Reticular Formation

Question 1

Describe the neurons of the reticular formation. What is their ogranization, medial to lateral and up and down? What are their roles?

Answer 1

up and down: tend to have long ascending and descending projections
medially: mixed population of small, medium, and large cells
laterally: mostly small small cells
have a role in the integration and distribution of a large amount of motor, sensory, and autonomic functions

Question 2

What are some general functions of the reticular formation? (5)

Answer 2

1. Arousal: RF required for consciousness, and plays an important role in letting people get to sleep, too
2. Motor: flexion. Medullary reticulospinal tract inhibits extension and promotes flexion.
3. Motor: Extension. Pontine reticulospinal tract promotes extension.
4. Autonomic functions: regulates breathing and cardiac function
5. . Autonomic: regulates pain input to the dorsal horn of the spinal cord.

Question 3

What are the dual components of the reticular activating system?

Answer 3

arousal produced by activation of midbrain and potine reticular formation (cats with lesions here were comatose)
AND
sleep-inducing regions in the caudal brainstem: medial reticular formation of the medulla, some of Raphe nuclei, and nucleus solitarius, which is non-reticular

Question 4

What are the monoamine cell groups of the reticular formation? (4 categories)

Answer 4

1. Raphe nuclei (make 5-HT) in midline of medulla, pons, and mesencephalon/midbrain.
2. Noradrengergic groups A1 and A5 in the lateral tegmentum of the medulla and pons that go to the spinal cord to affect autonomic function
3. Locus coeruleus below the rostral floor of the 4th ventricle. goes basically everywhere in the forebrain
4. Dopamine cell groups to the substantia nigra (A9) and A10 that go to the basal ganglia and to the nucleus accumbens, respectively.

Question 5

What reticular nuclei have cerebellar connections?

Answer 5

lateral reticular nucleus

paramedian nucleus

Question 6

What is the lateral reticular formation? What are the important connections?

Answer 6

“association area”
gets info from all sensory modalities except epicritics from the dorsal column system
projects onto neurons in the medial reticular formation

Question 7

What is the medial reticular formation? What are the important connections?

Answer 7

“output structure”

1. Descending neurons to the ventral horn (motor)
2. Reticular activating system: ascends to the intralaminar nuclei of the thalamus, then to other thalamic nuclei and cortex
3. REM sleep: caudal portions of the brain stem. Works with nucleus solitarius to induce REM sleep

Question 8

What do barbituates do to the reticular formation?

Answer 8

depress the reticular formation and decrease REM sleep.

Question 9

What are the monoamine cell groups in the medulla RF? (3 kinds of functions). Include the locations of the cell groups, where they go, and what they do.

Answer 9

Midline Raphe nuclei (5-HT rlelease). descending projections to the autonomic nuclei in the spinal cord to control breathing and heart. Descending projections may also work to inhibit pain transmission by inhibiting release of substance P.

Laterally, A1 noradrendergic cell groups surround the lateral reticular nucleus. project to spinal cord to influence autonomic functions

Question 10

What nuclei associated with the cerebellum are in the medulla? Include the locations of the cell groups, where they go, and what they do.

Answer 10

Lateral reticular nucleus. recieves spinocerebellar inputs and projects to the ipsilateral cerebellum via the inferior cerebellar peduncle.

Question 11

What does the lateral reticular formation do in the medulla? Include the locations of the cell groups, where they go, and what they do.

Answer 11

receives ascending sensory inputs. Project to the medial reticular formation.

Question 12

What does the medial reticular formation do in the medulla? Include the locations of the cell groups, where they go, and what they do.

Answer 12

Remeber: medial reticular formation is the output system.
medial 2/3s yield the medullary reticulospinal tract. Medullary reticular spinal tract descends to the ventrolateral spinal cord and synapses on alpha and gamma motor neurons to inhibit extension (thus promoting flexion). It receives inhibitory input from the red nucleus; without that, you see the four point extension of decerebrate posturing.
Lateral part of the medial reticullar formation projects UP to the thalamus and forebrain to promote consiousness as part of the reticular activating system.

Question 13

What do the monoamine cell groups do in the pons? Include the locations of the cell groups, where they go, and what they do.

Answer 13

Midline: Pontine Raphe Nuclei (5-HT) go up to hypothalamus, thalamus, limbic forebrain, basal ganglia, and cerebral cortex
Lateral: A5 noradrenergic cell group near the VII nerve nucleus. sends descending projections to the autonomic centers of the spinal cord
Locus coeruleus: Goes to basically eveywhere in the forebrain. Located just beneath the rostral floor of the 4th ventricle.

Question 14

What are the nuclei associated with the cerebellum in the pons? Include the locations of the cell groups, where they go, and what they do.

Answer 14

Paramedial pontine reticular formation (PPRF): near the abducens nerve nucleus. Involved in control of horizontal gaze through connections with vestibular and oculomotor nuclei and with the frontal eye fields.

Question 15

What should I know about the lateral reticular formation in the pons?

Answer 15

similar to in the medulla: association with input from everywhere but the epicritics. projects to the medial reticular formation.

Question 16

What does the medial reticular formation do in the pons? Include the locations of the cell groups, where they go, and what they do.

Answer 16

lateral and rostal portions: facilitate extensor muscles via medial reticulospinal tract.
Also, reticular activating system as in the medulla.

Question 17

What are the monoamine cell groups in the midbrain? Include the locations of the cell groups, where they go, and what they do.

Answer 17

Raphe: as in pons, these project up to the hypothalamus, thalamus, limbic forebrain, basal ganglia, and cerebral cortex.
Noradrenergic: fibers from the locus coeruleus go everywhere.
Dopanime cell groups:
1. Ventral tegmental area (A10): srounds the interpeduncular nucleus. origin of mesolimbic and mesocortical pathways to forebrain. Mesolimbics innervates the nucleus accumbens, olfactory tubercle, and amygdala. Mesocortical innervates libic structures like the frontal and cingulate cortex.
2. A9 substantia nigra to basal ganglia.

Question 18

What does the lateral reticular formation do in the midbrain?

Answer 18

As in the pons, this receives sensory input and projects to the medial reticular formation.

Question 19

What does the medial reticular formation do in the midbrain? Include the locations of the cell groups, where they go, and what they do.

Answer 19

Notable because there ar eno reticulospinal components. But, still does reticular activating system. the medial part is calle dthe mesencephalic reticular fortmation.

Question 20

What are the midline thalamic nuclei? Input? Output? purpose?

Answer 20

receive inputs from the brainstem reticular formation.
interconnected with hypothalamic and limbic structures. may mediate visceral and affective components of the system like affective pain.

Question 21

What are the intralaminar thalamic nuclei? Input? Output? Purpose?

Answer 21

receive input from the brainstem reticular formation.
within the internal medullary lamina of the thalamus (?). centromedian most obvious. rostral most extension of the brain stem reticular formation.
project to surrounding thalamic nuclei (anterior, ventral, and lateral). may explain why the reticular system has such broad effects on consciousness. Intralaminar nuclei may also project to secondary sensory cortex. may generate much of the syncronized activity seen on EEG.

Question 22

What is the reticular thalamic nucleus?

Answer 22

Used to considered part of the reticular activating system, but no more- those functions belong to the intralaminar thalamic nuclei.