How is information communicated between neurons

In the neuron, a protective covering called myelin grey insulates the axon and increases the speed of electrical communication along the length of the neuron. Image: Opus Design.

Neurons are the most fundamental unit of the nervous system, and yet, researchers are just beginning to understand how they perform the complex computations that underlie our behavior. Some of these axons can be very long and most of them are very short. The electrical signal that runs along the axon is based on ion movement. Myelin is a fatty layer formed, in the vertebrate central nervous system, by concentric wrapping of oligodendrocyte cell processes around axons.

Neurons in the peripheral nervous system are also myelinated, but the cells responsible for myelination are Schwann cells, rather than oligodendrocytes. Adjacent sections of axon in a given neuron are each surrounded by a distinct myelin sheath.

Glial cells provide scaffolding on which the nervous system is built, help neurons line up closely with each other to allow neuronal communication, provide insulation to neurons, transport nutrients and waste products, and mediate immune responses. Neurons , on the other hand, serve as interconnected information processors that are essential for all of the tasks of the nervous system. This section briefly describes the structure and function of neurons.

Neurons are the central building blocks of the nervous system, billion strong at birth. Like all cells, neurons consist of several different parts, each serving a specialized function. This membrane allows smaller molecules and molecules without an electrical charge to pass through it, while stopping larger or highly charged molecules. Figure 1. This illustration shows a prototypical neuron, which is being myelinated. The nucleus of the neuron is located in the soma, or cell body.

The soma has branching extensions known as dendrites. The neuron is a small information processor, and dendrites serve as input sites where signals are received from other neurons. These signals are transmitted electrically across the soma and down a major extension from the soma known as the axon , which ends at multiple terminal buttons. The terminal buttons contain synaptic vesicles that house neurotransmitters , the chemical messengers of the nervous system. Axons range in length from a fraction of an inch to several feet.

In some axons, glial cells form a fatty substance known as the myelin sheath , which coats the axon and acts as an insulator, increasing the speed at which the signal travels.

The myelin sheath is crucial for the normal operation of the neurons within the nervous system: the loss of the insulation it provides can be detrimental to normal function. Multiple sclerosis MS , an autoimmune disorder, involves a large-scale loss of the myelin sheath on axons throughout the nervous system. The resulting interference in the electrical signal prevents the quick transmittal of information by neurons and can lead to a number of symptoms, such as dizziness, fatigue, loss of motor control, and sexual dysfunction.

While some treatments may help to modify the course of the disease and manage certain symptoms, there is currently no known cure for multiple sclerosis. In healthy individuals, the neuronal signal moves rapidly down the axon to the terminal buttons, where synaptic vesicles release neurotransmitters into the synapse. The synapse is a very small space between two neurons and is an important site where communication between neurons occurs.

Once neurotransmitters are released into the synapse, they travel across the small space and bind with corresponding receptors on the dendrite of an adjacent neuron. The neurotransmitter and the receptor have what is referred to as a lock-and-key relationship—specific neurotransmitters fit specific receptors similar to how a key fits a lock. The neurotransmitter binds to any receptor that it fits. Figure 2. Each vesicle contains about 10, neurotransmitter molecules. We begin at the neuronal membrane.

The neuron exists in a fluid environment—it is surrounded by extracellular fluid and contains intracellular fluid i. The neuronal membrane keeps these two fluids separate—a critical role because the electrical signal that passes through the neuron depends on the intra- and extracellular fluids being electrically different. This difference in charge across the membrane, called the membrane potential , provides energy for the signal. The electrical charge of the fluids is caused by charged molecules ions dissolved in the fluid.

The semipermeable nature of the neuronal membrane somewhat restricts the movement of these charged molecules, and, as a result, some of the charged particles tend to become more concentrated either inside or outside the cell.

Like a rubber band stretched out and waiting to spring into action, ions line up on either side of the cell membrane, ready to rush across the membrane when the neuron goes active and the membrane opens its gates i. Ions in high-concentration areas are ready to move to low-concentration areas, and positive ions are ready to move to areas with a negative charge.

In addition, the inside of the cell is slightly negatively charged compared to the outside. This provides an additional force on sodium, causing it to move into the cell. Figure 3. Other molecules, such as chloride ions yellow circles and negatively charged proteins brown squares , help contribute to a positive net charge in the extracellular fluid and a negative net charge in the intracellular fluid. Imagine that you want to tell your friends something new; you could whisper it into their ears or shout it out loud.

This is rather like two forms of communication that occur within your brain. Your brain contains billions of nerve cells, called neurons, which make a very large number of connections with specialized parts of other neurons, called dendrites, to form networks.

If we understand how and what neurons communicate with each other, we will have a chance to correct disturbances in communication that may result in altered behaviors and brain disorders. We know that the human brain is the most complex structure. It has approximately 80 billion nerve cells, called neurons. Eighty billion 80,,,! This is more than 10 times as many neurons as there are people living on Earth. Neurons talk to each other using special chemicals called neurotransmitters.

There are many different sorts of neurotransmitters: some stimulate neurons, making them more active; others inhibit them, making them less active.

Neurons control literally everything you do. Neurons come in many forms, shapes and sizes, but it is helpful to think of a neuron like a tree. A neuron has three main parts, the cell body, an axon, and the dendrites Figure 1.

The tree trunk cell body stores genetic information DNA in a compartment called the nucleus. The cell body also contains the chemical machinery to produce the neurotransmitters that the neuron uses to communicate with each other.

Dendrites were once thought to be like antennae, just receiving signals from other neurons, but, as I explain, they can do more than this.

The tree root axon is the structure used by a neuron to connect with and talk to another neuron. An axon carries information similar to a cable that carries electricity. When one neuron wants to share a message with another, it sends an electrical impulse, called an action potential, down its axon until it reaches the axon terminal, at the end of the axon. Think of an axon terminal as an airport terminal. An airport terminal is filled with passengers waiting to depart, whereas an axon terminal is filled with neurotransmitters waiting to travel to the next neuron.

When the action potential reaches the axon terminal, some of the neurotransmitters in the terminal are dumped into a tiny gap between the terminal and the dendrite of another neuron. This gap is called a synapse—it is so tiny that it is measured in nanometers or billionths of a meter. The neurotransmitter crosses the synapse and binds to a specialized site, called a receptor, on the other side. Each neurotransmitter binds only to its specific receptor, just as a key fits only in a particular lock.

Depending on the neurotransmitter, it either stimulates the other neuron or inhibits, making it either more likely or less likely to fire an action potential of its own.