chapter 2: neurons and glia

Neurophilosophy
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the soma (the body) of the neuron houses•Cytosol: •Organelles: •Cytoplasm: •contents within a cell membrane (e.g., organelles, excluding the nucleus) - ribosomes - rough er -smooth er - golgi apparatus - mitochondriathe nucleus - small spherical•Central Dogma of Biology •DNA > RNA> Protein •Gene expression •Transcription •RNA processingdictates specialization and function of neuronsgene expressioncytosol: organelles: cytoplasm:- watery fluid inside the cell - membrane-enclosed structures within the soma - •: everything between the neuronal membrane and the nucleus •contents within a cell membrane (e.g., organelles, excluding the nucleus)Rough Endoplasmic Reticulum:•Ribosomes the major site for protein synthesis •Rough endoplasmic reticulum (the Nissl bodies) •Protein synthesis, packaging, and transport •Protein synthesis also on free ribosomes; polyribosomessmooth er:•Smooth ER - functions •SER next to RER - folds proteins destined for neuronal membrane •Other SER - regulates intracellular substances like calcium (sarcoplasmic reticulum in muscles)Golgi apparatus(golgi complex) - Sites for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substancesthe neuronal membrane•Barrier that encloses cytoplasm •~5 nm thick •Protein concentration in membrane varies. •Structure of discrete membrane regions influences neuronal function.•Neuronal membrane is arguably the single-most important organelle in the neuron?•Gives the neuron its electrical propertiesthe cytoskeleton•Not static, dynamically regulated •Internal scaffolding of neuronal membrane •Three structuresthree structures of cytoskeleton•Microtubules (largest; tubulin protein) •MAPs associated with several neurological diseases •Microfilaments (smallest; actin protein) •Neurofilaments (intermediate filaments)the axon•Axon hillock (beginning) •Axon proper (middle) •Axon terminal (end)differences between axon and soma•ER does not extend into axon •All proteins MUST originate in the soma •Protein composition in membrane different than soma •Will make sense when we discuss action potential vs graded potentialthe axon terminal•Site where axon contacts other neurons (usually at dendrites) •May branch to form other synapses •Called axon collaterals •Occur at 90 deg. angles•Differences between the cytoplasm of axon terminal and axon•No microtubules in terminal •Presence of synaptic vesicles in terminal •Abundance of membrane proteins •Large number of mitochondria •High energy for neurotransmitter release, reuptake, breakdown, and recyclingthe synapse•Site of signaling between neurons •Space between two cells - synaptic cleft •Synaptic transmission - chemical signal •Neurotransmitters as chemical signals •Electrical-to-chemical-to-electrical transformation•Synaptic transmission dysfunction•leads to mental disorders •Site of many psychoactive drugs (cocaine) and therapeutics for mental illness (SSRIs)axoplasmic transport•Remember: ribosomes not readily found in terminals •Movement of vesicles from soma to terminals and vice versa carried by motor proteins using cytoskeleton as highway trafficking systemAnterograde transport•from soma to terminal •"forward transport" ie the same direction as the action potential/electrical signaling •Uses kinesin motor proteinRetrograde transport•- from terminal to soma •"backward transport" ie opposite direction as AP/electrical signaling •Uses dynein motor proteindendrites•postsynaptic neurite •"Antennae" of neurons •Receive signals from presynaptic neurons •Contain receptors - detect/bind neurotransmittersdendritic tree• all dendrites from a single neuron •Each branch called dendritic branch •Shapes/sizes of dendritic trees used to classify types of neuronsdendritic spines•Increase the surface area of the dendrites •Changes in morphology seen in cognitive disorderssingle neurite two or more neurites-unipolar -bipolar: two (found in dorsal root ganglia) -multipolar: more than two (most neurons in the brain)Classification based on dendritic and somatic morphology-Stellate cells (star-shaped) and pyramidal cells (pyramid-shaped) - Spiny or aspinous•Classification by connections within the CNS•Primary sensory neurons, motor neurons, interneurons•Classification based on axonal lengthGolgi Type 1 Golgi Type 2golgi type 1•Called projection neurons •Long axons, extend from one part of the brain to anothergolgi type 2•Called local circuit neurons •Short axons, do not extend far beyond the cell body•Classification based on gene expression•Tools such as qPCR help elucidate cell specific gene expression patterns •Patterns dictate type and function of cells•Creation of transgenic mice•Example of "ChAT-Cre mice" •Green fluorescent protein (GFP) •Can be inserted under the promotor of a gene •Each time gene is expressed, a green fluorescent protein is also made•Classification based on neurotransmitter (NT) type•Neurons differ widely in the NTs they produce •GABAergic neurons produce NT GABA •Cholinergic neurons produce NT Acetylcholine (Ach)function of glia "the glue"•Support neuronal functions in many waysastrocyte•Most numerous glia in the brain •Fill spaces between neurons •Only leave about 20 nm •Influence neurite growth •Regulate chemical content of extracellular space •Restrict spread of neurotransmitters •Remember synapse is a space •Contain specific proteins for removing used NT from synapse, stopping signal •Regulate ion composition in extracellular space •Ie K+Myelinating glia•provide layers of membrane to insulate the axons •Remember nerves act as wires - myelin, oligodendroglia. schwann cells - insulate axonsmyelin•proteinaceous/fatty sheath •Insulates axonsOligodendroglia•(in CNS) •Produce and wrap CNS neurons •ONE oligodendrocyte can wrap many axonsSchwann cells•Schwann cells (in PNS) •Produce and wrap peripheral nerves •One Schwann cell wraps one axonnode of ranvier•Region where axonal membrane is exposed •Concentration of ion channels •Increases speed of transmission down axon •Saltatory conductionEpenymal cells•Cells of the choroid plexus •Direct cell migration during neural development •Line the ventricles, regulate cerebrospinal fluid production and composition •Likely have many undiscovered functions in brain health - type of glia•Microglia as phagocytes (immune function)•Macrophages (garbage disposals) of the brain •Play key role in synapse remodeling - type of glia•Vasculature - arteries, veins, and capillaries•Deliver oxygen, glucose, and other nutrients to brain cells - type of glia as well as lymphatics in the brain