易

易經

Variation Weavings

周易

Cycles Variations

Metadatabase

⚊ connected

⚋ idle

Neuronal wiring and the “connectome”

a term coined by Olaf Sporns  (Resources)

About 100 billion neurons form a complex and interconnected network in our brain, allowing us to generate complex thought patterns and actions. Neurons come in all sizes and shapes, but they mostly have long protrusions that connect to neighbouring cells through specialized information-transmission structures called synapses.

Proper brain functioning relies on very controlled branching of neuronal cell extensions called axons and dendrites, and the correct formation of synapses at precise locations along these branches. Specifying synapse formation determines where and how many potential connections a neuronal cell is "allowed" to form. Therefore, controlling synapse numbers at each neuronal branch is essential for the correct formation of complex brain circuits.

In a human fetus, almost a trillion neurons are produced. During the last month of pregnancy, they are produced at the unbelievable rate of 250,000 per second.  Eighty-to-hundred billion of these neurons will be utilized through experience and become permanent, while the other 900 billion will be pruned – that is, carefully dismantled with the material recycled by the brain’s unique immune system.

Later, during life, a relatively small number of new cells will be added in several parts of the adult brain related to memory and learning.  Amazingly, each of the remaining neurons can connect with up to a hundred thousand other cells. This number of connections is a truly enormous number: 10 thousand trillion. Even further complicating this picture is that these connections occur in many different ways, including different placements on neurons, as well as connections with the larger number of other brain cells that aren’t neurons.  Many of these connections change every day. While popularly it is thought that there is just one axon, in reality, the one axon ends with a large number of different connections.  As well, one neuron can have as many as 100,000 dendrites.

Yet another complication is that the cortex is divided into approximately 40 regions where there are different shaped neurons (approximately 750 million for each type of neuron) that have different architecture, density, size and connection properties. A recent analysis used genetic (instead of anatomic) data of each neuron type to construct a map and found that these two maps are not identical.  For example, the occipital and parietal regions have many different genetic types of neurons.

Many communications in the brain do not seem to be carried by wired connections but, rather, are the result of electromagnetic brain waves that connect different neuron groups.  In fact, new research has noted that brain circuits can avoid information traffic jams by using different frequencies of brain waves at the same anatomical point. More recent developments show that electrical information has been noted in the local region between cells, and cells have been noted to communicate by photons. The many ways that neurons communicate must all be related at the same time to the workings of the mind.