Organ of visionOrgan of vision

The Five SensesThe Five Senses

TouchTouch HearingHearing SIGHTSIGHT TasteTaste SmellSmell

““Special” sensesSpecial” senses Special senses Special senses

monitor vision, monitor vision, hearing, olfaction, hearing, olfaction, gustation, and gustation, and equilibrium through equilibrium through specialized sense specialized sense organsorgans

These sense organs These sense organs are highly specializedare highly specialized

External AnatomyExternal Anatomy

Sensory Organ for visionSensory Organ for vision

-Situated in bony, orbital cavity for protection-Situated in bony, orbital cavity for protection

– Eyelids= shades that add protection form injury, Eyelids= shades that add protection form injury, strong light , duststrong light , dust

– Eyelashes= hairs to filter dust & dirtEyelashes= hairs to filter dust & dirt

External AnatomyExternal Anatomy

SightSight

The eye is the organ that captures light.The eye is the organ that captures light.

SightSight

Color BlindnessColor Blindness

All sensory receptors send info to All sensory receptors send info to the CNS via an action potential… the CNS via an action potential…

At the CNS, info is routed according to the At the CNS, info is routed according to the stimulus and its locationstimulus and its location

The stronger the stimulus, the higher the The stronger the stimulus, the higher the frequency of action potentials frequency of action potentials

Some receptors adapt, that is their Some receptors adapt, that is their sensitivity to a stimulus is reduced if the sensitivity to a stimulus is reduced if the stimulus is continually applied (smell)stimulus is continually applied (smell)– The RAS can heighten or reduce awareness of The RAS can heighten or reduce awareness of

sensory informationsensory information

A complex sensory organ: the eye.A complex sensory organ: the eye.

is surrounded by accessory structures that is surrounded by accessory structures that act to protect, lubricate, and support itact to protect, lubricate, and support it

is a light, compact, durable, and highly is a light, compact, durable, and highly specialized hollow organ that weighs about specialized hollow organ that weighs about 8 oz and measures 1 inch in diameter. 8 oz and measures 1 inch in diameter.

is divided into anterior (aqueous) & posterior is divided into anterior (aqueous) & posterior (vitreous) cavities.(vitreous) cavities.

its walls are made of 3 “tunics” its walls are made of 3 “tunics”

Accessory structures of the eye…Accessory structures of the eye… eyelids (palpebrae)eyelids (palpebrae) eyelashes & browseyelashes & brows exocrine glandsexocrine glands lacrimal apparatuslacrimal apparatus ConjunctivaConjunctiva 6 extrinsic occulomotor 6 extrinsic occulomotor

muscles:muscles:– the inferior, superior, lateral the inferior, superior, lateral

and medial and medial rectus muscles rectus muscles – the superior and inferior the superior and inferior

oblique musclesoblique muscles

Within the upper eyelidWithin the upper eyelid– Tarsal plates, connective tissue gives upper lid Tarsal plates, connective tissue gives upper lid

shapeshape– Meibomian glands, in the plates, lubricate the Meibomian glands, in the plates, lubricate the

lids, stops overflow of tears, airtight seal when lids, stops overflow of tears, airtight seal when lids closedlids closed

Cornea – clear, covers & protects iris & Cornea – clear, covers & protects iris & pupilpupil

Lacrimal apparatus – irrigates conjunctiva Lacrimal apparatus – irrigates conjunctiva & cornea& cornea

– 3 parts3 partsA.A. Lacrimal gland, upper, outer corner of eye = tearsLacrimal gland, upper, outer corner of eye = tears

B.B. Puncta= inner canthus, tear drainagePuncta= inner canthus, tear drainage

C.C. Nasolacrimal duct= allows tears to drain from Nasolacrimal duct= allows tears to drain from puncta to nasolacrimal sac. Tears then empty into puncta to nasolacrimal sac. Tears then empty into the inferior meatus of the nosethe inferior meatus of the nose

Extraoccular musclesExtraoccular muscles

6 muscles 6 muscles – Attach eyeball to orbitAttach eyeball to orbit– Straight and rotary movementStraight and rotary movement– Four straight musclesFour straight muscles

1.1. Superior rectusSuperior rectus

2.2. Inferior rectusInferior rectus

3.3. Lateral rectusLateral rectus

4.4. Medial rectusMedial rectus

Two slanting/ oblique musclesTwo slanting/ oblique muscles5.5. Superior Superior

6.6. Inferior Inferior

Humans have a Binocular, single – image Humans have a Binocular, single – image visual system – Eyes normally move as a visual system – Eyes normally move as a pairpair

• Eye movement stimulated by Cranial NervesEye movement stimulated by Cranial Nerves• III OculomotorIII Oculomotor• IV TrochlearIV Trochlear• VI AbducensVI Abducens

Eye anatomy…..Eye anatomy…..

http://www.macula.org/http://www.macula.org/anatomy/eyeframe.htmanatomy/eyeframe.htmll

The hollow eye is divided The hollow eye is divided into 2 cavities:into 2 cavities:

An anterior cavity which An anterior cavity which contains aqueous humorcontains aqueous humor

A posterior cavity which A posterior cavity which holds vitreous humorholds vitreous humor

Humors act to stabilize eye Humors act to stabilize eye shape and provide shape and provide nutrients nutrients

The Tunics of the eye…The Tunics of the eye…

FibrousFibrous - the sclera & - the sclera & anterior cornea anterior cornea

VascularVascular – contains blood – contains blood vessels, lymphatics, vessels, lymphatics, choroid & intrinsic muscles choroid & intrinsic muscles of the iris &ciliary bodies of the iris &ciliary bodies (they support the lens)(they support the lens)

Neural Neural – the retina, it – the retina, it contains the rods and contains the rods and cones (photoreceptor cells), cones (photoreceptor cells), bipolar &ganglion cells bipolar &ganglion cells

Exposed part of the eyeExposed part of the eye– Conjunctiva, folded envelope b/t eyelids & Conjunctiva, folded envelope b/t eyelids &

eyeball eyeball thin mucous membrane, transparent protective thin mucous membrane, transparent protective

covering of the exposed part of the eye.covering of the exposed part of the eye. Palpebral conjunctiva lines the lids, is clear but has Palpebral conjunctiva lines the lids, is clear but has

sm .bld. Vesselssm .bld. Vessels Bulbar conjunctiva is over eyeball, white sclera show Bulbar conjunctiva is over eyeball, white sclera show

through, merges at limbus with corneathrough, merges at limbus with cornea

Retinal organization …Retinal organization … The retina is made of several cell layers:The retina is made of several cell layers:

– Photoreceptor cellsPhotoreceptor cells – rods lie along the – rods lie along the periphery & cones lie at the back of the retinaperiphery & cones lie at the back of the retina

– Bipolar cellsBipolar cells synapse with the rods and cones synapse with the rods and cones– Ganglion cellsGanglion cells synapse with the bipolar cells synapse with the bipolar cells– The axons of the ganglion cells form the The axons of the ganglion cells form the optic optic

nervenerve– http://www.macula.org/anatomy/retinaframe.htmlhttp://www.macula.org/anatomy/retinaframe.html

http://www.macula.org/anatomy/anatomy.htmlhttp://www.macula.org/anatomy/anatomy.html

Macula luteaMacula lutea – area on – area on the retina where the the retina where the visual image forms, it visual image forms, it contains only cones with contains only cones with the greatest numbers at the greatest numbers at the the fovea centralisfovea centralis

Optic DiscOptic Disc or or “blind spot”“blind spot” is the area where the is the area where the ganglion cell axons exit ganglion cell axons exit the eye to form the optic the eye to form the optic nervenerve

Other structures of the eye:Other structures of the eye:

LensLens – held in place by suspensory ligaments, it – held in place by suspensory ligaments, it functions to focus the visual image onto the retinafunctions to focus the visual image onto the retina

Cornea Cornea – clear portion of the fibrous tunic it is – clear portion of the fibrous tunic it is contiguous with the scleracontiguous with the sclera

Iris Iris – part of the vascular tunic, it contains blood – part of the vascular tunic, it contains blood vessels, pigment, and 2 smooth muscle layers to vessels, pigment, and 2 smooth muscle layers to control the width of the pupil.control the width of the pupil.

Ciliary bodyCiliary body – a thick region of the choroid that – a thick region of the choroid that encircles the lens and supports the suspensory encircles the lens and supports the suspensory ligments of the lens ligments of the lens

Accommodation- Accommodation- focusing an image on the retina by focusing an image on the retina by changing lens shapechanging lens shape

light bends/refracts as it passes from 1 medium to light bends/refracts as it passes from 1 medium to another. In the eye it goes through the cornea, a. another. In the eye it goes through the cornea, a. humor, lens, & v. humor. The refraction of light is humor, lens, & v. humor. The refraction of light is constant through all but the lensconstant through all but the lens

The lens changes shape to keep the image The lens changes shape to keep the image focused on the retina for greatest visual acquityfocused on the retina for greatest visual acquity

Accommodation occurs with response to light and Accommodation occurs with response to light and to the distance of the object being viewedto the distance of the object being viewed

http://www.kscience.co.uk/animations/eye.shttp://www.kscience.co.uk/animations/eye.swfwf

The Physiology of Vision…The Physiology of Vision…How is it that we see?How is it that we see?

Photoreceptors respond to visible light:Photoreceptors respond to visible light: Rods – sensitive to photons (energy) but Rods – sensitive to photons (energy) but

not their wavelength (color) allow for vision not their wavelength (color) allow for vision at night/dim lightat night/dim light

The 3 types of Cones (green, red, blue) The 3 types of Cones (green, red, blue) need bright light & are responsive to need bright light & are responsive to wavelength: they allow us to “see” color wavelength: they allow us to “see” color

Lack of functional cones = colorblindness Lack of functional cones = colorblindness

The visual pathway….The visual pathway….

Photoreceptor stimulationPhotoreceptor stimulation Bipolar cell activation Bipolar cell activation Stimulation of ganglion cell’s whose axons form the…Stimulation of ganglion cell’s whose axons form the… Optic nerve that cross at the diencephalon and goes to the Optic nerve that cross at the diencephalon and goes to the

thalamus that routes info to the visual cortex of occipital thalamus that routes info to the visual cortex of occipital lobe and the reflex centers of brain stem lobe and the reflex centers of brain stem

At the optic chiasm, a partial crossover of nerve fibers At the optic chiasm, a partial crossover of nerve fibers occursoccurs

http://www.sumanasinc.com/webcontent/anisamplhttp://www.sumanasinc.com/webcontent/anisamples/neurobiology/visualpathways.htmles/neurobiology/visualpathways.html