How the Brain Works

The brain transmits messages by using electrical activity. Unlike other cells and tissue in the body, nerves communicate with each other by sending electrically charged signals to each other- specifically by activating changes in the sodium and potassium concentrations of neighboring nerves.

The Senses

Signals such as pain or temperature of the arm or hand work by send messages along a pathway from nerves in the hand to the spinal cord and then to the brain, registering simple sensory information such as touch, temperature, position, etc.

Emotions

Emotional input is much more complicated than sensory input. Often, the initial trigger for an emotion is something simple, like a smell or a sound or spoken words. But the brain takes the initial sensation - for example, the words, “Why did you do this?” and produces a thought. The brain’s response to the simple words, “Why did you do this?” includes subtle emotions and decision-making in response to a combination of simple words, tone of voice, facial expression, and the specific situation. The final response in the brain requires communication between many nerves through electrical activity in several pathways that are finally combined to make a decision.

How Electrical Activity Works in the Brain

Nerves are a type of cell in the body. The membrane around the nerve, called a cell membrane, encloses and borders each individual nerve. Sodium (we get it from salt) and potassium (we get it from bananas and some other types of food) both reside directly inside and directly outside the cell membrane.

The ratio of sodium inside the nerve and outside the nerve is maintained at a very specific concentration when the nerve is resting, or inactive. Similarly, the ratio of potassium inside the nerve and outside the nerve is maintained at a precise concentration when the nerve is inactive.

When a nerve is activated, some of the sodium gates in the nerve cell membrane open, allowing more sodium into the cell and shifting the charge (voltage) of the nerve cell.

This change in voltage triggers an electrical excitation that is transmitted to the next nerve cell along a pathway. Likewise, subsequent nerve cells' sodium gates open, allowing more than usual sodium to enter each cell along the pathway and activating each cell, causing a chainlike electrical reaction. In this way, nerves operate somewhat like electrical wires, sending messages throughout the body from an area of origin to a final destination. These voltage mediated messages travel along pre-designated routes from nerve to nerve.

Learning

Learning to walk, speak, write, knit or play basketball is the result of practice, which fosters new networks between neurons in the brain to achieve complex tasks. We learn actions and we also learn to have emotional responses to certain situations based on previous experiences.

Stroke and Electrical Activity in the Brain

Every time the brain registers sensation, has a thought, experiences an emotion, learns something new or repeats a learned activity, the whole process is made possible by the opening of sodium gates located at the nerve cell membrane, electrically stimulating the nerve.

When a stroke occurs, the interruption of blood flow to a region of the brain prevents the brain cells from receiving vital blood. This is called ischemia and it results in death of the affected neurons (brain cells.) This brain cell death is called an infarct. When neurons die, they become unable to properly transmit electrical activity.

Most of the time, infarcts cause loss of function. Sometimes, infarcts and cell death can result in disorganized electrical activity of the affected cells. This process may generate misfiring neurons, manifesting as seizures. Some stroke survivors experience seizures as a result of a stroke.

The electrical activity within the brain requires healthy brain tissue. A stroke disrupts brain tissue function.  Not surprisingly, researchers have investigated the possibility of electrically stimulating the brain to help with stroke recovery.

Sources

Bozzone, Donna, Green, Douglass, Biology for the Informed Citizen, Oxford University Press, 2014

Starr, Cecie, McMillan, Beverly, Human Biology, 10th Edition, Brooks/Cole, Cengage Learning, 2014

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