Axon hillock

Axon hillock or origin cone (Latin anatomist colliculus axonis, .. Axon engl hillock ) refers to the origin of the neurite or axon at the cell body ( perikaryon ) of a nerve cell ( initial Segmentum ) before the initial segment and the following main course route and the subsequent terminal branches. This is not the actual area of ​​the axon belonging Axonhügels is free of Nissl bodies.

The axon hillock is the place of origin of action potentials (AP ) which are propagated through the axon, but also ( retrograde) can be passed through the soma into the dendritic tree.

Anatomy

Light microscopy, the axon hillock is when stained with basic dyes from brightly as permanent zone.

Electron microscopy can be seen that the axon hillock continues in the initial segment as at this point not yet surrounded by myelin Präaxon (only in vertebrates ). The density of the ribosome decreases in the course, and the entering of the perikaryon to the neurites microtubules form bundles which extension extends to the end of the initial segment. Until then, a dense layer ( engl. dense layer), which is six to ten nanometers below the plasma membrane or the Axolemms extends. If at the initial segment synapses formed so lacks the dense layer at these locations.

Function

The axon hillock is the essential Summationsort of postsynaptic potentials for excitatory ( excitatory EPSP ) and inhibitory ( inhibitory, IPSP ). Principle finds a potential summation according to the laws of electro- tonic propagation of potential changes occur at any point in the cell. However, most neurons are less excitable at the membrane of the cell body ( soma) and dendrites, the threshold potential is higher. Your neurite other hand, is more excitable, so that at the origin of the neurite, the origin cone or axon hillock, usually first action potentials are triggered and thus potential differences are integrated. Due to the relatively high concentration of sodium ion channels in the area of ​​Axonhügels ie the summation of potential changes decide at this point whether a Propagated excitation is from the local synaptic potentials.

Nevertheless, it is possible that the axon hillock was made through the soma and dendrites also then called retrograde conduction of the action potential formed. The retrograde conduction of action potentials into the dendritic tree plays a role in plastic changes of synapses.