1.3 Special Sense Organs (Eye) Flashcards
The eye:
Extremely complex organ
Where is the derived from?
both the ectoderm and mesoderm
Ectoderm =
Light structure
Ex: lens
Mesoderm =
Muscles that control eye movement
Explain What is happening in this diagram:
Part 1 of 4
The wall (optic sulci) of the diencephalon begins to extend toward the surface of the ectoderm
Explain What is happening in this diagram:
Part 2 of 4
-The optic sulcus deepens to become the optic vesicle
- The optic vesicle continues to grow toward the ectoderm which is induced to thicken (forming the optic or lens placode) and later
- The optic or lens placode will later begin to invaginate against the optic vesicle
Explain What is happening in this diagram:
Part 3 of 4
- The optic or lens placode begins / continues to invaginate against the optic vesicle
- The optic vesicle starts to undergo infolding and transforms from a single- wall to a double-walled optic cup
- The inner and outer layers begin to behave differently
Explain What is happening in this diagram:
Part 4 of 4
- The 2 layers of the optic cup differentiate
- Outer layer: becomes thinner and starts to express melanin granules, later develops into pigmented layer of the retina
- Inner layer: Thickens and develops into the sensory layer of the retina
- ectoderm invaginates fully to form the lens vesicle
Where does the optic sulci develop from?
diencephalon
What structures are derived from the ectoderm?
lens and retina
What structures are derived from the mesoderm?
muscles that derive from the eye
What holds the lens of the eye in place?
Ciliary body
Accommodation:
ability for light to focus on the retina
List the transparent media of the eye: What do these structures allow?
- conjunctiva
- cornea
- aqueous humour
- lens
- vitreous humour
Allow light to pass through all the way to retena
Conjuctiva
- Continuous with the skin of eyelids
- Stratified squamous epithelium
- Goblet cells: secrete deepest, mucus, layer of tear film, which adheres tears to surface of globe
Sign of infection for Conjuctiva?
excessive mucous / stickyness on eyelids (conjungtivitious)
Conjunctiva function:
thin, clear, mucous membrane over cornea and sclera that lubricates eye
Does the cornea have blood cells?
no
Cornea:
transparent and avascular refracting light onto lens and focuses it on the retina
Where does the cornea get nutrition from?
It’s avascular so it gets its nutrition / O2 from aqueous layer and O2 from air
What does the aqueous humour do?
Provides nutrients for lens and cornea
- Maintains intraocular pressure
- Replaced several times a day
What are the stages of the aqueous humour?
- Produced in ciliary body
- flows from the posterior chamber via the pupil and comes out the anterior chamber
- Then it drains through the vessels of the cornea and iris (canal of schlemm)
- The remaining liquid drains out of the episcleral venous system
Lens:
- This is the derivative of the optic placode
- Onion structure of lens fibers - live cells
- Cuboidal epithelium
- Capsule, with rostral and caudal sutures
- Softer cortex, firmer nucleus (firm/sclerotic with age)
- No blood vessels or nerves
- nutrients from aqueous
The vitreous humour:
- exerts pressure inside eyeball, this maintains retia position
- Secreted by ciliary up to the time of maturity
- Gelatinous: water, hyaluronic acid and collagen
- Hyaloid canal - remnant of blood vessels present during development
What does vitreous humour prevent?
Retinal detachment
Rods vs. cones?
rods = night vision
cones = daylight vision
Macula:
ability to focus on high definition
What is in the photoreceptor region of the eye?
cone and rod
Once light hits the rods and cones but region does it go to?
The Fovea and Macula region
What are the 3 parts of the uveal tract?
- Choroid (forms majority of the inside eye
- Ciliary body
- Iris
3 qualities of the Choroid:
- tapetum lucidum: refracts light inwards (inner: nearest retina
- vascular: blood supply
- black/connective (outer: nearest retina)
Iridic granules: sympathetic vs. parasympathetic
Sympathetic: larger pupil
Parasympathetic: small pupil
ciliary body
aqueous, vitreous, and lens accommodation ( ability for light to focus directly on retina)
Iris
pupil size: center part = smooth muscle
The sclera - outer wall
- At the limbus – The sclera continuous with cornea.
- The sclera is also continuous with dura at the optic stalk. (Recall that retina formation as an evagination of diecephalon).
Extraocular muscles: pulls eye to midline
medial rectus
Extraocular muscles: Pulls the eye outwards
lateral rectus
Extraocular muscles: pulls eye down
ventral rectus
Extraocular muscles: pulls the eye up
dorsal rectus
oblique muscles
rotate eye within eye in globe
retractor muscles:
pulls eye inwards when pressure is applied
- protective mechanism, 3rd eyelid may also pop out to prevent the eye from being destroyed
What muscles is nerve III associated with?
-dorsal, medial, and vetral rectus
-ventral oblique
The retractor muscle of the eyeball and lateral straight muscle are associated with which nerve?
Nerve VI
The trochlea with the tendon of the dorsal oblique muscle is associsted with which nerve?
Nerve IV
What do most of the rectus muscles do?
keep the eye straight or turn the eye within the globe
Describe the structure of the adnexa: Deep mucous
from conjunctival goblet cells that adhere tears to conjunctiva
Describe the structure of the adnexa: Middle aqueous layer
from main 3rd eyelid lacrimal glands that cleanse, have IgA, oxygenate, &fill optical defects
Describe the structure of the adnexa: Superficial oily layer
from tarsal glands (modified sebaceous) that prevents evaporation
Pupillary light -
(N. III) parasympathetic - pupil becomes smaller
Pupil dilation -
sympathetic - pupil becomes larger
Menace response -
VII, neck (involves cortex, cerebellum, and rostral colliculi
Fixating response -
III, IV, VI
Define Horner’s syndrome & symptoms often seen
disruption in the sympathetic nerve supply:
· partial ptosis (drooping or falling of upper eyelid)
· miosis (constricted pupil)
· facial anhidrosis (loss of sweating)
· decreased intraocular pressure
Define Strabismus
Abnormal eye position caused by malfunction of nerve(s) controlling muscles involved with eye movements
PTOSIS:
Unilateral - lesion of n.III to LPS or n.VII to face; sympathetic to smooth muscle (Horner’s)
Bilateral - often a lesion of VII nuclei
MIOSIS
Unilateral - Orbital, e.g. Horner’s, pilocarpine or uveitis
Bilateral - tectal lesion, ‘UMN’ releasing higher inhibition of both E-W nuclei - guarded
MYDRIASIS
Unilateral - Orbital, e.g. atropine or glaucoma
Bilateral - indicates central brainstem lesion affecting both Edinger-Westphal nuclei – grave
What cranial nerves control extrinsic muscles?
Cranial nerves III, IV, VI
What cranial nerves control autonomic control?
CN III and CCG
Pathology may result from?
brainstem or individual nerve lesions
