Axon mounds

Structure of a nerve cell
	dendrit Cell body Axon Cell nucleus Ranvier ; lace ring Axon terminals Schwann cell Myelin sheath

Axon hill or cone of origin ( Latin - anatom. Colliculus axonis ; English axon hillock ) denotes the point of origin of the axon or neurite on the cell body of a nerve cell , the perikaryon .

The axon hill lies in front of the initial segment ( Segmentum initiale ) and the following main course of the axon as well as its subsequent end branches . This area of the axon hill, which does not yet belong to the actual axon, is free of Nissl clods .

The axon hill is the place where action potentials (AP) arise, which are transmitted via the axon, but can also (retrograde) be directed via the soma into the dendrite tree.

anatomy

Under the light microscope , when stained with basic dyes , the axon hillock separates as a zone that remains light.

With an electron microscope it can be seen that the axon hillock continues into the praxon, which is the initial segment and is not yet surrounded by myelin at this point (only in vertebrates ). The density of the ribosomes decreases over time, and the microtubules entering the neurites from the perikaryon form bundles, the extent of which extends to the end of the initial segment. Until then, even a thick layer (engl. Covers dense layer ), the six to ten nanometers below the plasma membrane or of the axolemma located. If synapses are formed on the initial segment , the dense layer is missing at these points.

function

The axon hill is the main place of summation of postsynaptic potentials, for excitatory ( excitatory , EPSP ) and inhibitory ( inhibitory , IPSP ). In principle, a potential summation takes place according to the laws of electrotonic propagation of potential changes at every point in the cell. But most nerve cells on the membrane of the cell body (soma) and dendrites are less excitable, the threshold potential is higher. Your neurite, on the other hand, is more easily excitable, so that at the origin of the neurite, the origin cone or axon hill, action potentials are usually triggered first and thus potential differences are integrated here. Due to the relatively high density of sodium ion channels in the area of the axon mound, the summation of potential changes at this point decides whether the local synaptic potentials become a forwarded excitation .

Retrograde forwarding

Nevertheless, it is possible that from the axon hill there is also a retrograde conduction of the action potential via the soma and to the dendrites. The retrograde conduction of the action potentials into the dendrite tree plays a role in plastic changes in synapses.

Individual evidence

↑ ^a ^b axon mounds. In: Clemens Cherry: Biopsychologie from A to Z . Springer textbook, ISBN 3-540-39603-9 , pp. 30/31.
^ Theodor H. Schiebler, Horst-W. Korf: Anatomy: histology, history of development, macroscopic and microscopic anatomy, topography. 10., completely revised. Edition. Steinkopff, 2007, ISBN 978-3-7985-1770-7 , p. 72.
↑ to Präaxon in crustaceans ( Crustacea ) see Ronald M. Harris-Warrick (ed.): Dynamic biological networks - The stomatogastric nervous system. Massachusetts IT, 1992, p 43. (English)
↑ ^a ^b Robert F. Schmidt, Florian Lang, Manfred Heckmann (eds.): Physiology of humans: with pathophysiology: with pathophysiology with revision. 31., rework. u. actual Edition. Springer, Berlin / Heidelberg 2010, ISBN 978-3-642-01650-9 , p. 94/95.

Web links

Axon hill - definition in the lexicon of neuroscience at Wissenschaft-online.de

[Kirschbaum-1] axon mounds. In: Clemens Cherry: Biopsychologie from A to Z . Springer textbook, ISBN 3-540-39603-9 , pp. 30/31.

[2] Theodor H. Schiebler, Horst-W. Korf: Anatomy: histology, history of development, macroscopic and microscopic anatomy, topography. 10., completely revised. Edition. Steinkopff, 2007, ISBN 978-3-7985-1770-7 , p. 72.

[3] to Präaxon in crustaceans ( Crustacea ) see Ronald M. Harris-Warrick (ed.): Dynamic biological networks - The stomatogastric nervous system. Massachusetts IT, 1992, p 43. (English)

[Schmidt-4] Robert F. Schmidt, Florian Lang, Manfred Heckmann (eds.): Physiology of humans: with pathophysiology: with pathophysiology with revision. 31., rework. u. actual Edition. Springer, Berlin / Heidelberg 2010, ISBN 978-3-642-01650-9 , p. 94/95.