descending tracts

Question 1

1. What are lower motor neurons, and where are they located?

Answer 1

Motor neurons in the anterior gray columns of the spinal cord that send axons through the anterior roots to innervate skeletal muscles.

Question 2

2. What are upper motor neurons?

Answer 2

Neurons that originate in the brain (cerebral cortex, brainstem) and influence lower motor neurons via descending tracts.

Question 3

3. What are the three types of neurons involved in motor control?

Answer 3

First-order (cerebral cortex), second-order (internuncial neuron in spinal cord), third-order (lower motor neuron to muscle).

Question 4

4. What is the function of the corticospinal tract?

Answer 4

Controls voluntary, skilled movements, especially in distal limbs.

Question 5

5. What is the function of the reticulospinal tracts?

Answer 5

Influence voluntary movement and reflex activity by facilitating or inhibiting motor neurons.

Question 6

6. What is the function of the tectospinal tract?

Answer 6

Controls reflex postural movements in response to visual stimuli.

Question 7

7. What is the function of the rubrospinal tract?

Answer 7

Facilitates flexor muscles while inhibiting extensor muscles.

Question 8

8. What is the function of the vestibulospinal tract?

Answer 8

Facilitates extensor muscles and inhibits flexor muscles to maintain balance.

Question 9

9. What is the function of the olivospinal tract?

Answer 9

Its role is uncertain, but it may be involved in muscular activity.

Question 10

10. What is the function of descending autonomic fibers?

Answer 10

Regulate visceral activity through connections with autonomic motor neurons.

Question 11

11. Where do corticospinal tract fibers originate?

Answer 11

Primary motor cortex (area 4), secondary motor cortex (area 6), and parietal lobe (areas 3, 1, 2).

Question 12

12. What structure organizes the body’s motor control in the cortex?

Answer 12

The motor homunculus.

Question 13

13. Describe the pathway of corticospinal fibers.

Answer 13

Corona radiata → internal capsule → basis pedunculi → pons → medullary pyramids → spinal cord.

Question 14

14. Where do most corticospinal fibers decussate?

Answer 14

In the pyramids of the medulla oblongata.

Question 15

15. What are the two corticospinal tracts, and how do they differ?

Answer 15

Lateral corticospinal tract (crossed, controls limb muscles) and anterior corticospinal tract (uncrossed, controls axial muscles).

Question 16

16. Where do corticospinal fibers terminate?

Answer 16

In the anterior gray column, mostly on internuncial neurons.

Question 17

17. Where do reticulospinal tracts originate?

Answer 17

Scattered neurons in the reticular formation of the brainstem.

Question 18

18. What are the two divisions of the reticulospinal tract?

Answer 18

Pontine reticulospinal (uncrossed, anterior white column) and medullary reticulospinal (crossed and uncrossed, lateral white column).

Question 19

19. What is the function of the reticulospinal tracts?

Answer 19

Modulate voluntary movement, reflexes, and autonomic functions.

Question 20

20. Where does the tectospinal tract originate?

Answer 20

Superior colliculus of the midbrain.

Question 21

21. Where does the tectospinal tract terminate?

Answer 21

In the anterior gray column of the cervical spinal cord.

Question 22

22. What is the function of the tectospinal tract?

Answer 22

Controls reflex postural movements of the head and neck in response to visual stimuli.

Question 23

23. Where does the rubrospinal tract originate?

Answer 23

Red nucleus of the midbrain.

Question 24

24. What is the function of the rubrospinal tract?

Answer 24

Facilitates flexor muscles and inhibits extensor muscles.

Question 25

25. Where does the vestibulospinal tract originate?

Answer 25

Vestibular nuclei in the pons and medulla.

Question 26

26. What sensory input influences the vestibulospinal tract?

Answer 26

Input from the inner ear (vestibular nerve) and cerebellum.

Question 27

27. What is the function of the vestibulospinal tract?

Answer 27

Facilitates extensor muscles and inhibits flexor muscles to maintain balance and posture.

Question 28

28. Where does the olivospinal tract originate?

Answer 28

Possibly from the inferior olivary nucleus of the medulla.

Question 29

29. Why is the olivospinal tract debated?

Answer 29

Its existence and function remain uncertain.

Question 30

30. Where do descending autonomic fibers originate?

Answer 30

Higher autonomic centers (cerebral cortex, hypothalamus, amygdala, reticular formation).

Question 31

31. How do descending autonomic fibers influence visceral activity?

Answer 31

By synapsing with autonomic motor neurons in the lateral gray column.