Motor Tracts - CST Flashcards
Inability to correctly imitate gestures; cannot perform the motor sequence correctly although they know the position of the limb
Apraxia
Right vs. Left disorientation; inability to recognize things
Agnosia
What is the course of Upper Motor Neurons and where will you find them?
From the cortex to the spinal cord - found higher up in the CNS
What is the course of Lower Motor Neurons and where will you find them?
From the spinal cord to the skeletal muscle - found in anterior horn of spinal cord
Where is the primary motor cortex?
Precentral gyrus
An area anteriorly to the precentral gyrus that involved broca’s area?
Premotor cortex
What do lentriculostriate infarcts cause?
Motor and/or sensory deficits and cognitive dysfunction
What are lentriculostriate infarcts caused from?
Ischemia of watershed region - area supplied by distal branches of MCA and ICA
What type of tract is the Corticospinal Tract?
DESCENDING
The CST upper motor neurons start on what cells and where?
Pyramidal cells (Betz) in the ganglionic layer (5) of the cortical lamina in the primary motor cortex of the precentral gyrus
What is descending in the CST pathway?
Upper motor neurons
Where do 80% of the CST upper MNs cross?
At the pyramids in the posterior medulla (pyramidal decussation)
Where do the other 20% of the CST fibers that did not cross go?
Stay midline and ipsilateral to the anterior white column
The Corticospinal tract fibers that crossed midline become what tract?
Lateral Corticospinal Tract (LCST)
The Corticospinal tract fibers that did NOT cross midline become what tract?
Anterior Corticospinal Tract (ACST)
Describe the pathway of the LCST
The descend in the lateral white column and then synapse to lower motor neurons in the anterior grey horn
What is the main innervation of the LCST?
Distal limb musculature for fine movement
What type of lower MN’s do the LCST upper MN’s synapse on to?
Alpha and some gamma motor neurons
When and where do the corticospinal fibers in the ACST cross?
At their respective spinal levels, they cross the anterior white column to synapse to alpha motor neurons in the anterior grey horn
Lesions of the CST would be found above what?
Posterior medulla
Lesions of the CST produce?
Contralateral spastic hemiplegia or hemiparesis
Lesions of the LCST produce?
Ipsilateral paralysis of distal limb musculature below the level of adhesion
What do lesions of the Lower Motor Neurons result in?
Flaccid paralysis, areflexia, atonia, atrophy and fasciculations
Muscle is completely limp
Flaccid paralysis
NO muscle reflex due to loss of efferent component of the arc
Areflexia
Destruction of gamma MN
Atonia
Fasciculations
Twitching
What do corticobulbar fibers travel through?
Genu of internal capsule
When do corticobulbar fibers usually cross?
Lower pons between CN V and VI
Where do the upper motor neurons start for the corticobulbar fibers?
Precentral gyrus (primary motor cortex)
Direct corticulobulbar fibers terminate where?
LMN’s of the trigeminal, facial and hypoglossal nuclei
Lesions of the uncrossed CBT?
Contralateral supranuchlear facial palsy
What area of the face does supranuchlear facial palsy affect?
Lower quadrant of facial muscles
Lesions of the crossed CBT?
Ipsilateral cranial nerve palsies
These fibers may play a role in recovery from lesions of the direct CBT
Indirect corticobulbar fibers
Which portion of the facial nucleus receivers corticobulbar fibers from the contralateral cortex?
Anterior portion
The posterior portion receives from both hemispheres
Unilateral lesions of the Corticobulbar fibers ABOVE the facial nucleus result in what?
Contralateral supranuchlear facial palsy
Central lesion of the facial nerve (ipsilateral side)
Bell’s palsy
Why is the posterior portion of the facial nucleus not affected by a unilateral lesion?
It receives innervation from both hemispheres!
What does the posterior portion of the facial nucleus supply?
Upper quadrant of facial muscles
How may a person look if they have contralateral supranuchlear facial palsy?
Unable to smile/lift ONE SIDE of their mouth - rest of the face (3/4) is functioning properly
What is the main innervation of the ACST?
Axial musculature (large midline groups) - not a huge deficit if this pathway is lesioned
Purpose of the corticobulbar fibers?
Innervation for voluntary movements of the face!
Purpose of the CST?
Innervation for voluntary movements of the limbs and body!
