The Tritocerebrum

The tritocerebrum is the third and structurally the most discrete of the three preoral neuromeres, with sensory motor connections with the third metamere of the head. An analysis using expression of the segmentation border gene engrailed has demonstrated the appendage-type identity of the labrum, which supplies a major input into the tritocerebral ganglion, thus establishing its sensory supply and metameric relationships. The tritocerebrum also supplies motor neurons to labral muscles. The tritocerebrum receives a substantial supply of terminals from interganglionic interneurons with dendrites in the anterior medial protocerebrum (according to the neuraxis), which itself receives inputs from the median bundle originating in the subesophageal ganglion with some additional elements recruited from the thoracic ganglia. The tritocerebrum gives rise to descending neurons to the thoracic and abdominal ganglia, as does the deutocerebrum. However, even though Rajashekhar and Singh have described its general architecture and relationships with the protocerebrum, relatively little is known of the tritocerebrum's relationships to other brain regions or about its intrinsic connections. In all neopteran insects it is the protocerebrum that shows the greatest elaboration.

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