Control L13 descending pathways Flashcards
What fibre tracts in the spinal cord are involved in the descending pathways?
Lateral corticospinal tracts
Ventral corticospinal tracts
What are 3 descending pathways?
Corticospinal
Sorticonuclear
Extrapyramidal
What neurones are involved in descending pathways?
Upper and lower
What are properties of upper motor neurones?
Mainly originate in the cerebrum and subcortical structures
Influence lower motor neuron activity
Modify local reflex activity
Superimpose more complex patterns of movement
What are properties of lower motor neurones?
Originate from the brainstem and spinal cord (ventral grey horn)
Are peripheral nerves to motor end plates and neuromuscular junctions
Where are cell bodies of lower motor neurones found?
Ventral grey horn of the spinal cord
Why can motor neurones be called efferent nerves?
As the travel away from the spinal cord into the peripheries
What is another name for the corticonuclear pathway?
Corticobulbar
What are the 4 types of extrapyramidal pathways?
Reticulospinal
Vestibulospinal
Rubrospinal
Tectospinal
What is the purpose of extrapyramidal oathways?
Don’t cause movements but helps co-ordinate them e.g. with posture
Where does the corticospinal pathway travel through?
Cerebral cortex (precentral gyrus in lateral corticospinal) —> internal capsule —> brainstem
Where does the corticonuclear pathway travel?
Cerebral cortex —> precentral gyrus —> internal capsule —> spinal cord
What are the lower motor neurones of the corticocspinal pathway?
Spinal nerves
What are the lower motor neurons of the corticonuclear pathways?
Cranial nerves
Where do nerve fibres cross to the opposite side in the corticospinal pathways?
The desscuation of the pyramids
What are the three main parts of the internal capsule ?
Anterior limb
Gene
Posterior limb
How are nerve fibres organised in the internal capsule?
Somatotopically - face in genu then arms, trunk, limb moving into the posterior limb
Where does the internal capsule connect to/descending fibres of upper motor neurones travel through at the midbrain?
The crus cerebri
Why is the internal capsule vulnerable?
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
How do descending fibres of the corticospinal pathway travel in the brainstem?
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
Roughly what percentage of nerve fibres cross over at the dessucation of the pyramids?
85%
What happens to the upper motor neurones that don’t cross over at the dessucation of the pyramids?
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
What is the role of the descending fibres in the anterior corticospinal tracts that provide bilateral Innervation?
Supply axial musculature
What is the role of descending fibres in the lateral corticospinal tracts that provide ipsilateral Innervation?
Supplies limb musculature
Where do lower motor neurones exit the spinal cord in the corticospinal pathway?
Ventral rootlets and roots
How do lower motor neurones of the corticospinal pathway extend to the skeletal/striated muscles?
Via the segmental spinal nerves
How will patients with a lesion to the ventral grey horn damaging corticospinal pathways present?
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
What are common causes of lower motor lesions in the corticospinal pathway?
Where are common lesions affecting the upper motor neurones of the corticospinal pathway?
How will a patient with a lesion damage to the upper motor neurones of the corticospinal pathway present?
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
What sign may show there is an upper motor neuron injury?
Babinski sign (an extensor plantar response)
Why are axial muscle groups not affected by upper motor neuron lesions in the pathway?
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
Where do fibres for the corticonuclear pathway originate?
Pre central gyrus
Is innervation from the corticonuclear pathway unilateral, contralateral or bilateral?
Bilateral
What cranial nerve nuclei are in the midbrain?
Occulomotor, trochlear, abducens
What cranial nerve nuclei are in the pons?
Trigeminal, facial
What cranial nerve nuclei are in the medulla?
Glossopharyngeal, vagus, accessory and hypoglossal
Why is facial nerve and hypoglossal nerve innervation different to the other cranial nerves?
Lower facial and hypoglossal nucleus have contralateral inneravtion instead of bilateral innervation
Which area of the face is innervated by the lower facial nuclei?
The lower face
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)?
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.
Where will the tongue deviate to if there is a lower motor neuron lesion in the left hypoglossal nerve?
The tongue will deviate to the left (ipsilateral to the lesion)
Where will the tongue deviate if there is a lesion of upper motor nerve fibres coming from the right side of the cortex?
Deviate to the left (contralaterally to the lesion)
