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
There are 12 pairs of 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
Cranial Nerve
Major Function
I Olfactory
Smell
II Optic
Vision
III Occulomotor
Eyelid and Eyeball movement
IV Trochlear
Innervates superior oblique
Turns eye downward and laterally
V Trigeminal
Chewing
Face and Mouth touch/pain
VI Abducens
Turns eye laterally
VII Facial
Controls most facial expressions
Secretion of tears & saliva
Taste
VIII Auditory (Vestibulocochlear)
Hearing
Equilibrium sensation
IX Glossopharyngeal
Taste
Senses carotid blood pressure
X Vagus
Senses Aortic blood pressure
Slows heart rate
Stimulates digestive organs
Taste
XI Spinal Accessory
Controls Trapezius & SCM
XII Hypoglossal
Controls the tongue (motor) Movement
Controls swallowing movement
Characteristics
 Measures about 1”
and is shaped as a
sphere
 See only anterior 1/6
Accessory Structures
Extrinsic Eye Muscles
 Eyelids
 Conjunctiva
 Lacrimal apparatus

Site where
conjunctiva
merges with
cornea
Eyebrow
Palpebral
fissure
Pupil
Lacrimal
caruncle
Lateral
commissure
(canthus)
Medial
commissure
(canthus)
Iris
Eyelid
Eyelid
Eyelashes
Sclera
(covered by
conjunctiva)
Figure 8.1
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


Ciliary glands – modified sweat gland


Produces oily secretion - lubrication
Found between the eyelashes
Conjunctive – lines eyelid and covers the
outer surface of the eyeball

Secretes mucous
Lacrimal
gland
Excretory duct
of lacrimal gland
Conjunctiva
Anterior
aspect
Eyelid
Eyelashes
Tarsal
glands
Eyelid
Figure 8.2a
Conjunctivitis
Characteristics
 Inflammation of the
conjunctiva
Pink Eye

Infectious
conjunctivitis
Lacrimal
gland
Excretory ducts
of lacrimal gland
Lacrimal sac
Lacrimal canaliculus
Nasolacrimal duct
Inferior meatus
of nasal cavity
Nostril
(b)
Figure 8.2b
1. 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 Canaliculi
a. Sends tears into the Lacrimal sac
b. Lacrimal sac receives the tears
4.
Naso lacrimal Duct
a. empties the tears into the Nasal Cavity
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
1. Attach to the outer surface of the eye
2. Produce Gross eye movment
Muscle
Action
Innervation
Lateral Rectus
Moves eye laterally
VI (Abducens)
Medial Rectus
Moves eye medially
III (Occulomotor)
Superior Rectus
Elevates the eye
Turns eye Medially
III (Occulomotor)
Inferior Rectus
Depresses the eye
Turns eye medially
III (Occulomotor)
Inferior Oblique
Elevates the eye
Turns eye laterally
III (Occulomotor)
Superior Oblique
Depresses eye
Turns eye laterally
IV (Trochlear)
Superior
oblique muscle
Superior
oblique tendon
Superior
rectus muscle
Conjunctiva
Lateral rectus
muscle
Optic
nerve
Inferior Inferior
rectus oblique
muscle muscle
(a)
Figure 8.3a
Trochlea
Superior
oblique muscle
Superior
oblique tendon
Axis at
center of
eye
Superior
rectus muscle
Inferior
rectus muscle
Medial
rectus muscle
Lateral
rectus muscle
(b)
Figure 8.3b
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 Humors
4. Lens – supported upright within the cavity
a. Divides the eye into 2 chambers
1. Aqueous humor – Anterior Chamber
2. Vitreous Humor – Posterior chamber
1. Fibrous Layer – outermost layer
A. Sclera – protective layer
1. Thick glistening white connective tissue
2. 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 injury
b. great ability to repair
6. only body tissue that can be transplanted without
rejection
a. no blood supply – no immune system
2. 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 vision
1. Pupils constrict (contraction of circular
muscles)
b. Dark and far vision
1. Pupils enlarge (radial fibers contract)
3. 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 Phagocytes
a. remove dead/ damaged receptor
cells
b. stores Vitamin A
c. 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 cellsOptic Nerve
3. Leave the retina via the optic nerve and
travel to the optic cortex
Ciliary body
Ciliary zonule
Cornea
Iris
Pupil
Aqueous
humor (in
anterior segment)
Lens
Scleral venous sinus
(canal of Schlemm)
Vitreous humor
(in posterior segment)
Sclera
Choroid
Retina
Fovea centralis
Optic nerve
Central artery and
vein of the retina
Optic disc
(blind spot)
(a)
Figure 8.4a
Ciliary body
Iris
Margin
of pupil
Aqueous humor
(in anterior
segment)
Lens
Cornea
Ciliary zonule
Vitreous humor
in posterior segment
Retina
Choroid
Sclera
Fovea centralis
Optic disc
Optic nerve
(b)
Figure 8.4b
Ciliary body
Ciliary zonule
Cornea
Iris
Pupil
Aqueous
humor (in
anterior segment)
Lens
Scleral venous sinus
(canal of Schlemm)
Vitreous humor
(in posterior segment)
(a)
Ciliary body
Iris
Margin
of pupil
Aqueous humor
(in anterior
segment)
Lens
Cornea
Ciliary zonule
(b)
Sclera
Choroid
Retina
Fovea centralis
Optic nerve
Central artery and
vein of the retina
Optic disc
(blind spot)
Vitreous humor
in posterior segment
Retina
Choroid
Sclera
Fovea centralis
Optic disc
Optic nerve
1. Distributed over the entire Retina except where the optic
nerve leaves the eye
2. Optic disc – (the point where the optic nerve leaves the eye)
a. Blind spot
3. 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 light
2. allows for peripheral vision
3. night blindness – results from an
interference with rod function
Causes
a. Vit A deficiency
b. Leads to a deterioration of the
neural retina tissue
c. Vit A can help to restore function if taken
PRIOR to degeneration
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)
Pigmented
layer of retina
Rod
Cone
Neural
Layer
2 ganlion
chain
Bipolar
cells
Ganglion
cells
(a)
Pathway
of light
Rhodopsin
(purple pigment
in Rods)
a. formed from
union of Opsin
and Retinal
(modified Vit A)
Kinked shape.
Process of
bipolar cell
Rod
cell
body
c. Once
colorless, the
Retinal is now Vit
A again
Inner
fibers
Rod cell
body
Cone
cell
body
Outer
fiber
Nuclei
Mitochondria
Inner
segment
b. Retinal
straightens when
hit with light
(purple color
changes to yellow
(bleaching)
Synaptic
endings
Retinal
(visual yellow)
Discs
containing
visual pigments
Pigmented
layer
d. once the Vit A
returns to its
kinked form, it
combines with
Opsin to
regenerate into
Rhodopsin
(An ATP-requiring
process)
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
Outer
segment
Pigment cell
nucleus
Melanin
granules
Light absorption
causes
Rhodopsin
(visual purple)
Releases
Opsin
Bleaching of
the pigment
Pigmented
Neural layer
layer of
of retina
retina
Central
artery
and vein
of retina
Sclera
Optic
nerve Choroid
(b)
Optic
disc
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
Macula
Fovea
centralis
Lateral
Blood
vessels
Optic disc Retina
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. Blue
2. Green
3. Green and Red - called the red cones, only respond
to red
Intermediate colors
Multiple impulses yield a blend of colors as interpreted by the
visual corex
Blue/Red  Purple
when all 3 cones are stimulated
eyes
will result in White color
color mix occurs at the Brain
Red
Yellow
Green
Light absorption by cone populations
560 nm
(red cones)
530 nm
(green cones)
420 nm
(blue cones)
380
450
500
550
600
650
Wavelengths (nanometers)
700
750
Lens
1. focuses light to the Retina
2. Biconvex crystal like structure
3. 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 Humor
b. Reabsorbed into the venous blood through the
Sclera Venous sinus or (Canal of Schlemm)
1. located at the junction of the Sclera/Cornea
2. Posterior (Vitreous) segment
1. Contains clear fluid called Vitreous Humor (Body)
2. Prevents collapse of the eyeball
3. Maintains intraocular pressure
4. Provides nutients for lens/cornea
Imbalance Disorders
Color blindness
1. The lack of all 3 cones
2. Most common – lack of red or green receptors
a. 2 colors seen as one, depends on the cone
b. gene for color vision on X chromosome
c. sex linked – seen more in males
Cataracts
1. Hard opaque hazy distorted appearance
2. results in blindness
3. Risk factors
a. Diabetes, sunlight, smoking
4. treatment – surgery, lens replacement
Glaucoma
1. results from an increase of the pressure in the eye
2. due to a build up of Aqueous Humor
3. Test: Tonometer (puff of air)- measures the
internal pressure of the eye
 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
Macula
Fovea
centralis
Lateral
Blood
vessels
Optic disc Retina
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.
AV nicking
AV nicking
Hypertensive retinopathy with AV nicking
and mild vascular tortuosity
Resting 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
Retina
Light from distant source
Focal point
(a)
Light from near source
Focal point
Retina
(b)

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

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


Results from an eyeball that is too long



Lens accommodates (bulges) to focus images onto the Retina
Lens that is too strong
Cornea that is too curved
Correction

Requires a concave lens to diverge the light rays before entering
the eye
Focal
plane
Correction
None required
Concave lens
(a) Emmetropic eye
(b) Myopic eye
(nearsighted)
(c) Hyperopic eye
(farsighted)
Convex lens

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 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




Optic tract fibers synapse with neurons in the thalamus
These axons for the Optic Radiation


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
These run to the Occipital lobe – visual cortex
They then synapse with the cortical cells

This is where visual interpretation and vision occur
Fixation point
Right eye
Left eye
Optic
nerve
Optic
tract
Optic
chiasma
Optic
radiation
Thalamus
Occipital lobe
(visual cortex)

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

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



External Muscles – the rectus and oblique muscles


Control eye movement
Responsible for convergence (Reflexive movement)




Photopupupillary Reflex – constriction of pupils when suddenly exposed to light
Accomodation Reflex – Constriction of pupils when viewing close objects
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)