Descending Tracts Flashcards
What are the pyramidal tracts?
Latera corticospinal tract
Anterior corticospinal tract
Corticobulbar tract
What do the pyramidal tracts control?
Voluntary movement
Corticospinal supplies the musculature of the body
Corticobulbar supplies the musculature of the head and neck
Where do the pyramidal tracts originate?
Cerebral cortex (Motor cortex/Pre-motor area/Supplementary motor area/somatosensory cortex)
Describe the path of the lateral corticospinal tract.
Inputs from Cerebral cortex
Descend through internal capsule (white matter pathway between thalamus and basal ganglia)
midbrain (crus cerebra),
pons,
medullary pyramids, - divides into anterior and lateral tracts
Lateral corticospinal tract decussates and descends contralaterally in spinal cord
Terminate in ventral horn at spinal level supplied.
(Synapse with alpha-motorneurone or interneurone)
Describe the path of the anterior corticospinal tracts.
Cerebral cortex Descend through internal capsule the midbrain (crus cerebri) Pons Medullary pyramids Descend to cervical and thoracic levels Decussate at a certain vertebral level and synapse with lower motor neurones in ventral horn
Where do the corticospinal tracts decussate?
Lateral - in the medulla
Anterior - spinal cord
Why is the corticospinal tract vulnerable to damage from haemorrhage?
Passes through the internal capsule which is innervated by the medial meningeal artery.
The internal capsule is susceptible to compression from haemorrhagic bleeds, known as a ‘capsular stroke‘
What does the corticobulbar track supply?
Cranial nerves.
Muscles of head and neck
Where does the corticobulbar tract originate?
Cortex:
30% motor cortex
30% premotor area and supplementary motor area
40% somatosensory cortex
Describe the path of the corticobulbar tract.
Cerebral cortex Internal capsule Brainstem - decussates Terminate on cranial nerve motor nuclei in brainstem, midbrain, pons, medulla. Synapse with lower motor neurones.
Where does the corticobulbar tract decussate?
May fibres from corticobulbar tract innervate lower motor neurones bilaterally
except:
Upper motor neurones for facial nerve have contralateral innervation
Upper motor neurones for hypoglossal nerve (12) only provide contralateral innervation
Where do the pyramidal pathways terminate?
Lateral corticospinal - contralateral spinal cord ventral horn
Anterior corticospinal - contralateral spinal cord ventral horn
Corticobulbar - Contralateral (and some ipsilateral) motor cranial nerve nuclei.
What are the extrapyramidal tracts
Brainstem pathways: vestibulospinal tectospinal Reticulospinal Rubrospinal/rubrobulbar Olivospinal
What do the extrapyramidal tracts control?
Automatic, involuntary movements and tone, balance, posture
Origin of vestibulospinal tract?
Vestibular nuclei in pons
Path of vestibulospinal tract
Vestibular nuclei pons
Ipsilateral spinal cord
Terminates on alpha motor neurones and interneurones
Function of vestibulospinal tract
Balance and posture by innervating anti-gravity muscles (flexors of arm and extensors of leg)
Origin of tectospinal tract
Tectum (colliculi) of midbrain (Superior colliculi (visual input) inferior colliculi (auditory input).
Path of tectospinal tract?
(receives input from optic nerves) Tectum of midbrain Decussates immediately in midbrain Spinal cord Terminates in cervical cord and brainstem nuclei
Function of tectospinal tract
Directing head movement in response to visual and auditory stimuli
Origin of reticulospinal tract
Reticular formation in pons (medial reticulospinal tract) and medulla (lateral reticulospinal tract)
Path of reticulospinal tract
Remains ipsilateral (partially decussates in brainstem) Innervates motor neurone, regulating posture and rhythmic movement.
Function of reticulospinal tract
Automatic movement Medullary tract (lateral) innervates flexor reflexes, inhibits extensor - inhibits voluntary movement and reduces tone
Pontine (medial) facilitates extensor reflexes - facilitates voluntary movement and increases tone
Origin of rubrospinal/rubrobulbar tract
Red nucleus of midbrain
Path of rubrospinal/rubrobulbar tract
Red nucleus, midbrain
Decussates immediately in midbrain
Terminates on alpha motorneurones/interneurones
Function of rubrospinal/rebrobulbar tracts
Facilitate flexion - controls flexor tone, fine control of hand movements.
Rubrobulbar - controls tone of facial muscles
Where do the extrapyramidal tracts decussate?
Vestibulospinal - ipsilateral
Tectospianl - immediately in midbrain
Reticulospinal - ipsilateral (partially in brainstem)
Rubrospinal/rubrobulbar - immediately in midbrain
Why does damage to the corticobulbar tracts only result in mild muscle weakness? What is the exception to this?
Mostly bilateral innervation of LMN
Except CNXII - lesion of UMN will result in spastic paralysis of contralateral genioglossus - deviation to contralateral side to lesion
CNVII - UMN lesion will result in spastic paralysis of muscles in contralateral lower quadrant of face
How does UMN and LMN lesion of CNXII differ?
In UMN tongue away from lesion as contralateral innervation
In LMN lesion, tongue toward lesion.
