Aksoneja

Aksoneja (Finnish for axons) are long, slender projections of neurons that conduct electrical impulses away from the neuron's cell body. They form the primary conduits of neural communication, connecting neurons with muscles, glands, and other neurons. Each axon begins at the axon hillock and extends to terminals called synaptic boutons, with lengths ranging from micrometers to over a meter in humans.

Structure and insulation: The axon is surrounded by a specialized membrane rich with voltage-gated ion channels. The interior contains a cytoskeleton of microtubules, neurofilaments, and actin filaments. In the central nervous system, many axons are myelinated by oligodendrocytes; in the peripheral nervous system, myelination is provided by Schwann cells. Myelin sheaths enable saltatory conduction, with action potentials leaping between nodes of Ranvier. Axon diameter influences conduction velocity.

Physiology: Axons propagate action potentials through sequential depolarization. Anterograde transport moves organelles and proteins from the soma to the synapse via kinesin motors; retrograde transport returns signaling molecules to the cell body via dynein motors.

Synapses and signaling: At the presynaptic terminal, neurotransmitters are released, transmitting signals to postsynaptic cells.

Development and pathology: Axons grow during development via growth cones guided by molecular cues. In the peripheral nervous system, axons can regenerate after injury; central nervous system axon regeneration is limited by inhibitory molecules and glial scarring. Axonal damage and transport defects are features of many neurodegenerative diseases (e.g., ALS, Alzheimer's) and traumatic injuries.

History: The understanding of axons and their role in neural circuits was advanced by early neuroanatomists such as Golgi and Cajal, whose work helped establish the neuron doctrine and the concept of separate axons transmitting signals.