Control L13 descending pathways

Question 1

What fibre tracts in the spinal cord are involved in the descending pathways?

Answer 1

Lateral corticospinal tracts
Ventral corticospinal tracts

Question 2

What are 3 descending pathways?

Answer 2

Corticospinal
Sorticonuclear
Extrapyramidal

Question 3

What neurones are involved in descending pathways?

Answer 3

Upper and lower

Question 4

What are properties of upper motor neurones?

Answer 4

Mainly originate in the cerebrum and subcortical structures
Influence lower motor neuron activity
Modify local reflex activity
Superimpose more complex patterns of movement

Question 5

What are properties of lower motor neurones?

Answer 5

Originate from the brainstem and spinal cord (ventral grey horn)
Are peripheral nerves to motor end plates and neuromuscular junctions

Question 6

Where are cell bodies of lower motor neurones found?

Answer 6

Ventral grey horn of the spinal cord

Question 7

Why can motor neurones be called efferent nerves?

Answer 7

As the travel away from the spinal cord into the peripheries

Question 8

What is another name for the corticonuclear pathway?

Answer 8

Corticobulbar

Question 9

What are the 4 types of extrapyramidal pathways?

Answer 9

Reticulospinal
Vestibulospinal
Rubrospinal
Tectospinal

Question 10

What is the purpose of extrapyramidal oathways?

Answer 10

Don’t cause movements but helps co-ordinate them e.g. with posture

Question 11

Where does the corticospinal pathway travel through?

Answer 11

Cerebral cortex (precentral gyrus in lateral corticospinal) —> internal capsule —> brainstem

Question 12

Where does the corticonuclear pathway travel?

Answer 12

Cerebral cortex —> precentral gyrus —> internal capsule —> spinal cord

Question 13

What are the lower motor neurones of the corticocspinal pathway?

Answer 13

Spinal nerves

Question 14

What are the lower motor neurons of the corticonuclear pathways?

Answer 14

Cranial nerves

Question 15

Where do nerve fibres cross to the opposite side in the corticospinal pathways?

Answer 15

The desscuation of the pyramids

Question 16

What are the three main parts of the internal capsule ?

Answer 16

Anterior limb
Gene
Posterior limb

Question 17

How are nerve fibres organised in the internal capsule?

Answer 17

Somatotopically - face in genu then arms, trunk, limb moving into the posterior limb

Question 18

Where does the internal capsule connect to/descending fibres of upper motor neurones travel through at the midbrain?

Answer 18

The crus cerebri

Question 19

Why is the internal capsule vulnerable?

Answer 19

As small end arteries are vulnerable to vascular damage - especially in hypertensive individuals - so can be lesions/bleeds which put important sensory and motor fibres in this area at risk

Question 20

How do descending fibres of the corticospinal pathway travel in the brainstem?

Answer 20

Through the cerebral peduncles into the basil pons and then the pyramids of the medulla. most of the fibres cross over at the dessucation of the pyramids and descend in the lateral corticospinal tract to provide contralateral Innervation

Question 21

Roughly what percentage of nerve fibres cross over at the dessucation of the pyramids?

Answer 21

85%

Question 22

What happens to the upper motor neurones that don’t cross over at the dessucation of the pyramids?

Answer 22

They travel through the spinal cord ipsilaterally in the anterior corticospinal tract to provide bilateral Innervation i.e. the Innervation to both sides of the body

Question 23

What is the role of the descending fibres in the anterior corticospinal tracts that provide bilateral Innervation?

Answer 23

Supply axial musculature

Question 24

What is the role of descending fibres in the lateral corticospinal tracts that provide ipsilateral Innervation?

Answer 24

Supplies limb musculature

Question 25

Where do lower motor neurones exit the spinal cord in the corticospinal pathway?

Answer 25

Ventral rootlets and roots

Question 26

How do lower motor neurones of the corticospinal pathway extend to the skeletal/striated muscles?

Answer 26

Via the segmental spinal nerves

Question 27

How will patients with a lesion to the ventral grey horn damaging corticospinal pathways present?

Answer 27

Flaccid paralysis of involved muscles
Diminished (hyporeflexia) or a send (areflexia) tendon reflexes at level of lesion
Muscle wasting
Muscle weakness/reduced power
Hypotonia
Fasciculation/fibrillation

Question 28

What are common causes of lower motor lesions in the corticospinal pathway?

Question 29

Where are common lesions affecting the upper motor neurones of the corticospinal pathway?

Question 30

How will a patient with a lesion damage to the upper motor neurones of the corticospinal pathway present?

Answer 30

Initially - flaccid paralysis of limbs contralaterally to the lesion and loss of tendon reflexes

After several days/weeks - function recovers but hypertonia so increased, brisk spinal reflexes (hyperreflexia) below lesion, spastic paralysis of involved muscles, loss of fine motor control/inability to carry out fine movements of hands and feet

Question 31

What sign may show there is an upper motor neuron injury?

Answer 31

Babinski sign (an extensor plantar response)

Question 32

Why are axial muscle groups not affected by upper motor neuron lesions in the pathway?

Answer 32

As controlled by nerve fibres in the anterior cortical tract which innervate bilateral so will still have Innervation from fibres on unaffected side if one side is damaged

Question 33

Where do fibres for the corticonuclear pathway originate?

Answer 33

Pre central gyrus

Question 34

Is innervation from the corticonuclear pathway unilateral, contralateral or bilateral?

Answer 34

Bilateral

Question 35

What cranial nerve nuclei are in the midbrain?

Answer 35

Occulomotor, trochlear, abducens

Question 36

What cranial nerve nuclei are in the pons?

Answer 36

Trigeminal, facial

Question 37

What cranial nerve nuclei are in the medulla?

Answer 37

Glossopharyngeal, vagus, accessory and hypoglossal

Question 38

Why is facial nerve and hypoglossal nerve innervation different to the other cranial nerves?

Answer 38

Lower facial and hypoglossal nucleus have contralateral inneravtion instead of bilateral innervation

Question 39

Which area of the face is innervated by the lower facial nuclei?

Answer 39

The lower face

Question 40

How will the face be affected by a TIA at the level of the internal capsule compared to a facial canal infection (Bell’s palsy)?

Answer 40

With a TIA at the level of the internal capsule there would be facial weakness in only the lower face as bilateral innervation of the upper face means it will not be affected, where as there will be lower and upper facial weakness with infection in the facial canal/Bell’s palsy as it is a lower motor neuron injury of the whole facial nerve so will affect both the upper and lower face.

Question 41

Where will the tongue deviate to if there is a lower motor neuron lesion in the left hypoglossal nerve?

Answer 41

The tongue will deviate to the left (ipsilateral to the lesion)

Question 42

Where will the tongue deviate if there is a lesion of upper motor nerve fibres coming from the right side of the cortex?

Answer 42

Deviate to the left (contralaterally to the lesion)