Hi, I’m Dr. Scott Branson. While watching this series of videos you will be introduced to neurons, neurotransmitters, and the ways in which chemical substances alter brain chemistry.

This overview is important for counselors and other mental health professionals, as understanding the ways in which chemical substances alter brain chemistry is foundational to working with clients who are using chemical substances including marijuana, alcohol, and even prescription medications, such as selective serotonin re-uptake inhibitors and other anti-depressants. Neurons are responsible for our so called brain chemistry, which is foundational to our emotions and thoughts, as well as the ways in which we interact with the world. While counselors don’t prescribe medications, they will inevitably work with clients who are taking medications, and the information in this video will help them to conceptualize how medications impact the brain at a molecular level.

Neurons are critical to our everyday functioning, as they are responsible for transmitting and processing information. For example, sensory neurons help us to experience the world around us by transmitting information from our five senses to our brains, while motor neurons transmit signals from our brains to our muscles, so we can do things like walk, talk, and breathe. While nerve cells are found throughout the body, for this video we will be focusing on neurons found in the central nervous system. In other words, the brain and spinal cord. Neurons in the central nervous system are chemically isolated from the rest of our bodies by a system called the blood brain barrier, although they do connect to our peripheral nervous system, which includes all of the nerves outside of the brain and spinal cord. The blood brain barrier was discovered more than a century ago, when a researcher named Paul Ehrlich injected blue dye into animals’ blood streams. Ehrlich noticed that the blue dye would spread throughout the animals’ bodies, but it would not enter the brain or spinal cord. Ehrlich then injected the dye directly into animals’ brains, and observed that the dye would stain the brain and spinal cord, but that it would not affect the rest of the body. As we will learn, neurons are highly sensitive, and the blood brain barrier is critical to ensuring that the environment around neurons is consistent. Without the blood brain barrier, neural communication would be seriously disrupted.

So let’s dive in and look at the parts of a neuron. There are many different types of neurons, all of which have four central parts: the soma or cell body, dendrites, an axon or axons, and terminal buttons.

The first part of a neuron we will look at is called the soma.

The soma is the cell body, and it can vary in size from a few micrometers to several millimeters in size, depending on the cell type. The soma contains several ingredients that are critical for cell functioning, one of which is the cell nucleus. If we look inside the cell nucleus, we can see proteins and genetic materials, such as ribonucleic acid, also known as RNA, and deoxyribonucleic acid, or DNA. Thus, the cell nucleus contains the cell’s genetic material, which dictates the cell’s composition and activities. For this reason, the nucleus is sometimes called the control center of the cell. The cell nucleus is separated from the rest of the soma by a porous membrane, which allows certain proteins and genetic material to pass through.

Still inside the soma, or cell body, but outside of the nucleus, we find the rough and smooth endoplasmic reticula. The rough endoplasmic reticulum is responsible for synthesizing proteins, while the smooth endoplasmic reticulum produces steroid hormones in addition to manufacturing and metabolizing lipids. The smooth endoplasmic reticulum also helps to remove toxins from the cells.

The space within the soma is filled with a gelatinous substance known as the cytoplasm, which is primarily comprised of water. Vesicles are one organelle that transport materials through the cell’s cytoplasm. The cytoplasm contains a number of other organelles, or little organs, which are critical to the cell’s functioning.

Mitochondria are another type of organelle found within the cytoplasm. Mitochondria are sometimes called the powerhouse of the cell, as they are responsible for manufacturing adenosine triphosphate, also called ATP. As we will find out in the video on signaling between neurons, ATP is critical to cell functioning, and the transmission of neural messages.

Other organelles that are generally found within the cytoplasm of animal cells include vacuoles, lysosomes, centrosomes, and the Golgi apparatus. Vacuoles are responsible for a range of potential functions including containing and removing cell waste, containing water, regulating the PH of the cell, and other potential functions depending on the cell type. Lysosomes contain enzymes, which digest a range of biomolecules. Lysosomes are also involved in functions such as cell repair and metabolism. Centrosomes are involved in cell reproduction. The Golgi apparatus is responsible for collecting, packaging, and dispatching proteins from the endoplasmic reticula, so that they can be used throughout the cell. For this reason, Golgi are sometimes called the cell’s post office.

Now that we have learned about the soma, or cell body, let’s look at some of the other parts of nerve cells. Dendrites are branch like structures that grow on neurons, that are responsible for receiving communications, in the form of neurotransmitters, from other neurons. Depending on the type of neuron, dendrites might be found growing around the soma, or on the end of an axon. The most common type of neuron found in the central nervous system is called a multipolar neuron. Multipolar neurons have dendrites growing out of the membrane of the soma, or cell body.

Dendrites are responsible for receiving messages and a part of the neuron called the terminal buttons are responsible for sending messages. When terminal buttons receive a signal, called an action potential, they release special chemicals called neuro transmitters. Neurotransmitters can either excite or inhibit neighboring cells, and are therefore responsible for communication between neurons. We will talk about neurotransmitters in an upcoming video, which will cover signaling between neurons.

Terminal buttons are connected to the soma by a shaft, called the axon. The place where the axon connects to the soma is called the axon hillock. Axons can be several feet long, depending on the type of neuron. The axon is wrapped in a protective sheath that speeds up signal transmission, while isolating the axon from neighboring neurons. This sheath is called the myelin sheath. For cells in the central nervous system, the myelin sheath is manufactured by a special type of cell, called an oligodendrocyte. The myelin sheath does not cover the whole axon, rather it consists of segments that are about a millimeter long, that are separated by small gaps. These gaps are called the nodes of Ranvier. Myelin sheaths on cells in the peripheral nervous system are manufactured by different cells called Schwann cells.
The oligodendrocytes that manufacture the myelin sheaths in the central nervous system are a special type of cell, called a glial cell. There are several different types of glial cells, and they are responsible for removing dead neurons, providing neurons with nutrients and chemicals that they need to function, and holding neurons in place.

Now that you are familiar with the parts of a neuron, including the soma or cell body, the dendrites that receive messages from the terminal buttons neighboring neurons, the axon, which can be several feet long, and the terminal buttons, which send signals to the dendrites of neighboring neurons using neurotransmitters, you are ready to check out the next video, which covers how neurons send signals within themselves.