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The Eye and Vision (Visual Stimulus from Eye to Brain (Converge on optic…

- - - - Continue to thalamus via the optic tracts
        
        each optic tract contains fibers from the lateral aspect of the eye on the same side and the medial aspect of the opposite eye
        
        each will carry information from the same half of the visual field
        
        most fibers at the paired optic tracts will pass to the lateral geniculate of the thalamus
        
        axons of the thalamic neurons project through the internal capusle
        
        extends to the primary cortex of the occipital lobes
- - - - hyperopia (farsightedness)
        
        parallel light rays from distanct objects are focused behind the retina so lens connot bring focal point onto retina even at full refractory power
        
        eyeball too short
      - astigmatism
        
        unequal curvatures in different parts of cornea/lens that leads to blurry images
      - myopia (nearsightedness)
        
        distant objects are focused in front of the retina rather than on it
        
        eyeball too long
    - - aqueous humor
        
        lens
        
        vitreous humor
        
        retina
    - - greatest refraction at cornea
      - amount of refraction is variable at the lens
    - - 1) requires accommodation of the lenses 2) occurs because ciliary muscles contract
    - - 1) lens is flattened 2) ciliary muscles are relaxes
- - - - choroid
        
        blood vessels that provide nutrients to all eye layers, brown pigment helps absorb light so doesn't scatter/reflect
      - ciliary body
        
        thickened ring of tissue that encircles lens, interlacing smooth muscle bundles which control lens shape
      - iris
        
        visible colored part of eye between cornea and lens
        
        helps vary pupil size
        
        2 smooth muscles layers in bunches of sticky elastic fibers
        
        sphincter papillae contract to constrict pupils (less light), parasympathetic control
        
        dilator pupillae contract and pupils dilate (more light), sympathetic control
    - - delicate, 2 layered retina (contains millions of photoreceptors)
        
        Outer pigmented layer absorbs light and prevents it from scattering in the eye, acts as a phagocyte to remove dead/damaged photoreceptor cells and store Vit. A
        
        single cell thick, abuts choroid and extends anteriorly to cover ciliary body and posterior face of iris
        
        Inner neural layer
        
        extends anteriorly to posterior margin of ciliary body
        
        3 distinct layers of retinal neurons
        
        bipolar cells
        
        ganglion cells (inner most)
        
        generates an action potential
        
        photoreceptors (outermost)
        
        transduces visible light energy
        
        Rods
        
        more numerous, dim light, and peripheral vision receptors
        
        2 more items...
        
        visual pigment = rhodopsin
        
        Cones
        
        operate in bright light and provide high-acuity color vision
        
        3 more items...
        
        3 distinct types of cones (each type most sensitive to a different wavelength range)
        
        1 more item...
        
        photopigments
        
        retinal
        
        1 more item...
        
        opsin
        
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        location
        
        2 more items...
    - - sclera
        
        white/opaque, tough and tendon-like
        
        protects/shapes eyeball and provides anchoring site for extrinsic eye muscles
      - cornea
        
        anterior portion, transparent and bulges
        
        forms window that lets light enter eye and is major part of light bending apparatus
        well supplied with nerve endings
- - - - Step 3: retinal isomerase conversts trans-retinal back to its cis-form
        
        Step 4: photopigment is regenerated
        
        enzymes slowly converts trans-retinal back to its cis-retinal form, requires ATP
- - - - in the light, cGMP breaks down, cation channels close, Na/Ca stop entering, and cell hyperpolarizes to -70 mV
    - - light triggers pigment breakdown
        
        cGMP gated channels close and inflow of Na slows
        
        hyperpolarization (-70 mV)
        
        glutamate stops being released
        
        lack of IPSPs in bipolar cells
        
        depolarization
        
        1 more item...
        
        glutamate inhibited action potential