Sunday, July 24, 2016

Introduction to Psychopharmacology - Part 4 (Action Potentials)

Action Potentials - How Neurons Communicate with each other. 

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

Now that we have talked about neurons individually, we are going explain how they communicate between each other. We mentioned in the last post that they do it by action potentials. Today we are going into detail of what are these, how they work, and why they work. There are two important features in this process: electric charge and chemicals, specifically sodium, potassium, and calcium. 

What is it?


An action potential is the electricity traveling inside a neuron (remember that our brain works on electricity). It starts at the axon hillock, which is the part located before the axon and after the soma, and ends in the terminal button. When it reaches its end, neurotransmitters, which are chemicals that send messages across neurons (1), are released from the terminal button. After that they bind on the receptors of another neuron (receptors are usually on the dendrites, but the can be in other parts of the neuron). They either inhibit a neuron, and thus stop it from firing another action potential, or they can excite the neuron, making it fire another action potential. This is a basic description of how neurons are modulatory, but the real process is much more complicated.



Synapse

Before starting  adumbrating the process of an action potential it is important to describe what the synapse is. There are three parts that are important: the presynaptic cell, the post-synaptic cell, and the presynaptic cleft. The latter is the space between neurons. It is important to state that neurons never touch each other, there is always a small space between them. The presynaptic neuron is the neuron that is above or before the synaptic cleft, it is the terminal button pointing at the receptors of the other cell. The post-synaptic cell is the neuron that is after or below the synaptic cleft, it is the receptor side that receives the neurotransmitters (NTs). Thus, the presynaptic neuron releases NTs, they travel through the synaptic cleft and they bind to the receptors on the post-synaptic cell.



Chemicals

We already mentioned the three important chemicals for action potentials: potassium, sodium, and calcium. The former is concentrated more on the inside of a neuron; it is what gives the neuron a negative charge. When neurons are not firing, which is called the resting membrane potential, they have a negative charge, which is a critical component in order to fire action potentials (we will cover more of this later). Sodium is concentrated more on the outside of the cell and it gives it a positive charge. This means that the inside of a neuron is negatively charged and positively on its exterior. Calcium is needed so that neurotransmitters can be released.

Channels

There are two types of channels in the membrane of a neuron. They are ligand-gated and voltage-gated channels. The former opens up when a ligand, which can be a neurotransmitter or a drug, binds to the receptors of the channel. The latter opens up when a specific charge is detected.

Action Potentials

We already talked about how neurons have a negative charge. Their resting potential is -70 millivolts (mV). This means that neurons are polarized when they are resting (remember this is one of the reasons why neurons are specialized cells).

 Neurotransmitters can do two things when they bind: They can either excite the neuron or inhibiting it from firing another action potential. These are called excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) (2). EPSPs start to depolarize the neuron. If they do not change the charge to -55 mV an action potential is not fired. These are called failed initiations. However, if it does reach the threshold of  -55 mV, depolarization starts to occur. This means that sodium channels open up and sodium enters the cell. It does this for two reasons. The first one has to do with the electric charge of a neuron. Remember that in chemistry positives attract. Therefore, because the inside of a neuron is negative, the sodium, which has a positive charge, tries to enter it once the sodium channels open up.

 This is why it is important that neurons have a negative charge in order to fire an action potential. Once the cell depolarizes an action potential is fired. When the neuron reaches a positive charge, the sodium channels close and the potassium one opens up, and by potassium leaving the cell the neuron starts to repolarize. Potassium channels are not efficient, in the sense that they know when to close up. For this reason, the cell hyperpolarizes. This means that it obtains a more negative charge than when it is at the resting potential. During this period, which is also called absolute refractory period, actions potentials cannot be fired. The potassium channels close at this point and a sodium and potassium pump return the cell to the resting membrane potential. As you saw the first two channels were voltage dependent, they needed a specific charge to be opened. This means that action potentials don't really require energy, however, the sodium and potassium pump does and it uses ATP as its source of energy. When the action potential reaches the terminal buttons, voltage-dependent calcium channels open up and help neurotransmitters release. They in turn either inhibit the next neuron from firing an action potential or they excite it and the process repeats itself over and over again.   



References
1. http://www.nimh.nih.gov/health/educational-resources/brain-basics/brain-basics.shtml

2. http://www.ncbi.nlm.nih.gov/books/NBK11117/

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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References

1. http://www.mind.ilstu.edu/curriculum/neurons_intro/neurons_intro.php

2. http://www.britannica.com/science/sensory-neuron

http://vanat.cvm.umn.edu/neurLab1/neuron.html

3. Physiology of Behavior by Neil Carson

4. http://neuroscience.uth.tmc.edu/s2/chapter02.html

Tuesday, July 5, 2016

Introduction to Psychopharmacology - Part 2 (How are Drugs Processed?)

The Processing of Drugs

Drug action does not only depend on the chemical structure of a drug but also on factors like the rate in which it can be absorbed by the body; this factor is known as bioavailability (1). There are five factors that contribute to bioavailability that constitute the pharmacokinetic elements of drug action (2). Pharmacokinetics is the study of how drugs are absorbed, dispersed, processed, and eliminated from the body (3). The five factors are:

1. Routes of administration.

This is the way in which drugs enter the body. There are two major divisions in which a drug can be administered: Enteral, which refers to passing thorugh the intestine or gastrointestinal tract (4), and parentenal, which is all the methods in which the drug do not passes through the gastrointestinal tract (5). We will cover five methods of administration.


The first one is by means of injection. We will cover several types of injections, the first one being intravenous (IV) injection. This one goes right in to the bloodstream so the drug effects are instantaneous (6). The second one is the peritoneal injection, which is administered in the peritoneal cavity (duh!). This is a semipermeable wall in the abdomen (7). The next injection is intramuscular, which is delivered into the muscles and the last one is the subcutaneous injection, which is delivered under the skin (8). The cartoon to the right depicts a peritoneal injection.




The second route to administer a drug is by oral administration. Researchers don't usually use this method for two reasons. The first one is that if the experimenter is dealing with animals, they (the animals, not the researchers) might not want to consume the drug because of its flavor. The other reason is that the chemical can be destroyed by a stomach acid (9). Nevertheless, this method can be used with humans if it is administered with a sublingual method (This means placed under the tongue). In this way, the drug enters the bloodstream, thus, not being affected by the stomach acid.


The third method is called intrarectal and it is administered through the anus (10). I hope you can understand why I didn't put a real photo here. It is important to note that because of they way it is introduced into the body, many researchers opt out of his method. Nevertheless, it is commonly used with humans. Inhalation is the fourth method. Drugs like marijuana and nicotine are usually smoked (9). This method is efficient in the sense that a lesser dose is needed for the same effect when compared to the other methods such as oral administration (7). The last method is called topical. This is applied to surfaces of the body such as the skin (8), colon, vagina, urethra, conjunctiva of the eye, or the nasopharynx (2).

Each route of administration has advantages and disadvantages. For example, taking drugs orally makes it safer for the person (it avoids the use of needles), but it has a slower rate of absorption. In addition, taking a drug intravenously makes it reach the brain faster, resulting in quicker drug effects, but it is harder to self-administer and it requires sterile needles. Moreover, using an intramuscular injection creates a slow and steady rate of absorption, but it irritates the person at the site of the injection and it also requires sterile needles (2). 

2. Absorption and Distribution.

This refers to the way in which the drugs enter the blood plasma and is transported throughout the body (2).

3. Binding

This refers to the way that the drug in the blood plasma attaches to receptors or when it is stored temporarily in bone or fat (2).

4. Inactivation

This process, which is also known as biotransformation, is the way in which a drug becomes inactive "through a chemical change, usually by metabolic processes in the liver." (2)

5. Excretion

This refers to the way in which the drug is eliminated from the body through urine feces, saliva, and sweat (2). The most common one being urine.



Sources
1. http://www.merriam-webster.com/dictionary/bioavailability

2. "Psychopharmacology: Drugs, the Bran, and Behavior," by Jerrold S. Meyer and Linda F. Quenzer. 

3. http://www.merriam-webster.com/dictionary/pharmacokinetics

4. http://medical-dictionary.thefreedictionary.com/enteral

5. https://www.britannica.com/topic/parenteral-administration

6. https://www.nlm.nih.gov/medlineplus/ency/article/002383.htm

7. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3189662/

8. http://www.merriam-webster.com/dictionary/subcutaneous

9. "Physiology of Behavior" by Neil Carson

10, http://www.ncbi.nlm.nih.gov/pubmed/6126289

Sunday, July 3, 2016

Introduction to Drugs and behavior/Psychopharmacology - Part 1

Psychopharmacology - What is it?




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

Psychopharmacology is defined as the study of how drugs affect mood, thinking, and behavior (1). Thus, in this introduction, we will explore the effects and the processing of drugs from a biopsychological perspective. First, we have to define some of the terminology. We will start with what a drug is. In one of part of our introduction to biopsychology (http://hbookreviews.blogspot.com/2016/04/introduction-to-psychobiology-part-4.html), we learned that a drug is a chemical that comes from the outside of our bodies and changes the normal functions of the cells when taken in low doses (2). The changes produced on a molecular level when a drug binds to the receptor of a neuron are called drug action (3). But the changes that occur on a physiological and/or psychological level are called drug effects. To give you an example that will mark the differences between drug action and drug effect we will cover two drugs: atropine and morphine. The former affects the eye by dilatating the pupil (this is the drug effect) when applied to the eye muscles of the iris (this would be the site of the drug action). Morphine also has the same drug effect (widening the pupil), but not the same site of drug action (nothing happens if applied to the eye, but the drug effect occurs when the morphine is taken internally). We will cover more specific drug effects later. Right now we have to explore four branches of effects. They are: 


  • Therapeutic effects: These are desired physiological or psychological changes. For example, when a teenager takes an antidepressant, he or she expects that some of the symptoms that belong to major depressive disorder disappear.
  • Side effects: These are all the changes that were not therapeutic. In other words, the undesired changes in the body and mental processes. To use the example above, side effects would be how the risk of suicide doubles for teenagers when they take an antidepressant rather than a placebo (4).
  • Specific drug effects: These are effects that are dependent on the physiology of the person or animal.
  • Nonspecific drug effects: These are the effects that instead of depending on the biochemistry of an individual, they rely on the individual's background. An example of something that depends greatly on an individual's background instead of the physiology of the person is a placebo (this is a sugar pill). This pill can have therapeutic and side effects that belong to other drugs, even if it the placebo does not have the biochemical interaction that causes the other drugs to produce those effects.

Placebos are important because they are used to understand how much of the drug effects are caused by the individual's expectations and how much by the biochemical interaction of the drug. Thus, when researchers do an experiment with drugs (with drugs, not on drugs), or an experiment in general, they divide their test subjects into at least two groups: control and experimental groups. The former gets the placebo and the latter the drug, but neither groups is aware of what they were given. Because of the influence of the placebo and other factors, psychopharmacologists usually engage in a type of study called double blind procedure. This is similar to the set up of the experiment mentioned above. However, in this case, neither the participant nor the researcher knows which group received the drug or the placebo. This helps eliminate the expectations that influence test results by both parties.

Feel free to leave a comment and don't forget to subscribe by email!
Sources
1. "Psychopharmacology: Drugs, the Bran, and Behavior," by Jerrold S. Meyer and Linda F. Quenzer.

2. "Physiology of Behavior" by Neil Carson

3. https://www.britannica.com/topic/drug-action

4. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2799109/