Neurons, or nerve cells, form the communication network of the nervous system. Each neuron has a long projection called an axon that transmits signals to other cells. To maintain this extensive structure, the neuron relies on an internal “highway” system known as axonal transport. This process moves mitochondria, lipids, proteins, and other materials to and from the neuron’s cell body, ensuring the cell’s functional integrity.
Anterograde Transport
Anterograde transport describes the movement of materials away from the cell body, also called the soma, and down the axon toward the synapse. This “forward” flow is driven by a motor protein named kinesin, which “walks” along microtubule tracks that run the length of the axon. Kinesins use energy from ATP hydrolysis to move their cargo toward the axon terminal. An arrow pointing away from the cell body represents this direction of transport.
The cargo moved via anterograde transport includes new proteins and lipids for axon maintenance and growth. It also transports organelles, such as mitochondria, which supply the energy for synaptic activity. Vesicles containing neurotransmitters are another type of cargo moved in this outward direction to the presynaptic terminal.
Retrograde Transport
Retrograde transport operates in the opposite direction, carrying materials from the axon back toward the cell body. This “backward” journey is managed by a motor protein called dynein. Dynein moves along the same microtubule tracks as kinesin but travels toward the soma, where waste products can be degraded and recycled. An arrow pointing from the axon terminal back toward the neuron’s center indicates retrograde transport.
This return pathway is not just for waste removal; it is also a communication channel. It transports chemical signals from the synapse that inform the cell body about the status of the axon terminal. This process also carries aging or damaged organelles away from the axon for breakdown. Some viruses and toxins exploit this pathway to travel from the periphery to the central nervous system.
Matching Labels to Direction
To correctly label a diagram of axonal transport, the direction of the arrow is the main indicator. An arrow pointing from the soma down the length of the axon represents the outward flow of materials. This arrow should be labeled Anterograde Transport. This process is driven by kinesin motor proteins.
Conversely, an arrow that points from the axon terminal back toward the cell body illustrates the return flow. This arrow should be labeled Retrograde Transport, a movement facilitated by the motor protein dynein.