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MD2002 > Descending Motor Pathways > Flashcards

Descending Motor Pathways Flashcards

1
Q

what tasks are goal directed/purposeful movements split into?

A
  1. goal or purpose
  2. activation of relevant movement
  3. feedback of movement
  4. refinement/correction of movement
  5. cessation on completion
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2
Q

what are features of upper motor neurons?

A
  • found in cortex and brainstem nuclei
  • restricted to CNS and do not contact muscle
  • executive function for lower motor neurons (LMNs) and circuits controlling LMNs
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3
Q

what are features of lower motor neurons?

A
  • found in brainstem and spinal cord
  • not restricted to CNS and
    stimulate muscle to contract
  • motor function to muscles
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4
Q

what does the corticobulbar tract influence?

A

facial muscles and descending UMN of brainstem

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5
Q

what does the vestibulospinal tract influence?

A

balance

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6
Q

what does the reticulospinal tract influence?

A
  • muscle tone
  • head orientation
  • breathing
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7
Q

what does the rubrospinal tract influence?

A

cerebellar influenced upper limb movement

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8
Q

what does the tectospinal pathway influence?

A

head movements to follow sight

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9
Q

what are the two major descending motor pathways?

A
  1. lateral pathways - conscious movement
  2. ventromedial -
    unconscious movement
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10
Q

what are features of the lateral pathways?

A
  • principally controlled by cerebral cortex via 2 corticospinal pathways
  • general control of voluntary movement
  • mainly associated with control of distal muscles
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11
Q

what are features of the ventromedial pathways?

A
  • principally controlled by brainstem
  • control of posture and rhythmic movements associated with locomotion
  • control axial and proximal muscles
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12
Q

what are the descending ventromedial pathways?

A
  • vestibulospinal (balance)
  • reticulospinal (muscle tone, head orientation, breathing)
  • rubrospinal (cerebellar influenced upper limb movement)
  • tectospinal (head movements to follow sight)
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13
Q

what sensory inputs are utilised in controlling posture?

A
  1. muscle proprioceptors:
    - detect changes in muscle length/tension
  2. sense of balance (vestibular apparatus:
    - derived from head movements relative to earths gravitational field
  3. visual inputs:
    - detecting movements in visual field representing movement of body
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14
Q

where is the sensory info for posture integrated?

A

in the brainstem

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15
Q

what are the sections of the brainstem?

A
  • midbrain
  • pons
  • medulla
  • spinal cord
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16
Q

what are the 2 principle pathways controlling posture?

A
  • vestibulospinal

- reticulospinal

17
Q

what are principle effect of the lateral vestibulospinal pathway?

A
  • facilitate extensor motor neurones and inhibit flexor motor neurones innervating the ipsilateral medial and axial muscles
18
Q

what does the lateral vestibulospinal pathway also activate?

A
  • alpha MNs

- gamma MNs

19
Q

what are the overall effects of the lateral vestibulospinal pathway?

A

increase tone to the antigravity msucles

20
Q

what does activating alpha and gamma MNs cause?

A

enhanced muscle spindle mediated by stretch flexes

21
Q

what does the medial vestibulospinal pathway control?

A

head and eye movements - usually in response to moving target

22
Q

what do unplanned head movements activate?

A

vestibular apparatus which projects to later vestibular nucleus

23
Q

what is the role of the lateral vestibular nucleus?

A
  • links info from vestibular apparatus with visual and tectal sensory info
  • transmits signals to cranial nerves controlling head, neck and eye movements
24
Q

what does the reticulospinal pathway co-ordinate?

A

movement and posture

25
Q

where does the reticulospinal pathway receive sensory info from?

A
  1. vestibular nuclei
  2. cortical areas for voluntary movement
  3. proprioception, vision etc
26
Q

what are characteristics of voluntary movement?

A
  1. purposeful - non automatic pr stereotyped response
  2. conscious reaction to external stimulus, imagination or by wilful decision
  3. goal directed - where goal could be achieved by different strategies
  4. often learned - may initially need much concentration but with practice, movement achieved fluently, efficiency/accuracy improves
27
Q

what is the first branch off the corticospinal tract?

A

corticobulbar tract

28
Q

what does the corticobulbar tract have influence over?

A

control over unconscious motor output (planned movements)

29
Q

what is happens at the second branch of the corticospinal tract?

A

pyramidal decussation (90-95%) at L2

30
Q

what are corticospinal lesions?

A
  • upper motor neurons

- relatively common as these axons are very long (therefore vulnerable)

31
Q

how are signs of lesions presented as?

A

positive: the appearance of an abnormal response
negative: a loss of function

32
Q

what is Babinski sign?

A

extensor plantar reflex - an example of positive sign following corticospinal lesions

33
Q

what do corticospinal lesions give rise to?

A

upper motor neurone syndrome

34
Q

what are lower motor neurons?

A

motor neurons whose cell axons leave the CNS and innervate muscle

35
Q

what can lesions of axons from lower motor neurons cause?

A
  • muscle paralysis
  • reduced motor tone
  • reduced stretch flex
  • fasciculation
  • atrophy
36
Q

what differences are there in how lower and upper motor neurone lesions present?

A

upper motor:

  • no atrophy or fasciculation
  • muscle tone increase often leading to painful spasticity
  • exaggerated reflexes
  • decrease in power
37
Q

what is hypertonia caused by?

A

hyperexcitable spindle neurons which induce over-reactive stretch responses

MD2002 (85 decks)

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