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Anatomy of the Eye & the 12 cranial nerves. 12 Cranial Nerves. I Olfactory II Optic III Oculomotor IV Trochlear V Trigeminal VI Abducens VII Facial VIII Auditory ( Vestiblochlear ) IX Glossopharyngeal X Vagus XI Accessory XII Hypoglossal. - PowerPoint PPT Presentation
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ANATOMY OF THE EYE & THE 12 CRANIAL NERVES
I Olfactory
II Optic
III Oculomotor
IV Trochlear
V Trigeminal
VI Abducens
VII Facial
VIII Auditory (Vestiblochlear)IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal
12 CRANIAL NERVES
There are 12 pairs of cranial nerves. I Olfactory
II Optic
III Oculomotor
IV Trochlear
V Trigeminal
VI AbducensVII FacialVIII Auditory (Vestiblochlear)IX GlossopharyngealX VagusXI Accessory XII Hypoglossal
Cranial Nerve Major FunctionI Olfactory Smell
II Optic Vision
III Occulomotor Eyelid and Eyeball movement
IV Trochlear Innervates superior obliqueTurns eye downward and laterally
V Trigeminal ChewingFace and Mouth touch/pain
VI Abducens Turns eye laterally
VII Facial Controls most facial expressionsSecretion of tears & salivaTaste
VIII Auditory (Vestibulocochlear) HearingEquilibrium sensation
IX Glossopharyngeal TasteSenses carotid blood pressure
X Vagus Senses Aortic blood pressureSlows heart rateStimulates digestive organsTaste
XI Spinal Accessory Controls Trapezius & SCM
XII Hypoglossal Controls the tongue (motor) MovementControls swallowing movement
ANATOMY OF THE EYE
Characteristics Measures about 1”
and is shaped as a sphere
See only anterior 1/6
Accessory Structures
Extrinsic Eye Muscles
Eyelids Conjunctiva Lacrimal apparatus
Figure 8.1
Site whereconjunctivamerges withcornea
Palpebralfissure
Lateralcommissure(canthus)
IrisEyelid
Eyebrow
EyelidEyelashes
PupilLacrimalcaruncleMedialcommissure(canthus)
Sclera(covered byconjunctiva)
ANATOMY OF THE EYE Anterior Aspects of the Eye Eyelids- provide protection Medial/Lateral Commissure (corners of
the Eye) Palpebral fissure- space b/w eyelids Eyelash- extends from the eyelid Tarsal glands- Modified sebacious gland
Produces oily secretion - lubrication Ciliary glands – modified sweat gland
Found between the eyelashes Conjunctive – lines eyelid and covers the
outer surface of the eyeball Secretes mucous
Figure 8.2a
Lacrimalgland
Conjunctiva
Anterioraspect
EyelidEyelashesTarsalglandsEyelid
Excretory ductof lacrimal gland
HOMEOSTATIC IMBALANCE OF THE EYE
Conjunctivitis Pink Eye Characteristics Inflammation of the
conjunctiva
Infectious conjunctivitis
Figure 8.2b
LacrimalglandExcretory ductsof lacrimal gland
Lacrimal canaliculusNasolacrimal ductInferior meatusof nasal cavity
Nostril
Lacrimal sac
(b)
LACRIMAL APPARATUS1. Consists of the lacrimal glands and ducts to drain
the secretions into the nasal cavity 2. Lacrimal Glands
Located above the lateral end of each eye Releases tears- dilute salt solution Tears flush the eye across the canaliculi medially into the Lacrimal Canaliculi
3. Lacrimal Canaliculia. Sends tears into the Lacrimal sacb. Lacrimal sac receives the tears
4. Naso lacrimal Duct a. empties the tears into the Nasal Cavity
LACRIMAL SECRETIONS
5. Lacrimal Secretions (Tears) contain mucuos, Antibodies and Lysozyme (destroy bacteria)
6. Nasal Mucosa Connects with the lacrimal duct system Effects of Nasal Mucosa will reach the eye
6 EXTRINSIC EYE MUSCLES
1. Attach to the outer surface of the eye 2. Produce Gross eye movment
6 EXTRINSIC EYE MUSCLES
Muscle Action Innervation
Lateral Rectus Moves eye laterally
VI (Abducens)
Medial Rectus Moves eye medially
III (Occulomotor)
Superior Rectus Elevates the eyeTurns eye Medially
III (Occulomotor)
Inferior Rectus Depresses the eyeTurns eye medially
III (Occulomotor)
Inferior Oblique Elevates the eyeTurns eye laterally
III (Occulomotor)
Superior Oblique
Depresses eyeTurns eye laterally
IV (Trochlear)
Figure 8.3a
Superioroblique muscle
Superioroblique tendon
Superiorrectus muscle
Conjunctiva
Lateral rectusmuscle
Opticnerve
Inferiorrectusmuscle
Inferiorobliquemuscle
(a)
Figure 8.3b
Trochlea
Superioroblique muscle
Medialrectus muscle
Lateralrectus muscle
Superioroblique tendon
Superiorrectus muscle
(b)
Inferiorrectus muscle
Axis atcenter ofeye
EYEBALL
1. Hollow Sphere 2. Composed of 3 layers a. Fibrous layer - Outside layer b. Vascular layer - Middle layer c. Sensory layer - Inside layer
3. Inner sphere filled with fluid called Humors4. Lens – supported upright within the cavity
a. Divides the eye into 2 chambers1. Aqueous humor – Anterior Chamber2. Vitreous Humor – Posterior chamber
LAYERS FORMING THE EYE WALL1. Fibrous Layer – outermost layer
A. Sclera – protective layer1. Thick glistening white connective tissue2. seen in the anterior as the “white of the eye”
B. Cornea
1. the central anterior portion of the fibrous layer 2. crystal clear (window of the eye) – light enters 3. many nerve endings – pain fibers 4. If touched, blinking and tearing occur 5. Exposed part of the eye
a. subject to injuryb. great ability to repair
6. only body tissue that can be transplanted without rejection
a. no blood supply – no immune system
LAYERS FORMING THE EYE WALL2. Vascular Layer (Choroid)– middle layer of the eyeball
a. Blood rich nutritive tonic that contains dark pigment b. Prevents the scattering of light inside the eye
c. Anteriorly, modified to form two smooth muscle structures
1. Ciliary body – attaches to lens by ligaments called Ciliary Zonule
2. Iris – filled with pigment (circular and radial smooth muscle)
3. Pupil – rounded opening to the ris a. Bright light and Close vision1. Pupils constrict (contraction of circular
muscles) b. Dark and far vision1. Pupils enlarge (radial fibers contract)
LAYERS FORMING THE EYE WALL3. Sensory Layer (Retina) Retina – innermost 2 layered retina
a. Extends anterior to the ciliated body b. Outer Layer – pigmented
1. Prevents the scattering of light inside the eye like the choroid
2. Acts as Phagocytesa. remove dead/ damaged receptor
cellsb. stores Vitamin Ac. Inner Layer – Neural layer - transparent
Sensory Layer (Continued) c. Inner Layer – Neural layer – transparent 1.contains millions of receptor Cells called Photoreceptors(Rods and Cones) 2. Impulse pathway travels from:
(2 neuron chain) photoreceptors bipolar cells ganglion cellsOptic Nerve 3. Leave the retina via the optic nerve and travel to the optic cortex
Figure 8.4a
Ciliary bodyCiliary zonule
CorneaIrisPupil
Lens
ScleraChoroidRetina
Fovea centralis
Optic nerve
(a)
Aqueoushumor (inanterior segment)
Scleral venous sinus(canal of Schlemm)
Optic disc(blind spot)
Central artery andvein of the retina
Vitreous humor(in posterior segment)
Figure 8.4b
Ciliary body
Iris
LensCorneaCiliary zonule
(b)
RetinaChoroidScleraFovea centralisOptic discOptic nerve
Marginof pupil
Aqueous humor(in anteriorsegment)
Vitreous humorin posterior segment
FIGURE 8.4INTERNAL ANATOMY OF THE EYE (SAGITTAL SECTION).
Ciliary bodyCiliary zonuleCorneaIrisPupil
LensScleral venous sinus(canal of Schlemm)Vitreous humor(in posterior segment)(a)
Ciliary bodyIris
LensCorneaCiliary zonule(b)
ScleraChoroidRetina
Fovea centralis
Optic nerve
Central artery andvein of the retinaOptic disc(blind spot)
RetinaChoroidScleraFovea centralisOptic discOptic nerve
Aqueoushumor (inanterior segment)
Vitreous humorin posterior segment
Marginof pupilAqueous humor(in anteriorsegment)
PHOTORECEPTOR CELLS (RODS & CONES)1. Distributed over the entire Retina except where the optic
nerve leaves the eye2. Optic disc – (the point where the optic nerve leaves the eye)
a. Blind spot3. Rods and Cones are not evenly distributed a. Rods – dense at the peripheral edge of the retina
decrease in number as you move to the center of the Retina
1. see shades of gray in dim light2. allows for peripheral vision3. night blindness – results from an
interference with rod function Causes a. Vit A deficiencyb. Leads to a deterioration of the neural retina tissuec. Vit A can help to restore function if taken
PRIOR to degeneration
PHOTORECEPTOR CELLS (CONT’D)
3. (Continued) b. Cones
1. allows us to see details and colors in bright light
2. most dense in the center of the Retina 4. Fovea Centralis a. Lateral to each blind spot
b. tiny pit containing only Cones c. area of greatest visual acuity
(sharpness)
FIGURE 8.5A THE THREE MAJOR TYPES OF NEURONS COMPOSING THE RETINA.
RodCone
(a)
Pathwayof light
Pigmentedlayer of retina
Bipolarcells
Ganglioncells
Neural Layer
2 ganlion chain
A CLOSER LOOK 8.1 VISUAL PIGMENTS—THE ACTUAL PHOTORECEPTORS
Process ofbipolar cell Synaptic
endings
Light
Light
Light
Innerfibers Rod cell
bodyRodcellbody
Conecellbody
Outerfiber
Nuclei
Mitochondria
Inne
r se
gmen
tPi
gmen
ted
laye
r
Discscontainingvisual pigments
Pigment cellnucleus
Outersegment
Melaningranules
Rhodopsin(visual purple)
Light absorptioncauses
Opsin
Retinal(visual yellow)
Releases
Bleaching ofthe pigment
Outer segment – attached to the cell body, light trapping contains visual discs to trap light. a. bleaching – results from stimulation of light, pigment regenerates b. this causes electrical changes in the photoreceptor cells-nerve impulse sent to brain
Rhodopsin (purple pigment in Rods) a. formed from union of Opsin and Retinal (modified Vit A)Kinked shape.
b. Retinal straightens when hit with light (purple color changes to yellow (bleaching)
c. Once colorless, the Retinal is now Vit A again
d. once the Vit A returns to its kinked form, it combines with Opsin to regenerate into Rhodopsin(An ATP-requiring process)
FIGURE 8.5B THE THREE MAJOR TYPES OF NEURONS COMPOSING THE RETINA.
Pigmentedlayer of retina
Neural layerof retina
Centralarteryand veinof retina Optic
disc
Opticnerve(b)
ScleraChoroid
5. Macula (macula lutea) (from Latin macula, "spot" + lutea, “yellow")
a. is an oval-shaped highly pigmented yellow spot near the center of the retina b. It has a diameter of around 1.5 mm c. defined as having two or more layers of ganglion cells d. Fovea Centralis is located near the center
a. contains the largest concentration of cone cells in the eye and is responsible for central, high resolution vision.
e. Because the macula is yellow in color it absorbs excess blue and ultraviolet light that enter the eye 1. acts as a natural sunblock (analogous to sunglasses) f. The yellow color comes from its content of lutein and Zeaxanthin
a. Zeaxanthin is found mostly at the macula
b. Lutein found in the retina. c. There is some evidence that these carotenoids protect the pigmented region from some types of macula degeneration
FIGURE 8.8 THE POSTERIOR WALL (FUNDUS) OF THE RETINA AS SEEN WITH AN OPHTHALMOSCOPE.
Foveacentralis
Macula Bloodvessels
Optic disc Retina
Lateral
Medial
Macular Degeneration
1. There is a loss of peripheral vision 2. it may go unnoticed for some time 3. damage will result in loss of central vision
3 Types of cones Each most sensitive to a particular wavelength of light
1. Blue2. Green3. Green and Red - called the red cones, only
respond to red
Intermediate colorsMultiple impulses yield a blend of colors as interpreted by the visual corex
Blue/Red Purplewhen all 3 cones are stimulated eyes
will result in White colorcolor mix occurs at the Brain Red
Yellow Green
FIGURE 8.6 SENSITIVITIES OF THE 3 CONE TYPES TO THE DIFFERENT WAVELENGTHS OF VISIBLE LIGHT.
560 nm(red cones)530 nm
(green cones)
420 nm(blue cones)
Light
abs
orpt
ion
by c
one
popu
latio
ns
380 450 500 550 600 650 700 750Wavelengths (nanometers)
Lens 1. focuses light to the Retina
2. Biconvex crystal like structure3. Held upright in position by suspensory ligaments called
(Ciliary Zonules) which attach to the Ciliary body.
Lens Divides the eye into 2 chambers: 1. Anterior (Aqueous) segment
a. contains clear fluid called Aqueous Humorb. Reabsorbed into the venous blood through
the Sclera Venous sinus or (Canal of Schlemm)
1. located at the junction of the Sclera/Cornea2. Posterior (Vitreous) segment
1. Contains clear fluid called Vitreous Humor (Body)
2. Prevents collapse of the eyeball3. Maintains intraocular pressure
4. Provides nutients for lens/cornea
LENS Imbalance Disorders
Color blindness1. The lack of all 3 cones2. Most common – lack of red or green receptorsa. 2 colors seen as one, depends on the coneb. gene for color vision on X chromosomec. sex linked – seen more in malesCataracts1. Hard opaque hazy distorted appearance2. results in blindness3. Risk factorsa. Diabetes, sunlight, smoking4. treatment – surgery, lens replacementGlaucoma 1. results from an increase of the pressure in the eye2. due to a build up of Aqueous Humor3. Test: Tonometer (puff of air)- measures the internal pressure of the eye
FIGURE 8.7 PHOTOGRAPH OF A CATARACT.
CATARACT
GLAUCOMA
OPHTHALMOSCOPIC EXAM Ophthalmoscope
Instrument that illuminates the interior of the eye
Able to view the Retina, Optic disc, Blood vessels at the Fundus, Macula, Fovea Centralis
Fundus Exam – used to detect pathology Diabetes – vascular blotches (micro aneurisms) Arteiosclerosis – copper wiring reflex
(Hypertensive Retina) Degeneration of the optic nerve and retina
See pale optic nerve – loss of axons & myelin
Diabetic Retinopathy See microanneurisms (blotches) Hard exudates (yellow) and cotton
wool spots (white)
Macular Degeneration – pigmented spotting on Retina
FIGURE 8.8 THE POSTERIOR WALL (FUNDUS) OF THE RETINA AS SEEN WITH AN OPHTHALMOSCOPE.
Foveacentralis
Macula Bloodvessels
Optic disc Retina
Lateral
Medial
Fundus photographs of the right eye (left image) and left eye (right image). The gaze is into the camera, so in each picture the macula is in the center of the image, and the optic disk is located towards the nose.
DIABETIC RETINOPATHY
HYPERTENSIVE RETINOPAHY
COPPER WIRE REFLEX
Hypertensive retinopathy with AV nicking and mild vascular tortuosity
AV nicking
MACULAR DEGENERATION
PHYSIOLOGY OF VISIONResting Eye
Distant Objects Set for distant vision Light from over 20 feet away approaches as parallel
rays Lens does not need to change shape for focus
Closer Objects Light tends to scatter, diverge – spread out Lens must bulge more
A. Ciliary body contracts B. Allows lens to become more convex
FIGURE 8.9 RELATIVE CONVEXITY OF THE LENS DURING FOCUSING FOR DISTANT AND CLOSE VISION.
Retina
Focal pointLight from distant source(a)
Light from near source
Focal pointRetina
(b)
PHYSIOLOGY OF VISION
Accomodation The ability for the eye to focus on close objects
Real Image The image that is formed on the Retina as the result
of the light bending activity Reversed (L to R) and upside down (inverted)
Like the microscope
FIGURE 8.10 REAL IMAGE (REVERSED LEFT TO RIGHT, AND UPSIDE DOWN) FORMED ON THE RETINA.
NEAR SIGHTED VS. FAR SIGHTED Emmetropia
The ability of the eye to focus images correctly on the Retina
Harmonious vision
Near Sightedness Called Myopia Occurs when parallel rays from a distant object fail to
reach the Retina Distant objects appear blurry Nearby objects are in focus
Lens accommodates (bulges) to focus images onto the Retina Results from an eyeball that is too long
Lens that is too strong Cornea that is too curved
Correction Requires a concave lens to diverge the light rays before
entering the eye
IF I CAN’T SEE THINGS FAR AWAY, AM I NEARSIGHTED OR FARSIGHTED?
Focalplane
(a) Emmetropic eye
Correction
None required
Concave lens
Convex lens(b) Myopic eye (nearsighted)
(c) Hyperopic eye (farsighted)
NEAR SIGHTED VS. FAR SIGHTED Farsightedness
Called Hyperopia Occurs when the parallel rays focus behind the Retina
in a resting eye where the lens is flat and ciliary muscles relaxed
Results from an eveyball that is too short or a lazy lens See distant objects clearly- ciliary muscles contract Close objects blurr- lens can’t bulge enough to move
rays forward The patient will be subject to eye strain from an
overuse of the ciliary muscles
Correction Requires a convex lens to converge light rays before
they enter the eye Can see far, not close
Astigmatism When the eyeball has unequal curvatures in different
parts of the cornea Results in blurry images
Points of light not focused as points on the retina, seen as blurry lines
Require special cylindrically ground lens
VISUAL FIELDS & VISUAL PATHWAYS TO THE BRAIN
Visual Pathways Axons from the Retina exit the posterior eye via the
Optic Nerve Approach the Optic Chisma (Chism=cross) Forms fibers called the Optic Tracts
Contain medial fibers of the medial retina from the eye of the opposite sider
Contains lateral fibers of the lateral retina from the eye of the same side
Optic tract fibers synapse with neurons in the thalamus
These axons for the Optic Radiation These run to the Occipital lobe – visual cortex
They then synapse with the cortical cells This is where visual interpretation and vision occur
FIGURE 8.11 VISUAL FIELDS OF THE EYES AND VISUAL PATHWAY TO THE BRAIN.
Fixation point
Right eye Left eye
Opticchiasma
OpticnerveOptictract
Opticradiation
Occipital lobe(visual cortex)
Thalamus
VISUAL FIELDS Visual fields
Each side of the brain receives input from both eyes Lateral field from the eye-same side Medial field from the eye-opposite side
Each eye has a different view with an overlap of the visual fields
Humans have Binocular vision- two eyed Provides depth and perception Three dimensional vision
Visual fields Hemianopia – a loss of the same side of the visual field of
both eyes Results from damage to the visual cortex on one side (CVA’s) The person will not be able to see past their own visual field
from either side, depending on the sit of the CVA Accomodation will be needed for rehabilitation
EYE REFLEXES Reflexes
Both the internal and external(extrinsic) eye muscles are needed for eye function
Internal muscles – controlled by the autonomic nervous system Includes the ciliary body – changes lens shape, curvature Radial and circular muscles – control the opening of the Iris
Photopupupillary Reflex – constriction of pupils when suddenly exposed to light Accomodation Reflex – Constriction of pupils when viewing close objects
External Muscles – the rectus and oblique muscles Control eye movement Responsible for convergence (Reflexive movement)
Eyes move medially – controlled by cranial nerves III, IV and VI Provides depth and perception Three dimensional vision
Reading Requires the continuous work of both sets of muscles
Ciliary body helps to bulge the lens Circular constrictor muscles of the Iris produce the accomodation pupillary
reflex Extrinsic Muscles converge the eyes and to follow printed lines (eye strain)