Senses - photoreceptors

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what is the purpose of photoreceptors?

- Detect light
- Eyes (vision)

What are the three divisions of the eyes?

- Eyelids (palpebrae)
- Lacrimal glands
- Cavities

eyelids (palpebrae): division of eye

- Protect & lubricate
- Tarsal glands: produce oily secretions (most internal structure)
- Conjunctiva: epithelium in contact w/eye that doesn't cover entire anterior portion of eye(most external structure)

What is conjunctivitis?

Inflammation of conjunctiva

Lacrimal glands: division of eye

- Mostly superior & lateral portion of eyes
- Produce tear in corner of eyes

Tears

- Produced by lacrimal glands
- Lubricate eye & nourish cells in cornea
- Drained medially into superior & inferior lacrimal glands, then nasal cavity

Cavities: division of eye

- Anterior cavity: filled w/aqueous humor (watery)
- Posterior cavity: filled w/vitreous body

=Aqueous humor

- Anterior cavity
- Replaced every 90 minutes
- Fills space behind cornea & iris
- Glaucoma results from excessive pressure due to insufficient drainage (high pressure --> damage eye)

Vitreous body

- Posterior cavity
- Much more dense than aqueous humor (gelatin)
- Very transparent
- Produced once during development, not replaced as adults
- If something is wrong it can hinder vision
- Normal to start accumulating dark spots w/age

What are floaters?

Dark spots in the body due to debris in vitreous bdy

What are the three layers of the eyeball?

- Fibrous tunic (external)
- Vascular tunic (intermediate)
- Nervous tunic (internal)

Fibrous tunic: external layer of eyeball

- Cornea
- Sclera

cornea (fibrous tunic; external layer of eyeball)

- Anterior cover of eye
- Very transparent
- Nourished by tears
- Epithelium, connective tissue
- No blood vessels
- No rejection after transplants

Sclera (fibrous tunic; external layer of eyeball)

- Posterior cover
- Ends at cornea
- White portion of eye
- Dense irregular connective tissue
- Gives round shape to eye

Vascular tunic: intermediate layer of eyeball

- Choroid
- Ciliary body
- Iris
- Lens

Choroid (vascular tunic; intermediate layer of eyeball)

- Line posterior portion of sclera, blood vessels, melanocytes
- Nourish & capture scattered light

ciliary body (vascular tunic; intermediate layer of eyeball)

- Posterior to cornea
- Structure in continuation of ciliary muscle
- Secrete aqueous humor

Iris (vascular tunic; intermediate layer of eyeball)

- Surrounds pupil
- Most external structure
- 2 portions w/space in middle (fibers form circle around central opening: pupil)
- Pigments produce colors of eyes

Pupil

- Black/dark part of eye (hole)
- Circular & radial smooth muscles adjust diameter
- Control amount of light to retina (passage for light)
- Close when lot of light (becomes smaller)

Lens (vascular tunic; intermediate layer of eyeball)

- Posterior to iris
- Focuses light on retina
- Muscle & lights deform iris

Retina (nervous tunic; internal layer of eyeball)

- Contains photoreceptors that allow us to see by detecting light
- Optic disc
- Central fovea

Optic disc of retina (nervous tunic; internal layer of eyeball)

- Blind/dark spot
- Optic nerve & vessels enter eye
- No photoreceptors

Central fovea of retina (nervous tunic; internal layer of eyeball)

- Aligned w/lens, pupil, cornea
- Ideal position for best image
- High density photoreceptors (most are cones)
- Don't have blood vessels passing through

What are the layers of the retina of the nervous tunic (internal layer of eyeball)?

- Pigment layer (most external): melanocytes (absorb light) & red eyes when flast illuminates reitna
- Photoreceptor layer (intermediate): rods & cones
- Several layers of neurons (internal): local image processing

What are the rods of the photoreceptor layer of the retina?

- Most sensitive to light
- Black & white images
- Fills most of retina
- Used at night to find way to bathroom

what are the cones of the photoreceptor layer of the retina?

- 3 types to give 3 different perceptions of colors of light
- Color vision
- Sharper image

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