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Photoreception - Vision. Eyelids (palpebrae) separated by the palpebral fissue Eyelashes Tarsal glands Lacrimal apparatus Vision Accessory structures.

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Presentation on theme: "Photoreception - Vision. Eyelids (palpebrae) separated by the palpebral fissue Eyelashes Tarsal glands Lacrimal apparatus Vision Accessory structures."— Presentation transcript:

1 Photoreception - Vision

2 Eyelids (palpebrae) separated by the palpebral fissue Eyelashes Tarsal glands Lacrimal apparatus Vision Accessory structures of the eye

3 The eye can only perceive a small portion of the spectrum of electromagnetic waves

4 Vision In order to see an object: - 1- the pattern of the object must fall on the vision receptors (rods and cones in the retina)  accommodation - 2- the amount of light entering the eye must be regulated (too much light will “bleach out” the signals) - 3- the energy from the waves of photons must be transduced into electrical signals - 4- The brain must receive and interpret the signals

5 External Features and Accessory Structures of the Eye

6 External Structures of the Eye Conjunctiva covers most of eye Cornea is transparent anterior portion

7 Lacrimal Apparatus Secretions from the lacrimal gland contain lysozyme Tears form in the lacrimal glands, wash across the eye and collect in the lacrimal lake Pass through the lacrimal punctae, lacrimal canaliculi, lacrimal sac and nasolacrimal duct

8 The eye Three layers – Outer fibrous tunic Sclera, cornea, limbus – Middle vascular tunic Iris, ciliary body, choroid – Inner nervous tunic Retina

9 The Sectional Anatomy of the Eye

10 Internal Structures of the Eye Ciliary body – Ciliary muscles and ciliary processes, which attach to suspensory ligaments of lens Retina – Outer pigmented portion – Inner neural part Rods and cones

11 Sectional Anatomy of the Eye

12 Regulation of the Amount of Light Entering the Eye The iris controls the amount of light entering the eye cavities The contraction of radial or circular smooth muscles located within the iris permit changes in the pupil diameter


14 The Pupillary Muscles

15 Retina Retina contains rods and cones – Cones densely packed at fovea (center of the macula lutea) Retinal pathway – Photoreceptors to bipolar cells to ganglion cells, to the brain via the optic nerve Axons of ganglion cells converge at blind spot (optic disc) – Horizontal cells and amacrine cells modify the signal passed along the retinal neurons

16 The Organization of the Retina

17 Retinal structure Three cell layers: -- outer layer: photoreceptors- rods and cones -- middle layer: bipolar neurons -- inner layer: ganglion cells

18 The Organization of the Retina

19 Ciliary body and lens divide the anterior cavity of the eye into posterior (vitreous) cavity and anterior cavity Anterior cavity further divided – anterior chamber in front of eye – posterior chamber between the iris and the lens Eye Anatomy

20 The Circulation of Aqueous Humor

21 Aqueous humor circulates within the eye – diffuses through the walls of anterior chamber – passes through canal of Schlemm – re-enters circulation Vitreous humor fills the posterior cavity. – Not recycled – permanent fluid Fluids in the eye

22 Eye Abnormalities Glaucoma Cataract

23 Posterior to the cornea and forms anterior boundary of posterior cavity – Posterior cavity contains vitreous humor Lens helps focus – Light is refracted as it passes through lens – Accommodation is the process by which the lens adjusts to focus images – Normal visual acuity is 20/20 Lens

24 Image Formation

25 Accommodation It is the process of adjusting the shape of the lens so that the external image fall exactly on the retina

26 Accommodation

27 Accommodation Abnormalities

28 Myopia Hyperopia Astigmatism: the cornea is irregular  irregular pattern of vision Presbyopia: stiffening of the lens occurring with aging  increased difficulty with near vision

29 Rods – respond to almost any photon Cones – specific ranges of specificity Visual Physiology

30 Rods and Cones

31 Outer segment with membranous discs Narrow stalk connecting outer segment to inner segment Light absorption occurs in the visual pigments – Derivatives of rhodopsin Photoreceptor Structure

32 Phototransduction - General Photons hit the pigment of a photoreceptor    enzymes are activated in the cell which modify its state of polarization  the signals are sent to visual area of the occipital lobe of the brain through the optic nerve



35 Photoreception - In More Detail

36 Photoreception

37 Bleaching and Regeneration of Visual Pigments

38 Integration of information from red, blue and green cones Colorblindness is the inability to detect certain colors Color sensitivity

39 Dark adapted – most visual pigments are fully receptive to stimulation Light adapted – pupil constricts and pigments bleached. Retinal Adaptation

40 Large M-cells monitor rods Smaller more numerous P cells monitor cones The Visual Pathway

41 Convergence and Ganglion Cell Function

42 Vision from the field of view transfers from one side to the other while in transit Depth perception is obtained by comparing relative positions of objects from the two eyes Seeing in Stereo

43 Neural processing The bipolar neurons and ganglion cells process the signal In the fovea where the acuity is the highest: 1 cone  1 bipolar cell  1 ganglion cell At the periphery: many rods  1 bipolar cell … acuity is much decreased Other cells in the retina participate in signal processing

44 The Visual Pathways

45 Input to suprachiasmic nucleus affects the function of the brainstem Circadian rhythm ties to day-night cycle, and affects metabolic rates Visual Circadian Rhythm

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