Ascending and Descending tracts Flashcards
What modality are ascending tracts
Sensory
What modality are descending tracts
Motor
What is the DCML
Dorsal Column Medial Lemniscus tract
What sensation does the DCML detect
fine touch
conscious proprioception
Where do fibres in the DCML tract cross over to the contralateral side
2nd order nerves cross over at the level of the medulla
What is the dorsal column in the spinal cord made up of
fasiculus gracilis
fasiculus cuneatus
From where does the nucleus gracilis carry information
Legs
From where does the nucleus cuneatus carry information
arms
What is the STT
Spinothalamic tract
What sensation does the STT detect
pain
temperature
crude touch / deep pressure
Where do fibres in the STT cross over to the contralateral side
2nd order neurons cross over segmentally at the level they enter the spinal cord
What action does the corticospinal tract help control
fine motor movement
What is the corticospinal tract also known as (CST)
pyramidal tract
what kinds of corticospinal tracts are there
lateral and ventral
_% fibres cross over __ in the lateral CST
85% fibres cross over the midline at the decussation of the pyramids in the medulla
where do fibres in the ventral CST cross over
segmentally in the spinal cord as they need to leave
What is the internal capsule
deep subcortical tissue of white matter, all modalities run through this
Give examples of extra-pyramidal tracts
tectospinal - input to H+N region
reticulospinal - reticular formation at core of brainstem (pons and medulla): consciousness, breathing, cariac
vesticulospinal - input to anti-gravity muscles
What is Brown Séquard syndrome
hemisection of the spinal cord resulting in:
ipsilateral loss of fine touch, proprioception and fine movement (DCML + CST)
contralateral loss of pain and temperature (STT)
Where is the primary somatosensory cortex found
post central gyrus
Where is the primary somatomotor cortex found
pre central gyrus
How many neurons are involved in ascending tracts
3
1st, 2nd and 3rd order neurons
How many neurons are involved in descending tracts
2
UMN + LMN
Where do 3rd order neurons in ascending tracts synapse
thalamus in the brain
path of the corticobulbar tract
passes through internal capsule to reach the brainstem
fibres in the corticobulbar tract innervate CN nuclei bilaterally except __
CN VII
UMN of facial nerve has contralateral innervation of muscles of the lower face and bilateral innervation of muscles of the upper face
ie R brain controls left lower facial muscles
CN XII
UMN of hypoglossal has contralateral innervation to the tongue
central lesion of CN VII causes forehead sparing/involvement
and give an example of this
sparing
because upper facial muscles have bilateral innervation
stroke
peripheral lesion of CN VII causes forehead sparing/involvement
and give an example of this
involvement
Bell’s palsy
what is the rubrospinal tract
originates in the red nucleus of the midbrain
excites upper limb flexors
inhibits upper limb extensors
the rubrospinal tract innervates both upper and lower limbs, true or false
FALSE
only innervates upper limbs
what is the reticulospinal tract
originates in pons/medulla
excites upper and lower limb extensors
in terms of descending tracts, what is the order of dominance over the body
- corticospinal tract
- rubrospinal tract
- reticulospinal tract
what happens if the CST is lost
rubrospinal tract is next dominant
therefore upper limb flexion ie decorticate posturing
what happens is the rubrospinal tract is lost
reticulospinal tract is next dominant
therefore there is both upper and lower limb extension ie decerebrate posturing
fasciculus gracilis is from below/above T6
below
