We often make that mistake in teaching.
In my neurobiology class this semester, I asked my students on Day One to draw and label a picture of a neuron.
The pictures fell into two broad categories. About a third were unlabelled (some of them may not have heard me ask for the labels). Of the two thirds that were labelled, essentially all of them were vertebrate spinal cord motor neurons: a multipolar cell body and one long myelinated axon.
I’m puzzled as to why, of all the many types of neurons, these one have become viewed as “typical.” I know the trivial answer: they’re the ones shown in all the introductory general biology textbooks. And I understand why invertebrate neurons are not shown as examples, because neuroscience is mostly concerned with human brains.
Even within humans, spinal cord motor neurons are not typical. Many of the neurons in the brain are not myelinated (the “grey matter,” as it’s sometimes called). And neurons come in many shapes, and the axon is often not easily distinguished from all the other branches coming from the cell.
In teaching, we often make the same mistake of showing one example as representative, when it’s about as representative as the middle-aged white guy in a business photo.Which is to say, not at all.
Collage of neurons from here.