Mitochondria display atypical morphological features in physically restrictive axons.

(A–C) Three different 3D segmented reconstructions showing representative examples of mitochondria (“Mito1,” “Mito2,” and “Mito3”) residing partially in the varicosity (“Var”) and adjoining axon segments, demonstrating different morphological states at the transition from the varicosity into the restricted space of the axon segment. Additional organelles occupying the axon space are also segmented. For ease of visualization, not all of the organelles and structures in the varicosity are shown. The plasma membrane (dark blue), microtubules (light blue), mitochondrial outer membrane (dark green), endoplasmic reticulum (yellow), and vesicles (dark purple) are highlighted.