![]() Mitochondria are densely packed within the soma. Axonal mitochondria are small and sparse, whereas dendritic mitochondria are larger and occupy a greater volume of the process. ( B) Schematic showing the compartments of a neuron, depicting the long axon and multiple dendrites from the cell body (soma), containing the nucleus. Highlighted within the boxes are the axonal (i) and dendritic (ii) compartments (enlarged beneath) scale bar: 20 µm, 10 µm in enlargements. Ankyrin-G staining (magenta) shows the axonal initial segment, used to identify the axon. ( A) Primary rat hippocampal neuron expressing a mitochondrially targeted fluorescent protein (MitoDS-Red). Neuronal mitochondria exhibit compartment-specific morphologies Mitochondria act as signalling hubs, buffer Ca 2+, have roles in apoptosis, and are sites of reactive oxygen species (ROS) signalling and of metabolite generation (reviewed in ). It is now clear that beyond ATP generation via oxidative phosphorylation (OXPHOS), mitochondria are integral to many signalling pathways. įurthermore, the concept of mitochondria as simply the ‘powerhouse of the cell’ has expanded. The balance between these opposing processes are stringently regulated and can be adjusted to modify the overall mitochondrial morphology in response to changing energy demands and cellular stress. Fusion and fission are governed by the interplay between different GTPases, which form fusion and fission machinery at the mitochondrial membranes. Together, these processes fine-tune mitochondrial function to match energy supply and demand, to facilitate transport to sites of high energy expenditure, to allow exchange of components between mitochondria and to mediate the specific removal of damaged organelles. ![]() The continuous fusion, fission (division) and movement of mitochondria, together with other essential behaviours, including cristae remodelling, biogenesis and mitophagy (selective mitochondrial autophagy) are collectively termed ‘mitochondrial dynamics’. Indeed, the word mitochondria derives from the Greek words mitos, meaning thread, and chondros, meaning grain, alluding to the many morphologies the mitochondria adopt, recognised over 100 years ago (Benda, cited in ). ![]() Utilising improved imaging techniques, it is now appreciated that mitochondria do not exist as isolated structures (often how they are depicted in textbooks), rather they comprise an interconnected, cell-wide, dynamic network. Our understanding of mitochondria has changed dramatically over the past few decades. Here, we review the role that mitochondrial dynamics play in neuronal function, how these processes support synaptic transmission and how mitochondrial dysfunction is implicated in neurodegenerative disease. Moreover, it is now clear that deficiencies in mitochondrial dynamics can be a primary factor in many neurodegenerative diseases. The transport mechanisms and mitochondrial dynamics that underlie these differences, and their functional implications, have been the focus of concerted investigation. In axons mitochondria are small and sparse whereas in dendrites they are larger and more densely packed. Intriguingly, axonal and dendritic mitochondria exhibit different morphologies. Mitochondria do not exist in isolation, but constantly undergo cycles of fusion and fission, and are actively transported around the neuron to sites of high energy demand. Thus, maintaining the health and efficient function of mitochondria is vital for neuronal integrity, viability and synaptic activity. Neurons are highly polarised, complex and incredibly energy intensive cells, and their demand for ATP during neuronal transmission is primarily met by oxidative phosphorylation by mitochondria.
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