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Neuro > Descending Tracts > Flashcards

Descending Tracts Flashcards

0
Q

What are the two main sets of descending pathways?

A

Pyramidal

Extra pyramidal

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1
Q

What motor functions do descending tracts mediate?

A 
Voluntary movement
Involuntary movement
Regulation of muscle tone 
Modulation of spinal segmental reflexes 
Regulation of visceral functions
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2
Q

What are the two pyramidal pathways?

A

Corticospinal

Corticobulbar

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3
Q

What are the 5 extra pyramidal tracts?

A 
Reticulospinal
Tectospinal
Rubrospinal
Vestibulospinal 
Olivospinal
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4
Q

Define an upper motor neurone

A

An upper motor neurone is a neurone of the brain that innovates lower motor neurones of the spinal cord and brain stem either directly or through an interneurone

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5
Q

What are corticospinal neurones?

A

Upper motor neurones that project to the spinal cord

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6
Q

What are corticobulbar neurones?

A

An upper motor neurone that projects to lower motor neurones of the brainstem

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7
Q

What is the function of the basal ganglia?

A

To control movement by receiving inputs from the cerebral cortex and feedback signals to different regions of the frontal cortex involved in the initiation of movement

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8
Q

What is the function of the cerebellum?

A

To receive inputs from most parts of the central nervous system that contribute to motor function

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9
Q

What is the function of the corticospinal tract?

A

Precise voluntary movements

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10
Q

Where is the corticospinal tract originate?

A

30% primary motor cortex
30% premotor cortex
40% somato-sensory cortex

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11
Q

What proportion of the motor cortex produces movement of the lower limb?

A

Dorsal and medial aspects of the precentral gyrus

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12
Q

What proportion of the motor cortex produces movement of the upper limb?

A

Lateral aspect of the precentral gyrus

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13
Q

What proportion of the motor cortex produces movement of the face and tongue?

A

Far lateral aspect of the precentral gyrus

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14
Q

What is the significance of the fibres that arise from the primary motor cortex of the corticospinal tract?

A

They are responsible for voluntary control over precise movements that affect the distal musculature
The actions are upon the central horn cells via interneurons
They are heavily dependent on feedback signals

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15
Q

What is the significance of the fibres that arise from the primary somatosensory cortex that projects to the dorsal column?

A

They serve as a sensory filtering mechanism and allows specific sensory signals such as positioning of a limb and force of contraction to reach the relevant areas of the primary motor cortex while preventing sensory signals relevant to the movement from reaching cortical neurones

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16
Q

What is the significance of area six and the premotor cortices of the corticospinal tract?

A

Provide a programming mechanism for the sequencing of response patterns that are essential for producing movements such as walking and lacing up shoes
Project directly to spinal cord and send signals to the primary motor cortex

17
Q

Where does the corticobulbar tract originate?

A

Lateral aspect of the primary motor cortex

18
Q

What does the corticobulbar tract function as?

A

It serves as an UMN to the cranial nerve motor nuclei onto which they make synaptic contact
They are responsible for voluntary control over muscles of facial expression, eye movements and opening and closing of the jaw and movements of the tongue

19
Q

Which corticobulbar tract are not bilateral?

A

CN VII below the eyes

Hypoglossal nucleus

20
Q

What tracts are responsible for axial musculature?

A

Reticulospinal and vestibulospinal

21
Q

Where does the lateral reticulospinal tract arise from and where does it go to?

A

The medulla and goes to all levels of the spinal cord

22
Q

Where it is the medial reticulospinal tract arise from and where does it go?

A

It arises from the pons and goes to all levels of the spinal-cord

23
Q

What is the medial reticulospinal tract responsible for?

A

Voluntary or cortically induced movements and increased muscle tone

24
Q

What is the lateral reticulospinal tract responsible for?

A

Inhibits voluntary movements and cortically induced movement and decreases muscle tone

25
Q

What side does the reticulospinal tract go to?

A

It remains ipsilateral

26
Q

Where does the vestibulospinal tract arise from?

A

The medial and lateral vestibular nuclei

27
Q

Where does the medial vestibulospinal tract project?

A

The cervical levels

28
Q

What does the medial vestibulospinal tract do?

A

It activates then UMN of the spinal accessory nerve

It is responsible for rotation and lifting of the head and the shoulder blade Important for posture and balance

29
Q

What does the lateral vestibulospinal tract do and where does it project?

A

Its projects to all spinal levels Important in the innovation of the extensor muscles
Important for antigravity muscles of the lower limbs in posture and balance

30
Q

Where does the tectospinal tract arise and where does it project to?

A

The superior colliculus of the midbrain

All levels of spinal cord

31
Q

Does the tectospinal tract desiccate?

A

Yes it crosses to the contralateral side in the dorsal tegmental ganglion

32
Q

What is the tectospinal tract responsible for?

A

Coordination of eye-head movements Responses to visual and auditory stimuli

33
Q

Where does the rubrospinal tract originate and why does it descend to?

A

Red nucleus and descends to the cervical level

34
Q

Does the rubrospinal tract desiccate?

A

Yes it crosses over immediately to the contralateral side in the ventral tegmental deccussation

35
Q

What is the rubrospinal tract responsible for?

A

It facilitates motor neurones that innovate flexor muscles and provides tone in facial muscles

36
Q

Why do you get clonic jerks during sleep?

A

There is massive inhibition when falling asleep but so much conductance that you excite them so there is a reverse potential
It is still inhibition but it’s so deep it appears as excitement
In babies clonic movement is due to descending pathways not being fully formed yet

37
Q

Explain how gamma motor neurones regulate tone?

A

They innovate intrafusal muscle fibres and splits to make 2 terminal points
It produces local contraction at the terminal points and a stretch in the centre which activates alpha motor neurones
The muscle is always under tonic activity from gamma motor neurones

38
Q

Explain muscle recruitment order

A

The smallest neurones are innovated first and therefore you can decide how much force you generate with increasing power

39
Q

Explain why descending inhibition does not affect the monosynaptic reflex

A

This is because there is only one synapse so it is still hit by inhibition but it doesn’t inhibit it effectively due to decreased synapses.

Neuro (10 decks)

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