descending tracts Flashcards
(28 cards)
what are the descending tracts for?
motor signals sent from brain to lower motor neurones
lower motor neurones that directly innervate muscles to produce movement
what can the motor tracts be functionally divided into?
- pyramidal tracts
- extrapyramidal tracts
describe the general passage of the pyramidal tracts and what is it responsible for?
- originate in cerebral cortex
- carry motor fibres to spinal cord and brain stem
- responsible for voluntary control of musculature of body/face
describe the general passage of the extrapyramidal tracts and what is it responsible for?
- originate in brain stem
- carry motor fibres to spinal cord
- responsible for involuntary and automatic control of all musculature e.g. muscle tone, balance, posture, locomotion
what can be said about all neurones in descending motor system?
- no synapses within descending pathway
- at termination of desc tracts, neurones synase with lower motor neurone
- so all neurones in dec motor system = upper motor neurones
what can the pyramidal tracts be subdivided into?
- corticospinal tracts (supplies musculature of body)
- corticobulbar (supplies musculature of head and neck)
where does the corticospinal tract begin? what do they receive input from?
- begin in cerebral cortex
- receive a range of inputs from: primary motor cortex, premotor cortex, supplementary motor cortex, somatosensory area
when happens to the neurones after originating from the cortex?
- neurones converge
- descend through internal capsule
- neurones pass through crus cerebri of midbrain
- pons
- medulla
why is the internal capsule clinically important?
internal capsule particular susceptible to compression from hemorrhagic bleeds
“capsular stroke”
can cause lesion of descending tract
what happens in the most inferior part of the medulla?
tract divides into 2:
- lateral corticospinal tract decussate, descend into spinal cord, terminate at ventral horn, from here lower motor neurones go onto supply muscles of body
- anterior corticospinal tract remains ipsilateral, decussate and terminate in ventral horn of cervical and upper thoracic segmental levels
where do the corticobulbar tracts arise from? what inputs?
- lateral aspect of primary motor cortex
- receive same inputs as corticopsinal tracts
describe the passage of this tract
- fibres converge and pass through internal capsule to brainstem
where do the neurones terminate?
on motor nuclei of cranial nerves
here they synapse with lower motor neurones –> carry motor signals to muscles of face and neck
what is important to remember about the organisation of the corticobulbar fibres?
many of these fibres innervate motor neurones bilaterally
where does the extrapyramidal tract originate and what does it do?
- brainstem and carry motor fibres to spinal cord
- involuntary and automatic control of all musculature
what are the 4 tracts?
- vestibulospinal
- reticulospinal
- rubrospinal
- tectospinal
which ones decussate?
rubrospinal and tectospinal
so provide contralateral innervation
where do the vestibulospinal pathways arise? where does it convey info to?
- vestibular nuceli which receive input from organs of balance
- convey balance info to spinal cord (remains ipsilateral)
what do fibres in this pathway control?
control balance and posture by innervating anti-gravity muscles (flexors of arm, extensors of leg)
what are the 2 reticulospinal tracts and where do they arise?
- medial reticulospinal tract arises from pons
- lateral reticulospinal tract arises from medulla
what does the medial reticulospinal tract facilitate?
voluntary movements, inc. muscle tone
what does the lateral reticulospinal tract facilitate?
inhibits voluntary movements, dec. muscle tone
where does the rubrospinal tract originate? what kind of innervation does it have?
- originates from red nucleus
- as fibres emerge, they decussate and descend into spinal cord
- contralateral
what is the function of the rubrospinal tract?
exact function unclear
thought to play role in fine control of hand movements
