CNS3 Vision (Sept 24, 2024) PDF

PHS 3341, CNS 3 Vision Sept 24, 2024 Objectives: 3.0 Describe the structural and functional components of the eye 3.1 Explain the concepts of refraction, image formation, accommodation 3.2 Describe the molecular and neural processing of visual signals in the retina 3.3 Describe the neural pathway...

PHS 3341, CNS 3 Vision Sept 24, 2024 Objectives: 3.0 Describe the structural and functional components of the eye 3.1 Explain the concepts of refraction, image formation, accommodation 3.2 Describe the molecular and neural processing of visual signals in the retina 3.3 Describe the neural pathway for vision 3.4 Describe the descending control and simple reflex functions of the system 3.5 Describe degenerative conditions associated with the visual system Readings: Chapter 5 pp. 157-172  The visual system The eye – basic anatomy Visual system circuits The retina Phototransduction Retinal physiology Non-visual functions  Retinal degeneration Macular degeneration: ~1.4 million Canadians Glaucoma: ~450 000 Canadians Retinitis pigmentosa: ~10 000 Canadians ~50 000 Canadians go blind every year Costs to the health system estimated to be ~$9 billion per year Cajal ca. 1880 https://www.brainfacts.org/thinking-sensing-and-behaving/vision/2014/a-journey-through-the-visual-system Figure 4-7, p. 153 Copyright © 2016 by Nelson Education Ltd. 5 Light refraction 6  Refraction ** ** Figure 4-14, p. 158 Copyright © 2016 by Nelson Education Ltd. 7 Light refraction 8  Oculomotor nerve (III) ≠ Optic nerve (II) CNS (II) (VI) (IV) (III) PNS Control of eye movement = brainstem Accommodation = midbrain Vision = thalamus Retina G G G Figure 3-1, p. 92 10  CNS vs. PNS - development Why is the Eye/Visual system considered CNS instead of PNS? Retina develops directly from the neural tube. Optic nerve is myelinated by oligodendrocytes Eye is protected by a variety of barriers Visual system – CNS vs. PNS Kristen Kwan, University of Utah  Blood, Barriers, Humours * Avascular* Blood supply - Retina  Humours Glaucoma Visual system (thalamus) (occipital lobe)  The retina Human retina: 120 million rods 6 million cones ~1 million RGCs ~1000 mm2 Repetitive columnar organization Cajal ca. 1880  The retina 7 neural cell types Rods Cones Bipolars Amacrines Horizontals Ganglion Cells Müller glia (microglia, astrocytes, vascular cells) Cajal ca. 1880  The retina Optic nerve head (blind spot) Cajal ca. 1880 The retina is very well conserved across evolution Karthik Shekhar, UC Berkeley The retina is very well conserved across evolution The retina is very well conserved across evolution Walther Gehring ….but some species have high acuity areas The human fovea Visual system - retinotopy Ipsilateral = same side Contralateral = crossed (~retinal homunculus) Longitudinal fissure Visual system - retinotopy macrocolumns Ocular dominance columns (V1) Hubel DH and Wiesel TN (1977) Phototransduction Photoreception  Photoreceptors Photoreception Human retina: 120 million rods - night vision - Rhodopsin 6 million cones - high acuity colour vision - Cone opsins (Red/Green/Blue)  Visual cycle Vitamin A R/G colourblindness? 11-cis retinal Opsin (GPCR protein) Visual cycle 11-cis Light photon Outer segments - Photoreceptive organelles Phototransduction CNG channel (guanylyl cyclase) Na/Ca-K exchanger  Retinal physiology (2) b a (1) electroretinography (1) (2) Photoreceptors Bipolars Light Neural Signal Optic nerve Brain  How is the signal from rod hyperpolarization inverted? 1) When rods transduce light, they hyperpolarize (A wave), and reduce glutamate release 2) ‘On bipolars’ respond via mGluR6. This leads to depolarization (B wave) Optic nerve Light Neural Signal How is the signal from rod hyperpolarization inverted?  Colour Vision Helmholtz: trichromacy Hering: Opponent Process theory 4 colours in opponent pairs Figure 4-21, p. 166  Colour Vision Retinal interneurons integrate the signals of photoreceptors to compute features LM = green S = blue The retina – circuit mosaics The retina – circuit mosaics The retina – circuit mosaics  The retina – circuit mosaics RGCs (mouse) ~45 subtypes ~45 information channels  Visual system Photoreceptors are analogous to a digital camera (or CRT) – detect R/G/B and B/W …but the retina is not like a camera. It is a complex feature detector and processor The eye also has non-visual functions  Non-visual functions of the eye Pupillary light reflex (Vestibulo-ocular reflex) (Oculocephalic reflex (doll’s eye reflex)) (Palpebral oculogyric reflex (Bell’s reflex))  Non-visual functions of the eye Circadian rhythms  Intrinsically photosensitive RGCs hypothalamus thalamus ipRGCs (melanopsin/Opn4) Samer Hattar, NIMH  Intrinsically photosensitive RGCs Samer Hattar, NIMH