NEU 302 1st Edition Exam 3 Study Guide Lectures 1 15 Neuroscience EXAM 3 30 from Exam 1 50 from Exam 2 20 New Info Exam 1 Material 30 Lecture 1 January 15th Central Visual Pathways Chapter 12 1 After the signal of light is transduced in the eye where does the signal go or project to a Projections from the retina i The signal goes from the optic disk of the retina to the optic nerve and finally to the optic chiasm 1 60 of ganglion cell axons are contralateral a Cross midline at optic chiasm b They are the ganglion cells from the nasal retina 2 40 of ganglion cell axons stay ipsilateral on same side ii After the signal passes the optic chiasm the axons are referred to as the optic tract b Retinogeniculostriate Pathway i Optic Tract Lateral Geniculate Nucleus LGN Striate Cortex V1 ii Lateral Geniculate Nucleus LGN 1 Located in the ventral lateral thalamus 2 Segregated into 6 separate layers a Each layer processes specific aspects of the visual information b Layers 2 3 and 5 process visual info from ipsilateral same side eye or the Temporal Retina c Layers 1 4 and 6 process visual info from contralateral eye or the Nasal retina 3 There are different cells types in different layers of the LGN a Parvocellular Layers P Cells i More dorsal layers 1 Layers 3 4 5 and 6 ii Small neurons Petite iii Sustained response iv Convey Color information 1 Driven by different classes of cones 2 Sensitive to different wavelengths b Magnocellular Layers M Cells i Ventral Layers 1 Layers 1 and 2 ii Large neurons Mega 1 More extensive dendritic fields 2 Larger diameter axons iii Larger receptive fields iv Respond to the presentation of visual stimuli in a very quick short manner v Insensitive to different wavelengths 4 Segregation of input into the LGN i e what layer the signal goes to depends on the Ganglion Cell Type as well as the eye that signal is coming from 5 There are also receptive fields in the LGN similar to those found in the retina a On centre fields i When light is on the center of the field the cell increases firing ii When the cell is on the surrounding receptive field the cell inhibits firing b Off centre fields i Same as the on centre fields except the opposite ii Center inhibition iii Surround excite iii Striate Cortex myelin stria 1 V1 physiology aka Primary Visual Cortex aka Brodman area 17 cell density 2 1st visual area 3 Characteristics a Striated lines of gennari or striped tissue b Mostly buried in a sulcus Calcarine Sulcus in the occipital lobe iv Function provides your overall visual fields 1 Each eye produces a hemifield 2 There is overlap between these fields resulting in the binocular visual field a This field allows depth perception 3 v Consequences of lesions in pathway 1 Damage to retina or one of the optic nerves before chiasm a Loss of vision that is limited to the eye of origin b Still have bits of each visual field i Loss of peripheral vision in same eye ii Loss of binocular vision in contralateral eye but contralateral visual field is still intact 2 Damage to one of the Optic Tracts LGN or Optic radiation a After Optic chiasm b Results in Loss of vision of entire contralateral visual field c Complete loss of vision in affected area of binocular visual field d Referred to as Homonymous Hemianopsia 3 Damage to Optic chiasm a Loss of vision in temporal visual field only i Parts of visual field loss from both eyes ii Most peripheral part lost iii Nasal retina info lost b Referred to as i Bitemporal Hemianopsia ii Heteronomous Hemianopsia 4 Smaller visual field deficit referred to as Scotomas instead of anopsias c Other targets of Retinal Ganglion Cells i Pupillary Light Reflex 1 Controls pupil constriction in response to light 2 Pathway a Optic Nerve Pretectum Edinger Westphal Nucleus EWN Preganglionic parasymp fiber in cranial nerve 3 Ciliary Ganglion Pupillary Constrictor Muscle 3 This pathway has bilateral projections from the retina a Both EWN are activated by only one Pretectum b Allows both eyes to be influenced simultaneously 4 Consequences of lesions a Normal i Both stimulated eye direct response and unstimulated eye consensual response constrict in the light b Damage to Oculomotor Nerve or EWN in Brainstem i Direct response but no consensual response ii Problem with visceral motor outflow to problem eye c Damage to sensory input to problem eye i Retina or optic nerve damage ii Light in one eye has direct and consensual response iii Light in the problem eye has no direct or consensual response ii Superior Colliculus 1 Dorsal surface of the midbrain 2 Coordinates head and eye movements to visual as well as other targets 2 Organization a V1 i Retinotopic Organization 1 Left visual field of each eye projects to the right hemisphere and visa versa 2 Adjacent neurons have receptive fields that include slightly different but overlapping parts of the visual field 3 Cells in each structure in each structure can be seen as contributing to a map of the visual field ii Laminar Organization 1 Divided into 6 principle layers 2 Lateral Geniculate Neurons terminate most heavily in layers 4C and 4A of the cortex a 4C is dominated by spiny stellate neurons whose dendrites are confined to this layer b Axons from here convey the activity supplied by the LGN to other cortical layers 3 Pyramidal neurons located in the superficial layers of visual cortex project to the extrastriate cortical areas 4 Pyramidal neurons located in the deeper cortical areas project to subcortical targets like the LGN or superior colliculus 5 The organization serves to segregate populations of neurons that have distinct patterns of connectivity iii Columnar Organization 1 Combines the input from two eyes 2 Since the LGN processes the inputs from the ipsilateral eye and the contralateral eye in different layers a Individual LGN nuclei are strictly monocular 3 The information from the left and right eye is conveyed by the geniculate axons to terminate in alternating eye specific Ocular Dominance Columns within cortical layer 4 4 The signals now converge as the layer 4 neurons synapse on individual neurons in other cortical layers a Though the neurons are binocular the relative strength of the input from the two eyes varies from neuron to neuron b Receptive Fields i The single simple cells that capture light in retina go to the LGN and act as onand off center activation with overlapping receptive fields ii The light activation of the population of receptive fields then synapse with one neuron that is