What is a neuron?
A single neuron is not very effective, but groups of neurons work together in the brain to process information, activating muscles and glands, and creating intelligent thought. Millions of neurons may form transmit information to one another to establish a simple idea. Presently, the brain consists of over 100 billions neurons, though scientists postulate the number is greater, having discovered increasing numbers after every advance in sophisticating equipment for scrutinization. Neurons group together to create nerves, which, unlike neurons, are visible to the naked eye.
What does a neuron look like?
Each neuron is in some sense physically unique, though most have four parts. The dendrite receives information from other neurons, and so does the soma, or cell body, though the soma also sends messages, or nerve impulses, down the thin axon. Commonly, axons have axon terminals, which connect with dendrites and somas of other neurons, thus establishing a flowing nerve impulse. Most axons have a thin layer of cells, the neurilemma, wrapped around them, so that damaged fibers may travel a tunnel like path as they repair themselves. The average brain consists of approximately 3 million miles of .1 millimeter long axons.
How does a neuron function?
Ions within and outside cause neurons to have roughly minus seventy million volts. The resting potential of an inactive neuron is risen and lowered by other neurons acting upon it. When the electrical charge reaches minus fifty millivolts, the neuron will reach it’s threshold and an action potential, more commonly known as a nerve impulse, will travel down the axon at speeds amounting to 200 miles per hour. Ion channels will open along the axon membrane during action potential, permitting sodium ions to first travel into the soma and then down the axon.
After the neuron fires it’s impulse, a negative after-potential occurs, which means the neurons momentarily refuse to transmit more impulses. This occurs because potassium ions escape from neurons when the ion channels open, however, ions travel back into the neuron, preparing it to function once again.
The almost insignificant space separating neurons is the synapse. After action potential, neurotransmitters, chemicals which alter neuron’s activity, are released into the synapse, which are received by the numerous receptor sites on other neurons’ membranes. These neurotransmitters either “excite” or “inhibit” a neuron; a neurons may receive a thousand messages at once, and depending on whether the majority excite, or inhibit, the neuron will release action potential or remain stagnant, respectively.
Frequently, instead of impulses passing from axon to axon, axons will be coated with a fatty layer, myelin, and impulses will jump from gaps in the myelin. This produces quick reflexes, such as stopping short before traffic when a stop light turns red. If myelin is damaged, a person may suffer from numbness, weakness, paralysis. Multiple sclerosis arises when the immune system damages the myelin.
To What Do Neurons Connect?
Neurons connect to he Central Nervous System, composed of the brain and spinal cord. In fact, the only reason the Central Nervous System functions at all are because of neurons. Neural networks, or considerable amounts of neurons working together, allow the brain to perform tasks, and are connected to other neural networks.
Coon, Dennis and Mitterer, John O., Introduction to Psychology
MIRECC, VA Desert Pacific Healthcare System, Understanding the Brain: How Neurons Communicate