Lecture 7-Descending Pathways (Cortiobulbar)

Question 1

Where do projections come from?

Answer 1

Consists of projections from the primary motor cortex (MI), premotor cortex (PMC), and somatosensory cortex (SI).

Question 1

What is the primary function of the Corticonuclear Tract in terms of synapses?

Answer 1

The Corticonuclear Tract mostly synapses with interneurons in the reticular formation (brainstem), which then project to cranial nerves.

Question 2

How are the internal capsule and corona radiata involved in the corticobulbar pathway?

Answer 2

The internal capsule acts as a pathway for motor commands from the cerebral cortex to cranial nerve nuclei in the brainstem, while the corona radiata continues to transmit these commands to control facial and head muscles and functions such as speaking and swallowing.

Question 3

The corticonuclear tract fibers do not project to the motor nuclei of which nerves? where do they recieve projections from?

Answer 3

The oculomotor, trochlear, and abducent nerves ;
These nuclei receive motor signals from the cerebral cortex indirectly, and do so via a different group of fibers that takes a different route

Question 4

Function of corticobulbar pathway

Answer 4

transmit motor commands from the cerebral cortex to the motor nuclei of certain cranial nerves, which control various motor functions of the head and face, tongue (larynx and phaynx)

Question 5

Pathway of the Corticobulbar Tract

Answer 5

1)Upper motor neurons of the cranial nerves originate from the precentral gyrus in the cerebral cortex.
2) The neurons descend as the corticobulbar tract down to the midbrain.
* Neurons branch off to synapse with three nuclei.
⚫ CN III | Oculomotor nucleus
* CN IV | Trochlear nucleus
* CN VI | Abducent nucleus
3)The corticobulbar tract continues down through the cerebral peduncles in the midbrain to the pons.
* Neurons branch offto synapse with two nuclei
* CNV | Motor trigeminal nucleus
CN VII | Facial nucleus
4) The corticobulbar tract continues down through the pons to the medulla oblongata, where neurons synapse with four more nuclei which lplay a role in motor control of throat and neck muscles, as well as in functions like swallowing, speaking, and head and neck movements.
* CN IX | Glossopharyngeal nucleus
* CNX | Vagal nucleus
* CN XI | Accessory nucleus
* CN XII | Hypoglossal nucleus

Question 6

What cranial nerve nuclei do upper motor neurons synapse with in the midbrain?

Answer 6

In the midbrain, the corticobulbar tract branches off to synapse with the oculomotor nucleus (CN III), trochlear nucleus (CN IV), and abducent nucleus (CN VI).

Question 7

In the pons, which cranial nuclei do upper motor neurons synapse with?

Answer 7

In the pons, upper motor neurons synapse with the motor trigeminal nucleus (CN V) and facial nucleus (CN VII).

Question 8

What happens in the medulla oblongata in relation to upper motor neurons?

Answer 8

In the medulla oblongata, upper motor neurons synapse with the glossopharyngeal nucleus (CN IX), vagal nucleus (CN X), accessory nucleus (CN XI), and hypoglossal nucleus (CN XII).

Question 9

How is the control of facial muscles divided in terms of contralateral and bilateral control?

Answer 9

Neurons controlling the lower half of the face have contralateral control, while neurons controlling the upper half of the face have bilateral control.

Question 10

What is the pathway for the corticotectal tract from the visual association areas?

Answer 10

The corticotectal tract originates from the visual association areas and projects to the oculomotor accessory nuclei and deep layers of the superior colliculus.

Question 11

What is the role of neurons in the oculomotor accessory nuclei, and where do they project?

Answer 11

Neurons in the oculomotor accessory nuclei project to the oculomotor, trochlear, and abducens nuclei. These nuclei, in turn, project to the muscles controlling eye movements.

Question 12

What is the function of the Corticotectal Tract?

Answer 12

Coordinates eye movements by connecting visual association areas in the brain with the nuclei responsible for controlling various eye muscles.

Question 13

What role do neurons within the oculomotor accessory nuclei play in the Corticotectal Tract?

Answer 13

Neurons in the oculomotor accessory nuclei send signals to the oculomotor, trochlear, and abducens nuclei, which control the eye muscles.

Question 14

What is the primary function of the Tectospinal Tract?

Answer 14

The Tectospinal Tract coordinates head and eye movements by relaying signals from the deep superior colliculus project to interneurons in cervical and upper thoracic spinal levels

Question 15

Pathway of Tectospinal Tract

Answer 15

1) Superior colliculus of the midbrain receives input from the optic nerves
2) The neurons then quickly decussate to the opposite side of the brainstem, and enter the spinal cord, connecting with interneurons in the cervical and upper thoracic regions.
4) These interneurons coordinate head and eye movements to align with visual stimuli, facilitating quick and precise responses to visual cues.

Question 16

Where does the Corticorubral Tract originate, and what is its target in the midbrain?

Answer 16

The Corticorubral Tract originates in the primary somatosensory cortex (SI) and projects to the red nucleus in the midbrain.

Question 17

Function of the Corticorubral tract

Answer 17

Contributing to motor coordination and control,fine movements

Question 18

Rubrobulbar Pathwat

Answer 18

Origin: Begins in the red nucleus in the midbrain.
1) Trigeminal Nucleus: Some fibers terminate in the trigeminal nucleus, processing facial sensory information, including crude touch, pain, and temperature.
2) Facial Nucleus: Other fibers continue to the facial nucleus, contributing to the control of the upper half of the face, involved in movements such as smiling.
3) Still other rubrobulbar fibers terminate in the lateral reticular nucleus, as well as the nucleus gracilis and nucleus
cuneatus in the medulla.
4) The fibers that terminate in the
nuclei gracilis and cuneatus are involved in inhibitory modulation of afferent signals from the spinal cord.

Question 19

Where does the Rubrospinal Tract descend in the spinal cord?

Answer 19

Tract descends in the lateral funiculus of the spinal cord

Question 20

What is the primary function of the Rubrospinal Tract in humans?

Answer 20

Involved in fine control of digits, particularly the movement of the hand, but its role is relatively minor in humans due to the dominance of the corticospinal tract.

Question 21

How does the Rubrospinal Tract influence the upper limb muscles?

Answer 21

Facilitates contralateral upper limb flexor muscles and inhibits the extensors (helps bend your upper arm muscles while preventing them from straightening, especially in your hands and fingers. This makes it easier to control your upper limb movements, like picking things up)

Question 22

Reticulospinal Tract Origin

Answer 22

The reticular formation of the brainstem. However, the RST can receive inputs and interact with other motor control regions, including the primary motor cortex (PMC) and the supplementary motor cortex (SMC),

Question 23

How does Reticulospinal tract reach various brainstem nuclei?

Answer 23

The Reticulospinal Tracts travel through the corticonuclear and corticospinal tracts to reach various brainstem nuclei.

Question 24

What is the pathway of the Medial Reticulospinal Tract?

Answer 24

The Medial Reticulospinal Tract descends ipsilaterally along the anterior funiculus, which is the front part of the spinal cord.

Question 25

What is the pathway of the Lateral Reticulospinal Tract?

Answer 25

The Lateral Reticulospinal Tract descends bilaterally along the lateral funiculus, located on the side of the spinal cord.

Question 26

Where do the Reticulospinal Tracts terminate?

Answer 26

The Reticulospinal Tracts terminate at all levels of the spinal cord.

Question 27

What are the main functions of the Reticulospinal Tracts?

Answer 27

Involved in maintaining posture and orienting the limbs. They also play a role in regulating certain autonomic functions like pupil dilation, heart rate modulation, and sweating.

Question 28

What is the key difference in the function of the Medial and Lateral Reticulospinal Tracts?

Answer 28

The Medial Reticulospinal Tract from the pons facilitates voluntary movements and increases muscle tone (muscles become tight, stiff, and harder to move) while the Lateral Reticulospinal Tract from the medulla inhibits voluntary movements and reduces muscle tone (muscles become soft, weak, and easier to move.

Question 29

What is the source of information relayed by the Vestibulospinal Tracts?

Answer 29

The Vestibulospinal Tracts relay information from the vestibulocochlear nerve (related to head movement) and the cerebellum (related to balance).

Question 30

What is the pathway of the Lateral Vestibulospinal Tract?

Answer 30

Descends through the anterior funiculus ipsilaterally and excites axial and proximal upper limb extensor muscles while inhibiting lower limb flexor muscles.

Question 31

Whats the role of the Lateral Vestibulospinal Tract?

Answer 31

Maintain posture and balance, particularly head and neck movements in response to vestibular input.

Question 32

How does the Medial Vestibulospinal Tract travel, and what functions does it serve?

Answer 32

The Medial Vestibulospinal Tract descends through the anterior funiculus ipsilaterally to cervical and upper thoracic levels.

Question 33

Function of Medial vestibulospinal tract

Answer 33

It is primarily involved in equilibrium-related movements of the head and neck, allowing for the maintenance of visual fixation on objects while moving the head.