Figure 1. Neuronal mitochondria.

Each neuron contains several hundred mitochondria that form cable-like structures along neuronal projections to help them meet their large energy demands. Neurons require energy to transport organelles and cargo along microtubules or actin fibres (motor molecules like dyneins, kinesins and myosin mediate this process) and to maintain ion gradients and the membrane potential by ATP-dependent Ca²⁺ and Na⁺/K⁺ pumps and ion channels. Additionally, neurotransmitter vesicle loading at pre-synaptic terminals and Ca²⁺-mediated neurotransmitter release into the synaptic cleft are also ATP-dependent events. Glutamate transporters mediate glutamate re-uptake from the synaptic cleft, and at the post-synaptic membrane, glutamate binding to NMDA receptors evokes Ca²⁺ influx, which in turn can activate Nitric Oxide Synthase (NOS) and stimulate the generation of Nitric Oxide (NO). Both, NO and Ca²⁺ can directly modulate mitochondrial function by altering the levels of ROS (H₂ O₂ and O_2-) and ATP production.(b) Fluorescence 3D microscope image of mitochondria in a dendritic arbor of a neuron expressing DsRed-Mito, a red fluorescent fusion protein targeted selectively to the mitochondrial matrix (scale bar:5 μm). (c) Slice through an EM tomographic volume showing a mitochondrion in a neuronal process. Mitochondrial length is typically 2-25 μm in neurites with a diameter of 0.5 μm (scale bar: 400 nm). Shown underneath is a view of the surface-rendered volume after segmentation of the same mitochondrion. The outer membrane is a translucent pale blue and individual cristae are shown in different colors.