Neuron: The fundamental particle of Neuroscience

The neuron is the basic functional unit of the nervous system.

It is mainly structured in three parts:

• Cell body, contains the nucleus and organelles
• Dendrites, branching extensions of the cell body that receive signals
• Axon, long projection off the cell body that sends signals

They are divided into two categories:

• sensory neurons that receive and transmit stimuli
• motor neurons that send a response in targeted cells

How many?

There are approximately 86 billion in a human brain and transmit electrical and chemical signals to one another

How do they function?

Once a neuron has been stimulated by some sort of stimulus, it generates an electric potential that travels down the length of the cell. This is the 'electro' part of electrochemical. Once the electric current reaches the axon terminal at the end of the cell, it triggers the release of certain chemical messengers. This is the 'chemical' part of electrochemical.

In more detail

1. Neurons begin at a resting potential of around -70 milivolts, during which no signals will be transmitted
2. An adjacent neuron sends neurotransmitters that bind to the dendrites of the neuron
3. If these neurotransmitters are excitatory, then gated ion channels will open up to permit ambient sodium ions (Na+) into the cell (making the potential more positive). If these neurotransmitters are inhibitory, then gated ion channels will open up to permit internal potassium ions (K+) out of the cell (making the potential more negative)
4. For an action potential to be generated, enough excitatory neurotransmitters must be present to raise the charge above a certain threshold level. Once this level is exceeded, an all-or-none electrical potential is sent down the length of the axon (depolarization)
5. After depolarizing, the neuron's ion pumps begin working to reestablish the resting potential. While the neuron is doing so, it enters a refractory period during which no further action potentials can be generated. (hyperpolarization)
6. Once the potential has been restored, the neuron is ready for a new stimulus

Source Wikiversity(!): https://en.wikiversity.org/wiki/Fundamentals_of_Neuroscience