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Striate Cortex Anatomy - Coggle Diagram

- - - - 6 layers
        
        Layer I, just under the pia mater, is largely devoid of neurons and consists almost entirely of axons and dendrites of cells in other layers
        
        three sublayers in layer IV (A,B,C)
        
        Layer IVC is further divided into two tiers called IVCα and IVCβ.
        
        separate LGN streams remain anatomically segregated in layer IVC
        
        Magnocellular LGN neurons project primarily to layer IVCα, and parvocellular LGN neurons project to layer IVCβ. (:world_map: B)
        
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        Koniocellular LGN axons follow a different path, making synapses primarily in layers I and III.
        
        radial connections
        
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        axons of some layer III pyramidal cells ex- tend collateral branches that make horizontal connections within layer III
        
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        ALSO!! the left eye and right eye inputs to layer IV are laid out as a series of alternating bands, like the stripes of a zebra
        
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        can be seen clearly in a Nissl stain of the cortex
        
        leaves a deposit of dye in the soma of each neuron
      - two principal cell types
        
        Spiny stellate cells
        
        seen primarily in the two tiers of layer IVC
        
        small neurons with spine-covered dendrites that radiate out from the cell body
        
        Pyramidal cells
        
        seen outside layer IVC
        
        also covered with spines BUT
        
        characterized by a single thick dendrite that ascends toward the pia mater and by multiple dendrites that extend horizontally.
        
        only pyramidal cells send axons out of the striate cortex to form connections with other parts of the brain (+into the white matter)
        
        exception: spiny stellate neurons in layer IVB that project to area V5
        
        inhibitory neurons, which lack spines, are sprinkled in all cortical layers as well. These neurons + spiny neurons form only local connections.
        
        Layer II, III, and IVB pyramidal cells send their axons to other cortical areas.
        
        Layer V pyramidal cells send axons all the way down to the superior colliculus and pons.
        
        Layer VI pyramidal cells give rise to the massive axonal projection back to the LGN.
        
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        Pyramidal cells also branch and form local connections in the cortex.
- - - - central few degrees of the visual field are overrepresented, or magnified, in the retinotopic map 🔍
      - when the retina is stimulated by a point of light, the activity in the striate cortex is a broad distribution with a peak at the corresponding retinotopic location. 📈
- - - - layers II and III play a key role in visual processing, providing most of the information that leaves V1 for other cortical areas
      - in cross sections appears as a colonnade, a series of pillars at regular intervals, running the full thickness of layers II and III and also in layers V and VI
        
        each blob centered on an ocular dominance stripe in layer IV.
        
        Between the blobs are “interblob” regions.
        
        receive direct LGN input from the koniocellular layers, as well as parvocellular and magnocellular input from layer IVC of striate cortex.