Sunday, July 17, 2016

Introduction to Psychopharmacology - Part 3 (Neurons)

The Structure and Functions of Cells of the Nervous System

To learn more about psychopharmacology, please check out "Psychopharmacology: Drugs, the Brain, and Behavior," by Jerrold S. Meyer and Linda F. Quenzer.

Before continuing with our discussion about drugs and their effect on behavior we have to talk about the brain. Now, there are two reasons why this discussion is essential. The first one is that the brain is essential in behavior. For example, the mouth is needed to speak, but Broca's area also forms an important part for the production of speech. Moreover, the legs are needed to walk, however, the basal ganglia is necessary for movement. As you can see, the brain is a required component for every behavior and if the part brain is damaged the behavior ceases to exist. Thus, the brain is necessary for behavior. The second reason is that the brain is sufficient for the study of drugs and their effects. We know that behavior, or people in general, are a complex result of several factors influencing each other. We could study variables like diet, sex, and age. But because all of these factors have in the end an impact on the brain, it ends up being sufficient for the study of psychopharmacology.

We'll start the discussion of the brain by focusing on the structures of the nervous system. Let's start with neurons. They are cells in the central nervous system (CNS) that process information (1). There are several types of neurons such as sensory neurons, which receive info from places such as the skin and sends it to the CNS (2), motor neurons, which send information to the muscles so they can move, and interneurons, which are located between a sensory and a motor neuron (4).

Fun Fact: It is estimated that there are around 100 billion neurons in the brain (4)

We already talked about the CNS, but what is it? Well, to put it simply, it is composed of the brain and the spinal cord. If you noticed that there is a CENTRAL nervous system, then there should be one not so central. This is called peripheral nervous system (peripheral means outside), and it's every part of the nervous system that is outside of the brain and spinal cord.

Let us go back to neurons and talk about their parts. The structure of a neuron depends on its function, however, there are similitudes between all of them. These include the soma, which is the cell body of a neuron, the dendrites, which look like tree branches and receive information, an axon, which is the part of the neuron that sends info, the synapse, which is the space between a terminal button and a dendrite. Think of a neuron functioning as a telephone, the dendrites is where you hear the person speak to you (although there are some exceptions where they send signals, but this is uncommon) and the terminal button is where the microphone for you to speak is located.

Types of neurons

The most common type of neuron is called multipolar (3). This has one axon and many dendrites attached to its soma. A bipolar neuron has an axon from one side and a dendrite from the other.

Bipolar Neuron

Another type is the unipolar neuron. This cell has only one stalk that divides into the axon and the dendrites. Bipolar cells are usually found in sensory systems such as vision. Unipolar neurons usually work with somatosensory functions such as feeling pain and temperature (5). Both of them receive information from the physical world and send it into the CNS.

One way of sending information is with neurotransmitters. They are released by the terminal buttons when an action potential happens. A neurotransmitter is a chemical that has an effect on another neuron (remember how the synapse is the space between a terminal button and a dendrite? Well, when the neurotransmitter is released it travels in this space in search of a receptor usually on a dendrite of another cell) either by inhibiting or exciting it. This is how neurons communicate.

Specialized Cells

Neurons are considered specialized cells for three reasons. The first one is that they are polarized. This refers to the fact that neurons are negatively charged on the inside. This allows them to communicate via action potentials (We will talk specifically about this later). The second reason is that they are excitable. This means that neurons are able to change their charge. (Our brain works on electrical activity generated by chemicals). The third reason is that they are modulatory. Each neuron is able to communicate with many other neurons. In other words, every thought we have, every movement we make, every behavior, can be observed in the brain in the form of electric activity across neurons. 

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3. Physiology of Behavior by Neil Carson