Final Exam Study Guide
Final Exam Study Guide NSCI 3310
Popular in Cellular Neuroscience
Joseph Merritt Ramsey
verified elite notetaker
Popular in Neuroscience
This 310 page Study Guide was uploaded by Joseph Merritt Ramsey on Sunday December 6, 2015. The Study Guide belongs to NSCI 3310 at Tulane University taught by Jeffery Tasker in Fall 2015. Since its upload, it has received 146 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.
Reviews for Final Exam Study Guide
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 12/06/15
November 11, 2015 Sensory Systems Continued – Auditory Specific Systems o 1. Somatic Sensory Assessing I) Modality (Receptors) II) Intensity III) Location IV) Duration Aspects of Touch with All Components Considered Primary Afferent Neuron Styles Neural Pathways for the Somatic Sensory System Somatic Sensory Cortex Somatatopic Organization Lateral Inhibition in the Somatic Sensory System o 2. Auditory System Physical Aspects of Sound Physical Aspects of the Ear Transduction of Sound Frequency Sensitivity Tonotopy Innervation of the Hair Cells Spiral Ganglion Cells – these cells collect to become the auditory nerve 3:1 Ratio of Outer Hair Cells to Inner Hair Cells o Outer – one spiral ganglion cell can synapse multiple times to an outer hair cell 1. One of the main jobs of the outer hair cells is to amplify the sound signal (100x Amplification) 2. They have motor proteins in the membrane that allow for contraction, which contributes to basilar membrane oscillation 3. They also generate electrical responses through the cilia, but it is not significant with sound transduction o Inner – have multiple spiral ganglion cells, but one inner spiral ganglion can only synapse to a single inner hair cell Diagram Pathway from the Hair Cell o Medulla (2nd Synapse onto the Third Order Neuron) Ventral Cochlear Nucleus (projected slightly down) This eventually branches into segments that both move to the Superior Olivary Neuron (on either side of the brain) o A. One Contralaterally o B. One Ipsilateral Those branches synapse on the Superior Olive Neuron o Massive Synapses Dorsal Cochlear Nucleus (projected slightly up) Superior Olive Nucleus This becomes binaural (from both ears) o Foundation for location relative to the sound Receives information from left ear and right ear o Midbrain – Inferior Colliculus (Third Synapse, Fourth Neuron) o Thalamus – Medial Geniculate Nucleus (Fourth Synapse, Fifth Order Neuron; LGN is Visual) o Cortex – Primary Auditory Cortex (Fifth Synapse, Sixth Order Neuron) ( Spiral Ventral Superior Inferior MGN Primary Ganglion Cochlear Olivary Colliculus (Medial Auditory Nucleus Complex Geniculate) Cortex Integration of Superior Colliculus and the Cerebellum o Superior Colliculus has Visual inputs o Inferior and Superior Coordinate with Midbrain and Cerebellum for response to stimuli and movement Assessing I) Modality (Receptors) o The above descriptions fall into receptor, for the most part o Review specifically: Physical structure of the ear Transduction of sound Cilia on the Hair Cell II) Intensity o Simple Method for intensity based on coding properties 1. Spiral Ganglion Firing Rate Based on Sound Frequency (Frequency Code) The more intense the signal is, the more bending occurs in the cilia With more bending, more Potassium is allowed to enter, further depolarizing the cell and causing a stronger response o One Direction, Larger Polarization – at the peak, more Glutamate is released o Other Direction, Larger Hyperpolarization – at the troph, more silent 2. Number of Spiral Ganglion Recruited (Population Code) 3. Spiral Ganglion Firing Rate Based on Sound Intensity (Frequency Code Again) Here, the cell has a certain number for AP Frequency that it responds to based on a Sound Frequency (Diagram) Intensity increases Spiral Ganglion response at each sound frequency o Same as the Frequency and Population influences of Somatosensory III) Location o So how does the body tell where the sound is and where it is relative to the sound? A lot of it has to do with the two ear system – distance, timing, and transduction provide information to the body o Two Aspects/Perspectives to Consider: 1. Horizontal A. Delay o 0.6milisecond delay from left to right o They can also distinguish as small as a 2-Degree change off the direct vertical axis o The Superior Olive is sensitive to the Horizontal difference in sounds source B. Intensity o The first ear it reaches will have a more intense stimulus than the later one o The wave will fade some as it travels around the head 2. Vertical A. Physical Composition of the Ear o Different locations go through different paths, as mediated by the physical composition of the outer ear o Diagram o Relay Points Relay at the Superior Olivary Complexes Aspects o 1. Lengths of Axons o 2. Timing of Stimuli Signal will come with varying delays o And the distributed neurons will have different delays and responses o In some instances, the signal will reach the Olive Neuron Simultaneously, but farther to left or to right side This is the first level of Binaural Perception and Sound Localization The Superior Olive also Projects into other spots in the brain and the Nucleus (within itself, before moving on to Inferior Colliculus) Determining Frequencies 1) Tonotopy Of the Brain o Diagram o Follows a parallel pathway Hair cells in the specific regions of the basilar membrane project directly outward, so different regions synapse to particular and different Spiral Ganglion This spatial organization is maintained throughout And because the Cochleus is divided regionally by frequency, so is each of the next stations (all the way to the brain) Primary Auditory Cortex Located in the Temporal Lobe o Rostral – Lower Frequency o Caudal – Higher Frequency Ventral to the Lateral Fisher 2) Phase Locking o Definition For every peak of sound wave, we have an AP in the Spiral Ganglion But this doesn’t always occur with every sound wave at every step Each Step Loses some Signal Passively But when AP is generated, it always falls on a given peak of locus for the sound wave So various frequencies produce a specific pattern of AP Produciton o Also helps differentiate different pitches (in addition to the Tonotopy) o Diagram o Frequency Effect: Low – phase locking occurs High – the phase locking is lost with too much energy, brain must rely on Tonotopy o 3. Vestibular System General Overview Functions – balance, equilibrium, posture, head, body, eye movement Vestibular Labyrinth o Same region of the Auditory System o Two Structures 1. Otolith Organs – shaded; macula, one is horizontal, one vertical; fluid filled, moving around Gravity, Linear Acceleration Head Tilting Posture and Standing 2. Semicircular Canals – three, organized to cover all three dimensions; fluid filled, moving around Rotational Acceleration (3D) Head Rotation (3D) o Both utilize hair cells in a comparable way to the Auditory System Respond to the fluid movement within the Labyrinth Use the same mechanisms as the Cochlea Otolith Organs (Linear Acceleration) Overview o Macula is the sensory Organ (Comparable to the Organ of Coti in Auditory (so the transduction organ)) o Macula are the primary organ (have utricle and saccule components) o Have hair cells that move within a gelatinous cap The cilia are stuck in the gel The cap is made of Endolymph (has very high Potassium Concentration) So K can flow inward when Cilia move o The cap is covered in dense otoliths (Calcium Carbonate crystals) that move the gel Density means if they move, the cap moves, which means the hair cells move Diagram o Components Kinocilium – the largest, affects movement of all the others) Otoliths – small, Calcium Carbonate Crystals that move and pull because of the density Maculae o Directions Saccule – vertical Macula (detects movement up and down) Utricle – horizontal, hair cells stick up vertically (detects movement horizontally) o Directional interplay Inertia moves the gelatinous cap in linear direction o Synapse on the Scarpoganglion (the first neuron) Dual Ear System o Each ear has its own system, but the mirror is occurring in the other ear So if hair cells are moving toward longer cilia and depolarizing in one ear… They are moving toward smaller cilia and hyperpolarizing in the other… This duality gives information to the brain o They have opposite responses Semicircular Canals (Angular Acceleration) Diagram o Set up in large ringed circles O o Set up in 360 Coverage o Components Ampulla Cupula Cilia Endolymph Vestibular Axons Overview o Deals with angular acceleration (so change in speed) They have a 3Dimesional Structure to them o Does not change with velocity – changes with acceleration So it sort of has the effect of Adaptation in the Vestibular system, with a slightly altered graph Diagram The speed doesn’t matter – just the change o Mirror organization also occurs in Semi Circular Canals in 3D Angular Acceleration o Whole structure is filled with Endolymph (high Potassium) November 13, 2015 The Visual System Specific Systems o 1. Somatic Sensory o 2. Auditory System Physical Aspects of Sound Physical Aspects of the Ear Transduction of Sound Frequency Sensitivity Tonotopy Innervation of the Hair Cells Assessing I) Modality (Receptors) II) Intensity IV) Location Tonotopy into the Brain Phase Locking o 3. Vestibular System General Overview Otolith Organs Semicircular Canals Innervation and Transduction of the Vestibular Apparatus Hair Cells – activate axons of the ScarpoGanglion (first nerve) cells (The Vestibular Nerve) CNS Primary Projection – those axons project to the Vestibular Nucleus o Lateral Vestibular Nucleus – Otolith Organs o Medial Vestibular Nucleus – Semicircular Canals Higher Order Projections o 1. Brain – cerebellum, Hypothalamic Nuclei, neck motor neurons (Medial Projections) o 2. Spinal Cord – limb motor neurons, movement (Lateral Projections) o 3. Sensory Feedback – information on acceleration, head position, movement, sensory feedback o 4. Eyes (Motor Portion) Eye movement is directed and stabilized with the Vestibular System Known as Vestibulo-Ocular Reflex (VOR) Compensation for head movement – head moves in a given direction, the same side excitation ceases (so motor neurons acting against the direction of the head are activated) o 4. Optic System Nature of Light Light is Electromagnetic Radiation which has wavelengths Spectrum Concept o Light exists at all wavelengths, but visible is a narrow range between 400 and 700nm Properties of Light o 1. Reflection – causes light scattering; occurs to some degree on all objects o 2. Absorption o 3. Refraction – bent to varying degree as it travels, depending on the medium Importance in the eye? Cornea and Len Refract and Focus light Focused to the Fovea ¾ of the eye is covered by Retinal Space Eye Structural Overview Components o Cornea and Lens Most refraction (and the initial refraction) occurs at the Cornea The lends does fine tuning with refraction and focusing o Retina Located all the way in the back of the eye Photoreceptors present on the farther (most medial) layer Fovea (center of the retina) Layers separate allowing a direct path Highest Visual Acuity o Pigment Epithelium Located just behind the five layers Melanin is present and absorbs any stray light that goes through the main layers (Fovea and Photoreceptors) Prevents stray light reflection and unwanted activation or damage The pigment is Choroid Information Input o Light from environment is refracted and focused This light is based on reflection from the environment (sun is a source, what we see is reflection) It enters the eye and is bent immediately o Refraction (Bending) 1. Cornea – does the most bending of the light 2. Lens – fine-tuned bending The lens can shift and change size to adjust the refraction o The closer the object, the fatter the lens grows and focuses the light With age, the lens experience calcification and is not as flexible Retinal Components Retinal Layers o 1. Outer Nuclear Layer (Photoreceptors) Photoreceptors present here No other neurons have the pigment to protect (although evidence has no shown some Ganglion cells have pigments) o 2. Outer Plexiform Layer Refers to Plexus Fibers First layer is relaying Photoreceptors to the Interneurons o 3. Inner Nuclear Layer (Interneurons) Cell bodies from the three Interneuron types (Bipolar, Horizontal, Amacrine) o 4. Inner Plexiform Layer Connecting Interneurons to the Ganglion Cells o 5. Ganglion Cell Layer Ganglion cells actually send the action potential Come together to form the Optic Nerve Important Considerations of the Retinal Layers o 1. Photoreceptors are in the very back of the eye o 2. Axons cover the retina, but they are unmyelinated until they reach the optic nerve (so there’s a low impedence or reflection of light o 3. All layers are reflecting light, though, so light is scattered all throughout the eye. Because of this, there is less acuity outside of the fovea (peripheral vision) Fovea o Actions that increase visual acuity in the Fovea? 1. Light has a direct path to the Fovea There’s a sort of divot in the retinal cells that allows a direct path for fovea light So a minimal amount of reflection and refraction occurs 2. Cones are present in a very high density in the fovea Cones have the most acuity in response to light 3. Cornea focuses light towards the center in the fovea 4. Fewer blood vessels to inhibit in the fovea o Very center is the Foveola (least amount of resistance) Photoreceptors o Basic Morphology 1. Outer Segment – comparable to dendrite 2. Inner Segment – comparable to the soma 3. Synaptic Terminal o Pigments in the Receptors Rods – Rodopsin Cones – red, blue, green –opsin They’re present throughout the membrane layers o Rods Color blind pigment – doesn’t respond to a particular wavelength, just light Many more layers and pigment present than in Cones But they have a low acuity o Cones Different cones have different pigments present in them They also have less membrane space and therefore a much lower sensitivity to light that rods (therefore day sight) But they have a much higher acuity (because of color detection and spatial resolution) o Visual Acuity Factors with Cones and Rods? 1. Position (Cones are in the Fovea) Cones are primarily in the fovea, so their light is most direct 2. “Density” (Cones have a 1-to-1 connection to the Brain) Each cone has its own field that leads to a CNS connection Each has a specific pathway Comparable to the 2 Point discrimination test in the somatic system Phototransduction Process – the physical input to electrical signals o 1. Light Absorbed o 2. Opsin (7 Membrane Protein) Changes Conformations Retinal (or some protein, Retinal is in Rods) in the Opsin Retinal changes from 11-cis Conformation to an all trans Photoisomerizes Retinal o 3. G-Protein is triggered nd o 4. 2 Messenger Activated (cGMP Phosphodiesterase, which acts on cGMP) Changes cGMP to 5’GMP o 5. Deactivation of cGMP means the cGMP channel cannot be activated, so Sodium no longer flows in o 6. Results in an overall hyperpolarization of the membrane Overview o Dark Current This is the underlying current present in retinal cells even in the dark This current leaves the cell resting right around - 40mV cGMP binds ionotropically to a Sodium gate o Hyperpolarization But when cGMP is deactivated by cGMP Phosphodiesterase (to 5’GMP), the gate is closed Less Sodium entering the cell leads to a Hyperpolarization This hyperpolarization subsequently decreases Glutamate release from the Photoreceptor to the Bipolar Cell Color Construction o Multiple cones with various Opsins take in light and produce signals to make the color perception November 16, 2015 Sensory Systems Continued – Visual: Retinal Systems Specific Systems o 1. Somatic Sensory o 2. Auditory System o 3. Vestibular System General Overview Otolith Organs Semicircular Canals Connections in the CNS o 4. Visual System Properties of Light Phototransduction Retinal Circuits 5 Cell Types – broken into thee types o INPUT Neurons 1. Photoreceptors – take in information from environment o OUTPUT Neurons 2. Ganglion Cells – give information to brain o INTERneurons 3. Bipolar Cells 4. Horizontal Cells 5. Amacrine Cells 5 Cell Layers o Names Outer Nuclear (cell bodies) Outer Plexiform (synapses) Inner Nuclear (cell bodies) Inner Plexiform (synapses) Ganglion Cell (Ganglion Cells) o Outline The three main cell types have their own layer – Input Layer – Outer Nuclear Output layer – Ganglion Cell Interneuron Layer – Inner Nuclear Basic Circuit Set-Up o Diagram Two pathways – Direct/Vertical and Indirect/Lateral o Components: Photoreceptors – initiate the signal from light Horizontal Cell – mediate the lateral pathway Bipolar Cell – funnels signals into the Ganglion Amacrine Cell Ganglion Cell – transmits the final signal to brain; AP generated o Interneurons – Horizontal Cells Amacrine Cells o Optic Disk – Ganglion cells’ axons come together at the back of the eye to form the Optic Nerve Unmeyelianted sheath Comes together and forms the Disk Here, there are no more Neuron bodies and light reception cannot occur Center-Surround Field o Overview An antagonistic Receptor field (two forces working in contention) But here (unlike the somatosensory) the center can be on or off, depending on what is needed They will just be acting on opposite manners o Center Excitatory makes Surround Inhibitory o Receptor Fields The Photoreceptors are the primary neuron, so they have no receptor field Instead, the center-surround 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) o Known as luminesce contrast o The more focused the light is on the full portion of the retinal receptor field, the more effective it is The Ganglion Cells have receptor fields Direct (Vertical) – Center o Sent directly to Receptor, which communicates with Bipolar Cell, which then signals to the Ganglion Cell o Direct pathways cells use Glutamate Indirect (Lateral) – Surround o Sent to receptors in the surrounding cells, which communicate with the same Bipolar Cell as above, which then signals to the Ganglion Cell o Horizontal Cells (GABA) and Amacrine cells (Gap Junction and Glycine) are different than Glutamate With a given cell, the cells respond in different manners o But the Photoreceptor is always inhibited o 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) On Center o Light in the center causes excitation o Works through a horizontal interneuron Off Center o Light in the surround causes excitation o Still works through Horizontal Neuron Spot Diagram A background frequency exists (baseline measure) that is spontaneous Light changes this frequency, differing depending on its identity as Center or Surround The light can vary, covering all or some of the center, all or some of the surround, or even all of the field itself Diffuse covering – we see that the Center has a stronger output than the surround, so diffuse light affects center response slightly more Pathway for Direct In both, Hyperpolarization of the Cone is the first part o This always occurs because Photoreceptors always have Dark Current inhibition causing a Hyperpolarization Then the signal travels from the Cone to the Bipolar Cell (Interneuron) And then into the Ganglion cells, which lead to the Optic Nerve Diagram – different light spots elicit different cellular responses in the center Center is stronger o Center Cells (Bipolar Interneurons) These are the Direct/Vertical Pathways to the Ganglion cells The Dark Current (cyclic GMP channels close) causes a Hyperpolarization (foes from -40mV to -60mV) Results in an overall decrease of Neurotransmitter coming from the cone (Glutamate) So the Bipolar cell responds in some manner to the decreased amount of Glutamate present in the synapse o So everything is determined by the type of Ganglion cell responding Signals go from the Cones to the Bipolar Cells to the Ganglion Cones respond because of Dark Current (Cyclic GMP and mediating positive charge influx) o So Glutamate is constantly being released And the Bipolar Cells cause the actual on/off signal They all use Glutamate receptors o But some use mGluR, other iGluR, which respond differently to Glutamate o Can be On Center (Excitatory) or Off Center (Inhibitory) Part I: Cone-Bipolar Response Determines the On/Off response type o They generate the o The critical synapse o Based on the Bipolar Cell response to Glutamate Divided by the manner in which they respond to Glutamate o On – must turn the Hyperpolarization of the cone into a Depolarization SO Glutamate must be Inhibitory for On Center Ganglion So the receptors must be mGluR 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 This means the receptors must be iGluR So the constant presence of Glutamate decreasing results in a decreasing action of Excitation on mGluR’s Part II: Bipolar-Ganglion Response This synapse simply follows what has already been created and set in motion So the Ganglion cells simply use Ionotropic Glutamate Receptors (Excitatory) o Because whatever happens in the Bipolar happens in the Ganglion On o 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 Off o 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 o Surround Cells November 18, 2015 Sensory Systems Continued – Visual System: Rods and the CNS Specific Systems o 1. Somatic Sensory o 2. Auditory System o 3. Vestibular System o 4. Visual System Retinal Circuits Center-Surround Field o Center Cells (Cones) Center Review Diagram o Surround Cells (Cones) General Diagram Horizontal Cell connects to the Center Pathway from the Surround Cell Light hits the surround now More Detailed Pathway Diagram Shows how inhibition and Excitation work in conjunction Overall Breakdown 1. Surround Cone to Horizontal Cell o The Cone is still releasing Glutamate (in this case the surround cone) o Synapses onto the Horizontal Cell o This synapse is made of iGluR’s (an excitatory synapse) So whatever the Cone does the Horizontal Cell does o The Hyperpolarization of the Horizontal cell results in decreased output of its Neurotransmitter (GABA, so decreased inhibition = excitation) 2. Horizontal Cell to Center Cone o The Horizontal Cell Synapses onto the Center Cell o The Horizontal Cell is a GABAergic Cell So it releases GABA to affect the synapsed cell (The Adjacent Center Cone) This causes a depolarization on the center cell (Cone) o 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 3. Center Cone to Center Bipolar o And if the initial signal is opposite (caused by the surround response), then the subsequent cellular responses are also the opposite On Center Pathway (Surround Causes Inhibition) So A Depolarization of the On Center Cone due to Surround Horizontal Releases more Glutamate Leads to Hyperpolarization of On Center Bipolar Cell (because of mGluR’s) Leads to Hyperpolarization of On Center Ganglion Cell And a decrease in AP frequency in Ganglion Off Center Pathway (Surround Causes Excitation) So A Depolarization of the On Center Cone due to Surround Horizontal Releases more Glutamate Leads to Depolarization of Off Center Bipolar Cell (because of iGluR’s) Leads to Depolarization of Off Center Ganglion And an Increase in AP Frequency in the Ganglion o Glutamate Cells Photoreceptors – glutamate releasing to affect the Bipolar Cells 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) Spiral Ganglion – glutamate releasing to create an AP Pathway Described Rods o Overview They are also hyperpolarized when activated Same as all photoreceptors Have high sensitivity and low acuity Responsible for night vision But also tap into Cone Pathway 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 o So less Glutamate is excitatory 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 AII Amacrine Cell o AII Amacrine Cells Hyperpolarization of the rod causes less Glutamate onto Bipolar Cells (mGluR) The decreased inhibition (Because of the Metabotropic receptors on Rod Bipolar Cells) causes a Depolarization (Excitation) and a release of Glutamate onto the AII Amacrine Cells (iGluR) Amacrine cells Have iGluR receptors on their synapses, So the Inotropic Receptors Cause an Excitation of AII Amacrine This excitation causes a resulting AP (On Ganglion Cells) which leads to: 1. A Release of Inhibitory Glycine (onto off center Ganglion) o The other types of Inhibitory Neurotransmitter o Synapses to the Off Center Ganglion Cells 2. Spread of Depolarization (onto On Center Ganglion) o So if it only releases Glycine, how does it excite anything? o Through Gap Junctions o Uses an Electrical Synapse o So ion flow directly through Has to act on Two Types of Synaptic Cells Must act on On and Off Center Ganglion Cells Acts through Action Potential o Pathway 1. Rod to Bipolar Synapse Inhibition in the Rod causes Less Glutamate onto Bipolar Cell (Through mGluR) On response to Rod Synapse This Passive Depolarization releases more Glutamate onto AII Amacrine 2. Bipolar to AII Amacrine AII Amacrine Cells have iGluR, so they follow the previous trend Bipolar cells are Depolarized, releasing more Glutamate which excites the AII Amacrine Cells This excitation causes an Action Potential in the AII Amacrine 3. AII Amacrine to… AII Amacrine Project to On Center and Off Center Ganglion Cells Excited by increase of Glutamate from the Bipolar Cell, and results in AP The AP affects the Ganglion Cells o Through Glycine and Gap Junctions Important Note: Center/Surround Antagonism is lost in this mechanism So Night vision has lower resolution Also, center vision is not as clear when using the Rods pathway o Because Center is mostly comprised of Cones o Rods are congregated on Surround Light Regions o Rods are in the Periphery of the Retina Central Nervous System and Vision Ganglion Cells Synapse in the CNS – Types of Ganglion o Breakdown of Types 1. P-Cells Midget Cells Parvocellular Neuron Projections o Smaller Soma o Smaller Receptive Field (means higher spatial discrimination, more discrete signals) o Small (But Huge Amount) of dendrites Firs cell in pathway all the way to Visual Cortex 80% of Ganglion in Retina Red/Green Color Vision and Spatial Discrimination More sustained response 2. M-Cells Parasol cells for large dendrites Magnocellular (larger cells) o Large Somas o Large Receptor Fields (so insensitive to color, not as tuned to spatial discrimination but respond to low contrast light) Detect and respond to movement o Do so through adapting signals o Adapting results in Trangent response signaling 10% of Retinal Cells 3. Bistratified (NonM-NonP Cells) The remaining 10% of the retinal cells Intermediate size o Middle Soma o Middle Receptor Field Mediate Blue Yellow Color Detection 4. Specific Photopigment Cells These are in themselves light sensitive, not the photoreceptor They possess pigments that allow them to directly respond to light But don’t do so in the visual field o Instead regulate light levels and Circadian rhythms o Each has a targeted location in the Lateral Geniculate Nucleus (Thalamus) The Retinofugal Projection o The retinal axons cover ¾ of the inside of the eye Ganglion cell is the innermost layer They are unmyelinated until the form the Optic Nerve o At the Optic Chiasm, the axons enter the brain Some cross Contralaterally, some remain Ipsilateral o Eventually form the Optic Tract, located after the Optic Chiasm November 23, 2015 Sensory Systems Continued – Visual System Specific Systems o 1. Somatic Sensory o 2. Auditory System o 3. Vestibular System o 4. Visual System Retinal Circuits Center-Surround Field o Center Cells (Cones) o Surround Cells (Cones) Rods Central Nervous System and Vision Ganglion Cells Synapse in the CNS – Types of Ganglion The Retinofugal Projection Ganglion Cell Pathways o Four Primary Targets 1. Lateral Geniculate Main target for Visual Perception Nucleus in the Thalamus Specialized for visual input 2. Hypothalamic Suprachiasmatic Nucleus The intrinsically photosentive cells dealing with Circadian Rhythms connect in this region of the Hypothalamus Base of the Hypothalamus that controls everything regarding Circadian Rhythms o Regulated by your light/dark schedule Located just Doral of the Optic Chiasm 3. Pretectum Part of the Midbrain Responsible for Pupillary and Lens reflexes Adapts to light input 4. Superior Colliculus Also in Midbrain Controls head and eye movement Inferior Colliculus receives auditory inputs and coordinated with Superior Colliculus o Pathway Layout SEQUENCE: Ganglion Cells Optic Nerves Optic Chiasm Optic Tracts LGN Optic Radiation Primary Visual Cortex Radiating Fashion Projections from the LGN are radiating to synapse to the Cortex Outputs of Retinal Ganglion Cells o 3 Types of Information: Form, Color, and Motion All the information from the visual environment have to be processed and synthesized – broken down and reconstructed as something useful And there are different cells that deal with each type of input o Breakdown of Divisions 1. M Ganglion Cells Project to Magnocellular Layers in the LGN that are specific for these cells types These cells deal predominantly with movement and motion in the visual field 2. P Ganglion Cells Project to the Parvocellular Layers in the LGN These cells predominantly with form and color Vast majority of cells in the Retina 3. Bistratified Ganglion Cells Project to the intermediate layers, the Koniocellular Region These cells predominantly relay information about blue/green color Color Opponency System o Center Surround Opponency of Colors There are also color opponency to deal with different wavelengths of light inputs Center is tuned to one, Surround is tuned to another Works again through Horizontal Cells (Like On/Off Center Ganglion) o Red/Green Example Ganglion Cell (Diagram) Red Center and Green Surround Baseline signals exist Weak activation of the center occurs with Diffuse red light o Blue Yellow (Blue Center, Yellow Surround Example) Yellow Doesn’t Exist, so the perception of red and green creates yellow Does so through the reception of surround cells (so surround is yellow) o Results in a Saturation Process If cones are exposed to one color for a long period of time, they become saturated and desensitized to that given color frequency So looking away after saturation causes that frequency reception to be less prominent So if your red cones are desensitized, your green cones will have an increased activation Visual Field Projection o Light enters both eyes to provide input Entirety of visual field is comprised on both eyes Both eyes get inputs from both sides, but the eye on the side of the visual field perceives more on its given side because of the nose o Retinal Projections and the Visual Field Divided into quadrants Superior and inferior And Primarily into Temporal (closer to Temple) and Nasal (Closer to Nose) Those division take different paths to the brain And in the retina, the image is inverted and reversed because of the lens o Monocular Vision vs. Binocular Vision Each side only gets a part of the opposite side (So the Right eye perceives all of the right side and part of the left side) This is the Monocular Portion And the Fovea is the midpoint of the eye, where you will focus for vision The middle overlapping portion of the visual field is the Binocular vision, the portion that both eyes can see o Diagram (Looking at Binocular Vision) Nasal Hemiretina – everything Medial of the Fovea Temporal Hemiretina – everything lateral of the Fovea Temporal Crescents – the monocular portion that is only seen by one eye (specifically, the ipsilateral eye) o Optic Nerve and Optic Tract Ganglion cell axonal projection move into the brain (inputs from the left side and the right side) Half the axons go Ipsilateral (Temporal) and half go Contralateral (Nasal) Nasal Hemiretinas Cross to the Thalamus Temporal Hemiretinas Remain Ipsilateral to the Thalamus Overview 1. Each eye gets inputs from both o This information exists to the optic nerves 2. Each optic nerve carries information of the contralateral side o Based on light trajectory, the left side of the eye receives information from the right side of the field of vision o So, within the right eye, the right side of the retina perceives information from the Left Field (so the Temporal Crescent) and the left side of the retina perceives information from the nasal portion (the binocular portion) of the field 3. The Optic Nerves meet at the Optic Chiasm and Segregate 4. Once axons cross in the Chiasm, the Optic Tracts are formed o This makes the Optic Tracts exclusive to one side of the vision field – so left tract carries all of the right side information (right eye Temporal and left eye nasal hemiretinas) o Visual Deficits Optic Nerves have information from left and right sides of the vision Both are in retina Both are in Nerves But Segregation occurs at the Chiasm, so tracts have only Left or Right when reaching the LGN Inputs from both sides of the visual field becomes segregated as it becomes the optic tract So the right optic tract only contains information from the left side of the eye Consider the Left Tract (Right Side Vision): o 1. Temporal portion of the left eye (Stays) o 2. Nasal Portion of the Right Eye (Crosses) o Lesion Examples The patient cannot see the left temporal crescent. Where is the lesion? 1. Optic Nerves? o Cutting a single optic nerve could result in the single eye (left eye, inclusive of the temporal crescent) being lost, but the right eye could still see parts of the left hemisphere 2. Optic Chiasm? o Would cut out everything that crosses, so all temporal crescents (so binocular effect) 3. Optic Tracts? o Carry all of the left side vision on the right tract, so an entire hemisphere would be lost The Left Temporal Crescent can only be seen by the Left eye, and specifically by the right side of the retina o That right side forms the Nasal Hemiretina, which forms a Nerve before Crossing at the Chiasm o So cutting the nerve at the Left Optic Nerve (so vision from the left eye is lost, the monocular portion is lost) The entire right side of the visual field is lost. Where is the lesion? 1. Optic Nerves? o As seen before, cuts out single eye, not single hemisphere 2. Optic Chiasm o As noted, would cut out all crossings, so the Nasal Hemiretinas which see the Temporal Crescents 3. Optic Tracts o As noted, carries all information from one side of vision, so would cut out an entire hemisphere The right side is gone, so the Left tract must have been cut The temporal crescents on both sides are lost. Where is the lesion? 1. Optic Nerves? o As seen before, cuts out single eye, not single hemisphere 2. Optic Chiasm o As noted, would cut out all crossings, so the Nasal Hemiretinas which see the Temporal Crescents 3. Optic Tracts o As noted, carries all information from one side of vision, so would cut out an entire hemisphere So it had to have been the Chiasm, taking out both the Nasal Hemiretinal Nerves, which see the Crescents (binocular effect) Projections to the LGN o All opposite side visual field Right LGN receives information from the left visual field, and vice versa for the Left LGN o Made up of Six Layers and Intermediate Zones 1. Magnocellular Layers – receive from M Ganglion Cells Two Layers Layers 1-2 Devoted to movement and location, the “Where” signal 2. Parvocellular Layers – receive from P Ganglion Cells Four Layers (Because 80% is P-Cells)
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'