Lecture 15-Reticular Formation

Question 1

Where is the reticular formation found in the brainstem? What is it continuous with in the spine?

Answer 1

Found in all heights of brainstem → continuous w/ intermediate zone (Lamina VII) in spinal grey matter

Question 2

What are the four main columns of the reticular formation? What are they based on?

Answer 2

Based on distance from reticular midline
1. Median
2. Paramedian
3. Medial
4. Lateral

Question 3

What do the neurons in the MEDIAN zone of the reticular formation do?

Answer 3

Many neurons in the Median Zone synthesize serotonin.

Question 4

What are the functions of ascending projections from the median zone in the brain?

Answer 4

The ascending projections from the Median Zone target higher brain centers associated with sleep, contributing to the regulation of sleep.

Question 5

What are the functions of the descending projections from the Median Zone?

Answer 5

Descending projections to trigeminal spinal nucleus & dorsal spinal areas to modulate/suppress pain

Question 6

Where does the PARAMEDIAN zone of the reticular formation receive inputs from?

Answer 6

Inputs from cerebral cortex, spinal cord, dentate & fastigial nuclei of cerebellum, & vestibular nuclei

Question 7

What is the paramedian zone project to?

Answer 7

Project to vermis, uvula, and fastigial nucleus of cerebellum​

Question 8

Function of paramedian zone:

Answer 8

Coordination of intricate movements​

Question 9

What are the characteristics of the projections in the Medial Zone?

Answer 9

The Medial Zone is characterized by long ascending and descending projections.

Question 10

What do the ascending projections of the MEDIAL zone of the reticular formation go through? What two structures do they terminate at & for what functions?

Answer 10

Goes through central tegmental tract & terminates in hypothalamus (autonomic functions) & intralaminar nuclei of the thalamus (arousal)

Question 11

What do the descending projections of the MEDIAL zone of the reticular formation join?

Answer 11

Joins (lateral & medial) reticulospinal tracts for motor control of axial, trunk, & proximal limb muscles

Question 12

What two motor tracts originate in the medial zone? Where does each fibre group terminate at?

Answer 12

• Origin of reticulobulbar & reticulospinal tracts
• Reticulobulbar fibres termiate in cranial nerve sensory & motor nuclei
• Reticulocerebellar fibres terminate in cerebellum

Question 13

What is the MEDIAL zone of the reticular formation referred to as? What kind of cells are present

Answer 13

Output/motor/efferent zone → large (magno) cells

Question 14

What is the LATERAL zone of the reticular formation referred to as? What kind of cells are present?

Answer 14

Sensory/afferent → small (parvus) interneurons

Question 15

Where do the ascending & descending axons of the lateral zone terminate in? What tracts does the LATERAL zone contribute to? For what functions?

Answer 15

• Axons terminate in medial zone of reticular formation
• Contributes to reticulobulbar & reticulospinal tracts → modulate sensory info & maintain alertness

Question 16

Where does the parvocellular nucleus of the LATERAL zone of the reticular formation receive sensory info from? Where does it project this info to?

Answer 16

Receive sensory info from cerebrum, cerebellum, cranial nerves, & spinal cord → integrates & projects to medial zone of reticular formation

Question 17

Where does the reticular formation receive inputs from? What specific fibres descend down the corona radiata to terminate at the reticular formation? On what zone?

Answer 17

Inputs from all sensory systems, sensory cortex, MI, prefrontal cortex, cerebellum, hypothalamus, amygdala
Corticoreticular fibres descend down corona radiata to terminate at MEDIAL zone of reticular formation

Question 18

What modality processes go through the solitary tract to eventually project to the reticular formation?

Answer 18

GVA (general visceral afferent) processes go through solitary tract, terminate at solitary nucleus, then project to reticular formation

Question 19

In context to efferents of the reticular formation, what two tracts are associated with the reticular formation? What are they responsible for?

Answer 19

1. Lateral corticospinal tract for fine distal limb movement
2. Reticulospinal (lateral & medial) for balance, posture, structural movements

Question 20

Where does the pontine medial zone of the reticular formation project to? For what role?

Answer 20

Project to oculomotor & abducens nuclei for modulating horizontal eye movement

Question 21

Where do the corticoreticular fibres & the central tegmental tract terminate at in the reticular formation? For what function?

Answer 21

Terminate at medial zone of pontine & medullary reticular formation → modulate activity of reticulospinal & reticulobulbar neurons

Question 22

Where does the medial (pontine) reticulospinal tract terminate at in the reticular formation? For what function?

Answer 22

Terminates at ipsilateral spinal cord to synapse w/ interneurons, motoneurons, & 1st-order muscle spindle afferents → excite extensors & inhibit flexors of trunk & proximal limb muscles

Question 23

Where does the lateral (medullary) reticulospinal tract terminate at in the reticular formation? For what function?

Answer 23

Terminates at (ipsilateral) spinal cord to synapse w/ interneurons & motoneurons → inhibit extensors & excite flexors of trunk & proximal limb muscles

Question 24

List the projection pathway of the ascending reticular activation system (ARAS). What is it involved in?

Answer 24

Substantia nigra → thalamus → hypothalamus → cortex
Involved in sleep/wake cycle, control of consciousness, coordinating arousal in different areas

Question 25

In context to projections to the autonomic system, what tracts project to various autonomic nuclei? For what autonomic functions?

Answer 25

Reticulospinal & reticulobulbar tracts project to various nuclei → heart rate, breathing, blood pressure

Question 26

In context to modulating cranial nerve activity, differentiate between a Duchenne smile & a pyramidal smile.

Answer 26

Duchenne smile: has reticular activation involved to crinkle corners in eyes, makes smile seem more genuine
Pyramidal smile: doesn’t have crinkled eyes to make smile seem genuine

Question 27

How does the reticular formation modulate the endocrine system?

Answer 27

Has hypothalamic projections to pituitary gland

Question 28

What are the functions of each of the four zones?

Answer 28

Median Zone: sleep regulation/modulation and supression of pain
Paramedian Zone: Motor coordination.
Lateral Zone: Sensory processing, mediates modulation of sensory afferents, and maintenance of alertness
Medial Zone: influence the autonomic nervous, level of arousal and motor control of axial and proximal limb musculature

Question 29

The reticulobulbar tract (RBT) function:

Answer 29

Helps regulate various functions involving cranial nerves in the head and neck, including reflexes, facial expressions, speech, swallowing, and autonomic processes, by connecting the brainstem reticular formation to motor neurons in the cranial nerve nuclei.