Current presentation is intended for graduation course to study Nervous system in Human Medical Physiology.

1. Special Senses - Vision
Dr. Aniket A. Shilwant
Assistant Professor,
Dept. of Kriya Sharir
GJP-IASR, CVM University

2. Human Eyeball
• Bulbus oculi
• Diameter 24 mm
• 2segments
• Anterior – 1/6th portion – Cornea
• Posterior – 5/6th portion – Sclera
• Centre of anterior curvature – anterior pole
• Centre of posterior curvature – posterior pole
• Line joining both poles – Optical axis.
• Line joining to point on cornea to slight medial to anterior pole to fovea centralis (lateral to posterior
pole) – Visual axis (Light rays pass through visual axis)
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3. Layers of Human Eyeball
• Outer layer (Fibrous) – Cornea & Sclera
• Middle layer (Vascular) – Choroid, Ciliary
Body & Iris
• Inner layer (Nervous) – Retina
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4. Fibrous Coat – Cornea
• Transparent, colorless, thin layer covers 1/6th anterior part of eyeball
• Covers mainly iris & pupil thus Reflects color of pupil
• No blood supply, but abundant free nerve endings thus sensitive to pain
• 5layers-
• Stratified epithelium
• Bowmann’s membrane / anterior elastic lamina
• Substantia proper
• Descement layer / posterior elastic lamina
• Endothelial layer
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5. Fibrous Coat – Sclera
• Outer fibrous layer - White and elastic
fibers
• Covers posterior 5/6th part of eyeball
• Perforated part posteriorly where
optic nerve leaves – Lamina Cribrosa
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6. Vascular Coat – Choroid
• Thin layer
• Highly vascular as rich in capillary plexus, small arteries and veins
• Location- Between sclera and retina
• Forms posterior 5/6th part
• Choroid extended anteriorly by insertion of ciliary muscle
(junction – Ora serrata)
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7. Vascular Coat – Ciliary Body
• Thick anterior part of middle layer of eyeball.
• Location-in front of Ora Serrate
• Attaches to lens with - Suspensory ligaments
• 3parts
• Orbicularis ciliaris – Forms posterior 2/3rd of Ciliary
body
• Ciliary body proper – Ciliary muscles (Outer
Longitudinal & Inner Circular) – PNS
• Ciliary processes – Finger like process from inner
surface of Ciliary body toward central axis of eye.
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9. Vascular Coat – Iris
• Thin curtain like structure of eyeball forms circular Diaphragm.
• Location – In front of lens
• A central opening – Pupil
• Separates space between cornea and lens in 2chambers – Anterior &
Posterior
• Aqueous humor
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10. Shades of Iris & Pupil
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11. Nervous Coat – Retina
• Thin, delicate photo sensitive membrane
• Covers the area from optic disc to Ciliary body
• Ends at dentate border at Ora Serrata
• 10 layers
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12. Layers of Retina
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Layers of retina from outside in:
1. Layer of pigment epithelium
2. Layer of rods and cones
3. External limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion cell layer
9. Layer of nerve fibers
10. Internal limiting membrane.

13. Layers of Retina
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Layers of retina from outside in:
1. Layer of pigment epithelium –
Pigment granules – Melanin (Fuscin)
Epithelial cells – Storage (Vit. A –
Retinol & Phagocytic action – removal of
cellular debris)
2. Layer of Rods and Cones –
Photosensitive receptors

14. Layers of Retina
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3. External limiting membrane –
Supporting Muller fibers
4. Outer nuclear layer – Granular layer
of Rods & Cones having Nucleus
5. Outer plexiform layer – Reticular
meshwork – Synaptic Terminal fibers &
Dendrites of Bipolar cells

15. Layers of Retina
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6. Inner nuclear layer – Bipolar cells, Muller supporting
fibers, Synapses
(a. With ganglionic cell layer & outer plexiform layer)
7. Inner plexiform layer – Synapses (Ganglionic cells
bipolar cells)
8. Ganglion cell layer – Multipolar cell layer (Giant
ganglion cells & Midget Ganglion cells), Axons of these
cells leave orbit as – Optic nerve

16. Layers of Retina
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9. Layer of nerve fibers – Layer of
non-myelinated axons converges at
Optic disc & leave as – Optic Nerve
10. Internal limiting membrane –
Hyaline membrane separates Retina
from inner Vitreous body

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18. Retinal 10 layers
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21. Fundus Oculi - Macula Lutea / Fovea centralis 21
• Small, yellowish area, also called Yellow Spot
• Location – Lateral to optic disc in retina
• It is yellow due to presence of pigment which is
yellow in color
• It has depression in the centre where all retinal
layers become thin – Fovea centralis
• It is the area for precise vision as it contains only –
Cones
Dr. Aniket Shilwant, GJPIASR

22. Fundus Oculi – Optic Disc 22
• Pale disc
• Location – Centre of posterior wall of eyeball
• Formed by convergence of axons from ganglion
cells
• Contains all layers of retina except Rods & Cones
• Thus it is insensitive to light and hence called as –
Blind spot
Dr. Aniket Shilwant, GJPIASR

23. Physiology Of Vision
Retinal image formation
Photo sensitive receptors
Photo transduction
Visual pathway
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24. Retinal image formation
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• Light rays pass through 4medias to reach retina
• Cornea – Aqueous Humor - Lens – Vitreous Humor
• Retinal image formation
Refraction of light rays
Accommodation of lens
Constriction of pupil
Convergence of eyeball

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Refraction of light rays
• Light rays pass through 4refractory Medias
Lighter air – denser cornea
Denser cornea to less denser aqueous humor
Less dense aqueous humor to denser lens
Denser lens to less denser vitreous humor
Retinal image formation –Refraction of Light rays

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Accommodation of lens
• Ability of lens to gets adjust by giving
curvature to itself when an eye is focusing an
object
• It is done so because light rays must any how
fall on fovea centralis
• In nearby vision – ciliary muscle contracts –
thickened, shorten and bulging lens
• In distant vision – ciliary muscle relaxed –
flattened lens
Retinal image formation –Accommodation of Lens

27. Retinal image formation – Diameter of Pupil
Constriction of pupil
• Adjusting the diameter
of hole through which
light enters the eyeball
• Constricts – Bright
light
• Dilates – Dim light
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28. Convergence of eyeball
• Human eye – Single binocular vision
• As object moves closer to eyes, eyeball start moving
medially so that light rays must hit on identical spots on
retina.
• Medial rotation of eyeball for proper adjustment of
vision – Convergence of eyeball.
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Retinal image formation– Convergence of Eyeball

29. Photosensitive Receptors
• Present in 2nd Layer of Retina from outside
• Layer of Rods & Cones
• Rods – Rhodopsin
Chromophore (Vit. A – Retinal) & Opsin (Scotopsin)
• Cones – Photopsin
Chromophore (Vit. A – Retinal) & Opsin (Porphyropsin, Idopsin &
Cyanopsin)
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30. Photosensitive Receptors – Rods
• Cylindrical in shape
• Length – 40 µ to 60 µ Diameter – 2 µ
• Outer segment –
• Contains about 1000 floating flat membranous disks
• These disks contains photosensitive pigment – Rhodopsin
• Newly formed disks at the inner portion of outer segment and older
disks are pushed towards the tip.
• Rate of formation of membranous disks – 3 or 4 per hour
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31. • Inner segment –
• It is connected to outer segment by Cilium
• Contains large number of mitochondria
• Cell body –
• It is the portion containing nucleus of the cell.
• Synaptic terminal –
• It synapses with dendrites of bipolar cell and horizontal cell
• Involved neurotransmitter – Glutamate
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Photosensitive Receptors – Rods

32. FUNCTIONS OF RODS
• These cells have a very low threshold to light
• Very sensitive towards light
• Rod cell are responsible for Dim Light Vision or Night Vision or
Scotopic Vision
• Vision by Rod cell is black and white or rather grey
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Photosensitive Receptors – Rods

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34. Photosensitive Receptors – Cones
• Cone or Flask shaped
• Length - 35 µ to 40 µ Diameter – 5 µ
• Outer segment –
• Small, conical
• Does not contain separate membranous disks
• The inward folding of cell membrane called as – Saccules
• Photosensitive pigment synthesized in inner segment and
incorporated into folding forming saccule
• Inner segment –
• It is connected to outer segment by Cilium
• Contains large number of mitochondria
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35. • Cell body –
• It is the portion containing nucleus of the cell.
• Synaptic terminal –
• It synapses with dendrites of bipolar cell and horizontal cell
• Involved neurotransmitter – Glutamate
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Photosensitive Receptors – Cones

36. FUNCTIONS OF CONE CELL:-
• These cells have high threshold to light
• Cones are sensitive only to bright light
• Cone cell are responsible for Bright Light Vision or Daylight
Vision or Photopic Vision
• Cone cells are also responsible for Acuity of Vision and Color
Vision.
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Photosensitive Receptors – Cones

37. Dark & Light Adaptation
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Causes for Dark Adaptation
 Increased sensitivity of rods as a result of resynthesis of rhodopsin
 Dilatation of pupil
Causes for Light Adaptation
 Decreased sensitivity of rods as a result of resynthesis of rhodopsin
 Constriction of pupil

38. Photochemical changes in Synthesis of Rhodopsin
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Rhodopsin
Batho-Rhodopsin
Lumi-Rhodopsin
Meta-Rhodopsin I
Meta-Rhodopsin II
Scotopsin & Trans Retinal
Trans Retinal – Cis Retinal
Trans Retinol – Cis Retinol
Cis Retinal + Scotopsin

39. Photon absorbed
11 cis retinal gets decomposed to Metarhodopsin II (active from)by
Rhodopsin of Rod cell in retina
Metarhodopsin II activates G protein – Transducin
Transducin activates cGMP phosphodiesterase
Reduction of cGMP to 5’-GMP
Closure of sodium channels in membrane of visual receptors
Blocked entry of sodium ions leading to more negativity –Hyperpolarization
Development of Receptor Potential
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40. PHOTO-TRANSDUCTION
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Dark Current
Normally resting membrane potential = -70 to -90mV
RMP in visual receptors = -40mV
Sodiums leaked from inner segment
Re enters cells in outer segment via sodium channels
Na channels remain open in presence of cGMP
Entry of Na again back in cells gives mild depolarization
RMP remains constant = -40mV
This is dark current.

42. Photo-Transduction
• Light rays striking on retina
• Photon absorption
• Rhodopsin dissociation – Meta-
Rhodopsin & Retinene
• Meta-Rhodopsin stimulates Transducin
(G-protein)
• Transducin – cGMP
phosphodiesterase
• cGMP is hydrolyzed into 5’cGMP
• Decreased concentration of cGMP
• Closure of sodium channels
• Addition to this – Na+K+ pump
• Extra negativity inside cells
• Hyperpolarization
• Development of Receptor potential
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43. Visual Pathway
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• Axon fibers from retina leave eyeball as – Optic N.
• Crossing of fibers at – Optic Chiasma (Only Nasal Fibers crosses)
• Fibers thereafter terminate at –
 Lateral geniculate body (Thalamus)
 Superior colliculi (Midbrain)
• From both the optic radiations terminate at – Primary visual center
(Occipital lobe – Area no. 17)
• Primary visual centre is associated with –
 Visual Association Area (Area No. 18) &
 Occipital Eyefield Area (Area No. 19)

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45. Thank You All !!!
Dr. Aniket A. Shilwant
Assistant Professor
Department of Kriya Sharir
GJP-IASR, CVM University
Email –
ayuraniket18@gmail.com
http://ayugjac.edu.in/Staff_CV.aspx?dl=dn3Mja19480dn3Mja19
http://scholar.google.co.in/citations?user=636K2sMAAAAJ&hl=en
https://www.researchgate.net/profile/Aniket_Shilwant