Medial reticular formation

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Brain: Medial reticular formation
Taken from "The Brainstem Reticular Formation and its Significance for Autonomic and Affective Behavior". The above diagram illustrates the reticular nuclei in the brainstem in a tiered fashion

Surrounding the previously discussed ridge of serotonergic cells, the medial reticular formation has many roles and functions. The medial reticular formation is filled with a mixture of large and small neurons.

The most famous and prominent cells in this region are the giant neurons, located mostly within the medial RF.

These neurons have long axons in both the ascending and descending directions.

Through their projections, this portion of the RF has been known to mediate posture, movement, pain, autonomic function and arousal.

The nuclei of the medial reticular formation are:

• nucleus reticularis gigantocellularis
• nucleus reticularis pontis caudalis
• nucleus reticularis pontis oralis
• nucleus reticularis parvocellaris
• nucleus reticularis ventralis

These two columns have been the subject of much speculation and mystery because their intricate parts are so interwoven and specific.

In fact it has taken decades to unravel them to this point, and there are still far more mysteries to unravel for future neural scientists. (Above in figure one can be seen a color diagram of the lateral and medial reticular formation, separated into nuclei, which blend into one another).

Three out of the four nuclei mainly involved in mediating expiration and inspiration are located in the medial RF and should be discussed.

Respiration has an autorhythmia, thought to be mediated by the dorsal reticular formation.

Even when all afferent stimuli are eliminated, the respiration rhythm continues on.

Expiration is mediated by the nucleus reticularis parvocellularis and the dorsorostral portion of the gigantocellularis.

The nuclei which mediate inspiration are the rostral portion of the ventral reticular nucleus and part of the lateral RN.

The efferent fibers for the inspiration nuclei follow the motor path of the glossopharyngeal nerve and the vagus nerve.

This exhalation process takes place when the aforementioned nuclei inhibit the nuclei responsible for inspiration.

In order for this to take place there must be inhibitory connections from the expiring neurons to the inspiring neurons.

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Medial reticular formation: Gigantocellular - Caudal pontine - Oral pontine - Parvocellular - Ventral Lateral reticular formation: Lateral - Paramedian - Tegmental pontine