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Ciliary Zonule Sclera (Suspensory Choroid Ligament)

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ACTIVITIES Complete Diagrams PNS 18 and 19 Complete PNS 23 Worksheet 3 #1 only Complete PNS 24 Practice Quiz THE SPECIAL SENSES Introduction Vision RECEPTORS Structures designed to respond to stimuli Variable complexity GENERAL PROPERTIES OF RECEPTORS Transducers Receptor potential Generator potential GENERAL PROPERTIES OF RECEPTORS Stimulus causing receptor potentials Generator potential in afferent neuron Nerve impulse SENSATION AND PERCEPTION Stimulatory input Conscious level = perception Awareness = sensation GENERAL PROPERTIES OF RECEPTORS Information conveyed by receptors . Modality . Location . Intensity . Duration ADAPTATION Reduction in rate of impulse transmission when stimulus is prolonged CLASSIFICATION OF RECEPTORS Stimulus Modality . Chemoreceptors . Thermoreceptors . Nociceptors . Mechanoreceptors . Photoreceptors CLASSIFICATION OF RECEPTORS Origin of stimuli . Exteroceptors . Interoceptors . Proprioceptors SPECIAL SENSES Vision Hearing Olfaction Gustation VISION INTRODUCTION 70% of all sensory receptors are in the eye Nearly half of the cerebral cortex is involved in processing visual information Optic nerve is one of body’s largest nerve tracts VISION INTRODUCTION The eye is a photoreceptor organ Refraction Conversion (transduction) of light into AP’s Information is interpreted in cerebral cortex Eyebrow Eyelid Eyelashes Site where conjunctiva merges with cornea Palpebral fissure Lateral commissure Eyelid Medial commissure (a) Surface anatomy of the right eye Figure 15.1a Orbicularis oculi muscle Eyebrow Palpebral conjunctiva Cornea Eyelashes Bulbar conjunctiva Conjunctival sac Orbicularis oculi muscle (b) Lateral view; some structures shown in sagittal section Figure 15.1b ACCESSORY STRUCTURES Lacrimal apparatus . Lacrimal gland and ducts that connect to nasal cavity . Lacrimal secretion (tears) . Dilute saline solution . Mucus, antibodies, and lysozyme . Blinking spreads the tears toward medial commissure . Drain into the nasolacrimal duct Lacrimal sac Lacrimal gland Excretory ducts of lacrimal glands Lacrimal punctum Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril Figure 15.2 ACCESSORY STRUCTURES Six extrinsic eye muscles Superior oblique muscle Superior oblique tendon Superior rectus muscle Lateral rectus muscle Inferior rectus Inferior oblique muscle muscle (a) Lateral view of the right eye Figure 15.3a Controlling Muscle Action cranial nerve Lateral rectus Moves eye laterally VI (abducens) Medial rectus Moves eye medially III (oculomotor) Superior rectus Elevates eye and turns it medially III (oculomotor) Inferior rectus Depresses eye and turns it medially III (oculomotor) Inferior oblique Elevates eye and turns it laterally III (oculomotor) Superior oblique Depresses eye and turns it laterally IV (trochlear) (c) Summary of muscle actions and innervating cranial nerves Figure 15.3c THE EYEBALL Wall of eyeball contains three layers (tunics) . Fibrous . Vascular . Sensory (retinal) THE EYEBALL Three layers 1) Fibrous tunic . Sclera . Cornea Sclera Cornea Scleral venous sinus Fibrous Tunic Figure 15.4a Corneal Edema THE EYEBALL Three layers 2) Vascular tunic (uvea) . Choroid . Ciliary body . Ciliary processes . Ciliary muscle . Iris Ciliary body Ciliary zonule Sclera (suspensory Choroid ligament) Iris Pupil Cornea Lens Scleral venous sinus VascularTunic Figure 15.4a THE EYEBALL Three layers 3) Retina . Photoreceptor neurons . Rods and Cones . Bipolar neurons . Ganglion neurons . Optic nerve . Optic disc Ciliary body Ciliary zonule Sclera Choroid Retina Cornea Macula lutea Iris Fovea centralis Pupil Optic nerve Lens Scleral venous Central artery sinus and vein of the retina Optic disc (blind spot) Retina Figure 15.4a Photoreceptors Bipolar • Rod Ganglion cells cells • Cone Amacrine cell Horizontal cell Pathway of signal output Pigmented Pathway of light layer of retina (b) Cells of the neural layer of the retina Figure 15.6b Pathway of light Neural layer of retina Pigmented layer of retina Choroid Sclera Optic disc Central artery and vein of retina Optic nerve (a) Posterior aspect of the eyeball Figure 15.6a Blood supply to the retina THE EYEBALL Photoreceptors .Rods . More numerous at peripheral region . Dim light . Indistinct, fuzzy, non-color peripheral vision . About 100 million per eye THE EYEBALL Photoreceptors .Cones . Red, blue and green . Highest density in macula lutea . Concentrated in fovea centralis . Operate in bright light . High-acuity color vision Central artery and vein emerging from the optic disc Macula lutea Optic disc Retina Figure 15.7 THE EYEBALL Lens . Biconvex, transparent, flexible . Attached to ciliary body by suspensory ligaments . Allows precise focusing of light on the retina . Forms a partition . Creates an anterior and posterior cavity Emmetropic eye (normal) Focal plane Focal point is on retina. Figure 15.14 (1 of 3) Iris Posterior Lens epithelium segment Lens (contains Cornea vitreous 2 Corneal epithelium humor) Corneal endothelium Ciliary zonule Aqueous humor Anterior (suspensory Anterior ligament) segment chamber (contains Posterior aqueous chamber Ciliary body humor) 3 1 Scleral venous Ciliary 1 Aqueous humor is sinus processes formed by filtration Corneal- from the capillaries in scleral junction the ciliary processes. Ciliary 2 Aqueous humor flows from the Bulbar muscle posterior chamber through the pupil into the anterior chamber. conjunctiva Some also flows through the Sclera vitreous humor (not shown). 3 Aqueous humor is reabsorbed Cornea Lens into the venous blood by the scleral venous sinus. Figure 15.8 THE PHYSIOLOGY OF VISION Visual acuity . Ratio of distances . 20/20 . 20/40 . Less visual acuity . 20/15 . More visual acuity THE PHYSIOLOGY OF VISION 5 processes produce a visual image 1. Refraction 2. Accommodation 3. Pupil constriction 4. Convergence 5. Photoreception REFRACTION The bending of light rays Focal length is fixed in the eye Emmetropic eye (normal) Focal plane Focal point is on retina. Figure 15.14 (1 of 3) REFRACTION Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point The image formed at the focal point is upside-down and reversed right to left Sympathetic activation Nearly parallel rays from distant object Lens Ciliary zonule Ciliary muscle Inverted image (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Figure 15.13a REFRACTION Refracting media . Light is refracted by . Cornea . Aqueous humor . Lens . Vitreous humor Change in lens curvature . Allows for fine focusing of an image ACCOMMODATION Eye is adapted for distance vision . Ciliary muscle is relaxed = lens is flat As light moves closer greater curvature required . Ciliary muscle contracts = lens is curved Sympathetic activation Nearly parallel rays from distant object Lens Ciliary zonule Ciliary muscle Inverted image (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Figure 15.13a Parasympathetic activation Divergent rays Inverted from close object image (b) Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. Figure 15.13b ACCOMMODATION Near vision . Accommodation . Ciliary muscles contract . Eye strain . Near point . Maximum bulge . Aging CLOSE VISION Close vision requires .Accommodation .Pupil constriction . Prevents most divergent light rays from entering the eye .Convergence . Medial rotation of the eyeballs toward the object being viewed (binocular vision) CONSTRICTION OF THE PUPIL Contraction of the circular muscles Contraction of the radial muscles PHOTORECEPTION Sensory transduction . Light energy is converted into nerve impulses Takes place in retina . Photoreceptors PHOTORECEPTION Rods and cones . Outer segment of each contains visual pigments . Molecules that change shape as they absorb light Process of bipolar cell Inner fibers Synaptic terminals Rod cell body Rod cell body Nuclei Cone cell body Outer fiber Mitochondria Connecting Inner cilia segment Apical microvillus Discs containing visual pigments Discs being The outer segments Outer segment phagocytized of rods and cones Melanin Pigment cell nucleus are embedded in the Pigmented layer granules pigmented layer of Basal lamina (border the retina. with choroid) Figure 15.15a Rod discs Visual pigment consists of • Retinal • Opsin (b) Rhodopsin, the visual pigment in rods, is embedded in the membrane that forms discs in the outer segment. Figure 15.15b 11-cis-retinal 1 Bleaching of + 2H the pigment: Light absorption Oxidation by rhodopsin Vitamin A 11-cis-retinal Rhodopsin triggers a rapid Reduction series of steps in which retinal 2H+ changes shape Dark Light 2 Regeneration (11-cis to all-trans) of the pigment: and eventually Enzymes slowly releases from convert all-trans opsin. retinal to its 11-cis form in the pigmented epithelium; Opsin and requires ATP. All-trans-retinal All-trans-retinal Figure 15.16 In the dark Na+ Ca2+ In the dark, cGMP opens sodium channels and depolarizes Photoreceptor photoreceptors cell (rod) Ca2+ Inhibitory neurotransmitter is released (glutamic acid) Bipolar cells are constantly inhibited Bipolar in the dark cell Ganglion cell Figure 15.18 (1 of 2) Breakdown of In the light rhodopsin causes closing of sodium channels 1 cGMP-gated channels are closed, so Na+ influx Light stops; the photoreceptor hyperpolarizes.
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