Human brain BRAIN CELLS Human brain




BRAIN CELLS
The brain and spinal cord are made up of living cells, neurons and glial cells. Neurons send and receive electro-chemical signals to and from the brain and nervous system. There are about 100 billion neurons in the brain. There are many more glial cells; they provide support functions for the neurons, and are far more numerous than neurons.

There are many type of neurons. They vary in size from 4 microns (.004 mm) to 100 microns (.01 mm) in diameter. Their length varies from a fraction of an inch to several feet.
NEURON
Neuron

Neurons are nerve cells that transmit nerve signals to and from the brain at up to 200 mph (check this). The neuron consists of a cell body (or soma) with branching dendrites (signal receivers) and a projection called an axon, which conduct the nerve signal. At the other end of the axon the axon terminals transmit the electro-chemical signal across a synapse (the gap between the axon terminal and the receiving cell).
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The axon, a long extension composed of. . Bundles of axons are known as nerves or, within the CNS, as nerve tracts or pathways.
Myelin coats and insulates the axon (except for periodic breaks called Nodes of Ranvier), increasing transmission speed along the axon. Myelin is manufactured by Schwann's Cells, and consists of 70-80% lipis (fat) and 20-30% protein.

The cell body (soma) contains the neuron's nucleus (With DNA and typical organelles), . Dendrites branch from the cell body

A typical neuron has about 1,000 to 10,000 synapses (that is, it communicates with 1,000-10,000 other neurons, muscles cells, glands, etc.).

DIFFERENT TYPES OF NEURONS
There are different types of neurons. They all carry electro-chemical nerve signals, but differ in structure (the number of processes, or axons, eminating from the cell body) and are found in different parts of the body.