5: Upper And Lower Motor Neurones

Question 1

Where is the internal capsule?

Answer 1

Sandwiched between the thalamus and the lentiform nucleus

Question 2

What is the route of an upper motor neurones descent (pyramidal tracts)?

Answer 2

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

Question 3

Is the net effect of an UMN on a LMN excitatory or inhibitory?

Answer 3

Inhibitory

Question 4

What type of infarcts can occur in the internal capsule?

Answer 4

Lacunae infarcts

Leads to very specific deficits

Question 5

Where do the corona radiata converge?

Answer 5

At the internal capsule

Question 6

Upper motor neurones that supply the face are found in which part of the internal capsule?

Answer 6

The genu (“the knee” of the internal capsule)

Question 7

What are the signs of upper motor neurone damage?

Answer 7

Weakness
HypERtonia (spasticity)
HypERflexia
Extensor plantars (Babinski +ve)

Question 8

What would cause an UMN lesion?

Answer 8

Stroke

Spinal cord injury

Question 9

What would cause a LMN injury?

Answer 9

Peripheral neuropathy
Motor neurone Disease
Traumatic injury

Question 10

What are some signs of LMN lesions?

Answer 10

Weakness
Atrophy (as the LMN provides the muscle with growth factors to maintain muscle bulk)
Hypoflexia/ aflexia
Hypotonia
Fasiculation (uncontrolled muscle twitch)

Question 11

What is the Babinski sign?

Answer 11

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)

Question 12

What would cause a positive Babinski sign?

Answer 12

UMN lesion

Question 13

For a positive Babinski sign, would the big toe be plantar flexed or dorsiflexed?

Answer 13

Dorsiflexed

Question 14

Where are LMN cell bodies?

Answer 14

Mostly in the Ventral horn of the spinal cord

Some are in cranial nerve nuclei

Question 15

The corticobulbar tracts supply the muscles of which region of the body?

Answer 15

Muscle of head and neck

Question 16

Where do UMN of the corticobulbar tracts synapse with LMN?

Answer 16

On the motor nuclei of the cranial nerves

Question 17

Outline the knee jerk reflex.

Answer 17

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)

Question 18

What is the reciprocal inhibition of the patella reflex?

Answer 18

As the quadriceps is stimulated to contract, an inhibitory neurone relaxes the hamstring muscle (the antagonist muscle)

Question 19

How does the innervation differ between the upper and lower half of the facial nucleus?

Answer 19

Upper half is supplied by both the contralateral and ipsilateral motor cortex

Lower half is supplied only by the contralateral motor cortex

Question 20

How would an UMN facial lesion and a LMN facial lesion present?

Answer 20

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