Transcript 33. Organ of vision

Organ of vision
The Five Senses
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Touch
Hearing
SIGHT
Taste
Smell
“Special” senses
 Special senses
monitor vision,
hearing, olfaction,
gustation, and
equilibrium through
specialized sense
organs
 These sense organs
are highly specialized
External Anatomy
 Sensory Organ for vision
-Situated in bony, orbital cavity for protection
– Eyelids= shades that add protection form injury,
strong light , dust
– Eyelashes= hairs to filter dust & dirt
External
External
Anatomy
Anatomy
Sight
 The eye is the organ that captures light.
Sight
Color Blindness
All sensory receptors send info to
the CNS via an action potential…
 At the CNS, info is routed according to the
stimulus and its location
 The stronger the stimulus, the higher the
frequency of action potentials
 Some receptors adapt, that is their
sensitivity to a stimulus is reduced if the
stimulus is continually applied (smell)
– The RAS can heighten or reduce awareness of
sensory information
A complex sensory organ: the eye.
 is surrounded by accessory structures that
act to protect, lubricate, and support it
 is a light, compact, durable, and highly
specialized hollow organ that weighs about
8 oz and measures 1 inch in diameter.
 is divided into anterior (aqueous) & posterior
(vitreous) cavities.
 its walls are made of 3 “tunics”
Accessory structures of the eye…
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eyelids (palpebrae)
eyelashes & brows
exocrine glands
lacrimal apparatus
Conjunctiva
6 extrinsic occulomotor
muscles:
– the inferior, superior, lateral
and medial rectus muscles
– the superior and inferior
oblique muscles
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Within the upper eyelid
– Tarsal plates, connective tissue gives upper lid
shape
– Meibomian glands, in the plates, lubricate the
lids, stops overflow of tears, airtight seal when
lids closed
 Cornea – clear, covers & protects iris & pupil
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Lacrimal apparatus – irrigates conjunctiva
& cornea
– 3 parts
A. Lacrimal gland, upper, outer corner of eye = tears
B. Puncta= inner canthus, tear drainage
C. Nasolacrimal duct= allows tears to drain from
puncta to nasolacrimal sac. Tears then empty into
the inferior meatus of the nose
Extraoccular muscles
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6 muscles
– Attach eyeball to orbit
– Straight and rotary movement
– Four straight muscles
1.
2.
3.
4.
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
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Two slanting/ oblique muscles
5. Superior
6. Inferior
Humans have a Binocular, single – image
visual system – Eyes normally move as a
pair
• Eye movement stimulated by Cranial Nerves
• III Oculomotor
• IV Trochlear
• VI Abducens
Eye anatomy…..
 http://www.macula.org/
anatomy/eyeframe.htm
l
 The hollow eye is divided
into 2 cavities:
 An anterior cavity which
contains aqueous humor
 A posterior cavity which
holds vitreous humor
 Humors act to stabilize eye
shape and provide
nutrients
The Tunics of the eye…
 Fibrous - the sclera &
anterior cornea
 Vascular – contains blood
vessels, lymphatics,
choroid & intrinsic muscles
of the iris &ciliary bodies
(they support the lens)
 Neural – the retina, it
contains the rods and
cones (photoreceptor
cells), bipolar &ganglion
cells
 Exposed part of the eye
– Conjunctiva, folded envelope b/t eyelids &
eyeball
 thin mucous membrane, transparent protective
covering of the exposed part of the eye.
 Palpebral conjunctiva lines the lids, is clear but has
sm .bld. Vessels
 Bulbar conjunctiva is over eyeball, white sclera show
through, merges at limbus with cornea
Retinal organization …
 The retina is made of several cell layers:
– Photoreceptor cells – rods lie along the
periphery & cones lie at the back of the retina
– Bipolar cells synapse with the rods and cones
– Ganglion cells synapse with the bipolar cells
– The axons of the ganglion cells form the optic
nerve
– http://www.macula.org/anatomy/retinaframe.html
http://www.macula.org/anatomy/anatomy.html
 Macula lutea – area on
the retina where the
visual image forms, it
contains only cones with
the greatest numbers at
the fovea centralis
 Optic Disc or “blind spot”
is the area where the
ganglion cell axons exit
the eye to form the optic
nerve
Other structures of the eye:
 Lens – held in place by suspensory ligaments, it
functions to focus the visual image onto the retina
 Cornea – clear portion of the fibrous tunic it is
contiguous with the sclera
 Iris – part of the vascular tunic, it contains blood
vessels, pigment, and 2 smooth muscle layers to
control the width of the pupil.
 Ciliary body – a thick region of the choroid that
encircles the lens and supports the suspensory
ligments of the lens
Accommodation- focusing an image on the retina by
changing lens shape
 light bends/refracts as it passes from 1 medium to
another. In the eye it goes through the cornea, a.
humor, lens, & v. humor. The refraction of light is
constant through all but the lens
 The lens changes shape to keep the image
focused on the retina for greatest visual acquity
 Accommodation occurs with response to light and
to the distance of the object being viewed
 http://www.kscience.co.uk/animations/eye.s
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The Physiology of Vision…
How is it that we see?
 Photoreceptors respond to visible light:
 Rods – sensitive to photons (energy) but
not their wavelength (color) allow for vision
at night/dim light
 The 3 types of Cones (green, red, blue)
need bright light & are responsive to
wavelength: they allow us to “see” color
 Lack of functional cones = colorblindness
The visual pathway….
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Photoreceptor stimulation
Bipolar cell activation
Stimulation of ganglion cell’s whose axons form the…
Optic nerve that cross at the diencephalon and goes to the
thalamus that routes info to the visual cortex of occipital
lobe and the reflex centers of brain stem
 At the optic chiasm, a partial crossover of nerve fibers
occurs
 http://www.sumanasinc.com/webcontent/anisampl
es/neurobiology/visualpathways.html