Descending Pathways (section 3)

Question 0

Are the descending pathways excitatory to some motor neurons or inhibitor to other motor neurons?

Answer 0

Both. They are excitatory and inhibiting (depending upon spatial and temporal summation of thousands of inputs)

Question 1

The descending motor pathways work directly and indirectly with what neurons?

Answer 1

1. Alpha and gamma motor neurons of the ventral horn of the spinal cord
2. Cranial Nerve nuclei

Question 2

The descending pathways and somas they arise from are considered what type of motor neurons?

Answer 2

Upper Motor Neurons

Question 3

What are the lower motor neurons?

Answer 3

The alpha and gamma motor neurons

Question 4

Which tract is the largest and clinically most important descending motor tract?

Answer 4

Corticospinal tract

Question 5

Axons descending on the corticospinal tract arise from somas that lie mostly in what cortex?

Answer 5

Primary motor cortex

Question 6

Name the six structures that the corticospinal tract pass through in order?

Answer 6

1. Corona radiata
2. Internal capsule
3. Cerebral peduncles of midbrain
4. Pons
5. Medulla
6. Pyramids of the medulla (decussate)

Question 7

What percentage of fibers decussate in the pryramids of the medulla

Answer 7

85-90%

Question 8

Which specific corticospinal tract contain axons that cross and descend?

Answer 8

Lateral corticospinal tract

Question 9

Uncrossed fibers descend as what tract?

Answer 9

Anterior (Lateral) corticospinal tract

Question 10

What percentage of fibers are uncrossed as they descend as the anterior corticospinal tract?

Answer 10

10-15%

Question 11

Which tract is universally regarded as the descending pathway most concerned with voluntary, discrete and skilled movements?

Answer 11

Lateral corticospinal tract

Question 12

What tract projects mainly to the cervical and upper thoracic spinal cord?

Answer 12

Anterior corticospinal tract

Question 13

The lateral corticospinal tract is associated with innervation of what part of body?

Answer 13

Contralateral limbs

Question 14

Anterior corticospinal tract controls what portion of body?

Answer 14

Bilateral axial musculature (trunk)

Question 15

Which tract is involved with the motor nuclei of cranial nerves in the brainstem

Answer 15

Corticobulbar tracts

Question 16

Which cranial nerves are not associated with corticobulbar tracts

Answer 16

CN I
CN II
CN VIII

Question 17

Axons arise from somas in what region of the motor cortex that are involved in corticobulbar tracts?

Answer 17

the Face region of motor cortex

Question 18

Describe pathway of Corticobulbar tracts

Answer 18

Corona radiata
Internal capsule
cerebral peduncles

Question 19

At what level does crossing begin during the corticobulbar tracts

Answer 19

Crossing begins to occur at the level of the CN they are innervating

Question 20

Which projections of the corticobulbar tracts are not just simply crossed?

Answer 20

Those to the Facial Nucleus are Bilateral! (part is crossed, part is uncrossed)

Question 21

Cell bodies in Rubrospinal tract are located where in the midbrain?

Answer 21

Red Nucleus

Question 22

Are axons crossed or uncrossed in the rubrospinal tract?

Answer 22

Crossed

Question 23

What happens to the rubrospinal tract axons immediately when they exit their nucleus?

Answer 23

They cross to the opposite side in the ventral tegmentum of the midbrain

Question 24

Which tract has axons that are just anterior to the lateral corticospinal tract in the lateral funiculus of the spinal cord?

Answer 24

Rubrospinal tract

Question 25

Axons terminate at all spinal levels in rubrospinal tract but most terminate where?

Answer 25

in the cervical segments

Question 26

T or F Red nucleus receives input from both the cerebral cortex and cerebellum

Answer 26

True

Question 27

Rubrospinal tract and reticusospinal tracts are alternate routes for what?

Answer 27

achieving voluntary movement

Question 28

Function of rubrospinal tract?

Answer 28

Control of dextrous movement of contralateral upper extremity

Question 29

What are the two reticulospinal tracts?

Answer 29

Medullary (lateral) reticulospinal tract

Pontine (medial) reticulospinal tract

Question 30

What structures of the brainstem give rise to the reticulospinal tracts

Answer 30

Two large brainstem reticular formation regions in the pons and in the medulla

Question 31

How does the medullary reticulospinal tract descend? (crossed, uncrossed, etc.)

Answer 31

Crossed and Uncrossed (bilateral)

Question 32

The Medullary reticulospinal tract acts primarily on what type of motor neurons?

Answer 32

Gamma but some on alpha

Question 33

Function of Medullary Reticulospinal tract

Answer 33

Inhibit Lower Extremity extensors
Facilitate flexors
Reduce muscle tone in the Lower Extremities

Question 34

How does the Pontine reticulospinal tract descend? (crossed, uncrossed, etc.)

Answer 34

Mostly uncrossed

Question 35

Function of Pontine reticulospinal tract

Answer 35

Facilitates lower extremity extensor

This increases muscle tone especially to lower extremity