Raphe nuclei of medulla oblongata

The raphe nuclei of medulla oblongata are part of the larger group of raphe nuclei located along the midline of the brainstem, spanning the midbrain, pons, and medulla. These nuclei contain serotonergic neurons, which release serotonin (5-HT).

Organization of the Raphe Nuclei:

Raphe nuclei are divided into rostral nuclei (in the midbrain and rostral pons) and caudal nuclei (in the caudal pons and the medulla oblongata). Each group has distinct functions and projections:

• Rostral nuclei project to forebrain structures such as the amygdala, hippocampus, thalamus, and basal ganglia. These pathways regulate mood, response to stress, cognition, sleep-wake cycles, memory, appetite, and sexual function.

• The caudal nuclei are located in the caudal pons and in the medulla (i.e. the raphe nuclei of medulla oblongata). These nuclei send descending projections to the spinal cord and influence nociception and motor activity.

Caudal Raphe Nuclei of Medulla Oblongata:

The caudal group of raphe nuclei in the medulla includes:

• Raphe magnus: Found at the midline in the pons at the level of the facial nerve (nucleus of cranial nerve VII). Neurons here produce substances including serotonin, enkephalin, and others which are involved in the regulation of pain and movement.

• Raphe obscurus: Located midline in the dorsal medulla, it primarily expresses substance P and contributes to pain modulation.

• Raphe pallidus: Situated between the pyramids of the medulla, this nucleus also regulates pain and movement.

Raphe Nuclei in Pain Modulation:

The descending serotonergic pathways originating in the raphe magnus and other caudal medullary nuclei have a critical role in central pain modulation. These projections act on neurons in the spinal cord’s dorsal horn to modify responses to painful stimuli. Raphe nuclear input to pain-sensitive regions of the thalamus and the hypothalamic arcuate nucleus also contributes to analgesia.

Blood Supply:

The blood supply to the raphe nuclei comes from: Penetrating branches of the basilar artery (in the midbrain and pons), and branches of the anterior spinal artery (in the medulla).