Introductory Neurobiology Week 1
Introductory Neurobiology Week 1 Biol 3640
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This 11 page Class Notes was uploaded by lucy allen on Wednesday January 6, 2016. The Class Notes belongs to Biol 3640 at University of Denver taught by Dr. John C Kinnamon in Fall 2016. Since its upload, it has received 31 views. For similar materials see Introductory Neurobiology in Biology at University of Denver.
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Date Created: 01/06/16
-each brain has about 10 12neurons -each neuron has about 1000-10,000 synapses -midterm exams: true/false; short answer; MC; short essay -final exam: all multiple choice History of Neuroscience Prehistoric Origins Neuroscience -there is evidence of prehistoric brain surgery in which the patient survived -700 years ago, skull is evidence -Trepanation: used to cure headaches/mental illness, make hole in the skull -allow evil spirits to leave the brain and cure the patient -"the extraction of the stone of madness" Greece and Rome -Hippocrates (Greece) -brain is responsible for not just sensations, but it is also the 'sea of our intellect' -contrasted with Aristotle -Aristotle (Greece) -believed that the heart was the center of the intellect, brain is a radiator for cooling blood heated up by the heart -Galen (Rome) -based on wounds on warriors heads, would speculate on what the functional significance was -where wound was, effect on functions, inferred functions of brain regions -learned about neuroanatomy by studying animal brains, some was wrong due to this -coined the term cerebrum (soft) and cerebellum (hard) -concluded that cerebrum is responsible for sensations and cerebellum is responsible for motor functions (based on density) -conclusions were right, logic was wrong -these ideas (although illogical) persisted for a thousand years Renaissance to the 19th Century -Andreas Vesalius -published De humani corporis fabrica: study on human anatomy -contradicted Galen's work, viciously attacked by peers due to this -Jacobus Sylvius: believed Vesalius was a madman -"i'd rather be wrong with Galen than right with this innovator" -fluid mechanical theory: Vesalius thought of the brain as a hydraulic pump, pushing fluid down neuro-fibers into the muscles allowing for contraction -Rene Descartes -De Homine -agreed with fluid mechanical theory -also agreed with mind-body duality -demonstrated reflexes -Franciscus Sylvius -neuroanatomist, dutchman, did dissections of human brains -MD, studied kidney problems, came up with a diuretic -mixing oil of juniper berry and grain alcohol (GIN!) -called it Genever Nineteenth Century -neuroscientists have broken away from Galen's teachings -observed white/gray matter in the brain -white matter: axons en route from one part of the brain to the other, white due to myelination surrounding axons -at end of 18th century, showed that brain injury can cause malfunctions of sensory functions, etc. -knew that the brain communicated with the body via nerves -people began to understand that different parts of the brain perform different functions -Luigi Galvani and Emil du Bois-Reymond -if you electrically stimulate a nerve, a muscle can twitch -first evidence of electrochemical nature of nerve function -Charles Bell and Francois Magendie -different nerve routes entering the spinal cord carry different information -dorsal route carries sensory information to the spinal cord/brain -ventral route carries motor information away from the spinal cord -Franz Joseph Gall -Phrenology: different parts of the skull have different bumps/shape due to shape of the brain within it -phrenologists could tell personality traits, etc. based on this -proved false -Paul Broca -Broca's area -his patient had aphasia (cannot speak, can only say 'tan') -after patient's death, Broca observed lesion in "Broca's area" -showed that a specific part of the brain has a specific function -end of 19th century controversy -Neuron doctrine vs. reticular theory -Neuron Doctrine -nervous system is composed of individual neurons, the structural units of the nervous system, these units are closely opposed to each other but there is a cleft separating them -something passes across this so that nerves can communicate with each other -Cajal -supporter of Neuron Doctrine -used Golgi Stain to confirm neuron doctrine -credited for using Golgi Stain most effectively -"Father of Modern Neuroscience" -Reticular Theory -nervous system is more like circulatory system, larger nerves branch to form smaller nerves, and sensory nerves are continuous with motor nerves supporter: -Camillo Golgi -supporter of Reticular Theory -coined with silver chromate stain ("Golgi Stain") -shared 1906 Nobel prize Neuroscience Today Approaches to Studying Neuroscience Molecular Neuroscience -behavior of individual molecules Cellular Neuroscience -behavior of individual cells Systems Neuroscience -like the visual or auditory system, looking at collections of neurons and how they function Behavioral Neuroscience -behavior in response to stimulation and environmental situations Cognitive Neuroscience -can observe individual neurons -next up is observation of nerve bundles (a few to thousands of axons) -next level we can record individual axons -extracellular recording: uses an insulated electrode -coat a pin with plastic, sharpen the tip, impale this into a crayfish brain -the tip of the electrode should fall adjacent to a cell body of a nerve fiber -record activity from that nerve -intracellular recording: take a sharpened glass micropipette -heat it up, make it very thin at the time -impale the neuron with this microelectrode, get an intracellular recording -patch-clamp recording: used today, take a glass microelectrode and fire polish the tip, diameter is a couple micrometers -touch it to the surface of a neuron and apply suction -take a patch of membrane with you, which may (usually does) contain ion channels, recording from individual ion channels (BIG DEAL) -Neher and Sakmann got the Nobel prize for this in 1990 Molecular Biological Approaches -Oocyte expression: can take the oocytes and express ion channels in the egg cells, and record from these ion channels -In situ hybridization : determine the presence of RNA in a cell, important to know for presence of a protein in the cell -Antibodies: use antibodies targeted to different proteins in different biochemical pathways -Knock-outs: knock-out a protein, see the effects on the nervous system Imaging the Nervous System -to associate structure and function Microscopy Fluorescence Microscopy -not great resolution, but can tag antibodies with fluorescent dyes and image proteins involved in specific biochemical pathways -resolution has been improved with new techniques/technology -super-resolution microscopy, almost as good as electron microscopy Electron Microscopy -best resolving power X-Ray CAT Scan (Computed Tomography) -uses a series of x-ray images -get an image of the brain, not great, ok detail -hard to get detail of soft tissue with x-rays PET/SPECT MRI/MRM (Magnetic Resonance Imaging) -better for soft tissue imaging fMRI (Functional Magnetic Resonance Imaging) -imaging of cells that are more metabolically active in the brain -E.B. Wilson- first American cell biologist -key to every biological problem is in the cell Neurons and Glia -two types of cells of the nervous system -neurons -neurons decrease every day, lose between 75,000 to 200,000 due to poor health habits -involved in processing and transmission of information -receive signals from other neurons and from sensory sources, integration of information allows for decision making based on the circumstances -whether or not to make an action potential -release of neurotransmitters, and in what volume -some inputs are excitatory, others are inhibitory -dependent on oxygen, not good at ATP storage, use oxidative phosphorylation -other parts of the body than the brain can recover from prolonged oxygen deprivation, brain lasts for four minutes -glia -ten times as many glia than neurons -provide support for neurons, provide the myelin sheaths for axons and signal conductivity/capacitance reduction -responsible for the BBB -wrap themselves around blood vessels -condition the environment surrounding neurons, adjusting ionic environment and sometimes even containing neurotransmitters absorbed by the neurons for use -do not actively participate in signal transmission -but membrane potentials have been observed to change -plasticity: can form new pathways between neurons despite loss of neurons -as you age you lose plasticity Neuron Doctrine -Schleiden & Schwann "The Cell Theory" -cell theory: all organisms consist of one or more cells -cell is the basic unit of life -all cells rise from preexisting cells -outgrowth of the cell theory is the neuron doctrine, neuron would be the basic unit of the nervous system -axons split into finer branches, continuous with the finest branches of the dendrites, analogous to the capillaries in the circulatory system -Neuron Doctrine vs. Reticular Theory -Golgi (1873) -pyramidal cells are visible when Golgi-stained in slide 9 -Ramon y Cajal (1891) -Cajal: FATHER OF MODERN NEUROSCIENCE -shared Nobel Prize with Golgi in 1906 to prove Neuron Doctrine, used Golgi's stain -His -embryological studies, noticed that individual cells appeared, not one general reticulum forming gradually through development -also supported the Neuron Doctrine -Forel -studied neural responses to injury, if one cell dies not all die, just damaged ones die -also supported the Neuron Doctrine -electron microscopy -JD Robertson: showed unit membrane and discrete nature of cells -De Robertis, Palay, Palade, Peters -studied the nervous system and demonstrated the presence of synapses, show that nerve cells are separated from each other by a cleft Structure of A Typical Neuron -cell body: (soma or perikaryon), contains the nucleus -radiating out from cell body are the neurites -neurite: generic term meaning process -there are different types, ex: axons or dendrites -defined by presence of the nucleus -contains most of biosynthetic machinery, synthesizes neurotransmitters -axon: specialized for conduction of electrical activity over long distances, up to a m -axons branch -cross sections through axons using different preparations -Luxol wash: red is connective tissue, blue is axon -EM: white is axon, black is the myelination -slide 19: can see individual microtubules and microfilaments in the axon -dendrite: portion of the neuron specialized for receiving information from other neurons -dendritic spines: where presynaptic axon connects to postsynaptic dendrite -passively spreads an electrical potential to the cell body and the site of initiation of an action potential -slide 22: membrane is recycled via Clathrin coated vesicles -synapse: site of functional contact between two neurons or a neuron and an effector organ (muscle, gland) -electrical synapse: offer the advantage of speed, no delay -basically gap junctions -pores, allow ions and small molecular weight substances to pass through -current carried by ions which pass through the gap junction -junctions are close together -cleft is 2-4 nanometers (smaller than chemical) -chemical synapse: can have a delay, but offer advantageous regulation and strength of the synapse (amount of signal released) -cleft is about 16-30 nanometers (later than electrical) -electron microscopy -take a chunk of tissue, imbed it in an epoxy plastic, take a slice of the tissue within the plastic, stain it with heavy metal and look at it via electron microscopy -see dense regions take up heavy metal, lighter places without it -freeze fracture: look at the surface of membranes rather than a slice through the tissue -put chunk of tissue on a copper plate and freeze it (liquid nitrogen, instant freeze) -take plate out and put it on a frozen block, tap it to fracture the cube containing the tissue -makes it possible to image the surfaces of the membranes -put it in a vacuum, some ice disappears exposing more membrane -put it in a carbon evaporator, depositing a layer of carbon on top of the exposed membrane -strengthens the 'replica' but does not make it electron dense -to make it electron dense you spray platinum at an angle, now we can see it with a microscope -last step: but it in bleach, digesting away the tissue, leaving the carbon-platinum replica, which can be used for imaging in electron microscopy -can be concave or convex membrane depending on where it cuts -"insies" and "outsies" -Take Home Message: with freeze fracture microscopy we can look at the membranes and proteins on the surfaces of cells Types of Synapses -chemical synapses -opposed membranes (close together), cleft 16-30 nanometers wide -presynaptic thickening and postsynaptic thickening, shows up on the electron microscope as electron dense 'fuzzy stuff' -asymmetric synapse: prominent postsynaptic thickening compared to presynaptic thickening -synaptic vesicles can be 'grabbed' by 'egg-carton' type membrane, visible on slide 35 -synaptic vesicles contain small, charged neurotransmitters (40-70 nanometer diameter) -others contain large dense cord vesicles (diameter 90- 120nm) -typically contain peptides Classification of Synapses -axodendritic synapse: buteon synapses onto the dendrite of the postsynaptic cell -axoaxonal synapse: from the axon of one synapse onto the axon of another synapse -modulates the activity of synapse, presynaptic inhibition from here -reciprocal dendrodendritic synapse: both dendrites, but pre/post synaptic -serial: cell A synapses onto cell B which synapses onto cell C -electrical synapse: gap junctions, pores connecting the two presynaptic and postsynaptic cell -can be one way or two way Organelles that Compose a Neuron -history -Danielli: discovered the phospholipid bilayer -JD Robertson: identified the unit membrane (8-10 nanometers) -Singer: fluid mosaic model (phospholipid bilayer, membrane proteins) -capacitance -Plasma Membrane -not symmetrical, lots of choline on outer leaflet, lots of Phosphatidylinositol (involved in I3 second messenger pathway) on inner leaflet -membrane proteins -peripheral: often have a carbohydrate segment sticking out, important for cell signaling, recognition and communication -intrinsic (integral): pass all the way through the membrane -provide sites for neurotransmitters to bind to -can be ion channels -ion exchange (Na+/K+ ATPase pump) -cytoplasmic/skeletal: help to connect the membrane to the cytoskeleton -important for cell shape and structure -Nucleus -neurons cannot undergo mitosis, not entirely true -in the Hippocampus neurons can undergo mitosis, in an adult nervous system -clinically depressed people will have a loss of neurons, antidepressants increase then number of neurons in the brain -also can exercise -controls protein synthesis, formation of neurotransmitters and other macromolecules in the cell -location of the nucleus defines where the cell body will be -dense regions in slide 46 shows nuclei -Ribosomes and the Rough Endoplasmic Reticulum -protein synthesis occurs in the Rough Endoplasmic Reticulum (contains ribosomes), smooth endoplasmic reticulum has no associated ribosomes -rough endoplasmic reticulum is continuous with the nuclear envelope -slide 49: in the cytoplasm are polyribosomes, clusters of ribosomes not associated with the rough endoplasmic reticulum -Secretion and the Golgi Complex -Golgi is responsible for packaging of products into membrane -packages neurotransmitters into synaptic vesicles -then transported down the axon to the synapse -has a cis and trans face -cis face is the side that receives the products from the endoplasmic reticulum, the final product is released at the trans face -Lysosomes -organelles which digest worn out organelles, food particles, or viruses/bacteria in some cells -have digestive enzymes, can digest the phagocytic vesicle containing the target for degradation -Mitochondria -mitochondria: Greek for bread and grains -powerhouse, site of oxidative phosphorylation, create ATP which is necessary for neuronal function -common to see accumulation of mitochondria in the presynaptic vesicles -it is believed that they continue to provide ATP for synaptic function -cytoskeleton -microtubules -about 20 nanometers in diameter, composed of tubulin molecules -'stiff rod', skeleton for the neuron -microfilaments -composed of actin molecules, about 5 nanometers in diameter -important for movement -for change of shape in process output -neurofilaments (intermediate filaments) -can be composed of many substances, typically 10 nanometers in diameter -twisted rope, high tensile strength but flexible Axoplasmic Transport -important for transporting molecules, neurotransmitters and other metabolites from the cell body to the axon terminal -microtubules are used as the 'railroad tracks', motor molecules (ex: Kinesin and dynein) -Kinesin: anterograde transport, meaning transport from the cell body to the axon terminal -retrograde transport, meaning transport from the axon terminal back to the cell body -both anterograde and retrograde transport can occur simultaneously -REQUIRES ENERGY IN THE FORM OF ATP Classification of Neurons -number of neurites -unipolar: single process coming out from axon -bipolar: has two processes coming out -multipolar: has more than two processes coming out -anaxonal: amacrine, -dendrites/dendritic tree structure -pyramidal cells: the cells you think with in your cerebral cortex -stellate cells -spiny -aspinous -connections -primary sensory neurons: receive information directly -motor neurons -interneurons: neither sensory nor motor -we do our thinking with these, responsible for cognition -axon hillock: where axon potential is initiated, has a high concentration of sodium gated calcium channels -axon length -Golgi Type I (projection neurons) -up to the brain, goes a long distance -Golgi Type II (local circuit neurons) -might be present in one or two segments of the spinal cord -neurotransmitter -uses serotonin: serotogenic cell, etc. based on neurotransmitter used Glia -glia: Greek for glue -neuroglia: nerve glue -provide electrical insulation and manipulate ionic environment -can store neurotransmitters and make them available for the neurons astrocytes: type of glia, shaped like a star (astro = star) -provides insulation for neurons, fills space, provides BBB Myelinating Glia -oligodendrocytes: found in the central nervous system -Schwann cells: found in the peripheral nervous system, like in motor neurons -Node of Ranvier -breaks in myelination, where action potentials are regenerated -not all cells are myelinated, unmyelinated neurons are typically shorter and slower
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