L7 - Motor Pathways

Question 1

Where are the upper motor neurones found?

Answer 1

Cell body in the primary motor cortex
Found in the CNS
Axons descend via the corticospinal tract
Synapses in the ventral horn

UMN are not found in the cerebellum or basal ganglia

Question 2

Where are lower motor neurones found?

Answer 2

The cell body exists in the brain stem or the ventral horn

The axons run via the peripheral nervous system to a muscle

Question 3

Symptoms of a lower motor neurone lesion

Answer 3

Hypotonia
Areflexia - loss of reflexes 
Weakness
Paralysis - multiple cord segments 
Fasciculations
Atrophy of denervation
Fibrillation

Question 4

Atrophy of denervation

Answer 4

Loss of trophic support via growth factors released by lower motor neurones

Question 5

Fasciculations

Answer 5

Visible, uncoordinated, involuntary muscles contractions

Question 6

Hypotonia

Answer 6

Less background contraction therefore floppy

Question 7

Fibrillation

Answer 7

Uncoordinated muscle contractions that are not visible

Question 8

How can a lower motor neurone lesion occur

Answer 8

Cell body destruction
Transected axon

Can occur due to damage of the CNS or PNS

Question 9

How are the motor nuclei of cranial nerves created

Answer 9

The ventral horn extended from the spinal cord into the brain stem but were interrupted to form nuclei

Question 10

Upper motor neurone lesion

Answer 10

Lesion in the CNS only causing loss of normal inhibition to LMN and lack of voluntary control of LMN

Therefore:

• hypertonic
• hyper-reflexia
• weakness
• clasped knife rigidity
• atrophy of disuse
• spasticity

Question 11

Acute phase of UMN lesion

Answer 11

Flaccid paralysis - hypotonia causing spinal shock

Over a period of days to weeks hypertonia develops

Question 12

UMN lesion spasticity

Answer 12

Antigravity muscles dominate therefore:
Upper limb - flexed
Lower limb - extended

Question 13

Clasped knife rigidity

Answer 13

When pulling on limb, rigid up to a certain point where the limb gives way due to the Golgi tendon organ neurones

Question 14

Golgi tendon organ neurones

Answer 14

High threshold neurones that are stimulated by high tension

Stimulate inhibitory interneurones that causes relaxation of muscles

Question 15

UMN effects on lower motor neurones

Answer 15

• synapse onto inhibitory interneurones therefore background inhibition
• synapse directly onto LMN causing conscious excitation that overwhelms inhibition

Question 16

UMN pathway from cerebral cortex to LMN

Answer 16

1. Cell body in the primary motor cortex
2. Axons descend via the corona radiata
3. Axons converge at the internal capsule
4. Axons enter the brain stem via the cerebral peduncle
5. Axons descend down the anterior pons to the spinal cord via the corticospinal tract
6. 85% of the axons decussate at the anterior, inferior medullary pyramids and run via the lateral corticospinal tract
7. 15% continue ipsilaterally down the spinal cord and decussate at the level of the LMN of interest via the ventral corticospinal tract

Question 17

Lateral corticospinal tract neurones

Answer 17

Decussate at the medullary pyramids

Supply the LMNs that supply the distal, peripheral muscles

Question 18

Ventral corticospinal tract

Answer 18

• decussate at the level of the LMN of interest

- supply the LMNs that supply proximal postural muscles

Question 19

Where is the internal capsule found

Answer 19

Between the lentiform nucleus and the thalamus

Question 20

Corticonucleur tract

Answer 20

Some motor axons synapse and terminate in the brain stem

Question 21

Facial nerve motor nucleus

Answer 21

Split into:
- superior aspect which supply LMNs that supply the upper face e.g. forehead and upper eyelid

• inferior aspect suppling the lower face from the lower eyelid

Question 22

Facial nerve proper

Answer 22

Made up of LMNs only

Question 23

UMNs of the upper face

Answer 23

• The cell body is within primary motor cortex laterally

- supply contralateral and ipsilateral superior aspects of facial nuclei

Question 24

UMNs for lower face

Answer 24

• cell bodies in the primary motor cortex laterally

- only supply the contralateral side

Question 25

Facial nerve proper lesion

Answer 25

Loss of LMNs supplying the upper and lower face therefore Bell’s Palsy on the ipsilateral side

Question 26

Right UMN lesion of facial nerve

Answer 26

• The UMN of the upper face is affected contralaterally and ipsilaterally
• But the left contralateral and ipsilateral branch of the UMN supplying the upper face spares the forehead from weakness and paralysis on both sides
• the UMN supplying the contralateral lower face is affected therefore the left lower face becomes weak
• commonly caused by a stroke affecting the middle cerebral artery

Question 27

Internal capsule segments

Answer 27

Anterior limb - between the caudate nucleus and lentiform nucleus

Genus - bend contains the facial upper motor neurones

Posterior limb - between the lentiform nucleus and the thalamus

Question 28

Anterior limb

Answer 28

Allows the communication between the cerebral cortex and the cerebellum

Question 29

Posterior limb

Answer 29

Contains the descending motor neurones of the:

• face
• arms
• trunk
• legs

Contains the 3rd order sensory neurones of the

• face
• arms
• trunk
• legs