Chapter Sixteen 

The Final Execution

the process by which new neurons are formed in the brain

Adult neurogenesis involves several distinct stages:

beginning with the proliferation

Neurons are believed to be non-proliferating cells. However, neuronal stem cells are still present in certain areas of the adult brain, although their proliferation diminishes with age

of resident neural stem cells

That are ectodermal progenitor cells that can differentiate into various neural cell types like neurons, astrocytes, and oligodendrocytes

and progenitor cells,

a biological cell that can differentiate into a specific cell type however they only differentiate into their "target" cell type

followed by differentiation, migration, selection, and ultimately functional integration into the pre-existing circuitry

There are four principal types of neural circuits that are responsible for a broad scope of neural functions. These circuits are:

a diverging circuit,

one neuron synapses with a number of postsynaptic cells

integrates all the signals it receives to determine what it does next, for example, to fire an action potential of its own or not

A critical function of post-synapses, largely dependent on dendrites is:

plasticity,

Plasticity means first the ability of some organisms to develop into several possible phenotypes depending on the environment they face

Phenotypes are an individual's observable traits

the capacity of cells to undergo changes including differentiation

Coding genes and noncoding

the portions of an organism's genome that do not code for amino acids. Some non-coding DNA sequences:

Some non-coding regions appear to be mostly nonfunctional, such as introns,

pseudogenes

intergenic DNA,

and fragments of transposons and viruses. 

Regions that are completely nonfunctional are called junk DNA. I don’t like this term it must be there for a reason 

miRNAs exert major roles in regulating cellular networks

and de-differentiation

Each of these may synapse with many more making it possible for one neuron to stimulate up to thousands of cells.

a converging circuit,

inputs from many sources are converged into one output, affecting just one neuron or a neuron pool

a reverberating circuit,

produces a repetitive output. In a signalling procedure from one neuron to another in a linear sequence, one of the neurons may send a signal back to initiating neuron. Each time that the first neuron fires, the other neuron further down the sequence fire again sending it back to the source

and a parallel after-discharge circuit

involves multiple neurons firing in a coordinated manner to transmit information