Axoplasmas

Axoplasms are the cytoplasmic contents within an axon, the long projection of a neuron that transmits electrical impulses from the cell body to synapses. The axoplasm extends from the axon hillock to the axon terminals and is bounded by the axolemma. It remains contiguous with the soma through the axon but is organized to support rapid transport and local signaling along the nerve fiber.

The axoplasm contains the cytoskeletal framework (neurofilaments and microtubules), mitochondria, vesicles, ions, enzymes, and soluble proteins. In some regions, it also includes ribosomes and elements of rough endoplasmic reticulum, enabling limited local protein synthesis. The composition and organization of axoplasm support both the passive properties of the axon and active processes essential for neuronal signaling and maintenance.

A primary role of axoplasm is to participate in axonal transport, moving materials between the soma and distal synapses. Fast axonal transport uses motor proteins such as kinesin (anterograde) and dynein (retrograde) along microtubules to shuttle membrane-bound organelles and vesicles. Slow axonal transport carries soluble proteins and cytoskeletal components. Axoplasm also participates in local signaling and metabolic support at nerve terminals, contributing to the maintenance of ion homeostasis and synaptic function.

Pathologically, disruption of axoplasmic transport is associated with various neuropathies and neurodegenerative diseases. Following axonal injury, degeneration of the distal axoplasm (Wallerian degeneration) occurs, characterized by disintegration of axonal contents and accumulation of organelles in swollen segments.

The term axoplasm derives from axon plus plasma, reflecting its role as the cytoplasmic contents of the axon.