Motor Tracts - CST

Question 1

Inability to correctly imitate gestures; cannot perform the motor sequence correctly although they know the position of the limb

Answer 1

Apraxia

Question 2

Right vs. Left disorientation; inability to recognize things

Answer 2

Agnosia

Question 3

What is the course of Upper Motor Neurons and where will you find them?

Answer 3

From the cortex to the spinal cord - found higher up in the CNS

Question 4

What is the course of Lower Motor Neurons and where will you find them?

Answer 4

From the spinal cord to the skeletal muscle - found in anterior horn of spinal cord

Question 5

Where is the primary motor cortex?

Answer 5

Precentral gyrus

Question 6

An area anteriorly to the precentral gyrus that involved broca’s area?

Answer 6

Premotor cortex

Question 7

What do lentriculostriate infarcts cause?

Answer 7

Motor and/or sensory deficits and cognitive dysfunction

Question 8

What are lentriculostriate infarcts caused from?

Answer 8

Ischemia of watershed region - area supplied by distal branches of MCA and ICA

Question 9

What type of tract is the Corticospinal Tract?

Answer 9

DESCENDING

Question 10

The CST upper motor neurons start on what cells and where?

Answer 10

Pyramidal cells (Betz) in the ganglionic layer (5) of the cortical lamina in the primary motor cortex of the precentral gyrus

Question 11

What is descending in the CST pathway?

Answer 11

Upper motor neurons

Question 12

Where do 80% of the CST upper MNs cross?

Answer 12

At the pyramids in the posterior medulla (pyramidal decussation)

Question 13

Where do the other 20% of the CST fibers that did not cross go?

Answer 13

Stay midline and ipsilateral to the anterior white column

Question 14

The Corticospinal tract fibers that crossed midline become what tract?

Answer 14

Lateral Corticospinal Tract (LCST)

Question 15

The Corticospinal tract fibers that did NOT cross midline become what tract?

Answer 15

Anterior Corticospinal Tract (ACST)

Question 16

Describe the pathway of the LCST

Answer 16

The descend in the lateral white column and then synapse to lower motor neurons in the anterior grey horn

Question 17

What is the main innervation of the LCST?

Answer 17

Distal limb musculature for fine movement

Question 18

What type of lower MN’s do the LCST upper MN’s synapse on to?

Answer 18

Alpha and some gamma motor neurons

Question 19

When and where do the corticospinal fibers in the ACST cross?

Answer 19

At their respective spinal levels, they cross the anterior white column to synapse to alpha motor neurons in the anterior grey horn

Question 20

Lesions of the CST would be found above what?

Answer 20

Posterior medulla

Question 21

Lesions of the CST produce?

Answer 21

Contralateral spastic hemiplegia or hemiparesis

Question 22

Lesions of the LCST produce?

Answer 22

Ipsilateral paralysis of distal limb musculature below the level of adhesion

Question 23

What do lesions of the Lower Motor Neurons result in?

Answer 23

Flaccid paralysis, areflexia, atonia, atrophy and fasciculations

Question 24

Muscle is completely limp

Answer 24

Flaccid paralysis

Question 25

NO muscle reflex due to loss of efferent component of the arc

Answer 25

Areflexia

Question 26

Destruction of gamma MN

Answer 26

Atonia

Question 27

Fasciculations

Answer 27

Twitching

Question 28

What do corticobulbar fibers travel through?

Answer 28

Genu of internal capsule

Question 29

When do corticobulbar fibers usually cross?

Answer 29

Lower pons between CN V and VI

Question 30

Where do the upper motor neurons start for the corticobulbar fibers?

Answer 30

Precentral gyrus (primary motor cortex)

Question 31

Direct corticulobulbar fibers terminate where?

Answer 31

LMN’s of the trigeminal, facial and hypoglossal nuclei

Question 32

Lesions of the uncrossed CBT?

Answer 32

Contralateral supranuchlear facial palsy

Question 33

What area of the face does supranuchlear facial palsy affect?

Answer 33

Lower quadrant of facial muscles

Question 34

Lesions of the crossed CBT?

Answer 34

Ipsilateral cranial nerve palsies

Question 35

These fibers may play a role in recovery from lesions of the direct CBT

Answer 35

Indirect corticobulbar fibers

Question 36

Which portion of the facial nucleus receivers corticobulbar fibers from the contralateral cortex?

Answer 36

Anterior portion

The posterior portion receives from both hemispheres

Question 37

Unilateral lesions of the Corticobulbar fibers ABOVE the facial nucleus result in what?

Answer 37

Contralateral supranuchlear facial palsy

Question 38

Central lesion of the facial nerve (ipsilateral side)

Answer 38

Bell’s palsy

Question 39

Why is the posterior portion of the facial nucleus not affected by a unilateral lesion?

Answer 39

It receives innervation from both hemispheres!

Question 40

What does the posterior portion of the facial nucleus supply?

Answer 40

Upper quadrant of facial muscles

Question 41

How may a person look if they have contralateral supranuchlear facial palsy?

Answer 41

Unable to smile/lift ONE SIDE of their mouth - rest of the face (3/4) is functioning properly

Question 42

What is the main innervation of the ACST?

Answer 42

Axial musculature (large midline groups) - not a huge deficit if this pathway is lesioned

Question 43

Purpose of the corticobulbar fibers?

Answer 43

Innervation for voluntary movements of the face!

Question 44

Purpose of the CST?

Answer 44

Innervation for voluntary movements of the limbs and body!