Textbook Notes (367,974)
Canada (161,538)
Neuroscience (289)
NROB60H3 (151)
Chapter 2

CHAPTER 2 – Neurons and Glia.docx

11 Pages
75 Views
Unlock Document

Department
Neuroscience
Course
NROB60H3
Professor
Diane Mangalindan
Semester
Fall

Description
CHAPTER 2 – Neurons and Glia  Neurons are the most important cells for the unique functions of the brain  It is the neurons that sense changes in the environment, communicate these changes to other neurons, and command the body’s responses to these sensations  Glia/ glial cells are thought to contribute to rain function mainly by insulating, supporting, and nourishing neiboring neurons The Neuron Doctrine  Neurons are 40-200 times smaller than most cells which range of 0.01- 0.05 mm in diameter  Progress in cellular neuroscience was not possible before the development of the compound microscope in the late seventeenth century  Brain tissue has a consistency of jello – thus, the study of the anatomy of brain cells had to await the development of a method to harden the tissue without disturbing its structure and an instrument that can product very thin slices th  Early in the 19 century scientists discovered how to fix tissues by immersing them in formaldehyde and developed a special device called a microtome to make very thin slices  These technical advances spawned the field of histology – the microscopic study of the structure of tissues  The final breakthrough in neurohistology was the introduction of stains that could selectively color some parts of the cells in brain tissue  Franz Nissl showed that a class of basic dyes would stain the nuclei of all cells and also stain clumps of material surrounding the nuclei of neurons  Clumps are called nissl bodies and the stain is known as the nissl stain  Nissl stain distinguishes neurons and glia from one another and enables histologists to study the arrangement or cytoarchitecture of neurons in different parts of the brain  The study of cytoarchitecture led to the realization that the brain consists of many specialized regions (each which performs a different function) The Golgi Stain  Camillo golgi discovered that by soaking brain tissue in silver chromate solution (now called golgi stain) a small percentage of neurons became darkly colored in their entirety  This revealed that the neuronal cell body that is shown with the nissl stain, is actually only a small fraction of the total structure of the neuron  The golgi stain shows that neurons have at least two distinguishable parts: a central region that contains the cell nucleus, and numerous thin tubes that radiate away from the central region  The region that contains the cell nucleus has several names : cell body, soma, perikaryon  The thin tubes that radiate away from the soma are called neurites and the two types are axons and dendrites  Cell body usually gives rise to a single axon which is uniform diameter throughout its length and has branches that extend at right angles  It was recognized by the histologists of the day that axons must act like ‘wires’ that carry the output of the neurons  Dendrites rarely extend more than 2mm in length  Histologists recognized that because dendrites come in contact with many axons, they must act as the antennae of the neuron to receive incoming signal Cajal’s Contribution  Santiago Ramon y Cajal used the golgi stain to work out the circuitry of many regions of the brain – although they both had two different views  Golgi championed the view that the neurites of different cells are fused together to form a continuous reticulum/network  Cajal argued that the neurites of different neurons are not continuous with one another and must communicate by contact, not continuity  The idea that the neuron adhered to the cell theory is known as the neuron doctrine  With the rise of the electron microscope, it was finally possible to show that the neurites of different neurons are not continuous with one another The Prototypical Neuron  The inside of the neuron is separated from the outside by the limiting skin, the neuronal membrane, which gives each part of the cell its special 3D appearance The Soma  The cell body of the typical neuron is about 20 micrometer in diameter  The watery fluid inside the cell (cytosol) is a salty, potassium-rich solution that is separated from the outside by the neuronal membrane  Within the soma are a # of membrane-enclosed structures called organelles  Cell body of the neuron contains the same organelles that are found in animal cells  The most important ones are the nucleus, the rough ER, the smoothe ER, the golgi, and the mitochondria 1. The Nucleus  Spherical, centrally located, about 5-10 micrometers across  Contained within a double membrane called nuclear envelope  Within it are chromosomes, which contain the genetic material, DNA  The DNA in each of your neurons is the same which is the same as the DNA in your liver  What distinguishes a neuron from a liver cell are the specific parts of the DNA that are used to assemble the cell which are segments of DNA called genes  Each chromosome contains an uninterrupted double-stranded brain of DNA (2nm wide)  The reading of the DNA is known as gene expression  The final product of gene expression is the synthesis of molecules called proteins  Protein synthesis – the assembly of protein moleculesm occurs in the cytoplasm (but DNA never leaves the nucleus)  Therefore, there is an intermediary that carries the genetic message to the sites of protein synthesis in the cytosol  This function is performed by mRNA  Process of assembling a piece of mRNA that contains the info of a gene is called transcription  Protein coding genes are flanked by stretches of DNA that are not used to encode proteins but are important for regulating transcription  At one end of the genes is the promoter – the regions where the RNAP binds to initiate transcription  Binding of RNAP to promoters is regulated by other proteins called transcription factors  At the other end is a sequence of DNA called the terminator that the RNAP recognizes as the end point for transcription  Introns – additional stretches od DNA within gene that cannot be used to code for protein  Coding sequences are called exons  Initial transcript has introns and exons but then by a process called RNA splicing, the introns are removed and the exons are fused  Sometimes, specific exons are also removed with introns – alternative splicing  This way, a single gene can ultimately give rise to several different mRNAs and polypeptides  Building blocks of proteins are amino acids (20 different kinds)  Assembling of proteins from amino acids under direction of mRNA = translation  Central dogma = DNA  mRNA  Protein (beings with DNA of the nucleus and ends with the synthesis of protein molecules)  Molecular neurobiology = information contained in the genes is used to determine the structure and functions of neuronal proteins 2. Rough ER  Enclosed stacks of membrane dotted with dense globular structures called ribosomes (25nm in diameter)  Rough ER abounds neurons far more than glia or most other non- neuronal cells  rough ER is known as another name : Nissl bodies (organelle stained with dyes  rought ER is a major site of protein synthesis in neurons  RNA transcripts bind to ribosomes on ER  Ribosomes take raw material in the form of amino acids and manufacture proteins using the blueprint provided by the mRNA  Many ribosomes are freely floating and are called free ribosomes  Several ribosomes may appear to be attached to a single strand of mRNA (polyribosomes), and the associated ribosomes are working on it to make multiple copies of the same protein 3. Smooth ER and Golgi Apparatus  Remainder of cytosol of the soma is crowded with stacks of membranous organelles (smooth ER)  Smooth ER is continuous with rough ER  Golgi = stack of membrane-enclosed disks in the soma that lies farthest from the nucleus  it is the site of extensive ‘post-translational’ chemical processing of proteins  one important function of golgi is the sorting of certain proteins that are destined for delivery to different parts of the neuron, such as the axon and dendrites 4. Mitochondrion  In neurons, these sausage shaped strucutres measure about 1 micrometer in length  Withint he enclosure of their outer membrane are multiple folds of inner membrane called cristae  Between cristae is an inner space called matrix  Mitochondria is site of cellular respiration  within the inner compartment of mitochondrion, pyruvic acid enters krebs cycle  biochemical products of the krebs cycle provide energy that, in another series of reactions within the cristae (ETC) results in the addition of phosphate to ADP = ATP (cells energy source)  17 ATP molecules are released for every molecule of pyruvic acid  chemical energy in ATP is used to fuel biochemical rxns of neuron The Neuronal Membrane  the neuronal membrane serves as a barrier to enclose the cytoplasm inside the neuron and to exclude certain substances that float in the fluid that bathes the neuron  an important characteristic of neurons is that the protein composition of the membrane varies depending on whether it is in the soma, the dendrites or the axon  the function of neurons cannot be understood without understanding the structure and function of the membrane and its associated proteins The Cytoskeleton  gives the neuron its characteristic shape  bones of the cytoskeleton are microtubules, microfilaments and neurofilaments 1. Microtubules  20nm in diameter  big and run longitudinally down neurites  appears as straight, thick-walled hollow pipe  wall of the pipe is composed of smaller strands and each of those strands consist of the protein tubulin  a strand consists of tubulins stuck together like pearls on a string  process of joining small proteins to form a long strand is called polymerization and a resulting strand is polymer  polymerization and depolymerization of MTs and therefore of neuronal shape can be regulated by various signals within the neuron  microtubule-associated protein (MAPs) participate in the regulation of MT assembly and function  MAPs anchor the MT to one another and to other parts of the neuron ALZHEIMER’S DISEASE AND THE NEURONAL CYTOSKELETON  Neurites elaborate branching patterns, critical for info processing, reflect the organization of the underlying cytoskeleton  Devastating loss of brain function can result when the cytoskeleton of neurons is disrupted  Alzheimers disease is characterized by the disruption of the cytoskeleton of neurons in the cerebral cortex, a region of the brain crucial for cognitive function  One of the first disease symptoms was a strong feeling of jealousy towards her husband  Soon she showed rapidly increasing memory impairments  Following her death, changes in the neurofibrils elements of the cytoskeleton that are stained by silver solution were noted  The bielschowsky silver preparation showed very characteristic changes in the neurofibrils  Inside an apparently normal-looking cell, one or more single fibers could be observed that became prominent through their striking thickness and specific impregnability  At a more advanced stage, many fibrils arranged parallel showed the same changes and then accumulated forming dense bundles and gradually advanced to the surface of the cell  Eventually, the nucleus and cytoplasm disappeared and only a tangled bundled of fibrils indicated the site where once the neuron had been located  As these fibrils can be stained with dyes different from the normal neurofibrils, a chemical transformation of the fibril substance must have taken place  This might
More Less

Related notes for NROB60H3

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit