|Key West rooster, taken by me.|
The Nucleus Laminaris (NL) is a group of coincidence-detecting neurons which receive indirect input from both ears and is located in the bird auditory brainstem.
NL neurons show a peculiar dendrite pattern. These bipolar neurons fall into the particular category of football shaped cells which have dendrites coming out the top and bottom of their cell body. The cell body (soma) of these neurons are about the same size, but depending on where they are in the NL, the cells have either short, medium or long dendrites.
The ones near the midline have a bunch of short stubby little dendrites.
|Figure 2B from Smith and Rubel, 1979|
If they are a little further out from the midline, they have longer dendrites.
|Figure 3B from Smith and Rubel, 1979|
|Figure 10A Smith and Rubel 1979|
|From Figure6 Smith and Rubel 1979|
What is the purpose of having stubby or extended dendrites like this? Well, even in 1979 when Smith and Rubel reconstructed these neurons, they knew that these neurons had a special answer to the "form and function" question.
The amazing thing about these neurons is that they are 'tuned' to respond maximally to specific frequencies (sound waves). And just like strings on an instrument, the cells with shorter dendrites respond to higher frequencies and the cells with longer dendrites respond to lower frequencies.
Why is this? Dendrites don't actually vibrate like strings, but there must be some reason for a cell with short dendrites to respond to higher frquencies and a cell with long dendrites to respond to low frequencies.
The answer lies in what the Nucleus Laminaris actually does. In the next post we'll venture into the wilds of computational neuroscience and explore the reason behind this strange connection between dendrite shape and cell function.
Smith DJ, & Rubel EW (1979). Organization and development of brain stem auditory nuclei of the chicken: dendritic gradients in nucleus laminaris. The Journal of comparative neurology, 186 (2), 213-39 PMID: 447882