Axoplasmic transport

Under axonal transport means the transport of substances in the axon of a nerve cell. We distinguish a slow axonal transport, the runs in only one direction, from the cell body ( soma) to the peripheral end of the axon, and a fast axonal transport, which takes place in both directions.

Tasks of the transport system in the nerve cell

Almost all of the synthetic capacity of a nerve cell takes place in the soma. The source cell organelle of the synthesis products is usually the endoplasmic reticulum. The built there synthesis products are introduced in the Golgi apparatus in the axonal transport mechanism. The Golgi apparatus is located at the origin of this low microtubules at Axonursprung.

Slow axonal transport

The slow axonal transport concerns in the cell body synthesized proteins, most notably the structural proteins of the cytoskeleton such as tubulin and actin. More detailed investigations revealed that he in turn can be divided into two components with slightly different speed. The slower component SCa (slow component a) moves in axons of vertebrates only 0.2 to 1 mm a day on, the proteins involved remain close to each other for weeks. Most likely it involves a shift of intact microtubules and neurofilaments, as well as numerous associated with these proteins ( microtubule -associated proteins). Slightly faster component SCb consists of actin and numerous other proteins, including the enzymes of glycolysis and other processes of intermediary metabolism. Here is unclear whether it also is a shift of entire actin microfilaments or smaller aggregates.

Fast axonal transport

In case of fast axonal transport is mainly by vesicles, which are moved by motor proteins ( kinesin, dynein ) along the microtubules. It can reach speeds up to 40 centimeters per day. The transport may be carried out in both the downstream direction of the synapse, as well as in the opposite orientation from the synapse direction soma.

Anterograde transport

From the cell body to the synapse ( anterograde, downstream), membrane material and to secrete certain substances (such as neurotransmitters) transported. This is done through the granules or vesicles, which are attached to the motor protein kinesin.

Retrograde transport

In the reverse direction ( retrograde upstream) the speed is slightly slower; here end products of metabolism are transported back to the soma, as well as the decomposition and conversion given membrane material, as well as nerve growth factor, which is necessary for the survival of nerve cell. The retrograde transport is via the vesicles which are attached to the motor proteins dynein. But it can also foreign substances to be transported. So get herpes simplex and polio viruses by the retrograde transport into the brain. Also, the tetanus toxin is transported from the external wound on axons to the inhibitory Renshaw cells of the spinal cord, where it suppresses transmitter release, resulting in an ongoing contraction of the skeletal muscles, the lockjaw.

Swell

• Neurophysiology
• Cell Biology
• Biological process