would an UMN facial lesion and a LMN facial lesion present?
UMN facial lesion: paralysis of contralateral lower facial muscles (upper half of face still has collateral supply of ipsilateral motor cortex)
LMN facial lesion: paralysis of upper and lower facial muscles
