Notes for November 23-27
Notes for November 23-27 NSCI 3310
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Joseph Merritt Ramsey
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This 7 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 26 views. For similar materials see Cellular Neuroscience in Neuroscience at Tulane University.
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Date Created: 11/28/15
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 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 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 Primary 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 These a 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 Each eye gets inputs from both Once axons cross in the Chiasm, 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 The Optic Nerves meet at the Optic Chiasm and Segregate This makes the Optic Tracts exclusive to one side of the vision field 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 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 Magnocellular Layers – receive from M Ganglion Cells Two Layers Layers 1-2 Devoted to movement and location, the “Where” signal Parvocellular Layers – receive from P Ganglion Cells Four Layers (Because 80% is P-Cells) Layers 3-6 Respond to Form and Color Information, the “What” signal Half the layers are devoted to the contralateral eye (Nasal Signal that crossed) (1,4,6), while half are devoted to the Ipsilateral eye (so the Temporal signal) (2,3,5)