Structure
The axon hillock has a number of specialized properties that make it capable of action potential generation, including adjacency to the axon and a much higher density of voltage-gated ion channels than is found in the rest of the cell body. In electrophysiological models, the axon hillock is lumped in with the initial segment of the axon where membrane potentials propagated from synaptic inputs to the dendrites or cell body are summed. In dorsal root ganglion cells, the cell body is thought to have approximately 1 voltage-gated sodium channel per square micrometre, while the axon hillock and initial segment of the axon have about ~100-200 voltage-gated sodium channels per square micrometre; in comparison, the nodes of Ranvier along the axon are thought to have ~1000-2000 such channels per square micrometre. This clustering of voltage-gated ion channels is a consequence of plasma-membrane and cytoskeletal associating proteins such as ankyrin.
Read more about this topic: Axon Hillock
Famous quotes containing the word structure:
“There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.”
—Donald Davidson (b. 1917)
“Man is more disposed to domination than freedom; and a structure of dominion not only gladdens the eye of the master who rears and protects it, but even its servants are uplifted by the thought that they are members of a whole, which rises high above the life and strength of single generations.”
—Karl Wilhelm Von Humboldt (1767–1835)
“One theme links together these new proposals for family policy—the idea that the family is exceedingly durable. Changes in structure and function and individual roles are not to be confused with the collapse of the family. Families remain more important in the lives of children than other institutions. Family ties are stronger and more vital than many of us imagine in the perennial atmosphere of crisis surrounding the subject.”
—Joseph Featherstone (20th century)