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Final Study Guide Cellular neuroscience

by: Emma Notetaker

Final Study Guide Cellular neuroscience NSCI 3310

Marketplace > Tulane University > Neuroscience > NSCI 3310 > Final Study Guide Cellular neuroscience
Emma Notetaker
GPA 3.975

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Comprehensive study guide (lecture notes and powerpoint slides)
Cellular Neuroscience
Jeffrey Tasker
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This 36 page Bundle was uploaded by Emma Notetaker on Tuesday December 8, 2015. The Bundle belongs to NSCI 3310 at Tulane University taught by Jeffrey Tasker in Summer 2015. Since its upload, it has received 91 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.


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Date Created: 12/08/15
Monday, December 7, 2015 Final Exam Study Guide Auditory System • formation of sound waves: • air compression increases pressure • rarefaction decreases pressure both of these create sound waves (compression and rarefaction) • • waveform characteristics: • frequency: higher frequency = higher pitch • amplitude/intensity: higher = louder • structure of the ear: • outer ear • pinna - directs sound • auditory canal • middle ear • tympanic membrane: vibrates at frequency and amplitude of the sound wave (translated into physical movement) • ossicles: small bones that connect eardrum to oval window (at the beginning of the cochlea) • malleus, incus and stapes • sets up FLUID wave within cochlea • inner ear • vestibular apparatus • cochlea: fluid filled • fluid wave (from ossicles’ pounding on the oval window) at the same frequency and amplitude as the sound was • cochlea: • coiled, tube-like snail shell • 3, fluid filled structures • 2 large ones which contain perilymph (within helioctrema) • scala vestibulae • scala tympani • 1 small one in the middle • scala media: cochlear duct • isolated form cochlea AND brain • contains endolymph • contains organs of Corti (embedded in basilar membrane) • helioctrema: • apex of cochlea • contains scala vestibulae and scala tympani • sound transduction • organ of corti (within scala media) • hair cells: • whatever singular cilia does, the rest follow • separated by reticular lamina • at the base of hair cells, synapse with axons in spiral ganglion neurons 1 Monday, December 7, 2015 • inner hair cells: most important for hearing • most sensory signaling and transaction occurs here • outer hair cells: mainly for amplification of sounds • basilar membrane • tectorial membrane - rigid membrane • afferent axons • transduction mechanism: • fluid waves in Reissner membrane —> • oscillation in basilar membrane (which has hair cells embedded in it) —> • hair cells move—> • movement of stereo cilia (within tectorial membrane) • movement of stereo cilia: • forward and backward movement of stereo cilia • basilar membrane moves up, causes hair cells to move RIGHT on tectorial • basilar membrane moves down, causes hair cells to move LEFT • mechano-electric transduction: opening and closing of mechanically gated potassium channels • toward long cilia (on the right - forward): opens potassium channels • causes influx of potassium—> depolarization • this depolarization causes opening of voltage gated potassium channels • glutamate is released • toward short cilia (on the last - backward): closes potassium channels • hyperpolarization • hair cell receptor potential generation • endolymph: • HIGH potassium • LOW sodium • +80mV potential (same as potassium equilibrium potential) • EK = 0 mV • perilymph: • HIGH sodium • LOW potassium • 0 mV potential • hair cell: • -45 mV resting potential • repolarization: opening of K channels at base of hair cell • 2 different EK’s (one at base and one at apex) • auditory signals: • 1. sound waves • compression and rarefaction • sinusoidal wave in perilymph • mechanical pressure on oval window sets up fluid waves • 2. opening and closing of mechanically gated K channels • depolarization and hyper polarization of hair cells • reduces sinusoidal wave up to high frequencies • frequency sensitivity tonotopy • basilar membrane is narrow and rigid at the base • base is sensitive to high frequency 2 Monday, December 7, 2015 • wide and flexible at apex - SO apex is sensitive to low frequencies • each hair cell synapses on spinal ganglion neurons • these ganglion cells toward apex get lower frequencies, those towards base receive higher frequencies • innervation of hair cells • 3:1 ratio of outer to inner hair cells • inner hair cells transfer over 90% of hearing info (loss leads to deafness) • outer hair cells amplify basilar membrane oscillations 100x • motor proteins in membrane that can cause them to contract and expand to amplify • 95% of spiral ganglion neurons communicate via synapses with inner hair cells • each spiral ganglion cell synapses with SINGLE inner hair cell • cannot innervate ore than one outer hair cell • auditory pathways • spiral ganglion cell—> auditory nerve • auditory nerve —>ventral cochlear nucleus • ventral cochlear nucleus —> superior olive (medulla) • superior olive -> lateral lemniscus • lateral lemniscus —> inferior colliculus • inferior colliculus —> medial geniculate nucleus • medial geniculate nucleus —> auditory cortex • auditory encoding of • frequency: tonotopy • low frequencies: phase locking ONLY • frequencies that are too high or too low activate the same areas (cochlear sensitivity doesn't go below 200 Hz, so lower frequencies all activate the same area) • intermediate frequencies: use both phase locking and tonotopy • high frequencies: not fixed - rely OLNY on tonotopy • action potentials cannot follow frequencies higher than 4 kHz • intensity: larger oscillations of basilar membrane • changing frequency sensitivity by increasing sound intensity which changes the threshold of response • greater sound = greater inward currents • intensity coding • 1. spiral ganglion firing rate: frequency code • 2. number of spiral ganglion neurons recruited: population code • location (horizontal vs. vertical) • horizontal plane • interaural delay: different in time it takes sound to arrive at each ear (only works for sudden sound) • interaural intensity difference: difference in intensity at each ear based on the shadow of the head • vertical plane: localization based on curves and folds of pinna • reflects and bounces off different parts of the ear • most sound impinges on both ears at the same time • more physical - physical characteristics detect vertical sound • mechanism of sound localization • sensitivity of binaural neurons to sound location 3 Monday, December 7, 2015 • sound from left side initiates activity in left cochlear nucleus • sent to superior olive • from olive to right ear activating right cochlear nucleus • in the meantime, the other impulse (in left ear) has gone farther • both impulses reach olivary neuron 3 at the same time, summation generates AP on side farther from where sound came from (because the impulse travelled farther) • interaural intensity difference will be between 2 and 20 kHz Vestibular System • importance: balance, equilibrium, head, body and eye movement, posture • vestibular labyrinth: • 2 structures • 1. otolith organs: gravity and tilt • 2. semicircular canals: head rotation • both use hair cells, like auditory system, to detect changes • otolith organs • project to lateral vestibular nucleus detect changes in head angle and linear acceleration • • macular hair cells respond to tilt • macula (like organ of corti): sensory organ in utricle and saccule, contains hair cells • saccule: vertical acceleration • utricle: horizontal acceleration • mirror images in opposite ears depolarization with tilt in one direction, hyperpolarization in the other • • 2 ears have opposite responses • semicircular canals • hair cells: transduce movement in gelatinous cap (endolymph) • deflections in cilia and K influx via mechanically gated channels • otoliths: calcium carbonate crystals (detect acceleration) semicircular canals: angular acceleration (detects rotational movement) • • project to medial vestibular nucleus • structure: • hair cells in ampulla (bulge in canal) • cupula: gelatinous structure (hair cell embedded here) • canals filled with endolymph • contralateral canals have opposite responses • adapted to sustained rotation • vestibulo-ocular reflex (VOR) • eye motor compensation for head movement • inputs from vestibular apparatus project to neurons that control muscle in eyes to move appropriately • controls eye movements to counteract head movements • moves eyes in opposite direction that head is moving in order to keep a stable gaze Visual System • properties of light 4 Monday, December 7, 2015 • electromagnetic radiation • spectrum determined by wavelength • visible light 400-700 nm • less than 400: UV, xrays, gamma rays • more than 700: infrared, radar • travels in waves • reflects off objects, causes light scattering • reflection causes loss of visual acuity • refraction: light is bent to different degrees by going through different mediums • cornea and lens • refraction of light (focused at the retina) • most refraction occurs at cornea, fine-tunes by lens (lens focuses onto retina) • accommodation: lens changes shape with distance of object • rounder for closer objects • flatter for farther objects • retina • layered structure, covers 3/4 of the eye • photoreceptors: • capture photons and trigger sensory response • phototransduction • outermost layer of retina (layer 1) • fovea: • center of retina • region of highest visual acuity (blurred in rest of retina) - highest sensory resolution • area where the layers separate • pigment epithelium • contain melanin • absorb stray light that isn’t captured by photoreceptors (prevents light from reflecting around the inside of the eye) • 5 layers of retina: • 1. outer nuclear layer: photoreceptors • 2. outer plexiform layer: synapses between photoreceptors and interneurons • 3. inner nuclear layer: interneurons • 4. inner plexiform layer: synapses between interneurons and ganglion cells • 5. ganglion cells: innermost layer - output info from eye • send axons out over inner surface of retina to optic disk • collect to form optic nerve, which exits eye • axons are unmyelinated until they reach the optic nerve • each layer contains a 1:1:1 relationship between cones, bipolar and ganglion cells • image formation • corneal refraction: bending of light • caused by light passing through different mediums • lens changes to change resolution • focal distance: between cornea and convergence point • closer the light, the more round the lens is • more refraction —> more bending • closer the object is leads to more bending in the lens 5 Monday, December 7, 2015 • light path to photoreceptors • path to photoreceptors impeded by other layers • fovea is a DIRECT path to photoreceptors (layers path to allow access) • minimal reflection • least light distortion • center of retina directly behind cornea and lens • highest concentration of photoreceptors (rods/cones) —> high acuity • very center = foveola • photoreceptors: rods and cones • morphology: • outer segment: discs (like dendrites of neurons) • area that captures light • sends info to inner synaptic terminal • inner segment: soma • synaptic terminal • rods: night vision • single visual pigment: rhodopsin • cannot detect color, only light (more sensitive to light than cone) • more rhodopsin in rods than there is opsin in cones • low acuity • more photopigment • high sensitivity but low spatial resolution • converge onto bipolar cells • more layers of membrane creates more surface area —> leads to hight sensitivity and lower threshold (can detect 1 photon) • cones: day vision • 3 visual pigments: opsin (red, green and blue) • differential activation of different cones • low visual sensitivity because less pigment • high spatial resolution • 1:1 ratio to bipolar cells (interneurons that they project to) • factors contributing to visual acuity: • convergence of photoreceptor signals (central vs peripheral) • light access to photoreceptors • phototransduction • occurs at photoreceptor • opsin: 7 transmembrane protein (g protein coupled) • retinal: light absorbing, vitamin A derivative • light causes 11-cis to change to all-trans retinal • this change activates opsin, which triggers 2nd messenger cascade • 2nd messenger cascade • activation of photoreceptor is a HYPERPOLARIZATION (always) • decreases neurotransmitter release onto next cell • G protein: transducin • cGMP phosphodiesterase changes cGMP to 5’GMP (decreases concentration of cGMP) - inactivates cAMP or cGMP • causes closing of cGMP gated sodium channels - blocks dark current (current activated in the dark) • leads to hyper polarization (passive signaling) 6 Monday, December 7, 2015 • 5 cell types in retina • photoreceptors • outer nuclear layer • use glutamate • no center-surround receptive field • hyperpolarize in response to light • DO NOT generate action potential • bipolar cells • in inner nuclear layer • use glutamate • interneurons directly linking photoreceptors to ganglion cells • passive depolarization or hyperpolarization- do NOT produce action potentials • ionotropic • center-surround to direct/vertical pathways • horizontal cells • in inner nuclear layer • interneurons • use GABA • link neighboring photoreceptors • do NOT generate AP • amacrine cells • inhibitory interneurons • use glycine • DO generate AP (need to depolarize through electrical cell gap junction) • ganglion cells • form the optic disc (where axons come together to form optic nerve) • excitatory: use glutamate • will follow whatever bipolar cell does • DO generate AP in order to transmit signals to brain • basic retinal circuit • photoreceptors —> interneurons —> ganglion cells • center-surround receptive fields (antagonistic) • for contrast detection • diffuse light exhibits weak response • direct (vertical) pathways: center of receptive field • photoreceptor —> bipolar cell (center-surround) —> ganglion cell (centered - direct communication) • indirect (lateral) pathways: surround of receptive field • surround by way of horizontal cell projections • horizontal cell —> photoreceptors —> bipolar cells —> ganglion • horizontal cell SWITCHES polarity (so goes through path in opposite way) • if center is excitatory, surround is inhibitory (and vice versa) • on-center receptive field: light hitting center is excitatory • when light hits the center, surround gets synaptic signal from lateral pathway that causes opposite response (because lateral) • center pathways (cones) • differing (on or off center) because they respond differently to glutamate (from photoreceptors) • metabotropic 7 Monday, December 7, 2015 • on center bipolar cell synapse (depolarizes) • glutamate is inhibitory (mGluR’s) • hyperpolarization of cone from light —> less glutamate release onto both on center and off center bipolar cells • —> excitation of bipolar cell (from hyperpolarization) • off center bipolar cell synapse: • glutamate is excitatory (iGluR’s) • hyperpolarization of cone —> less glutamate release • —> inhibition of bipolar cell • bipolar cell and ganglion cell synapse • glutamate, excitatory (iGluR’s) • depolarization —> more glutamate release onto ganglion cell —> excitation • hyperpolarization —> less glutamate release —> inhibition of ganglion cell • surround pathways: indirect or lateral pathways to ganglion cells • increase spatial resolution • light activates cone in surround —> less glutamate release—> inhibits horizontal cell —> DEPOLARIZES cone in center —> goes to bipolar cell —> ganglion • depolarizes cone because GABAergic - causes less GABA release which excites cone (not in response to light but in response to this neurotransmitter • in dark, glutamate released tonically • all signals reverse with respect to center response: • depolarization of center cone —> increased glutamate release • hyperpolarization of on center bipolar cell —> decreased glutamate release • —> hyperpolarzation of on center ganglion cell • decreased spiking • depolarization of off center cone —> increased glutamate release • depolarization of off-center ganglion cell • increased spiking • rod pathways • NO center surround receptive fields • indirect pathways via rod bipolar cells and amercing cells • rod bipolar cells: on center bipolar cells • glutamate synapse activating metabotropic receptors to hyperpolarize • does not project directly to ganglion cells - goes to amacrine • amacrine cells: generate AP • use glycine as nt • mediates rod pathways through projecting to both on and off center ganglion cells • electrical synapses with on center ganglion cells • excitatory • depolarization • channels where ions can flow directly • presynaptic cell generates AP, which cause accumulation of positive charge in presynaptic cell • this charge flows through channels to depolarize postsynaptic cell • chemical synapse with off center ganglion cells • inhibitory • hyperpolarization by glycine release 8 Monday, December 7, 2015 • no center-surround antagonism: leads to loss of spatial resolution Central Visual System • ganglion cells - all project to brain via optic nerve • M cells • large cells - 5-10% of ganglion cells in retina • project to magnocellular neurons in LGN • large receptive field - mediates lower spatial discrimination • faster AP conduction • insensitive to color • responds to low contrast light • responds to motion and movement • transient (adaptive) response to center light (adapts rapidly) • P cells • small cells - 80-90% of total ganglion cells in retina • small receptive field - mediates hight spatial discrimination • slower AP conduction sustained response to center light - adapts slowly • • detects form and color • projects to parvocellular neurons in LGN • bistratified (nonM-nonP) • small cells - 5-10% • intermediate receptive field intermediate velocity and contrast detection • • detects color - blue and yellow • project to koniocellular regions between mango and parvocellular regions • light sensitive ganglion cells • have photopigment in membrane, can respond directly to light • don’t work for visual field but used in circadian rhythms retinofugal projection • • optic nerve - myelination begins • optic chiasm: crossover (axons enter brain here) • optic tract: fiber tract in brain (has 1/2 of axons from one eye, 1/2 from the other) • ganglion cell projections • lateral geniculate nucleus: perception • hypothalamic suprachiasmatic nucleus: circadian rhythms • pretectum: pupil ans lens reflexes • superior colliculus: eye and head movement • pathways to visual cortex • ganglion cell —> optic nerve • optic nerve —> optic chiasm • optic chiasm —> optic tracts • optic tracts —> LGN • LGN —> optic radiation (fans out from LGN) • optic radiation —> primary visual cortex • color opponency: • center-surround color opponent receptive field 9 Monday, December 7, 2015 • red-green: P cell receptive field • due to red and green cones • red in center, green in surround • blue yellow: bistratified cells • make yellow with red and green • surround has both red and green cones • visual field • objects inverted and reverse in retina (light crosses in lens) • both eyes get info from both sides • visual field divided into quadrants (and so is retina) • temporal and nasal hemiretinas, superior and inferior hemiretinas • hemiretinas receive light from opposite side of visual field • info from both eyes but only one side of visual field • axons from temporal DON’T cross - ipsilateral • axons from nasal cross to contralateral side in optic chasm • deficits • optic nerves: info from single eye about both sides of field • optic tracts: info from both eyes about opposite visual field • projections to LGN • info from: ipsilateral temporal retina and contralateral nasal retina (about OPPOSITE visual field) • LGN 6 layered structure • 3 layers for ipsilateral retina • 2, 3, 5 • 3 for contralateral retina • 1, 4, 6 • layers 1 and 2 devoted to magnocellular layers • layers 3-6 devoted to parvocellular • each layer also has bistratified cells projection to koniocellular LGN cells • intermediate zones in between layers • parvocellular neurons: “what” • form and color info • magnocellular neurons: “where” • location, movement • project to spiny stellate neurons in layer 4Ca • parallel visual streams • form, color and motion info carried by segregated, retinotopically organized pathways in brain • parvocellular, magnocellular and koniocellular layers in LGN • axons from ganglion cells make synapses to this relay • projections to primary visual cortex • occipital lobe • info from only half of visual field to each hemisphere • superior and inferior quadrants segregated • neocortex (6 layers) • inputs from each eye converge in layer 3 and 4B • LGN (parvocellular and magnocellular) project to layer 4C (this layer gets 90% LGN info) • magnocellular terminate in 4Ca 10 Monday, December 7, 2015 • parvocellular terminate in 4Cb • layer 4 divided into A, B and C, and C is divided into alpha and beta • local circuit projections: • spiny stellate neurons (nt=glutamate) • first relay neurons receiving inputs from LGN • produce glutamate - excitatory projections • retinotopic organization • about 50% of primary visual cortex devoted to fovea (largest representation) • due to number and density of receptors • more cones • in periphery, convergence of multiple photoreceptors on multiple cells (lower density, to less of the primary visual cortex devoted to these areas • different quadrants project to different regions of primary visual cortex • columnar organization • ocular dominance columns • alternating columns receive projections from each eye (between ipsilateral and contralateral eye) • in layer 4 • within each column, there is a blob and an inter blob (each eye divided into color and form info) • blos/interblobs • blob: color info • monocular - devoted to one eye • receptive fields: circular • no orientation or direction selectivity • interblob: between blobs • form info • location of ocular dominance columns • orientation columns: • cells in same column respond to same orientation of light • controlled by simple cells (rectilinear receptive fields • hold up to layer 4C (doesn’t respond to any orientation) • inferior layers all respond to same • if you go horizontally through multiple columns, go through 180 degrees • cortical hypercolumn • devoted to one spot on retina • can analyze every aspect of a portion of visual field (has all 3 types of columns) • M channels • motion info • separated into contralateral and ipsilateral eyes (ocular dominance column devoted to each eye) • some cells get monocular inputs, some get binocular inputs • higher order neurons in layer 4B • process: M cells —> magnocellular cells in LGN • magnocellular cells in LGN —>spiny stellate cells in 4Ca • spiny stellate cells —> higher order neurons in 4Cb • P channels • form and color info 11 Monday, December 7, 2015 • 4 layers of the LGN devoted to these • synapse onto spiny stellate neurons in 4Cb (80% of info from retina comes here) • projects to pyramidal neurons in layers 2-3 • glutamatergic neurons • some get inputs from one eye, some from two • spiny stellate neurons get input from LGN • retain center surround receptive fields • these project to pyramidal, higher order cells (glutamatergic, excitatory) • simple cells: • higher order cells • pyramidal • info from spiny stellate cells (each of which has center-surround receptive field - center is ON) • multiple fields combine to form one - MANY spiny stellate cells combine to project to ONE pyramidal cell • contain elongated rectangular receptive fields (on portion is vertical in center) • perceives outlines • orientation and position selective • layers 2-3 • inferior layers: pyramidal neurons that get input from adjacent areas of visual cortex and project to brainstem and hypothalamus • LGN has similar center-surround field • info transmitted directly from center and surround to different LGN neurons • forms a loop • cortical receptive fields • monocular receptive fields (layer 4) • layer 4C: similar to LGN cells (center-surround) • layer 4Ca: MOTION (no color) • layer 4Cb: color • binocular receptive fields (layers 1-3) • layers above 4; first binocular fields in pathway • direction selectivity (of motion) • neuron fires AP in response to moving bar of light • magnocellular inputs from LGN • more activity in response to moving certain direction • complex cells • binocular • orientation-selective (respond to oriented edges) • position unselective • on and off response to bar of light, but unlike simple cells, no distinct on and off regions • if anywhere within receptive field, will get same active levels • several simple cells with rectangular receptive fields will project onto single complex cell • keeps orientation selectivity but loses surround antagonism • pyramidal cells: input from simple cells • simple and complex cells responsible for perception of form! • higher visual cortices • dorsal stream: analysis of visual motion/visual control of action 12 Monday, December 7, 2015 • ventral stream: perception of the visual world/recognition of objects (shapes and colors) • hierarchy of complex receptive fields: • retinal ganglion cells • center-surround • sensitive to contrast and wavelength • striate cortex • orientation selectivity • direction selectivity • binocularity • extrastriate areas • selectively responsive Neurons and Glia • cells of the nervous system • neurons: signaling cells • transfer information through networks pyramidal cells: triangular, coordinate info within and send out (most have • SPINES) • stellate cells: starlike (dendrites in all directions) • dendritic spines very important for signal transmission • glial cells: support cells (through neuronal circuits) • maintain environment for neurons talk to neurons through neurotransmitters and gliotransmitters • • all cells in a network both presynaptic and postsynaptic • neuron morphological components • dendrites: • apical (off apex) and basal (off base) • dendritic spines: site of EXCITATORY synapses integrate inputs and changes inputs from other neurons • • influence postsynaptic cell • aspiny neurons both excitatory and inhibitory on dendritic shaft • primary fx: receive synapses • excitatory and inhibitory synapses • PASSIVE transmission of info • graded ,decremental communication • charge introduced a attracts OPPOSITE charges - influences in a domino-like effect • soma: cell body • nucleus: genetic material and RNA • protein synthesis and packaging • can also receive synaptic input (INHIBITORY) • axon: single axon • thinner than dendrites, always spiny • extends from soma via axon hillock or axon initial segment • region of change in chemical makeup (depolarization) • axon collaterals all from single stem 13 Monday, December 7, 2015 • if enough charge reaches initial segment to reach threshold, AP generation • changes signal from passive to active • all or none • nondecremental (regenerated at each successive segment) • projections: • intrinsic: local (one area) • interneurons, inhibitory • extrinsic (project outside local area • axon terminal: change from electrical to chemical (nt) • synaptic transmission to postsynaptic cells • electrical signal arrives at axon terminal and releases chemical signal • this opens electrical signals in postsynaptic cell • neuron doctrine: Cajal • neurons are not symmetrical • directionality is relative to given synapse • orthograde direction • backpropagation: active • active conductance in dendrites • retrograde transmission via dendritic transmitters • retrograde messengers: can have either positive or negative effect on synapses • influences forward direction of info flow (facilitates or inhibits nt release) • postsynaptic cell can release chemicals from dendrites onto presynaptic cell to influence the signal coming back • morphologies • unipolar: invertebrates • bipolar: limited inputs, small surface area (sensory) • pseudounipolar: sensory neurons • multipolar: Purkinje cells and pyramidal • glia • microglia: macrophages (phagocytic role) • scar formation, debridement • macroglia • 1. radial glia: path for migrating neurons in neural development • 2. oligodendrocytes: myelination in CNS • one glia covers several axons • 3. Schwann cells: myelination in PNS • neuronal regeneration • one covers one axon • 4. astrocytes: star glia • buffer extracellular ions: want to keep electrical properties of ecf • eliminate ions and recycle neurotransmitters • crosstalk with gliotransmitters • nt released by glia • active conductance from postsynaptic goes to astrocytes • calcium influx which activates gliotransmitter (ATP) on presynaptic cell • method for postsynaptic to influence presynaptic • functional components 14 Monday, December 7, 2015 • input: dendrites and synapse • receptors on dendrites and soma • NEGATIVE resting potential • depolarization via sodium influx • PASSIVE: decrementally mediates signal importance • signals starting farther out will be weaker • conversion from mechanical to chemical to electrical • integrative: axon hillock • generating AP (in sengment) • active; all or none • coded in number (length) and frequency • conductive: axon • output: axon terminal • release of nt • frequency and number converted to quantity of nt released • signals go through energy transduction circuit: • mechanical (stretch) —> passive electrical (dendrites) —> active electrical (axon) —> chemical (terminals) • knee-jerk reflex: monosynaptic circuit • muscle spindle detects stretch • AP conducted to dorsal to ganglion in spinal cord • then to motor neuron —> muscle —> extension • disynaptic: reflex inhbition Cell Biology • neurons differ from other cells by • excitability: ability to generate and potentiate AP • morphology: signals travel long distances • protein trafficking (axonal transport) - proteins are tagged and cells are directed along cytoskeleton • transcription: mRNA from DNA template • factors assemble at start of gene • factors read info on gene, helix unzips and copies one strand • tRNA and nuclear pores traffic proteins from nucleus cytoplasm • translation: protein synthesis • RNA goes to nucleus • ribosomes translate RNA into string of acids • free ribosomes in cytoplasm make proteins that STAY • membrane associated on RER make proteins to be exported • aminos brought to ribosomes by tRNA • protein classes: • cytosolic: made by free ribosomes • fibrillar: elements of cytoskeleton • enzymes • nuclear and mitochondrial • proteins translocated into here • bind to their DNA 15 Monday, December 7, 2015 • influence gene transcription • membrane associated • integral and peripheral • ER proteins • vesicle and lysosomes • golgi apparatus • vesicle formation • posttranslational modifications (ex: glycosylation • axonal and dendritic projections: • spines are made of ACTIN • specific microtubules found only on dendrites • cytoskeleton - 3 types of fibrillar proteins • microtubules • protein: tubulin • large hollow • polar (grows at positive end and shrinks at both) • dynamic instability • cilia and flagella • function is cell shape, organization, cargo/motility • neurofilaments • protein: cytokeratin • stable • microfilaments • protein: actin • polar: grow at one end and shrink at the other • dynamic process • function: cell shape, muscles, movement, cell division • axonal transport • fast anterograde • synaptic vesicles and secretory granules • active (ATP dependent) • move towards axon • protein: kinesin (head interacts with filament) • 400mm/day • retrograde • goes back to soma for degradation or recycling • 200-266 mm/day (1/2 to 2/3 speed of fast) • active (ATP dependent) • protein: dynein • slow axoplasmic • moves enzymes for cytoskeletal filaments • positive direction • PASSIVE - no proteins • .2-.5 mm/day Neuronal Membrane and Ion Channels • outer leaflet of the plasma membrane is POLAR, prevents ions from crossing without energy 16 Monday, December 7, 2015 • components of membrane • proteins: facilitate cross membrane flow • integral (amphipathic) • ion pumps • ion channels • peripheral: G proteins • carbohydrates: cell interactions • glycolipids: interactions with matrix and other cells • glycoproteins: protein-protein interactions • cholesterol: determined fluidity and stability • ion channels: ionotropic (ligand-gated) • ion selective: filter ions • selectivity determined by charge, size, water attachment • gates (not always open) • localized change in one region of the protein • OR general shape change • ball and chain possibility • DO NOT REQUIRE ATP (passive) • gates: • leak channels - ALWAYS open (flux ions at slow rates) • ligand-gated: dependent on nt to bind (ionotropic) • 2nd messenger gated (dependent on phosphorylation) • voltage-gated • mechanical • pumps and transporters: require ATP (active) Membrane Potential • membrane polarized at rest (negative inside, positive outside) • Vm = Vinside - Voutside ions loosely attached to each other through membrane: makes them always want to move • • ground (extracellular space) = 0mV • ion movement: 2 forces on ions • chemical: concentration gradient • electrical: charge interactions • flow of ions creates current (movement of charge) • current: I (measured in mA) • conductance: how well ion can go through (g) • ability to flux charge • same as permeability • resistance: how well can stop ion from getting through (R) • inversely related to conductance • membrane signals • hyperpolarization = negative • positive flows OUT • PASSIVE process (electrotonic) - proportionate to input • depolarization: POSITIVE • positive charge flow in 17 Monday, December 7, 2015 • NOT proportionate - increase in frequency and duration caused by increase in input • ACTIVE • ionic concentration gradients • high inside: only potassium (wants to flow out) • high outside: sodium, chloride, calcium (want to flow in) • current moves in direction of positive charge • ratios: (outside: inside) • sodium - 10:1 • potassium - 1:20 • chloride: 1.5: 1 • calcium: 10,000: 1 • pumps: active • potassium pumped in • extracellular K taken by astrocytes (ONLY K has leak channel in astrocytes) • sodium and calcium pumped out • calcium sequestered in intracellular storage depots • leak currents: passive • concentration gradient necessary • equilibrium is the endpoint • each ion has its own leak channel • eq. potential = flow in and out of particular ion • potassium leak channels: • open during rest • potassium out • most prevalent leak channels in neurons • equilibrium potentials: chemical gradient = electrical gradient • Nernst equation to determine equilibrium potentials • outside over inside (except for Cl because of Z) • ONE ion at a time • 61.5 log ([ion]o / [ion]i) • ENa: +62mV • EK: -80 mV • ECl: -65mV • ECa: +246mV • driving force: Vm - Eion • determines direction and force of ion flow • outward flow: positive leaving • inward flow: positive coming in • ex: sodium with positive driving force means sodium is going OUT, but calorie with positive driving force means that chloride is coming IN • resting membrane potential: NOT equilibrium (steady state - not all ions can be at equilibrium) • function of ion concentrations and permeability • Goldman-Katz equation: (out over in except for Cl) • Vm = 61.54 log (PK[K]o + PNa[Na]o + PCl[Cl]i) (PK[K]i + PNa[Na]i + PCl[Cl]o) • K has the highest effect on the resting potentials because the permeability is the highest (due to more potassium leak channels) • ion pumps: needed because leaks are not enough to maintain resist potential 18 Monday, December 7, 2015 • restore ion gradient and maintains potential • Na/K pump generates outward current (more + out) • hyperpolarizes membrane • Na binds, ATP phosphorylates protein —> 3 Na out, 2 K in • higher sodium concentration inside = quicker binding site activation = quicker pump activation AP Generation • current clamp: records voltage • electrode injects current into cell and elicits voltage change • positive injection depolarizes cell - if it reaches threshold there is AP • NS uses frequency coding - increased magnitude and duration of input causes higher frequency in AP • voltage clamp: measures current • clamps voltage at certain level • computer reads voltage and injects current to bring cell to command voltage (Vc) • negative feedback: injects current to bring Vc back to original current to exactly counteract potential • feedback current = membrane current • voltage: potential energy (difference in charge) • current: amount of electrons available • AP currents: • inward: sodium coming in evoked by depolarization • • mediated by voltage gated Na channels • ON at beginning of depolarization, OFF before end • TRANSIENT (inactivating) - on at beginning, off at end • faster than K • to prove: blocked by tetrodotoxin (TTX) which blocks Na only K working so current STAYS out (because K is persistent) • • outward: potassium going out • voltage sensitive - evoked by depolarization (mediated by voltage-gated K channels) • persistent current - turns on at beginning of depolarization and stays • proved by TEA: when only Na working current stops at end • feedback: • positive Na feedback (faster) • membrane depolarization • voltage gated Na activated • increased Na influx caused by more Na gates opening • membrane more depolarizes • sub threshold: leave loop, back to resting potential • above threshold: enter positive feedback loop (more depolarization, more Na, etc) • negative K feedback: • depolarization • activates voltage gated K channels (little delay after Na) 19 Monday, December 7, 2015 • increases K flux - fluxes out to reverse depolarization • causes Na influx to slow down until K dominates • hyperpolarization: exits feedback loop until back to resting • AP generation due to voltage gated channels • can open at any time but higher probability due to increased positive charge in cell • amino acids sense charge in cell and change shape in response to voltage • threshold around -40 mV • patch-clamp technique: single cell channel currents • glass electrode adheres to membrane to create high resistance seal • single channel currents are rectangular (because all or none) • different channels = different conductance ==> different amplitude • ex: if out when open: has to be either flow of K or Cl (because out is positive direction) • to determine where it will go, look at driving force (difference between membrane potential and ion equilibrium potential • single current amplitude is function of Vm • whole cell currents • blow out patch access to entire cell • summation of single cell currents • sodium currents: • rapid due to huge driving force • transient (inactivating) • 4 states due to 2 gates • activation (m): voltage sensor domain • opens in response to depolarization • deactivation: closing • rapid onset and offset • inactivation (h): ball and chain • when inside of channel positive due to depolarization: ball moves toward less positive channel to wedge closed • inactivates current • closes in response to depolarization • slow closing - terminates flow • membrane CANNOT be reactivated when ball and chain closed - causes absolute refractory period • all voltage-gated channels close after AP • resting potential returns due to leak channels staying open • establish steady state • more sodium than K fluxes after undershoot due to concentration gradient - way that it depolarizes back after undershoot • potassium currents: ONLY activation • depolarization: K flows out • dissipates depolarization and causes hyper polarization • SLOW • new channel closed • sustained - non-inactivating • refractory periods: chemical inactivation (ensure than AP goes forward) • absolute: sodium channels inactivated (ball blocking gate) • relative: sodium deinactivated (ball not blocking but voltage-gated channel closed) • higher threshold than normal - after hyper polarization 20 Monday, December 7, 2015 AP Propagation • conduction: • change in membrane permeability: opening in channels) • both active (depolarization) and passive (spread of cations through axon) • when AP: sodium channels open • initial segment: positive charge form sodium influx passively spreads up AND downstream (passive on both sides of initiation site) • downstream flow: charges next segment • positive depolarizes this to threshold, voltage gated sodium channels open, spreads up and down again • —> AP • upstream: no AP generated due to absolute refractory period • inactivated Na channels- Na won’t go back in until repolarized • prevents backpropagation • sticking electrode EXPERIMENTALLY into cell and injecting positive charge (where there was no AP before • AP fans out (back and forward propagation) • ANTIDROMIC spikes • antidromic: • in axon it’s only experimental (antidromic spike) • in dendrites it can occur naturally • so much positive charge and some makes it to dendrites • dendrites have nt in vesicles, they release • influences nt release from presynaptic cels • depends on number of voltage gated channels and dendrite leakiness • AP duration around 2 ms • velocity • axonal diameter: big = faster • myelin (changes velocity from 2 to 120 m/s • saltatory conduction: nodes of ranvier • high density of sodium channels - easy to generate AP • full number of K • increased Cm because can store charge easily - only one lipid bilayers separating charges on inside and outside • allow conduction because lots of interacting charges (due to lack of insulation) • internodes: myelin • no charge on inner layers myelin • very little interaction between charges inside and outside (very separated) • rapid conduction • low density of sodium • lower Cm (low capacity to store because of insulation) • diseases: • MS: demyelinating, inflammatory • charge escapes and disrupts conduction • Guillan-Barre: PNS (sensory and motor nerves) 21 Monday, December 7, 2015 Passive Cable Properties • synaptic potentials are passive - shape change and decrease in amplitude with distance • factors governing passive conductance • 1. membrane capacitance (Cm) - capacity to store charge • opposite charges “hold” each other in place across plasma membrane • function of SA —> bigger SA = bigger capacitance • specific accumulation per cm2 (gives us Vm) • 2. membrane resistance (Rm): resistance to current flow • inverse of conductance • function of the number off channels (more channels = less resistance) • 3. axial resistance: resistance of cytoplasmic axis (center of cable) • resistance of cytoplasm fluid • membrane: RC fluid • resistor: Rm (leak channels and leak currents) • capacitor: Cm (responsible for Vm) - capacitative current • no actual movement through Vm (pushed by positive on other side of membrane) • battery: Vm - separation between poles create current when poles connected • positive charge fans out • some depolarizes membrane (capacitance - pushes out + on other side via capacitative charge) • some leaks through ionic current - resistance • with each successive segment, less charge to change capacitance • Ohm’s law: V=IR • membrane excitability (change in V) • change in V proportional to change in I • magnitude of V determined by Rm • I-V curve is linear while PASSIVE (changes when threshold reached because voltage will change the curve) • membrane time constant: temporal integration • speed of charge/discharge in response to current (in one point in space) • time to charge to 63% Vmax OR discharge by 63% (to 37%) • T = RmCm • function of resistance (number of open channels) and capacitance (ability to store charge) • exponential decay • independent of distance • long T = SLOW response, short T = fast response • important in terms of cell integration over time of received inputs • length constant: spatial integration • distance of passive current spread • independent of time - exponential decay • lambda = square root of Rm/Ra • function of Ra (axial resistance) and Rm • distance to decay 63% • bigger lambda - greater distance • will be bigger at each successive segment because it starts off bigger (but still degrading - just bigger by comparison) 22 Monday, December 7, 2015 • larger lambda is more excitable (maintains over longer distance) • dendrites studded with synapses: signals are integrated at different times • practice with tau and lambda • If lambda is .1mm and threshold is 5mV above resting • lambda starts at 10 mV and one lambda away - will it generate AP?? - NO. by the time it reaches it will be 3.7 mV which is not at threshold Presynaptic Transmission • electrical synapse: gap junction • electrotonic coupling: PASSIVE spread of charge in living cell • direct ion flow • rapid - leads to tight synchrony • cytoplasmic bridge between cells - provides resistance • each cell provides hemichannel • connexon: each hemichannel • divided into 6 connexins • connexons gated by pH and intracellular calcium (usually open) close with low pH (acidic) or high calcium concentration • • current flow is bidirectional (both ways) • similar to passive signal conductance EXCEPT non-uniform axial resistance • coupling coefficient: efficiency of charge transfer • postsynaptic response/presynaptic response • function of gap junction channels (more gaps increases it) chemical synapse • • indirect • slower • unidirectional • functions: • presynaptic: AP —> calcium enters —> vesicle fusion —> nt release postsynaptic: nt binds —> opens channel —> influx or efflux of ions —> IPSP • or EPSP —> AP if threshold • axodendritic: can stimulate OR inhibit AP • on shaft: INHIBITORY (GABA) • favorable position to change postsynaptic cell because close to hillock • on spines: EXCITATORY (glutamate) • capable of influencing AP generation at axons (because before hillock) • axosomatic: INHIBITORY • capable of influencing AP generation at axons (because before hillock) • axoaxonic: incapable of influencing AP generation • only facilitates nt release • increasing or decreasing by changing membrane potential • OR change synaptic machinery • asymmetric: EXCITATORY (glutamate) • have PSD protein on them • symmetric: INHIBITORY (GABA) • presynaptic nt release • release (exocytosis) is CALCIUM dependent 23 Monday, December 7, 2015 • experiment: voltage clamp to record inward current • TTX blocks NA channels —> EPSP • cadmium clocks Ca channels —> NO EPSP • to activate voltage gated calcium channels - need depolarization! (via Na channels) • not DIRECTLY voltage dependent though - requires Ca • AP to terminal —> depolarization —> Ca gates open —> calcium comes in —> exocytosis • mechanism for exocytosis: • vesicle docking: SNARE proteins on vesicle and m


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