Descending Motor Pathways Flashcards
what tasks are goal directed/purposeful movements split into?
- goal or purpose
- activation of relevant movement
- feedback of movement
- refinement/correction of movement
- cessation on completion
what are features of upper motor neurons?
- 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
what are features of lower motor neurons?
- found in brainstem and spinal cord
- not restricted to CNS and
stimulate muscle to contract - motor function to muscles
what does the corticobulbar tract influence?
facial muscles and descending UMN of brainstem
what does the vestibulospinal tract influence?
balance
what does the reticulospinal tract influence?
- muscle tone
- head orientation
- breathing
what does the rubrospinal tract influence?
cerebellar influenced upper limb movement
what does the tectospinal pathway influence?
head movements to follow sight
what are the two major descending motor pathways?
- lateral pathways - conscious movement
- ventromedial -
unconscious movement
what are features of the lateral pathways?
- principally controlled by cerebral cortex via 2 corticospinal pathways
- general control of voluntary movement
- mainly associated with control of distal muscles
what are features of the ventromedial pathways?
- principally controlled by brainstem
- control of posture and rhythmic movements associated with locomotion
- control axial and proximal muscles
what are the descending ventromedial pathways?
- vestibulospinal (balance)
- reticulospinal (muscle tone, head orientation, breathing)
- rubrospinal (cerebellar influenced upper limb movement)
- tectospinal (head movements to follow sight)
what sensory inputs are utilised in controlling posture?
- muscle proprioceptors:
- detect changes in muscle length/tension - sense of balance (vestibular apparatus:
- derived from head movements relative to earths gravitational field - visual inputs:
- detecting movements in visual field representing movement of body
where is the sensory info for posture integrated?
in the brainstem
what are the sections of the brainstem?
- midbrain
- pons
- medulla
- spinal cord
what are the 2 principle pathways controlling posture?
- vestibulospinal
- reticulospinal
what are principle effect of the lateral vestibulospinal pathway?
- facilitate extensor motor neurones and inhibit flexor motor neurones innervating the ipsilateral medial and axial muscles
what does the lateral vestibulospinal pathway also activate?
- alpha MNs
- gamma MNs
what are the overall effects of the lateral vestibulospinal pathway?
increase tone to the antigravity msucles
what does activating alpha and gamma MNs cause?
enhanced muscle spindle mediated by stretch flexes
what does the medial vestibulospinal pathway control?
head and eye movements - usually in response to moving target
what do unplanned head movements activate?
vestibular apparatus which projects to later vestibular nucleus
what is the role of the lateral vestibular nucleus?
- links info from vestibular apparatus with visual and tectal sensory info
- transmits signals to cranial nerves controlling head, neck and eye movements
what does the reticulospinal pathway co-ordinate?
movement and posture
where does the reticulospinal pathway receive sensory info from?
- vestibular nuclei
- cortical areas for voluntary movement
- proprioception, vision etc
what are characteristics of voluntary movement?
- purposeful - non automatic pr stereotyped response
- conscious reaction to external stimulus, imagination or by wilful decision
- goal directed - where goal could be achieved by different strategies
- often learned - may initially need much concentration but with practice, movement achieved fluently, efficiency/accuracy improves
what is the first branch off the corticospinal tract?
corticobulbar tract
what does the corticobulbar tract have influence over?
control over unconscious motor output (planned movements)
what is happens at the second branch of the corticospinal tract?
pyramidal decussation (90-95%) at L2
what are corticospinal lesions?
- upper motor neurons
- relatively common as these axons are very long (therefore vulnerable)
how are signs of lesions presented as?
positive: the appearance of an abnormal response
negative: a loss of function
what is Babinski sign?
extensor plantar reflex - an example of positive sign following corticospinal lesions
what do corticospinal lesions give rise to?
upper motor neurone syndrome
what are lower motor neurons?
motor neurons whose cell axons leave the CNS and innervate muscle
what can lesions of axons from lower motor neurons cause?
- muscle paralysis
- reduced motor tone
- reduced stretch flex
- fasciculation
- atrophy
what differences are there in how lower and upper motor neurone lesions present?
upper motor:
- no atrophy or fasciculation
- muscle tone increase often leading to painful spasticity
- exaggerated reflexes
- decrease in power
what is hypertonia caused by?
hyperexcitable spindle neurons which induce over-reactive stretch responses
