vision i Flashcards
Visible light
400-700 nm
-vision converts (transduces) stimulus of light into a nervous impulse
The eye and vision
- 70% of body’s sensory receptors are in eye
- visual processing by ~ half cerebral cortex
- most of eye is protected by cushio of fat and bony orbit
Eye accessory structures
Palpebrae = eyelids (meet at commisures)
Eyelashes and eyebrows
extrinsic eye muscles
these structures protect and asist sensory structures of eye, but aren’t part of eye proper
Eyebrows
- overlie supraorbital margins
- func: shade eye from sunlight and prevent sweat from goin in eye
Eyelids
- protect eye anteriorly
- separated at palpebral fissure
- meet at medial and lateral commissures
- lacrimal caruncle = @ medial commissure–> has oil and sweat glands
- tarsal plate = supporting CT
Eyelashes
-nerve endings of follicles initiate reflex blinking
- lubricating glands associated with eyelids:
1) Tarsal (Meibomian) gland = modified sebaceous glands whose oily secretions lubricate lid and eye –> infection = chalazion
2)Ciliary glands b/t hair follicles = modified sweat glands –> infection = stye
Conjunctiva
- transparent mucous membrane
- produces lubricating mucous secretion
- palpebral conjunctiva lines eyelids
- bulbar onjunctiva covers white of eyes
- conjunctival sac b/t palpebral and bulbar conjunctiva
Lacrimal Apparatus
-tears from lacrimal apparatus:
lacrimal glands–> excretory lacrimal duct –> lacrimal puncta –> lacrimal canaliculi –> lacrimal sac –> nasolacrimal duct
Extrinsic eye muscle
cranial nerve III (oculomotor) -superior rectus (superior/medial) -inferior rectus (inferior/medial) -medial rectus (medial) inferior oblique (superior/lateral)
cranial nerve IV (trochlear)
-superior oblique (inferior/lateral)
cranial nerve VI (abducens)
-lateral rectus (lateral)
3 layers of the eyeball
- Fibrous tunic = outer layer
- sclera “white” of eye
- cornea - transparent coat - Vascular tunic/uvea = middle
- choroid
- ciliary body w/ processes and muscels
- iris - Retina = inner
- pigmented layer
- neural layer with optic disc and macula lutea/fovea centralis
Sclera
- posterior, white, dense irregular CT
- avascular
- protective covering
- provides shape
- sturdy anchor for extrinsic eye muscles (insertion)
Cornea
-anterior
-2 epithelial layers
-avascular
-transparent to let light thru
-pain receptors
-regeneration + repair
(lots of refraction)
Scleral venous sinus
- “canal of Schlemm)
- at junction of sclera and cornea
- fluid drains from anterior cavity of eye into blood
Choroid
posterior to ciliary body
- blood vessels
- pigments (melanocytes) absorb light rays
Ciliary body
- anterior to choroid
- ciliary processes = secrete aqueous humor made of filtrate from capilaries
- ciliary muscles = smooth muscle that alters lens shape –> alters tension of suspensory ligaments (ciliary zonules)
Iris
-colred part (variations of brown pigment)
smooth muscles
- circular (sphincter pupillae/ pupillary constrictor) –> parasymp
- radial (dilator pupillae/pupillary dilator) –> symp
Pupil
- central black hole
- size determines amt of light entering eye
- change in response to bright/dim light or emotions
Pigmented layer of retina
- outer layer
- nonvisual
- next to choroid layer
- absorbs stray light
- phagocytes
- stores vit A
Neural layer of retina
- inner layer
- visual
3 zones of neurons (post to ant)
- photoreceptors (rods and cones)
- bipolar cells
- ganglion cells (axon exit as optic nerve at optic disc=blind spot= no photoreceptors
- amacrine and horizontal cells modify elec. signals
- macula lutea and fovea centralis have a ton of cones for visual acuity
- ora serrata = boundary of photosensitive area
Interior of eyeball (parts)
lens
anterior cavity
posterior cavity
lesn
lacks blood vessels
- consists of a capsule with proteins (crystallins) in layers
- transparent
-divides eyeball into anterior and posterior cavities
anterior cavity
- divided into anterior and posterior chambers
- both filled with aqueous humor
- aqueous humor is constantly refreshing
posterior cavity
- “vitreous chamber”
- filled with jelly-like vitreous humor/ vitreous body
- vitreous humor is permanent
Circulation of aqueous humor
- forms by filtration from capillaries in ciliary processes
- flows from posterior chamber, thru pupil, to anterior chamber (some also flows thru vitreous humor)
- reabsorbed into venous blood by scleral venous sinus
