How Neurons Work

The human brain is a relatively large organ that is connected to the spinal column and controls everything we do; consciously or subconsciously...sometimes unconsciously. The brain consists of many parts that play varied roles in our survival. This article concerns itself with the cerebral cortex, which gives us the ability to think, process thought and the six senses into events we can consciously act upon. The cerebral cortex separates us from lower life forms such as dogs, cats, reptiles, etc. It also has many "folds" or valleys which contribute to the working surface area.

To break the cerebral cortex down even further, it is composed of billions of neurons or nerve cells and glial cells which support and provide nutrition for the neurons. There are billions more glial cells than neurons.

What comprises a neuron? The neuron is the functional cell of the brain. Many facets of its contribution to our daily lives remain a mystery; but, some things are known. For instance: A neuron is composed of three major parts; the axon, along which a nerve impulse and neurotransmitters pass; a dendrite, which contains the nucleus of the cell and receptors which allow certain chemicals to bind and thus effect the action of the cell; and, finally, the synapse. Consider the synapse as a "gap" between the end of the axon and the beginning of the dendrite. This synapse can be electrically compared to the spark gap on a spark plug, but it also contains hundreds of neurotransmitters which affect the speed and reliability of the synapse. We are concerned with the primary neurotransmitters: Serotonin, nor epinephrine and dopamine.

The axon portion of the nerve cell carries the impulse to the synapse. It is insulated by a substance called myelin which covers the axon in "hills and valleys" which are back to back. The dips or "valleys" are called nodes of Ranvier. The myelin "sheath" is composed of Schwann's cells which are about eighty percent lipids or fats. The remaining twenty percent is protein. Myelin can be compared to the insulation on a wire. It insulates itself from other axons in order to prevent a "short circuit".

The nerve impulse travels through the axon. The terminal end of the axon ends in a gap area called the synapse. On the other side of the synapse is the dendrite, another portion of the nerve cells, which carries many receptors for chemicals excreted into the synapse by the axon. The axon releases neurotransmitters into the synapse. When these neurotransmitters are attached to the receptors, a tiny electrical charge across the synapse is produced or suppressed. This is not a visible spark, but is created by "ions"; chemicals which have a positive of negative charge. After the synapse occurs, neurotransmitters are re-absorbed by the axon for future use. This "re uptake" of neurotransmitters and the time they spend in the synaptic gap, has a great affect on our mood.

A medicine to treat depression, such as Prozac, must first be able to cross the blood/brain barrier. This is a selective barrier within the brain's blood vessels that allow only certain chemicals to enter and leave. After Prozac has crossed this barrier, it is used in the axon to slow the re uptake of serotonin; a key component in preventing depression. Scientists have found that if they slow the re-uptake of serotonin back into the axon, overall mood is improved and depressive episodes are fewer if not non existent. Prozac is just one of the many medications called, "SSRI's" or selective serotonin re uptake inhibitors.

Good quality sleep is also necessary for the productivity of our daily lives. Sleep is induced partially by the pineal gland, located in the mid line of the brain. The pineal produces a substance called melatonin which induces sleep. If you have difficulty in falling asleep, melatonin can be bought in the vitamin section of your store. It is a naturally occurring chemical. It is thought that sleep allows us to take what we have learned and entrench it into a more permanent memory. It could also promote brain development, although this is not entirely understood nor substantiated.

Although there are still many areas and functions of the brain that remain unknown or misunderstood, research is on-going and strides are made every day. Scientists use squid to study nerve cells because their neurons are so much bigger than ours and function in many of the same ways.

Finally, neurons and glial cells in the brain have no pain receptors. Many brain surgeries are done while the patient is awake in order to allow the neurosurgeon to "map out" portions of the brain. This fact, in itself, is testament to the difference in loci of various performance units of the brain from person to person. For instance; Brocha's area, the area that controls speech is known to be in a certain area, but surgery around this area must be mapped if the doctor does not want to invade it. To summarize; it is known where the basic units of the brain are located; but, the boundaries are so individualized, they must be mapped to avoid invading an unwanted area.