Axon hillock
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- "Hillock" redirects here. A hillock is also a small hill.
The Axon Hillock is the anatomical part of a neuron that connects the cell body (the soma) to the axon. It is described as the location where the summation of Inhibitory Postsynaptic Potentials (IPSPs) and Excitatory Postsynaptic Potentials (EPSPs) from numerous synaptic inputs on the dendrites or cell body occurs.
It is electrophysiologically equivalent to the 'initial segment where the summated membrane potential reaches the triggering threshold, an action potential propagates through the rest of the axon (and "backwards" towards the dendrites as seen in Neural backpropagation). The triggering is due to positive feedback between highly crowded voltage gated sodium channels, which are present at the critical density at the axon hillock (and nodes of ranvier) but not in the soma.
Cell biologically, it is the neuronal equivalent of tight junctions, as it acts as a barrier for lateral diffusion of transmembrane proteins, GPI anchored proteins such as thy1, and lipids embedded in the plasma membrane.
[edit] External links
- Histology at OU 3_09 - "Slide 3 Spinal cord"
