Cells of the Nervous System. Physiological Psychology PSYC370 Thomas E. Van Cantfort, Ph.D. Cells of the Nervous System. Cells.

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1 Physiological Psychology PSYC370 Thomas E. Van Cantfort, Ph.D. Cells of the Nervous System Cells of the Nervous System Physiological psychology, as a science, is driven by an intense human need to understand the origins of mind and behavior. ÚWhat are emotions ÚMotives ÚMemories Why do we ÚSleep ÚExperience pain ÚSee colors How can people lose the capacity to ÚSpeak ÚMove ÚComprehend what they see What has gone wrong in those suffering from depression or schizophrenia?l Cells As we search for the answers to those questions by examining the function of the brain We discover repeatedly that much of the understanding can be found only within the working of that basic unit of life, the cell. Animals and plants are made up of various organs, ÚEach designed to perform vital service to the whole animal. < Heart < Lungs < Muscles < Blood vessels < Brain < Are all examples of organsl Cells (continued) Because the complete animal is essentially a collection of organs, it is called an organism. If we analyze the organs into the building blocks from which they are formed, we find that the basic unit is the cell. ÚCells with similar functions combine into groups called tissues, ÚSeveral types of tissue organized to do a particular job make up an organ. To understand how an organ works then, one must examine its cells.l Structure of a Cell Your body contains hundreds of different types of cells with different shapes and functions Cells are as different in their appearance and behaviors as different breeds of dogs Yet all human cells do have certain basic features and tasks in common. We shall start by examining a proto-typical cell from which we can glean the most general principles of cellular organization.l Because the inside of a cell is filled with fluid you might expect the cell to have a thick, protective skin. Amazingly, the cell membrane is only two molecule thick ÚWith little or no structural rigidity. ÚEssentially, it is two layers of phospholipid. ÚFloating in the membrane are a variety of protein molecules that have special functions. < Some detect substance outside the cell (such as hormone) and pass information about the presence of these substances to the interior of the cell. < Others control access to the interior of the cell, permitting some substances to enter and barring others. < Still others act as pumps, actively pushing certain molecules out of the cells and pulling them in.l

2 The Nucleus The nucleus of a cell is analogous to the brain of an organ; ÚIt is the control center ÚIssuing orders about all the various cellular functions Control is exerted by allowing particular chemical reactions to proceed and disallowing others. The instruction for what reactions to allow are coded into immensely long molecules of the chemical deoxyribonucleic acid (DNA) ÚA form of nucleic acid ÚThis DNA is stored in a web-work of strands within the nucleus called chromatin. ÚDNA molecules consist of long strands of smaller units called genes, ÚEach gene contains the plans for manufacturing a particular type of protein.l ÚTo initiate the manufacture of a needed protein, DNA creates another kind of molecule, ribonucleic acid (RNA). ÚDNA itself never leaves its station inside the nucleus. RNA first goes to the nucleolus, a special area of the nucleus in which the messenger ribonucleic acid mrna is combined with proteins to form tiny structure called ribosomes. Ú The mrna leave the nucleus through the many pores that puncture the membrane, separating the nucleus from the cytoplasm and attaches to ribosomes, where it causes the production of a particular protein. ÚProtein formation is vital to our understanding of learning, memory, and hormone function. Proteins are important in cell functions. ÚAs well as providing structure ÚProteins serve as enzymesl Enzymes Which direct the chemical processes of a cell by controlling chemical reactions. Enzymes are special protein molecules that act as catalysts; ÚThey cause a chemical reaction to take place without becoming a part of the final product themselves. ÚThere are enzymes that break molecules apart ÚThere are enzymes that join molecules together Enzymes in a particular region of a cell thus determine which molecules remain intact ÚAnabolic reactions join molecules together ÚCatabolic reactions break molecules apartl Organelles Surrounding the nucleus and enclosed by the cell membrane is a fluid called cytoplasm. ÚScattered throughout the cytoplasm are a variety of structures such as: ÚEndoplasmic reticulum ÚMitochondria ÚGogi apparatus ÚFilaments ÚMicrotubules < Mitochondria, endoplasmic reticulum and the Gogi apparatus can be thought of as microscopic organs of the cell < And so are called organelles.l Endoplasmic reticulum Endoplasmic reticulum comes in two varieties ÚRough ÚSmooth ÚBoth types consist of folded layers of membrane identical with the membrane that encloses the cell. ÚThe rough endoplasmic reticulum is the site of protein formation. ÚThe reticulum is the destination of the ribosomes that emerge from the nucleus of the cell with their cargo of mrna specification for the construction of new molecules. Rough endoplasmic reticulum will be involved with the production of substances secreted from the cell. ÚFor example, insulin is manufactured in certain cells of the pancreas.l The smooth endoplasmic reticulum is concerned with the transport of substance around the cytoplasm And provides channels for the secretion of various molecules involved in different cellular processes. Golgi Apparatus (complex) Another cell organelle is the Golgi apparatus and it is a special form of endoplasmic reticulum. ÚIt serves primarily as a wrapping or packaging agent. ÚThe Golgi apparatus also produces lysosomes < Small sacs that contain enzymes that break down substances no longer needed by the cell. < These products are then! Recycled! Or excreted from the cell.l

3 Mitochondria Mitochondria (singular: mitochondrion) are shaped like oval beads and formed of a double membrane. ÚThe inner membrane is wrinkled ÚThe wrinkles make up a set of shelves (called cristae) that fill the inside of the bead. < Mitochondria perform a vital role in the economy of the cell < Many of the biochemical steps involved in the extraction of energy from the breakdown of nutrients take place on the cristae.! The mitochondria provide the cell with a special molecule! Adenosine triphosphate (ATP) that is used as its immediate source of energy.! Adenosine diphosphate (ADP) and adenosine monophosphate (AMP)L Filaments Two structural elements make up the cytoskeleton: ÚArranged throughout the cell are microfilaments and microtubules. < Microfilaments are made of the same type of long proteins fibers that provide the motive force in muscles. < They are found under the membrane and give the cells their particular shape. < They probably also control the movement of proteins that are embedded in the membrane. ÚMicrotubules are larger than microfilaments and consist of bundles of filaments arranged around a hollow core. < They transport substances from place to place. < When molecules must be transported over relatively long distances within the cell they are piped through microtubules.l The Cell Structures of Neurons Neurons come in many shapes and varieties According to the specialized jobs they perform. They usually have, in one form or another, the following four structures or regions: ÚCell body or soma ÚDendrites ÚAxons ÚAnd terminal buttons (axon terminal, butons, synaptic knobs) Soma the soma (cell body) contains the nucleus and much of the machinery that provides for the life processes of the cell.l Structures of Neurons (continued) Dendrites Dendron is the Greek word for tree, and the dendrites of the neuron look very much like trees. ÚNeurons converse with one another ÚAnd dendrites serve as important recipients of these messages. Axon the dendritic and somatic membranes receiving messages from other cells in some cases from hundreds of other cells. ÚThese messages affect the activity of the neuron ÚWhich as a result may or may not transmit messages down it axon to other cells ÚThe axon is a long, slender tube < It carries information away from the cell body to the terminal buttons. < The message is electrical.l Structures of Neurons (continued) ÚMost axons divide and branch many times < These branches are called telodendria (singular: telodendron) At the end of the twigs are found little knobs called terminal buttons (axon terminal, butons, synaptic knobs) ÚWhich have a very special function: when a message is passed down the axon ÚThe terminal buttons of the transmitting cell secrete a chemical called neurotransmitters. ÚThe terminal buttons transfers information to: < Other neurons < Muscle cells < Or gland cellsl

4 Structures of Neurons (continued) Three Principle Types of Neurons 1) Bipolar neurons ÚBipolar neurons give rise to one axon and one dendritic tree, at opposite ends of the soma. ÚThese neurons are usually sensory; that is they convey information from the environment to the central nervous system. 2) Unipolar neurons ÚUnipolar neurons has only one stalk that leaves the some and divides into two branches a short distance away. < One branch is the axon < The other branch is the dendritic end ÚUnipolar neurons, like the bipolar neurons, transmit information from the environment to the CNSL Three Principle Types of Neurons (continued) Three Principle Types of Neurons (continued) 3) Multipolar neurons ÚMultipolar neurons are the most common type found in the central nervous system.l A) is a bipolar neuron B) is a unipolar neuronl Support Cells Neurons constitute only about half the volume of the CNS The rest consists of a variety of support cells. Because neurons have a very high rate of metabolism but have no means of storing nutrients, They must constantly be supplied with nutrients and oxygen or they will quickly die. Unlike most other cells of the body, neurons cannot be replaced when they die. We are born with as many as will ever have. Thus, the role played by the cells that support and protect neurons is very important to our existence.l Neuroglia Cells The most important supporting cells of the CNS are the neuroglia, or nerve glue. Glia (also called glial cells) do indeed glue the CNS together, but they do much more than that. ÚGlial cells surround neurons and hold them in place < Controlling their supply of some of the chemicals they need to exchange messages with other neurons < They insulate neurons from one another so that neural messages do not get scrambled < They even act as housekeepers, destroying and removing the carcasses of neurons that are killed! By injury! Or that die as a result of old agel

5 Neuroglia Cells (continued) Astrocyte There are several types of glial cells, each of which play a special role in the central nervous system. ÚAstrocyte means star cell, and this name is accurately describes the shape of these cells. < Astrocytes (or astroglia) are rather large, as glia go, and provide physical support to neurons. < They also clean up debris within the brain < And chemically buffer the fluid surrounding the neuron.l Microglia Microglia ÚNeurons occasionally die for unknown reasons or are killed by head injury, infection, or stoke. ÚMicroglia then take up the task of cleaning away the debris. < These cells are able to travel around the CNS < When they contact a piece of debris from a dead neuron, the push themselves against it, finally engulfing and digesting it. < We call this process phagocytosis (phagen, to eat ; kutos, cell ).L Oligodendroglia (continued) ÚOligodendroglia are residents of the CNS, and their principal function is to provide support to the axons and to produce the myelin sheath, which insulates most axons from one another. ÚIn the CNS the oligodendroglia support axons and produce meylin. < Myelin, 80% percent lipid and 20% protein, is produced by the oligodendroglia in the form of a tube surrounding the axon. < This tube does not form a continuous sheath; rather, it consists of a series of segments Each segment is approximately 1 mm long, with a small (1-2 :m) portion of uncoated axon between segments < This bare portion of axon is called a node of ranvierl Oligodendroglia

6 Schwann Cells (continued) ÚIn the peripheral nervous system (PNS) the Schwann Cells perform the same function. ÚSchwann cells differ from their CNS counterparts, the oligodendroglia, in an important way. < If damage occurs to a peripheral nerve the Schwann cells aid in the digestion of the dead and dying axons. < The the Schwann cell arrange themselves in a series of cylinders that act as guide for regrowth of the axons. < The distal portions of the servered axons die, but the stump of each servered axon grows sprouts, which then spread in all direction.l Schwann Cells (continued) < If one of these sprouts encounters a cylinder provided by a Schwann cell, the sprout will quickly grow through the tube while the other, nonproductive sprouts wither away. < If the cut ends of the nerve are still located close enough to each other, the axons will reestablish connections with the muscles and sense organs they previously served. ÚUnfortunately, the glial cells of the CNS are not so cooperative as the supporting cells of the PNS. < If axons in the brain or spinal cord are damaged, new sprouts will form, as in the PNS. However, the budding axons encounter scare tissue produced by the astrocytes < And they cannot penetrate this barrier.l Oligodendroglia & Schwann Cells M