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The structure of the neuron (Figure 2). 

The different regions of the brain are made from different nerve cells, which are called neurons that serve as the electro-chemical network of the brain. The neuron is made from the following parts (Figure 2):

• Cell body that contains the nucleus, which is the control center of the nerve cell.

• Dendrites (also called dendrons) are branches of short fiber extensions of the nerve cell that propagate the electro-chemical stimulation received from other neurons to its own cell body. The function of the dendrites is to receive information from other neurons (Figure 3).

• Axon (also called a nerve fiber) is a long, slender projection of a neuron, that conducts electro-chemical impulses known as action potentials, away from the  neuron cell body  to the dendrites of other neurons through synapses. The function of the axon is to transmit information to other neurons (Figure 3).

• Synapse is the space where an axon of one neuron connects to a dendrite of another neuron. The synapse is a small gap that has two borders. One side borders with an axon and that side is call pre-synapse. The other side of the synapse borders with a dendrite and that side is called post-synapse. The terminal end of an axon can have several synapses with dendrites of one or more neurons. Through the space of the synapse the axon of one neuron releases neurotransmitters to the dendrite of the other neuron (Figure 4). This is how information passes from one neuron to another.

• Myelin is a material rich in lipids and is white in color. Myelin sheets coat the axons to ensure their isolation from the environment. They prevent changes such as changes in temperature or changes in the chemical balance in the axon. This increases the conductivity of the information through the axons in the neural circuits. Since the appearance of myelin is white; hence, the name "white matter" of the region of the axons in the Central Nervous System (CNS). 

• Oligodendrocytes are cells that produce the myelin.

• Cortex is the most external layer of the brain. It is 2 to 5 millimeters thick and made of 6 cortical layers. Most of the cell bodies of the neurons in the brain are in the cortical layers. The part of the neuron that includes the cell body or the nucleus is not coated with myelin sheaths and therefore looks dark grey and is called "the grey matter". 

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Figure 2: A neuron = a nerve cell.

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Neural circuits are populations of neurons that are interconnected by synapses and create a network of information in order to carry out a specific function when activated. The largest and most important brain information processing of the neural circuit involves the cortex. The information or the electro-chemical impulses or signals pass through chains of neurons by the following sequence shown in Figure 3 from left to right: Axon to dendrite 1 to cell body 1 to axon 1 to dendrite 2 to cell body 2 to axon 2 to dendrite 3 to cell body 3 to axon 3 to dendrite... and so on.

 

Figure 3: The neural impulse transmission (action potential) propagates through the neural circuit.

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The transport of information between the neurons (Figure 4).

Neurotransmitters are signaling molecules that are released by the axon terminal of a neuron at the pre-synapse side, and they are bound to the receptors of the dendrites of another neuron at the post-synapse side (Figure 4). This causes an electro-chemical reaction in the dendrite of the other neuron. The electro-chemical reaction is called action potential or neural impulse.

In the execution of a function in the brain there are two important neurotransmitters.

1.Excitatory neurotransmitters: Glutamate is a principal excitatory neurotransmitter. It increases the chances to fire and generate an action potential and therefore it increases the speed in which the information passes through the neurons. This will increase the function that the neurons are responsible for.

2. Inhibitory neurotransmitters: Gamma-aminobutyric acid (GABA) is a principal inhibitory neurotransmitter. It decreases the chances to generate an action potential and therefore it decreases the speed in which the information passes through the neurons. This will decrease the function that the neurons are responsible for. [153].

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Figure 4: Transportation of information through the space of a synapse.

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