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Episode 17: Nervous Tissue
In Episode 17 of the Anatomy and Physiology on the Go podcast, host Gilda Harris explores the intricacies of nervous tissue, concluding a four-part series on human tissues. This episode delves into th...
Episode 17: Nervous Tissue
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Hello and welcome to the next episode of the Anatomy and Physiology on the Go podcast.
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The podcast intended to provide you with brief, important big picture ideas and concepts
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in the realm of human anatomy and physiology. I am your host, Gilda Harris, and I'm a professor
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at St. Philip's College in San Antonio, Texas. If you liked this episode, please be sure to
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subscribe to this podcast so that you're made aware of all the newest content that I create.
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Without further ado, let's get on to the next episode. Today's episode of the Anatomy
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and Physiology on the Go podcast will conclude a four-part series on tissues. Please recall that
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way back in episode one, I discussed that tissues are a collection of cells, tissues are a collection
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of similar specialized cells and cell products that perform a specific function. The study of tissues
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is called histology, the four types of tissues are epithelial, connective, muscle, and nervous.
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The content of this episode will cover nervous tissue. Nervous tissue is found in the brain,
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spinal cord, and nerves. Nervous system of the body is divided into two parts, central nervous system
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and the peripheral nervous system. The central nervous system consists of the brain and spinal
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cord which are both located centrally in your body. The peripheral nervous system consists of
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the branching peripheral nerves. Nervous tissue is responsible for coordinating and controlling
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many body activities through its ability to carry electrical signal from one part of the body
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to another. Nervous tissues stimulate muscle contractions, create an awareness of the environment,
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plays a major role in emotions, memory, and reasoning. There are two types of cells in the
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nervous tissues. Nurons and neuroglia cells. Nurons are the major cell of the nervous tissue
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while the neuroglia cells are supporting cells which provide nutrients and support to the neurons.
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We will now direct our focus on the neuron before moving to a brief discussion on the various
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types of neuroglia cells. We will have a much more in-depth conversation about nervous system in
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the future but for now let's learn the cells of the nervous system. Nurons are cells specialized
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in communication. They receive the information at the one end of the cell and transmit the signal
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through action potential to the next cell. Nurons are made up of three major parts,
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dendrites, the cell body, and the axon. The cell body is the large main portion of the neuron
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that contains the nucleus, nucleolus, and organelles of the cell. The cell body may also be called
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the soma, as soma is the Greek word for body. Multiple dendrites branch off the cell body as does
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the long axon. Dendrites are thin, branching proto-plasma projections from the cell body that function
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to receive messages. Their branching nature allows them to have a large surface area in which to
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receive the message from an upstream neuron. The dendrites then pass the message to the cell body
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for processing. The axon is also a proto-plasma projection from the cell body but is usually singular
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in nature and is both longer and thicker than the dendrites. The axon may be wrapped in an insulating
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layer called myelin sheet, which aids in speeding up the signal as it goes down a lengthy axon.
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The initial portion of the axon where transitions from the cell body to axon is called axon
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hilon. The end of the axon has several branching portions called telodendria. These telodendria end
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with an axon terminal which stores neurotransmitters, in vesicles, which carry the message across the
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synaptic cleft to the next cell. The longest axon in the human body are known in the sciatic nerves,
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which run from the base of the spinal cord to the big toe of each foot. In general, dendrites
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receive a message and transmit it to the cell body. The cell body then processes this message
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and sends it down the axon so it can be shared with the next cell. The next cell may be another neuron
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or muscle cell or a gland depending on the message. Think of it like this. Let's say you touch a hot
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stove with one of your fingers. Your fingers receives that message of the heat. The message goes to
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your palm for processing and then the message travels up your thick long forearm to the next recipient.
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In this example, your fingers are the dendrites, thin short recipients of the message. Your palm
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is the large cell body with the nucleus and organelles. Finally, the message transmits up your forearm
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or axon to continue going. That is the neuron. Let's change our focus to their supporting cells,
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the neuroglia cells. The neuroglia cell makes up more than half of the volume of the nervous
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tissue. They maintain homeostasis. They help form myelin. They provide support and protection
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of the neurons. There are four types of neuroglia cell in the central nervous system and two in
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the peripheral nervous system. The central nervous system consists of the brain and spinal cord.
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The four neuroglia cells of the central nervous system are the oligodendrocytes, the astrocytes,
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ependomal cells and microglia cells. Oligodendrocytes are the cells that coat the axon
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with their cell membrane to form a specialized layer called myelin, which insulates the axon and
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allows electrical signal to pass more rapidly down the axon. Without myelin, the signal travels
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significantly slower. Astrocytes are the most abundant neuroglia cells. They are star shaped,
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provide physical structure to the brain, provide glucose to the brain during times of increased
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demand and help maintain a blood brain barrier. The blood brain barrier acts effectively to protect
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the brain tissue from pathogens and other potentially toxic substances circulating in the blood.
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Ependomal cells line the spinal cord and ventricles of the brain. These cells are involved in
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the secretion and circulation of the cerebral spinal fluid. Cerebrospinal fluid also known as CSF
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functions as a shock absorber and provides nutrients. We will talk more about this in the future,
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but just know that ependomal cells are responsible for CSF production in the central nervous system.
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Microglia cells are the final CNS neuroglia cell. These are the immune cells of the central nervous
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system as they constantly patrol the cerebral microenvironment to respond to pathogens and damage.
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Those are the four types of neuroglia cells in the central nervous system. There are two
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neuroglia cells of the peripheral nervous system. As mentioned previously, the peripheral nervous system
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includes all of the peripheral nerves of the body. These two neuroglia cells of the peripheral
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nervous systems are the shwan cells and the satellite cells. Shwan cells are the primary neuroglia
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cells of the peripheral nervous system. Shwan cells wrap around the axon of the peripheral
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nerves to provide a mileage sheet to speed up conduction. In this way, shwan cells are similar to
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the oligodendrocytes of the central nervous system. Shwan cells are also involved in the maintenance
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of axons in our crucial for neural survival. If the axon of a peripheral nerve is damaged,
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the shwan cell can aid in digesting the damaged material and guide the formation of new
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axonal growth. Nerve cells of the central nervous system are unable to regenerate after injury,
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while nerve cells of the peripheral nervous system can regenerate. The current theory is that
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the shwan cell or one of the reasons why the peripheral nerves can repair. The last neuroglia
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cell is the satellite cells. Satellite cells are not well understood. They surround some cells of
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the peripheral nervous system. They are thought to provide nutritional support and protection.
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They may be analogous to the astrocytes of the central nervous system, but more research needs
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to be conducted to know for certain what these cells do. That's it for nervous tissue. We will
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spend a lot more time in the future discussing the brain, the spinal cord, action potentials,
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and nerves. But for now, this should serve as a good introduction to some of the key players
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in the nervous system. As always, please subscribe, comment, and share these episodes so that they
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continue being produced.