An axon with a myelinated initial segment in the bird auditory system.

In the bird auditory brainstem, nucleus laminaris neurons compute interaural time differences by comparing inputs from two ears. Laminaris neurons in barn owls have short dendrites and axons with myelinated initial segments. We examined laminaris cells in chickens with a range of dendritic lengths to determine if neurons with long dendrites had normal axons. Neurons with short dendrites had myelinated initial segments while neurons with long dendrites had normal initial segments. Thus, the myelinated initial segment may serve to move the spike-initiation zone away from the somatodendritic compartment that integrates inputs from the two ears.