Axon hillock
Axon hillock | |
---|---|
Details | |
Part of | Axon of a nerve |
System | Nervous system |
Identifiers | |
Latin | colliculus axonis |
TH | H2.00.06.1.00006 |
Anatomical terminology |
The axon hillock is a specialized part of the cell body (or
The axon hillock is the last site in the soma where
The axon hillock also delineates separate membrane domains between the cell body and axon.[4] This allows for localization of membrane proteins to either the axonal or somal side of the cell.
Structure
The axon hillock and initial segment have a number of specialized properties that make them capable of action potential generation, including adjacency to the axon and a much higher density of
In electrophysiological models, the axon hillock is included with the
Function
Both inhibitory postsynaptic potentials (
In its resting state, a neuron is polarized, with its inside at about −70 mV relative to its surroundings. When an
As sodium enters the cell, the cell membrane potential becomes more positive, which activates even more sodium channels in the membrane. The sodium influx eventually overtakes the potassium efflux (via the two-pore-domain potassium channels or leak channels, initiating a positive feedback loop (rising phase). At around +40 mV, the voltage-gated sodium channels begin to close (peak phase) and the voltage-gated potassium channels begin to open, moving potassium down its electrochemical gradient and out of the cell (falling phase).
The potassium channels exhibit a delayed reaction to the membrane repolarisation, and, even after the resting potential is achieved, some potassium continues to flow out, resulting in an intracellular fluid that is more negative than the resting potential, and during which no action potential can begin (undershoot phase/refractory period). This undershoot phase ensures that the action potential propagates down the axon and not back up it.
Once this initial action potential is initiated, principally at the axon hillock, it propagates down the length of the axon. Under normal conditions, the action potential would attenuate very quickly due to the porous nature of the cell membrane. To ensure faster and more efficient propagation of action potentials, the axon is
References
External links
- Histology image: 3_09 at the University of Oklahoma Health Sciences Center - "Slide 3 Spinal cord"