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Physiological Psychology
PSYC
Thomas E. Van Cantfort, Ph.D.
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. Ú (^) What are emotions Ú Motives Ú (^) Memories ‚ (^) Why do we Ú Sleep Ú Experience pain Ú (^) See colors ‚ (^) How can people lose the capacity to Ú Speak Ú (^) Move Ú (^) Comprehend what they see ‚ What has gone wrong in those suffering from depression or schizophrenia?L
Cells of the Nervous System
‚ (^) 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 , Ú (^) Each designed to perform vital service to the whole animal.
< Heart
< Lungs
< Muscles
< Blood vessels
< Brain
< Are all examples of organsL
Cells
‚ 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. Ú (^) Cells with similar functions combine into groups called tissues , Ú (^) Several 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
Cells (continued)
‚ (^) 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
Structure of a Cell
‚ 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 Ú (^) With little or no structural rigidity. Ú (^) Essentially, it is two layers of phospholipid. Ú Floating 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
‚ The nucleus of a cell is analogous to the brain of an organ; Ú (^) It is the control center Ú (^) Issuing 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) Ú A form of nucleic acid Ú (^) This DNA is stored in a web-work of strands within the nucleus called chromatin. Ú (^) DNA molecules consist of long strands of smaller units called genes , Ú (^) Each gene contains the plans for manufacturing a particular type of protein.L
The Nucleus (^) Ú (^) To initiate the manufacture of a needed protein, DNA creates another kind of molecule, ribonucleic acid (RNA). Ú (^) DNA 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. Ú Protein formation is vital to our understanding of learning, memory, and hormone function. ‚ (^) Proteins are important in cell functions. Ú (^) As well as providing structure Ú (^) Proteins serve as enzymes L
‚ (^) Which direct the chemical processes of a cell by controlling chemical reactions.
‚ (^) Enzymes are special protein molecules that act as catalysts ; Ú (^) They cause a chemical reaction to take place without becoming a part of the final product themselves. Ú (^) There are enzymes that break molecules apart Ú There are enzymes that join molecules together
‚ (^) Enzymes in a particular region of a cell thus determine which molecules remain intact Ú (^) Anabolic reactions join molecules together Ú Catabolic reactions break molecules apartL
Enzymes
‚ (^) Surrounding the nucleus and enclosed by the cell membrane is a fluid called cytoplasm. Ú (^) Scattered throughout the cytoplasm are a variety of structures such as: Ú (^) Endoplasmic reticulum Ú Mitochondria Ú (^) Gogi apparatus Ú (^) Filaments Ú (^) Microtubules
< Mitochondria, endoplasmic reticulum and the Gogi
apparatus can be thought of as microscopic organs of the cell
< And so are called^ organelles .L
Organelles
‚ (^) Endoplasmic reticulum comes in two varieties Ú Rough Ú (^) Smooth Ú (^) Both types consist of folded layers of membrane identical with the membrane that encloses the cell. Ú (^) The rough endoplasmic reticulum is the site of protein formation. Ú The 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. Ú (^) For example, insulin is manufactured in certain cells of the pancreas .L
Endoplasmic reticulum
‚ (^) 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. Ú (^) It serves primarily as a wrapping or packaging agent. Ú (^) The 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
Structures of Neurons (continued)
‚ 1) Bipolar neurons Ú (^) Bipolar neurons give rise to one axon and one dendritic tree, at opposite ends of the soma. Ú (^) These neurons are usually sensory; that is they convey information from the environment to the central nervous system. ‚ 2) Unipolar neurons Ú (^) Unipolar 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
Ú (^) Unipolar neurons, like the bipolar neurons, transmit information from the environment to the CNSL
Three Principle Types of Neurons
‚ 3) Multipolar neurons Ú (^) Multipolar neurons are the most common type found in the central nervous system.L
Three Principle Types of Neurons (continued)
Three Principle Types of Neurons (continued)
‚ A) is a bipolar neuron ‚ (^) B) is a unipolar neuronL
‚ (^) 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
Support 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. Ú (^) Glial 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
Neuroglia Cells
‚ There are several types of glial cells, each of which play a special role in the central nervous system. Ú Astrocyte 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
Neuroglia Cells (continued) Astrocyte
Ú (^) Neurons occasionally die for unknown reasons or are killed by head injury, infection, or stoke. Ú (^) Microglia 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
Microglia Microglia
Ú (^) Oligodendroglia 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. Ú (^) In 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
ranvier L
Oligodendroglia (continued) Oligodendroglia
