UMNs and Control of Movement Flashcards
What is the function of a simple spinal central pattern generator?
Can command rhythmic, alternating activity that moves a limb
What is the essential features of a simple spinal central pattern generator?
Excitatory interneuron displays oscillatory (pacemaker) activity
How many levels are involved in the motor control hierarchy?
At least three levels
How are controlled movements initiated and influenced?
By multiple sensory inputs and a need to move using internal mechanisms
What is the motor control hierarchy at its simplest?
High = neocortical association areas and basal ganglia Middle = motor cortex and cerebellum Low = brainstem and spinal cord
Where do the descending spinal tracts arise from?
Cerebral cortex and brainstem
What are the descending spinal tracts involved in?
Control of movement, muscle tone, spinal reflexes, spinal autonomic functions and modulation of sensory transmission to higher centres
What are the two important divisions of the descending spinal tract?
Lateral and ventromedial
What is the lateral pathway of the descending spinal tract involved in?
Voluntary control of distal musculature = under control from cerebral cortex
What is the ventromedial pathway of the descending spinal tract involved in?
Control of posture and locomotion = under control of brainstem
What is the major lateral pathway of the descending spinal tract?
Corticospinal tract = longest and one of largest CNS tract
Where are the cell bodies of the corticospinal tract located?
Motor cortex (BA4 and BA6) and somatosensory areas of the parietal cortex
Where do the axons of the corticospinal tract flow?
To the base of the medulla forming a tract (the medullary pyramid)
Where do most fibres of the corticospinal tract cross?
At the pyramidal decussation = forms the lateral corticospinal tract
What happens to fibres of the corticospinal tract that don’t cross at the pyramidal decussation?
Stay ipsilateral to form the ventral corticospinal tract and decussate more caudally
Where do axons of the corticospinal tract terminate?
In the dorsolateral region of the ventral horn and intermediate grey (location of LMNs and interneurons controlling distal muscles)
What side of the body do the motor centres of the left hemisphere control?
The right side of the body
What is a minor lateral pathway of the descending spinal tract?
The rubrospinal tract = exerts control over limb flexor muscle by exciting LMNs
Where are the cell bodies of the rubrospinal tract located?
In the red nucleus = receives input from the motor cortex and cerebellum
Where do the axons of the rubrospinal tract cross over?
Decussate at ventral tegmental decussation = descend spinal cord ventrolateral to the lateral corticospinal tract
Where do axons of the rubrospinal cord terminate?
In the ventral horn
What are lesions of the lateral column associated with?
Loss of fractionated movements
Slowing and impairment of accuracy of voluntary movement
Little effect on normal posture
What are some features of lesions to the corticospinal tract alone?
Deficits are as profound as those of lateral column but major recovery can occur
Weakness of distal flexors and inability to move fingers independently persists
What are the ventromedial pathways?
Vestibulospinal tract, tectospinal tract, pontine reticulospinal tract, medullary reticulospinal tract
Where are the cell bodies of the vestibulospinal tract located?
Reside in vestibular nuclei = receive input via CN VIII from the vestibular labyrinths
Where do the axons from the lateral vestibular nucleus descend?
Descend from Deiter’s nucleus ipsilaterally as the lateral vestibulospinal tract as far as the lumbar spinal cord = balanced posture
Where do the axons from the medial vestibular nucleus descend?
Descend as far as the medial vestibulospinal tract as far as the cervical spinal cord = activate cervical spinal circuits that control neck and back muscles
Where are the cell bodies of the tectospinal tract located?
Reside in superior colliculus = receives input directly from the retina and also from the visual cortex and afferents conveying somatosensory/auditory info
Where do the axons of the tectospinal tract cross over?
Decussate in the dorsal tegmental decussation = descend close to midbrain as the tectospinal tract to the cervical spinal cord
What does the superior colliculus act as in the tectospinal tract?
A map of the external world
Where does the pontine (medial) reticulospinal tract arise?
From the reticular formation = controlled by descending signals from the cortex and descends ipsilaterally
What does the pontine reticulospinal tract control?
Enhances antigravity reflexes of the spinal cord
Helps to maintain a standing posture by facilitating contraction of the extensors of lower limbs
Where does the medullary (lateral) reticulospinal tract arise?
From the reticular formation = controlled by descending signals from the cortex and descends bilaterally
What is the function of the medullary reticulospinal tract?
Opposes the action of the medial tract
Releases antigravity muscles from reflex control
