Aksonforgrening

Aksonforgrening (axon branching) describes the growth of lateral processes from an axon to form multiple synaptic connections. This process increases the connectivity and computational capacity of neural networks. Branching occurs mainly during development but can also occur in the adult nervous system during plasticity, regeneration, or after injury.

Branches arise mainly by two mechanisms: collateral sprouting from the axon shaft and bifurcation of the growth cone at the tip. In collateral sprouting, new protrusions emerge along the axon and stabilize into mature branches; in growth cone bifurcation, the growth cone splits into two or more filopodial streams that advance as distinct branches. Both mechanisms enable an axon to innervate multiple targets and refine circuit architecture.

Formation of branches depends on coordinated cytoskeletal remodeling. Actin drives protrusive structures such as filopodia, while microtubules invade nascent branches to stabilize and mature them. Guidance and trophic cues regulate where and when branching occurs. Intracellular signaling pathways, including MAPK/ERK, PI3K-Akt, and Rho family GTPases (Rac1, Cdc42 promote branching; RhoA can limit it), translate external cues into cytoskeletal changes. Extracellular factors such as neurotrophins (NGF, BDNF) promote outgrowth, while guidance molecules like semaphorins, netrins, slits, and ephrins steer branches. Cell adhesion molecules and the extracellular matrix also influence attachment and growth.

Significance and context: proper axon branching is essential for accurate synaptic targeting and functional circuitry. Abnormal branching patterns can contribute to neurodevelopmental disorders and impaired connectivity. Research methods include in vitro neuron cultures, live imaging of growth cones and axons, and genetic or pharmacological manipulations to study branching dynamics.