the axon hillock is the region of cell body from which axon originates.
the axon hillock is the region of cell body from which axon originates.
region of cell body from which axon originates?
the axon hillock
in other cases as seen in rat studies an axon originates from a dendrite; such axons are said to have "dendritic origin". some axons with dendritic origin similarly have a "proximal" initial segment that starts directly at the axon origin, while others have a "distal" initial segment, discernibly separated from the axon origin. in many species some of the neurons have axons that emanate from the dendite and not from the cell body, and these are known as axon-carrying dendrites. in many cases, an axon originates at an axon hillock on the soma; such axons are said to have "somatic origin". some axons with somatic origin have a "proximal" initial segment adjacent the axon hillock, while others have a "distal" initial segment, separated from the soma by an extended axon hillock.
axon
as previously stated, a neurite growing "in vivo" is surrounded by thousands of extracellular signals which in turn can be modulated by hundreds of intracellular pathways. it is therefore not surprising that it is not yet understood what determines neurite fate "in vivo." it is known that 60% of the time the first neurite that protrudes from the cell body will become the axon. 30% of the time, a neurite not destined to become the axon protrudes from the cell body first. 10% of the time, the neurite that will become the axon protrudes from the cell body simultaneously with one or more other neurites. it has been proposed that a minor neurite could extend outward until it touches an already developed axon of another neuron. at this point, the neurite will begin to differentiate into an axon. this is known as the touch and go model. however, this model does not explain how the first axon developed.
neurite