[31] Upper and Lower Motoneurones

Question 1

What are the upper and lower motoneurones responsible for?

Answer 1

Controlling movement

Question 2

Where does the upper motorneurone have its cell body?

Answer 2

In the primary motor cortex

Question 3

Where is the primary motor cortex found?

Answer 3

In the pre-central gyrus of the brain

Question 4

What is the result of the UMN being located entirely in the CNS?

Answer 4

Any upper motoneurone signs indicate a CNS lesion

Question 5

What does the UMN synapse with?

Answer 5

The LMN

Question 6

What happens to the LMN once it has synapsed with the UMN?

Answer 6

It enters the PNS

Question 7

Where are lesions affecting LMN found?

Answer 7

Either in the CNS or the PNS

Question 8

Where to the LMN come from?

Answer 8

• A large proportion come from the ventral horns of the spinal cord
• Some come from motonuclei in the brainstem

Question 9

Which brainstem motonuclei have LMN coming from them?

Answer 9

• The oculomotor nuclei
• The trochlear nuclei
• The trigeminal nuclei

Question 10

Where do the LMN coming from the oculomotor neurones supply?

Answer 10

The extraocular muscles

Question 11

Where do the LMN coming from the trochlear nuclei supply?

Answer 11

The superior oblique

Question 12

Where do the LMN coming from the trigeminal nuclei supply?

Answer 12

The muscles of mastication

Question 13

Describe the relationship between the cranial nerve nuclei and the vertebral columns

Answer 13

The cranial nerve nuclei are upwards extensions of the vertebral columns

Question 14

Where to the LMN have a pivitol role?

Answer 14

In the spinal tendon reflexes

Question 15

How do the spinal tendon reflexes work?

Answer 15

When the tendon gets hit, the muscle spindle gets stretched. This information is sent to the dorsal root. In the cord, it then travels down to the ventral root. Here, the sensory fibre synapses with a LMN supplying the muscle, causing contraction of the muscle

Question 16

What must happen to the antagonist in order for tendon reflexes to work?

Answer 16

They antagonists must be inhibited by reciprocal inhibition

Question 17

How does reciprocal inhibition work?

Answer 17

A colateral branch of the sensory neurone coming from the muscle spindle travels down the cord to a lower spinal cord segment. Here, it synapses with an inhibiitory interneurone, which synapses with LMNs, inhibiting their supply to the antagonistic muscle, causing relaxation

Question 18

What are the signs of LMN damage?

Answer 18

• Weakness
• Wasting
• Areflexia or hyporeflexia
• Hypotonia
• Fasciculations
• Fibrillation

Question 19

When does muscle wasting caused by LMN damage occur?

Answer 19

A few weeks after the damage

Question 20

Why does muscle wasting occur a few weeks after LMN damage?

Answer 20

Because LMN provide growth factors that are required for muscle bulk

Question 21

What are fasciculations?

Answer 21

Un-coordinated muscle contraction caused by ectopic ACh receptor expression

Question 22

Are UMN found in the basal ganglia and the cerebellum?

Answer 22

No

Question 23

What is the main effect of the UMN on the LMN?

Answer 23

Inhibitory, via inhibitory interneurones, but they also have a small excitatory projection

Question 24

Where do the UMNs have their cell bodies?

Answer 24

Within the motor cortex

Question 25

Where do the UMN go from the motor cortex?

Answer 25

They run through the corona radiatat

Question 26

What is the corona radiata?

Answer 26

A structure with 1000's of UMN axons radiating through the hemispheres

Question 27

Where do UMN run after passing through the corona radiata?

Answer 27

The internal capsule

Question 28

What is the internal capsule?

Answer 28

A white matter structure where all corona radiata axons converge

Question 29

Where does the internal capsule sit?

Answer 29

Between the lentiform nucleus and the thalamus

Question 30

Why is the internal capsule clinically significant?

Answer 30

Because it is frequent affected by stroke, with lacunar infarcts commonly occuring in the internal capsule

Question 31

Describe the topographical organisation of the internal capsule?

Answer 31

In transverse section, the V shaped internal capsule is organised into 3 parts- the anterior limb, the posterior limb, and the genue (point where the capsule bends). The fibres supplying the face are found in the genue, and the parts supplying the upper limbs -\> trunk -\> lower limb are found on the posterior limb (as you get more posterior)

Question 32

Where does the internal capsule join with the midbrain?

Answer 32

At the cerebral peduncles

Question 33

Where do the UMN go from the cerebral peduncles?

Answer 33

The medually pyramids

Question 34

What happens to the UMN in the medullary pyramids?

Answer 34

They move from the ventrally situated medullary pyramids to a lateral position on the opposite side of the brain stem, at a site called the decussation of the pyramids

Question 35

Why is the decussation of the pyramids significant?

Answer 35

Because it explains why the right side of the brain controls the left side of the body, and vice versa

Question 36

What % of corticospinal fibres go into the lateral corticospinal tract?

Answer 36

80%

Question 37

What are the fibres that don't decussate at the medually pyramids called?

Answer 37

The ventral corticospinal tract

Question 38

Where do the fibres in the ventral corticospinal tract cross the midline?

Answer 38

At the level they want to innervate

Question 39

What are the lateral corticospinal tracts important for?

Answer 39

Controlling the distal parts of the limbs

Question 40

What are the ventral corticospinal tracts important for?

Answer 40

Controlling the trunk musculature

Question 41

What phenomenon results from the UMN supply to the face?

Answer 41

Forehead sparing

Question 42

What pathway does forehead sparing occur via?

Answer 42

The corticobulbal pathway

Question 43

What route do UMN take in the corticobulbal pathway?

Answer 43

They pass from their origin in the motor cortex, through the corona radialis and internal capsule, to the facial nerve nuclei.

Question 44

What are the facial nerve nuclei divided into?

Answer 44

Superior and inferior portions

Question 45

What innervation does the superior portion of the facial nerve nuclei recieve?

Answer 45

Bilateral UMN innervation

Question 46

What innervation does the inferior portion of the UMN recieve?

Answer 46

Contralateral UMN innervation

Question 47

What is the superior portion of the facial nerve nuclei dedicated to?

Answer 47

The upper 1/2 of the face

Question 48

What is the inferior portion of the facial nerve nuclei deicated to?

Answer 48

The inferior 1/2 of the face

Question 49

What is the result of the UMN innervation to the facial nerve nuclei in an infarction of the genue of the internal capsule?

Answer 49

The upper 1/2 of the face (the forehead) is spared, as it is recieving bilateral innervation, so you therefore only get contralateral partial facial paralysis

Question 50

What does complete paralyis of half of the face suggest?

Answer 50

Ipsilateral damage to the facial nerve