Fig 6. Axon diameter for both morphologically classified spindle afferent subtypes.

(A) Histogram of axon diameters for afferents that were classified as primary or secondary endings based on morphological criteria. (B) Logistic regression model used to predict proprioceptive afferent subtypes based on diameter. Black dots represent the diameters of afferents that were classified as primary afferents based on morphologic criteria and therefore they have a 100% probability of being a primary afferent. The open circles illustrate the morphologically classified secondary endings, which have a 0% probability of being a primary ending. The gray line indicates the probability of an afferent being a primary based on diameter. The dotted lines illustrate the cut-off diameters (2.46 and 2.91 μm) for classifying afferents. Axons with diameters left of the first dotted line (diameter < 2.46 μm) were classified as group II afferents, axons with diameters between the dotted lines could not be classified based on diameter alone, and axons with diameters to the right of the second dotted line (diameter > 2.91 μm) were classified as Ia afferents.