Where, Oh Where Do the Ganglia Go (in Lampreys) – #365papers – 2018 – 50

Modrell, Hockman, Uy, Buckley, Sauka-Spengler, Bronner, and Baker, 2014, A fate-map for cranial sensory ganglia in the sea lamprey: Developmental Biology, v. 385, p. 405-416

What’s it about?

Fate-maps show where tissues in an embryo wind up in the adult. It is truly remarkable how cells move around in embryos. I mean, seriously.

In this case, the authors are tracing sensory ganglia, in particular, to branches of the trigeminal nerve: the ophthalmic (or profundal) and the maxillomandibular, which provide sensory functions to parts of the lips and mouth.

Why does it matter?

The trigeminal nerve, including the two branches studied in this paper, exist in all vertebrates, including us. The maxillomandibular branch gets its name because it innervates the jaws. Lampreys do not have jaws, so instead this branch innervates part of the breathing mechanism. This observation helps us better understand the origins of jaws in ‘higher’ vertebrates.

Why did I read this?

This is one of many papers I downloaded as I was attempting to better understand the origins of jaws for my vertebrate paleontology class. It wasn’t exactly what I needed, but it was interesting nevertheless.

What did I learn?

The big lesson for me is that the maxillomandibular branch of the trigeminal nerve is divided and separated into smaller branches that service the maxillary area and the mandibular area. The ophthalmic branch actually sits between the two parts of the maxillomandibular branch. This is an interesting observation, but may be specific only to lampreys.

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