BIOM1052 Special Senses 1_Eye & Vision PDF 2024

1/08/2024 BIOM1052 Special Senses The eye and vision Dr Judit Kibedi [email protected] 1 Acknowledgment of Country The University of Queensland (UQ) acknowledges the Traditional Owners and their custo...

1/08/2024 BIOM1052 Special Senses The eye and vision Dr Judit Kibedi [email protected] 1 Acknowledgment of Country The University of Queensland (UQ) acknowledges the Traditional Owners and their custodianship of the lands on which we meet. We pay our respects to their Ancestors and their descendants, who continue cultural and spiritual connections to Country. We recognise their valuable contributions to Australian and global society. 2 2 1  1/08/2024 Commitment to Diversity and Inclusion Diverse perspectives, abilities, experiences and backgrounds inspire creativity, encourage innovation and enrich our communities. Members of our broad community are valued and respected for their individuality. UQ strives to create a culturally safe, welcoming and inclusive workplace, with strong community connections and partnerships. CRICOS code 00025B 3 3 Special Senses Module Overview The Eye & Vision – Anatomy of the eye Lecture 1 – The Eye & Vision Function of the eye Lecture 2 – The Ear & Hearing Pupillary reflex Acuity & accommodation [and equilibrium, briefly covered] Phototransduction Lecture 3 – Taste and Smell The visual pathway Readings: Martini, Nath & Bartholemew (2018) Fundamentals of Anatomy & Physiology, 11th Ed, Chapter 17, pp 618-637 Marieb & Hoehn (2019) Human Anatomy & Physiology, 11th Ed, Chapter 15, pp 586-607 BIOM1052 | Special Senses 4 4 2  1/08/2024 Questions about the Special Senses https://padletuq.padlet.org/j_kibedi/biom1052-special-senses-questions-2024-gx9pploi3jqkcf0c BIOM1052 | Special Senses 5 5 Anatomy of the Eye BIOM1052 | Special Senses 6 6 3  1/08/2024 The eye and accessory structures Lacrimal apparatus provides lubrication & protection Tears → mucus, antibodies, lysosomes Tears drain into lacrimal sac Lacrimal gland produces and secretes tears Tears empty into nasal cavity via nasolacrimal duct Conjunctiva – Mucous membrane covering inner surface of eyelids & outer surface of eyeball BIOM1052 | Special Senses Marieb & Hoehn: Fig 15.2 7 7 Anatomy of the eyeball Two cavities Anterior cavity Posterior cavity Three tunics (layers) Fibrous Vascular Neural Martini et al: Fig 17.5 BIOM1052 | Special Senses 8 8 4  1/08/2024 A closer look at the two cavities Anterior cavity (aqueous humor) Anterior + posterior chambers Medium for diffusion of gases & nutrients Recycled & regenerated – Produced by ciliary body (~5mL/day) – Reabsorbed into venous blood via scleral venous sinus Maintains intraocular pressure ~16mmHg Posterior cavity (vitreous humor) Formed in embryo, lasts for life Transmits light Martini et al: Fig 17.09 Supports: – posterior surface of lens – neural layer of retina against pigmented layer Maintains intraocular pressure, counteracts forces of extrinsic eye muscles 9 9 Layers of the eye: Fibrous tunic Sclera – “white” of the eye Tough fibrous layer made of collagen & elastic fibers Maintains structural integrity & protection Anchor point for extrinsic muscles (recti) Sclera Capillaries and nerves project to internal structures Medial & Lateral Martini et al: Fig 17.5 rectus BIOM1052 | Special Senses 10 10 5  1/08/2024 Layers of the eye: Fibrous tunic Cornea Limbus Cornea Anterior, transparent portion of sclera Lacks blood vessels; nutrients and gases diffuse from tears Free nerve endings! Most sensitive structure of eye Sclera Limbus – regeneration of epithelium Martini et al: Fig 17.5 BIOM1052 | Special Senses 11 11 Layers of the eye: Vascular tunic Choroid Ciliary body Iris Rich in blood vessels Oxygen and nutrient supply for retina Choroid Melanocytes minimise light scattering Iris – the “coloured” part Changes pupil size Ciliary body Coordination of lens shape Martini et al: Fig 17.5 BIOM1052 | Special Senses 12 12 6  1/08/2024 The ciliary body Lens attached to ciliary body by suspensory ligaments Contraction and relaxation of ciliary body alters lens shape (flat vs round) Under ANS control Sherwood: Fig 6.20a BIOM1052 | Special Senses 13 13 Layers of the eye: Neural tunic (Retina) Pigmented layer: ─ Phagocytosis of dead photoreceptors ─ Nutrient delivery from choroid Neural layer: ─ Light detection → Rods and cones ─ Signal processing → Horizontal, Amacrine, Bipolar and Ganglion cells Martini: Fig 17.17 Fovea ─ Point of highest acuity ─ Exclusively and densely populated by cones Macula ─ Area immediately surrounding fovea ─ Rods, cones & processing cells Optic disc ─ Optic nerve & major blood vessels exit (Blind spot) ─ No rods, cones or processing cells https://www.frontiersi BIOM1052 | Special Senses n.org/articles/10.3389 14 /fcell.2022.878350/full 14 7  1/08/2024 Functions of the Eye BIOM1052 | Special Senses 15 15 The iris and the pupillary reflex Controls amount of light entering the eye (pupil) Two rings of muscle - Pupillary constrictors (sphincter pupillae, arranged longitudinally) - Pupillary dilators (dilator pupillae, arranged radially) Regulated by ANS Low light: SNS → pupil dilates High light: PNS → pupil constricts BIOM1052 | Special Senses 16 Martini et al: Fig 17.6 16 8  1/08/2024 Lens function The “crystalline lens” Up to 60% of mass is proteins First detectable at 5-6 weeks of gestation in humans! Transmits and focuses light onto retina BIOM1052 | Special Senses 17 17 Refraction Bending of light rays passing from one medium (air) to another (lens) Differences in density of medium alter the speed of light molecules, and leads to a change in direction (bending) Cornea provides ~80% refraction power, final 20% by lens Visual acuity depends on convergence of light rays onto retina via refraction by lens Retina Martini et al: Fig 17.10 BIOM1052 | Special Senses 18 18 9  1/08/2024 Lens function in near and far vision The focal point of the retina is the fovea. Accommodation – Increasing the refractive power of the lens to focus a near-source image on the fovea. BIOM1052 | Special Senses Sherwood: Fig 6.17 & 6.18 19 Refractive errors of vision Presbyopia: Age-related reduction in accommodation ability of lens Myopia (nearsighted) - eyeball too long or lens too strong Hyperopia (farsighted) - eyeball too short or lens too weak BIOM1052 | Special Senses Sherwood: Fig 6.17 & 6.18 20 10  1/08/2024 Visual processing Neural Retina Neural segment of retina – 3 layers of excitable cells Photoreceptor layer contains rods and cones Middle layer contains bipolar cells Inner layer contains ganglion cells Rods and cones absorb light. Bipolar cells connect photoreceptor cells with ganglion cells. Axons of ganglion cells join to form optic nerve. BIOM1052 | Special Senses 21 Photoreceptor structure and function Martini: Fig 17.14 Rods and cones consist of 3 parts Outer segment: Light-absorbing photopigments Pigment Epithelium Inner segment: Metabolic structures (absorbs photons not Synaptic terminals: Release of NT onto bipolar cells absorbed by visual pigments) Outer Segment Light detected by photopigments, two parts: Discs Opsin (transmembrane protein) Mitochondria ─ 4 types of Opsin in cones → 7 million Inner Segment Golgi colours!! Apparatus Nuclei ─ Rhodopsin is the photopigment in rods Cone Rod Retinal (derived from Vitamin A) Synapse Bipolar cell Light 22 11  1/08/2024 Phototransduction The process by which photoreceptors convert light into afferent sensory signals (AP’s) Photoreceptor Disc Na+ In the DARK Rhodopsin cGMP (RESTING state) Na+ channel Retinal in 11-cis (curved) form Chemically gated Na+ channels in outer photoreceptor segment are OPEN Continuous influx of Na+ → photoreceptor DEPOLARIZED at rest INHIBITORY neurotransmitters (Glutamate) released → Inhibitory Postsynaptic Potentials (IPSPs) in bipolar cells Bipolar Bipolar cells inhibited → Ganglion cells not stimulated Cell 23 23 Phototransduction Photoreceptor In the LIGHT Photon (ACTIVE state) Photon of light converts Retinal to 11- trans state → Rhodopsin bleaching Release of opsin triggers cascade of events causing Na + channels to CLOSE → photoreceptor HYPERPOLARIZED Absence of inhibitory Glutamate → bipolar cells DEPOLARIZE Excitatory neurotransmitters (also Glutamate!) released → Excitatory Postsynaptic Potentials (EPSPs) in ganglion cells Bipolar Action Potentials generated in Ganglion cells → convergence of ganglionic Cell axons, propagation of APs along optic nerve 24 24 12  1/08/2024 The visual pathway 1. Retina → optic nerve (CN II) 2. Medial fibres from each eye cross at the optic chiasm 3. Synapse at the thalamus (Lateral geniculate bodies) for sorting 4. Subconscious reflexes: Suprachiasmatic nuclei in hypothalamus → contribute to 1 regulation of circadian rhythm 2 Superior colliculi in midbrain → pupillary reflex & involuntary motor control of extrinsic muscles of eye 3-4 5. Visual information to occipital lobe via optic radiation. Integration from both eyes (stereoscopic vision) allows depth perception and 3D vision BIOM1052 | Special Senses 5 25 Martini et al: Fig 17.20 25 Clinical link – disorders affecting the eye Conjunctivitis Lacrimal Sac Mucocele Limbal stem cell deficiency Damage to corneal stem cells in the limbus Reduced corneal epithelium turnover, invasion of cornea by conjunctiva Limbal epithelial transplantation: 70-80% success recovering natural stem cell population Antibiotic eye drop (e.g. Clorsig) Surgery Macular degeneration Glaucoma Progressive, painless loss of foveal vision Build-up of waste products → blood vessels grow into retina or pigment epithelium cells die Failure to drain aqueous humor No cure, treatments improve visual impairment (e.g. antiangiogenics block ↑↑ intraocular pressure, compression of retina and optic nerve vascular endothelial growth) Late signs (halos around lights, blurring) → blindness Prostaglandins (increase outflow), Beta blockers (reduce fluid production), laser, surgery. BIOM1052 | Special Senses 26 For your interest only – clinical links not examined 26 13  1/08/2024 Terminology Check List Can you define/identify all of these terms? ❑ Conjunctiva ❑ Sclera ❑ Focal point ❑ Photopigment ❑ Lacrimal apparatus ❑ Cornea Limbus ❑ Accommodation ❑ Retinal ❑ Posterior cavity ❑ Choroid ❑ Retina ❑ Opsin Rhodopsin ❑ Anterior cavity ❑ Iris ❑ Pigmented layer bleaching ❑ Fibrous tunic ❑ Ciliary body ❑ Neural layer ❑ Glutamate ❑ Vascular tunic ❑ Sphincter pupillae ❑ Fovea ❑ Optic chiasm ❑ Neural tunic ❑ Dilator pupillae ❑ Macula ❑ Lateral geniculate ❑ Aqueous humor ❑ Suspensory ligaments ❑ Optic disc bodies ❑ Vitreous humor ❑ Lens ❑ Photoreceptor ❑ Suprachiasmatic nuclei ❑ Scleral venous sinus ❑ Visual acuity ❑ Bipolar cells ❑ Superior colliculi ❑ Extrinsic muscles ❑ Refraction ❑ Ganglion cells ❑ Optic radiation ❑ Optic nerve ❑ Occipital lobe 27 27 What should I know? – Be able to identify the structures of the eye including their location and functional role – Differentiate between the cavities and tunics of the eye – Explain the process by which the iris can control the amount of light entering the eye – Explain the processes by which the shape of the lens is altered for near and far vision – Explain phototransduction including what happens at rest vs upon activation by a photon of light – Describe the visual pathway from retina to occipital lobe – Recognise and use the correct terminology in these descriptions/explanations 28 28 14  1/08/2024 References Marieb EN & Hoehn K (2019). Human Anatomy & Physiology (11th Ed). Martini FH, Nath JL & Bartholomew EF (2018). Fundamentals of Anatomy & Physiology (11 th Ed). Saladin KS (2010). Anatomy & Physiology: The Unity of Form and Function (5 th Ed). Sherwood L (2016). Human Physiology: From Cells to Systems (9th Ed). Hernandez-Zimbron LF et al (2018). Age-Related Macular Degeneration: New Paradigms for Treatment and Management of AMD. Oxid. Med. Cell. Longev. 2018: 8374647. Sacchetti M, Rama P, Bruscolini A & Lambiase A (2018). Limbal Stem Cell Transplantation: Clinical Results, Limits, and Perspectives. Stem Cells Int. 2018: 8086269. 29 29 15