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Notes from Nov. 16-20

by: Joseph Merritt Ramsey

Notes from Nov. 16-20 NSCI 3310

Marketplace > Tulane University > Neuroscience > NSCI 3310 > Notes from Nov 16 20
Joseph Merritt Ramsey
Cellular Neuroscience
Jeffery Tasker

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November 16 - Retinal System: Cones November 18 - Retinal System: Rods and the CNS November 20 - No Class
Cellular Neuroscience
Jeffery Tasker
Class Notes
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This 12 page Class Notes was uploaded by Joseph Merritt Ramsey on Saturday November 28, 2015. The Class Notes belongs to NSCI 3310 at Tulane University taught by Jeffery Tasker in Fall 2015. Since its upload, it has received 18 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.


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Date Created: 11/28/15
November 18 2015 Sensory Systems Continued Visual System Rods and the CNS 0 Specific Systems 0 1 Somatic Sensory o 2 Auditory System 0 3 Vestibular System 0 4 Visual System I Retinal Circuits o CenterSurround Field 0 Center Cells Cones I Center Review Diagram 0 Surround Cells Cones I General Diagram 0 Horizontal Cell connects to the Center Pathway from the Surround Cell 0 Light hits the surround now I More Detailed Pathway Diagram 0 Shows how inhibition and Excitation work in conjunction I Breakdown 0 The Cone is still releasing Glutamate o Synapses onto the Horizontal Cell 0 This synapse is made of iGluR s an excitatory synapse I So whatever the Cone does the Horizontal Cell does 0 The Hyperpolarization of the Horizontal cell results in decreased output of its Neurotransmitter GABA o The Horizontal Cell Synapses onto the Center Cell 0 The Horizontal Cell is a GABAergic Cell I So it releases GABA to affect the synapsed cell The Adjacent Center Cone I This causes a depolarization on the center cell Cone 0 So the Center Cone is responding to the surrounding light It normally is Hyperpolarized so the surround results in Excitation Depolarization Still a passive charge 0 And if the initial signal is opposite caused by the surround response then the subsequent cellular responses are also the opposite So A Depolarization of the On Center Cone due to Surround Horizontal 9 Releases more Glutamate 9 Leads to Hyperpolarization of On Center Bipolar Cell because of mGluR s 9 Leads to Hyperpolarization of On Center Ganglion Cell 9 And a decrease in AP frequency in Ganglion o Glutamate Cells 0 Photoreceptors glutamate releasing to a ect the Bipolar Cells 0 Bipolar Cells On Center use mGluR because hyperpolarization of the Photoreceptor leads to less Glutamate released so it must be less inhibitory for the On Center Off Center use iGluR because hyperpolarization of the Photoreceptor leads to less Glutamate released so it must be less excitatory for the Off Center 0 Spiral Ganglion glutamate releasing to create an AP I Pathway Described o Rods 0 Overview I They are also hyperpolarized when activated Same as all photoreceptors I Have high sensitivity and low acuity Responsible for night vision I But also tap into Cone Pathway I Glutamate is inhibitory onto the Bipolar Cell Their bipolar cells are called Rod Bipolar Cells This generates an On Response always on the Rod Bipolar Cell and is a Center Cell And it is a Metabatropic Glutamate synapse again 0 So less Glutamate is excitatory I Do Bipolar Cells not synapse directly to the Ganglion cell to elicit the overall cellular response Does so through the Amacrine Cells various subtypes exist Most often the All Amacrine Cell o All Amacrine Cells I Have iGluR receptors on their synapses So Hyperpolarization of the rod causes less Glutamate onto Bipolar Cells mGluR The decreased inhibition Because Metabotropic causes a Depolarization Excitation and a release of Glutamate onto the All Amacrine Cells iGluR 0 So the Inotropic Receptors Cause an Excitation of All Amacrine This excitation and resulting AP causes On Ganglion Cells 0 1 A Release of Inhibitory Glycine onto off center Ganglion I The other types of Inhibitory Neurotransmitter I Synapses to the Off Center Ganglion Cells 0 2 Spread of Depolarization I So if it releases Glycine how does it excite anything I Through Gap Iunctions I Uses an Electrical Synapse I So ion ow directly through 0 Has to act on Two Types of Synaptic Cells 0 Must as on On and Off Center Ganglion Cells 0 Acts through Action Potential 0 Pathway I On response to Rod Synapse 0 Through mGluR 0 Passive Depolarization releases more Glutamate onto AII Amacrine I All Amacrine Project to on center and off center Ganglion Cells 0 Excited by increase of Glutamate from the Bipolar Cell and results in AP 0 Affects the Ganglion Cells 0 Through Glycine and Gap Junctions I But Center Surround Antagonism is lost in this mechanism 0 So Night Vision has lower resolution 0 Also center Vision is not as clear 0 Because Center is mostly comprised of Cones o Rods are congregated on Surround Light Regions 0 Rods are in the Periphery of the Retina I Central Nervous System and Vision 0 Ganglion Cells Synapse in the CNS Types of Ganglion o Breakdown of Types I 1 PCells 0 Midget Cells 0 Parvocellular Neuron Projections o Smaller Soma o Smaller Receptive Field means higher spatial discrimination more discrete signals 0 Small But Huge Amount of dendrites o Firs cell in pathway all the way to Visual Cortex o 80 of Ganglion in Retina 0 Red Green Color Vision and Spatial Discrimination o More sustained response I 2 MCells o Parasol cells for large dendrites o Magnocellular larger cells 0 Large Somas 0 Large Receptor Fields so insensitive to color not as tuned to spatial discrimination but respond to low contrast light 0 Detect and respond to movement 0 Do so through adapting signals 0 Adapting results in Trangent response signaling 0 10 of Retinal Cells I 3 Bistratified NonMNonP Cells 0 The remaining 10 of the retinal cells 0 Intermediate size 0 Middle Soma 0 Middle Receptor Field 0 Mediate Blue Yellow Color Detection I 4 Specific Photopigment Cells 0 These are in themselves light sensitive not the photoreceptor 0 They possess pigments that allow them to directly respond to light 0 But don t do so in the visual field 0 Instead regulate light levels and Circadian rhythms 0 Each has a targeted location in the Lateral Geniculate Nucleus Thalamus o The Retinofugal Projection o The retinal axons cover 3A of the inside of the eye I Ganglion cell is the innermost layer I They are unmyelinated until the form the Optic Nerve 0 At the Optic Chiasm the axons enter the brain I Some cross Contralaterally some remain Ipsilateral o Eventually form the Optic Tract located after the Optic Chiasm November 16 2015 Sensory Systems Continued Visual Retinal Systems Specific Systems 0 1 Somatic Sensory o 2 Auditory System 0 3 Vestibular System General Overview Otolith Organs Semicircular Canals o 4 Visual System Retinal Circuits 5 Cell Types broken into two types 0 INPUT I 1 Photoreceptors o OUTPUT I 2 Ganglion Cells 0 OTHER INTER I 3 Bipolar Cells I 4 Horizontal Cells I 5 Amacrine Cells 5 Cell Layers 0 Names I Outer Nuclear I Outer Plexiform I Inner Nuclear I Inner Plexiform I Ganglion Cell 0 Outline I The three main cell types have their own layer 0 Input Layer Outer Nuclear 0 Output layer Ganglion Cell 0 Interneuron Layer Inner Nuclear Basic Circuit SetUp 0 Diagram I Two pathways Direct Vertical and IndirectLateral 0 Components I Photoreceptors initiate the signal from light I Horizontal Cell mediate the lateral pathway I Bipolar Cell funnels signals into the Ganglion I Amacrine Cell I Ganglion Cell transmits the nal signal to brain AP generated 0 Interneurons I Horizontal Cells I Amacrine Cells 0 Optic Disk gangliong ceIIs axons come together I Unmeyelianted sheath I Comes together and forms the Disk I Here there are no more Neuron bodies and light reception cannot occur 0 CenterSurround Field 0 Overview I An antagonistic Receptor field two forces working in contention 0 But here unlike the somatosensory the center can be on or off depending on what is needed 0 They will just be acting on opposite manners 0 Center Excitatory makes Surround Inhibitory I Receptor Fields 0 The Photoreceptors are the primary neuron so they have no receptor field 0 Instead the centersurround system in terms of receptor fields is mediated by the Ganglion and Bipolar Cells Ganglion Cells lead to AP while Bipolar Cells do not Their response is transmitted passively which ultimately affects the Ganglion Cell in Action Potential The retina is tuned to perceive different light frequencies which leads it to detect contrast very effectively this is the method for viewing objects contrast tuned I Known as luminesce contrast I The more focused the light is on the full portion of the retinal receptor field the more effective it is The Ganglion have receptor fields 0 Direct Vertical Center I Sent directly to Receptor which communicates with Bipolar Cell which then signals to the Ganglion Cell I Direct pathways cells use Glutamate 0 Indirect Lateral Surround I Sent to receptors which communicate with the same Bipolar Cell as above which then signals to the Ganglion Cell I Horizontal Cells and Amacrine cells are different than Glutamate 0 With a given cell the cells respond in different manners I But the Photoreceptor is always inhibited I It s the response of the Bipolar Cell that determines the overall response The On or OFF signal is determined at the BiPolar Cells the interneuron o On Center I Light in the surround causes inhibition I Works through a horizontal interneuron 0 Off Center I Light in the surround causes excitation I Still works through Horizontal Neuron But Ganglion cells have a Ganglion Receptive Field o On Center 0 Off Center 0 Spot Diagram 0 A background frequency exists baseline measure that is spontaneous 0 Light changes this frequency differing depending on its identity as Center or Surround o The light can vary covering all or some of the center all or some of the surround or even all of the field itself 0 Diffuse covering we see that the Center has a stronger output than the surround so di use light a ects center response slightly more I Pathway for Direct 0 In both Hyperpolarization of the Cone is the first part 0 This always occurs because Photoreceptors always have Dark Current inhibition causing a Hyperpolarization 0 Then the signal travels from the Cone to the Bipolar Cell Interneuron 0 And then into the Ganglion cells which lead to the Optic Nerve I Diagram di erent light spots elicit d erent cellular responses in the center 0 Center is stronger 0 Center Cells I These are the DirectVertical Pathways to the Ganglion cells 0 The Dark Current cyclic GMP channels close causes a Hyperpolarization foes from 40mV to 60mV 0 Results in an overall decrease of Neurotransmitter coming from the cone Glutamate 0 So the Bipolar cell responds in some manner to the decreased amount of Glutamate present in the synapse 0 So everything is determined by the type of Ganglion cell responding Signals go from the Cones to the Bipolar Cells to the Ganglion o Cones respond because of Dark Current Cyclic GMP and mediating positive charge in ux 0 So Glutamate is constantly being released 0 And the Bipolar Cells cause the actual on off signal 0 They all use Glutamate receptors 0 But some use mGluR other iGluR which respond differently to Glutamate 0 Can be On Center Excitatory or Off Center Inhibitory ConeBipolar Response 0 Determines the On Off response type 0 They generate the o The critical synapse 0 Based on the Bipolar Cell response to Glutamate o Divided by the manner in which they respond to Glutamate o m must turn the Hyperpolarization of the cone into a Depolarization 930 Glutamate must be Inhibitory for On Center Ganglion I So the receptors must be mGluR I So the constant presence of Glutamate decreasing results in a decreasing action of Inhibition on mGluR s o Off must turn the Hyperpolarization of the cone into a Hyperpolarization SO Glutamate must be Excitatory for On Center Ganglion I This means the receptors must be iGluR I So the constant presence of Glutamate decreasing results in a decreasing action of Excitation on mGluR s I BipolarGanglion Response 0 This synapse simply follows what has already been created and set in motion 0 So the Ganglion cells simply use Ionotropic Glutamate Receptors Excitatory 0 00n 0 0 Off 0 Surround Cells Because whatever happens in the Bipolar happens in the Ganglion The depolarization of the Bipolar Cells causes an increased amount of Glutamate release which bind to iGluR s and Depolarize the Ganglion causing AP s The hyperpolarization of the Bipolar Cells causes a decreased amount of Glutamate release which bind to iGluR s and Hyperpolarize the Ganglion causing a decrease in AP frequency


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