NSCI2101 Exam 2 Lec 6

what are the 6 parts of the eye?

• iris

• pupil

• sclera

• cornea

• conjunctiva

• eyelids

conjunctiva

lines the inner surface of the eyelids and the surface of the sclera

• its not really noticeable except when there is irritation

• protects the outer part of the eye

• has a first line of defense against viruses and bacteria or infections coming through

conjunctivitis

also known as pink eye. is inflammation of the conjunctiva and can be the result of an allergic reaction or infection caused by a virus or bacteria

• usually viral and eye drops don’t really do anything for it

• very contagious

tear glands / lacrimal glands

• under the eyelid

• secretes lacrimal fluid (tears) that keep to surface of the conjunctiva and cornea moist

• tears are swept across the eye by the closing of the eyelid

where does lacrimal fluid drain?

into the nose at the medial corner of the eye (the tear duct)

why does your nose run when you cry?

because the tears drain out of the tear duct and into your nose

what happens if the tear ducts are blocked?

it will look like you’re crying all the time because there is nowhere for your tears to drain

how is the eyelid opened?

by a muscle inside the orbit that is innervated by the oculomotor nerve (CN III)

ptosis

being unable to open your eyelids or your eyelids being droopy as a result of an issue with the oculomotor nerve

how is your eyelid closed?

by muscles in the eyelid innervated by the facial nerve (CN VII)

what are the three layers of the eye?

outer, middle, and inner

what comprises the outer layer of the eye?

• cornea

• sclera (continuous with dura mater)

what comprises the middle layer of the eye?

• iris

• ciliary body

• choroid (continuous with pia/arachnoid mater)

what comprises the inner layer of the eye?

retina (continuous with optic nerve and brain)

what three layers of tissue enclose the eye and help keep it’s shape?

• sclera

• choroid

• retina

sclera

tough, white, fibrous tissue

• anterior portion is cornea

choroid

• highly vascularized

• continuous with the iris and ciliary body

pupil

opening in the center of the iris

optic disk

where the optic nerve exits the retina

blind spot

an area at the back of the eye where there are no photo receptors

retina

includes the fovea, where there are a lot of cones that pick up light and send it down your optic nerve

iris

includes:

• iris (pupil) dilator muscle that dilates it

• iris (pupil) sphincter muscle constricts iris

• pigment cells that give the iris it’s color

pupillary reflex

reflex that keeps both pupils roughly the same size

what happens if you shine light into one eye and the other eye doesn’t contract?

there is probably inflammation or a stroke in the brain

ciliary body

• causes the lens to suspend

• ciliary muscle allows for fine focus

• makes aqueous humor: a fluid that fills the anterior and posterior chamber of the eye

anterior chamber

space between the lens and the cornea

posterior chamber

space between the lens and the iris

aqueous humor

• fluid that is continuously made by the ciliary body

• maintains intraocular pressure

• drains via canals into the blood

• glaucoma can result if production and drainage are not in balance

glaucoma

condition that results from a blockage of aqueous humor in your eye that might result in blindness as the retina is being pushed on and it’s cells are being damaged

vitreous chamber

space between the lens and the retina

filled with vitreous humor

vitreous humor

• thick and gelatinous fluid

• can contain debris called floaters

what is the path of light into the eye?

cornea → anterior chamber → pupil → posterior chamber → lens → vitreous chamber → retina

cataract

cloudy spots in the lens of the eye that interfere with night vision, they get more common as you get older

what is the main focusing element of the eye?

the cornea as it’s the outermost part of the eye and does the most gross focusing

what part of the eye regulates the amount of light coming in?

the iris because it can constrict and expand

what part of the eye is for fine focus?

the lens

what happens to the cornea of nearsighted people?

the cornea focuses the light so that it comes to a point not all the way at the back of the eye

lens

it inverts and mirrors the image on the retina

retinal pigment epithelium (RPE)

contains melanin that aims to protect other cells in the eye from getting light damage

rods and cones

photoreceptors in the eye that pick up light and support the outer nuclear layer

outer nuclear layer

layer that contains all the nuclei of the rods and cones

photoreceptors

allow for the transduction of light into an electrical signal

inner nuclear layer

contains nuclei of bipolar cells, horizontal cells, amacrine, and Muller cells

ganglion cell layer

that is where the ganglion cells are and where they will send their axons to the optic nerve

inner and outer segments

where the rods and cones’ sensory apparatus is

outer and inner plexiform layers

where a lot of the synapses are happening in the eye

optic fiber layer

where a lot of ganglion cells axons are going

bipolar cells

the most direct route for rods and cones to talk to the ganglion cells

amacrine cells

modify how a signal passes to the ganglion cells

rods

most sensitive in low light

important for motion detection

cones

most sensitive in bright light

color sensitive

important for high acuity vision

are photoreceptors depolarized or hyperpolarized when no light is coming in?

depolarized

when photoreceptors have no light coming in, what neurotransmitter are they releasing into the synapse?

glutamate

opsins

light sensitive proteins in photoreceptors that bind retinol, which is a vitamin A derivative

• different opsins are sensitive to different wavelengths of light

the three types of cone cells are distinguished by the type of _____ they have, which are sensitive to different wavelengths

opsins

rhodopsin

light sensitive protein in rod cells

what percentage of men and women are colorblind?

8% of men and somewhat fewer women

what causes colorblindness?

having less or none of a particular opsin

what is required for night vision?

rhodopsin

vitamin a is required for the synthesis of what?

rhodopsin

vitamin a deficiency can result in…

night blindness

what mineral is needed for the transport of vitamin a?

zinc

zinc deficiency can exacerbate what?

night blindness

bipolar cells

cells in the inner nuclear layer that synapse with all other types of retinal neurons

• most direct route of transfer of visual information from photoreceptors to ganglion cells

• select type of information to relay to ganglion cells

how many rods normally connect to a single rod bipolar cell?

15-30

how many cones can connect to a cone bipolar cell?

one

• where you need higher acuity, you need a one-to-one relationship

horizontal cells

synapse with photoreceptor and bipolar cells

• enhance contrast through lateral interactions

amacrine cells

synapse with bipolar and ganglion cells

• helps adapt to changing light conditions

what are the two types of ganglion cells?

p type ganglion cells and m type ganglion cells

p type ganglion cells

• small dendritic arbor; receive information from few bipolar cells

  • important for color and form perception

m type ganglion cells

• large dendritic arbor; receive information from many bipolar cells

• important for motion perception

the axons of the retinal ganglion cells form what?

the optic nerve. they also carry visual information into the brain!

fovea

• specialized for high acuity vision

  • there are no blood vessels

  • only cone photoreceptors

  • other retinal cell types are pushed to the side

• the rest of the retina has more rods than cones

• use it for reading or identifying faces

peripheral retina

use it mostly to detect movement to attract our attention

extraocular muscles

move the eyes so that the object of interest falls on the fovea

optic nerve

axons from the retinal ganglion cells across the retina run to the optic nerve head

• optic nerve head is the start of the optic nerve

• there is no retina at the optic nerve head (blind spot)