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visual system 2 - Coggle Diagram

- - - - lateral geniculate nucleus
        
        relay centre that receives visual information from the retina and then relays this information into the visual cortext
        
        lan neurons maintain their topographic order in the cortex
      - superior colliculus or optic tectum
    - - striate cortex
  - - - neighbouring points on a sensory surface eg. the retina are connected to neighbouring points in the brain eg. SC or tectum
        
        neighbouring RGCs in the retina terminate to neighbouring locations in the tectum
        
        neighbouring RGCs in the retina make connections with neighbouring target cells in the tectum
      - facilities the proper sensory integration and sensory integration and sensorimotor transformations
    - - suggests that axons from the retina reach their correct destination in the brain such as the lateral geniculate nucleus or the superior colliculus based on chemical markers
        
        marers are specific to certain regions and help guide the axons to their correct position creating a map that corresponds to their point of origin in the retina
        
        process ensures that spatial info in the visual field is preserved in the visual centers of the brain
        
        critical aspect of visual perception, allows the brain to accurately interpret visual stimuli based on their location in the visual field
        
        is a complex process - involves delicate interplay of growth guidance and pruning mechanisms
        
        starts with the growth of retinal ganglion cell axons from the eye towards the brain
        
        during the journey these axons encounter various guidance cues in their environment that help steer them towards their target areas
        
        either attractive or repulsive depending on types of chemical markers expressed on the axons and in the environment
        
        upon reaching their target areas in the brain the axons undergo a process of refinement where excess axons are pruned away and the remaining ones establish synaptic connections with the neurons in these areas
        
        2 more items...
    - - these gradients provide a kind of coordinate system that helps each axon find its correct destination
    - - other factors like neural activity and mechanical forces thought to play roles in the process
    - - ephori's along with Eph receptors playa crucial role in the topographic mapping of retinal ganglion cell axons - molecules serve as guidance cues that help steer the axons towards their correct destination in the brain
      - ephori's are expressed ina. gradient across the retina, with ephrinA expressed ina. high-to-low gradient from the temporal to nasal retina, and ephrinB expressed in a high to low gradient from the ventral to the dorsal retina
        
        correspondingly their eps receptors are expressed in a gradient across the target areas in the brain
        
        when an exon encounters an ephori, it triggers a repulsion response that steers the axon away from areas of high ephori concentration. this mechanism helps to establish the spatial mapping between the retina and the brain, ensuring that axons from specific parts of the retina connect to the correct locations in the Brain
  - - - frogs behaved as though vision was normal - indicates that even though information received by brain is reversed, brain cannot adjust to the change
        
        frogs try to grab food that is opposite side
  - - - overshoot towards otic tectum or superior colliculus - interstitial axon branching/arborization, encounter ephrin gradients - map remodelling - mature map
  - - - shapers topographic targeting of RGC axons
      - correct eye specific segregation in the brain
  - - - axons form the optic nerve, which carries this visual information to various parts of the brain, including the SC
        
        uses information to control eye movements and other visual motor functions - connections between RGCs and SC established during development and are crucial for normal visual system functioning
  - - - provides positional information acting as guidance cues for navigating RGCs
        
        when ligands bind to their robot receptors on the RGC - triggers a response that influences the direction of growth on these cells
  - - - structural plasticity of Robo2-negative RGC axons or tectal dendrites is sufficient to compensate for the loss of this lamination cue
        
        structural plasticity that enables functional recovery in the astray tectum is likely to be part of a normal developmental program rather than a process triggered specifically by the loss of lamination cues
      - slit-robo2 signallign regulates the lamentation of both rgc axons and tectal dendrites
      - direction selectiove RGC responses are normal in robo2 mutants
      - tectal direction selective responses are initial affected in robo2 mutants but recover later
      - by bringing axons and dendrites in precise alignment robo2 speeds the functional development of retinotectal connections
- - - - can identify edges of perception easily
  - - - each optic nerve ivides at the optic chiasm so that information from both eyes for one half of the visual field is relayed in the optic tract
        
        RIGHT VISUAL FIELD PROJECTS TO LEFT HEMISPHERE
        
        LEFT VISUAL FIELD TO RIGHT HEMISPHERE
        
        visual information from left and right retinas remains segregated in the brain
    - - he zinc-finger transcription factor Zic2 and a member of the Eph family of receptor tyrosine kinases, EphB1, are both essential for proper development of the ipsilateral projection at the mammalian optic chiasm midline
      - Zic2 is not only required but is also sufficient to change the trajectory of RGC axons from crossed to uncrossed
      - this transcription factor regulates the expression of EphB1 in RGCs and also suggest the existence of an additional EphB1-independent pathway controlled by Zic2 that contributes to retinal axon divergence at the midline
    - - right eye can also detect left visual field and vv - project ipsilaterally, projecting to the same side of the brain
      - no mix of information
    - - in teleosts its observed that zebrafish RGCs only innervate contra laterally
  - - - most species have bilateral projections so more likely that teleosts lost it
- - - - light stimulates the photoreceptors in the retina which sends signals to the retinal ganglion ells
        
        the rgcs transmit these signals throguh the optic nerve to the pretectum in the midbrain
        
        neurons in the pretectum send signals to the edinger-westphal nucleus which is the parasympathetic pre-ganglionic nucleus that controls the sphincter muscle of the muplin
        
        the edinger-westphal nucleus sends signals via the oculomotor nerve to the ciliary ganglion
        
        post-ganglionic fibers from the ciliary ganglion innervate the sphincter muscle of the pupil, causing it to contact and the pupil to constrict in response to bright light
  - - - cdh6 is a calcium dependent cell adhesion prtoein
        
        in the context of the olivary pretectal nucleus, plays a crucial role in correct wiring of retinal projections, ensures that circuits necessary for pupillary light reflex are properly formed
    - - lots of guidance cues and molecules involved in setting up connections
- - - - part of the thalamus that is primary processor of visual info received from the retin
      - visual info is relayed to the primary visual cortex aka striate cortex in the occipital lobe of the brain
      - acts as a relay station for visual info from the eyes to the visual correct where info is interpreted and perceived as sight