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BIBB109 lecture 2 notes

by: at19

BIBB109 lecture 2 notes BIOL 101 001


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These notes cover basic theories that arose in the 20th century about neuroscience as well as basic physiology of the brain.
Introduction to Biology A
Dr. Brenda Casper/Mr. Fevzi Daldal
Class Notes
BIBB, neuron
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This 6 page Class Notes was uploaded by at19 on Tuesday January 26, 2016. The Class Notes belongs to BIOL 101 001 at University of Pennsylvania taught by Dr. Brenda Casper/Mr. Fevzi Daldal in Fall 2015. Since its upload, it has received 5 views. For similar materials see Introduction to Biology A in Biology at University of Pennsylvania.

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Date Created: 01/26/16
Lecture 2 Notes  Neurophilosophy--our approach, no separation of mind and brain  CNS--a central division, consisting of the brain and spinal cord  PNS--peripheral division, consisting of the network of nerves that course through the body  Neurons and Glia o Nervous system is made up of glia and neurons o Glia--insulate, support, and nourish neurons, important for injury (microglia, reactive gliosis), overcome barrier for treatment (glial scar that prevents new axons from forming) o Neurons  Process information  Sense environmental changes (external and internal)  Communicate changes to other neurons  Command the body's responses to these sensations (motor neurons)  Technical challenges o Brain cells (neurons and glia) are very small (.01-.05 mm diameter)  Cannot be seen with naked eye  Compound microscope allowed field of cellular neuroscience to start  Brain tissue like Jell-O--cannot be sliced into thin sections  Formaldehyde allowed scientists to fix the brain and use microtome to section it (crosslinks proteins)  Histology was born  Brain appears uniform under the microscope  How to differentiate cells and cellular structures?  Histology o Nissl Stain--stains nucleic acids (nucleus), mainly mRNA on rough ER and free ribosomes  Distinguishes between neurons and glia based on different staining patters  Stain facilitates the study of cytoarchitecture in the CNS  Shows brain is not uniform in cortex  Doesn't show shape of neuron  Is limited in what it can show about a neuron's morphology o Golgi Stain  Silver chromate solution  Only stains small percentage of neurons in their entirety --> fills a neuron to see it at cellular level (only stains 5%)  Shows two parts  Cell body = soma = perikaryon  Neurites: axons and dendrites  Reticular Theory o Golgi was leading proponent of reticular theory--neurites of different cells fused into a fully enclosed, continuous reticulum system or nerve net  Cajal and the Neuron Doctrine o Histologist and artist o Used golgi stain and a light microscope to draw neurons and neural circuits o The Neuron: The Basic Functional Unit of the NS o Differed in that neurons were in contact, but not continuous (synapse!) o Heated debate o (Neurites) Differences between axons and dendrites  Axons are the way a neuron sends an outgoing signal  Dendrites are where a neuron receives a signal o There is specificity to the connections among neurons (microcircuitry, tract systems) --> true, not random  1906 Nobel Prize o Golgi's Reticular Theory (couldn’t see it well enough) vs Cajal's Neuron Doctrine o Dually awarded the Nobel Prize  Neuron Doctrine o Over 50 years from Cajal to proof of synapse via electron microscopy)  Some elements of electrical synapses in invertebrates which supports Golgi o Neurons are the fundamental structural and functional unit of the CNS in the neuron (chemical pretransmission) o Neurons are the fundamental structural and functional units of the CNS is the neuron o Neurons are discrete cells  Connected but not continuous  Unidirectional info flow  Axon --> dentrite --> presynaptic cell --> post synaptic nerve --> dentrite --> axon  There is specificity to the connections among neurons  The prototypical neuron o 3 parts:  Dendrite  Dendritic tree  Coming from cell body  Shorter, stubbier, spinier than axon  Spines = cites of receptors for neurotransmitters  taper  Axon  Long, thinner, smoother  Branches = collaterals  Fewer branches  Diameter more uniform  Neurites - dendrites + axons  Cell body (soma)  Cytosol: water fluid in cell  Organelles: membrane enclosed  Cytoplasm: contends within cell membrane  Nucleus  Gene expression, mRNA processed in nucleus  Rough ER--bound, proteins with plasma membrane or exocytosed (eg neurotransmitters)  Free ribosomes--proteins that are released into cytosol  Smooth ER--folds protein, gives 3D structure, regulates Ca+ concentration  Golgi--post translational, modifications (phosphorylation), packages/labels  Mitochondria  Site of cellular respiration, Kreb's cycle yields ATP the cell's energy source  Brain v metabolically intense  Inherited via ova from mother  Neuronal membrane  Lipid bilayer  Polar, water soluble heads on the outside (hydrophilic)  Non-polar, water insoluble tails on the inside (hydrophobic)  Non polar, charged ions cannot pass through it without pores (channels with action potential)  Channel  5 polypeptide subunits  Cytoskeleton  Not static, internal scaffolding  Types  Microtubules (tubulin)  Dynamic--polymerizing and depolymerizing (for plasicity)  Form long scaffolds down neurites  Maintain cell shape  Neurofilaments (Intermediate filaments)  Most abundant, stable  Microfilaments  Near plasma membrane  Dynamic (for plasticity)  Tau protein o A microtubule associated protein (MAP) that stabilize axonal MTs by interacting with tubulin o Hyperphosphorylation of the tau protein (pTau) can result in self- assembly of neurofibrillary tangles (NFTs)  Lots of tangles = aggregates, hallmark of alzheimers o When misfolded, extremely insoluble aggregates that contribute to alzheimer's disease and CTE  CTE o Chronic traumatic encephalopathy (distinct from AD) o Found in individuals who have suffered repetitive brain trauma o First described as dementia pugilistica (DP), "Punch Drunk" o Characterized by symptoms of dementia (memory loss), aggression, confusion, and severe depression o Symptoms may appear years or many decades after the trauma o Found in 96% of NFL players and in 79% of all football players o Diagnosis only postmortem ask about it!!!  Read his paper!  The axon o Axon hillock (bginning)  Protein composition is different from soma  No protein synthesis o Axon proper  May have collaterals (branches)  May be very short (a few mm) to a meter or more  Variable diameters o Axon terminal (end)  "terminal bouton"  Presynaptic side  No microtubules  Presence of synaptic vesicles  Large number of mitochondria (high energy demand) o Synapse  Two sides  Presynaptic membrane (axon terminal)  Postsynaptic membrane (dendrite)  Synaptic cleft (space between)  Synaptic transmission  Chemical--neurotransmitters released o Axoplasmic Transport  No protein synthesis in axon  Anterograde transport along microtubules  Proteins are synthesized in the soma and shipeed down to the axon terminal along microtubules  Uses kinesin protein  Sloe 1-10mm/day  Fast 1000mm/day o Axoplasmic Transport  Retrograde  Signals to soma about metabolic needs of axon terminal  Terminal to soma transport along microtubules  Uses dynein  Dendrites o Antennae of neurons o Dendritic tree o Covered with neurotransmitter receptors o Some covered with dendritic spines o Dendritic Spines  Dymanic, grow, contract  First described by Cajal  1970s: studies of brains of children with DDs revealed fewer spines and altered morphology  2000s: 2-photon microscopy allows in-vivo visualization of activity  Spines form, enlarge, shrink, and retract throughout the animal's lifespan  Spinogenesis-->spine pruning --> maintenance  Classifying Neurons o Based on number of neurites on soma  Single neurite (unipolar)  Two or more neurites  Bipolar (two retina)  Multipolar (more than two) o Based on dendritic and somatic morphologies (how they look)  Stellate cells (star-shaped)  Pyramidal cells (pyramid-shaped)  Spiny or aspinous o By cnnections within the CNS  Primary sensory neurons, motor neurons, interneurons o Based on axonal length  Golgi type I: long axons  Golgi type II: short axons o Neurotransmitter type Cholinergic = acetycholine at synapses   Adrenergic = Neuredreneline  Glia o Function  Supports neuronal functions  Transporters for reuptake of ions and neurotransmitters in synapses (glutamate for example) o Cell types  Astrocytes  Most numerous glia in the brain  Regulates contents of extracellular space-- neurotrasnmitters  K+ spatial buffering  Influence neurite growth  Development, axon guidance  Blood-brain behavior  Protective device in capillaries (tight junctions) in the brain that prevent admittance of certain chemicals  Capillary endothelial cells  Send out end feet that envelop capillary endothelial cells that make the blood brain barrier, support tight junctions  Myelinating glia  Produce myelin sheath that insulates axons  Speeds up action potential, faster conduction down the axon  Oligodendrocytes (in CNS)  One cell can myelinate several axons  Demylenating diseases (MS)  Deteriorates, because normally an insulator, the axons cant signal as quickly  Nodes here too  Schwann cells (in PNS)  One cell myelinates a single axon  Node in ranvier (non-myelinated parts that allow sodium from node to node) Voltage gated   Region where axonal membrane is exposed  Don’t myelinate all of it to have sodium channels  Non-neuronal cells o Microglia  Microglia act as phagocytes to remove debris left by dead or dying neurons and glia  Bone marrow cell, immune system of the brain  Prevalent in neurodegenerative diseases or TBI  Not derived from same precursors that glia and neurons are  Respond to insult or injury in the CNS  Hematopoietic in orgin o Ependymal cells  Line the brain's ventricular system  Produce CSF  White matter --> mylenated axons


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