Exam 2: Vision (15 and 16) Flashcards
conjunctivitis
inflammation of the conjunctiva and can be the result of an allergic reaction or an infection causing pink eye
- produces mucus and tears to fight microbes
- does NOT cover the cornea and is continuous with the portion covering the sclera
what gland secretes tears?
lacrimal gland secretes lacrimal fluid (tears) to keep the conjunctiva and cornea moist
what cranial nerve innervates the levator palpebral superioris to open the eye?
CN 3 oculomotor
3 layers of the eye?
outer, middle, inner
what does the outer layer of the eye contain? (2)
- cornea
- sclera (continuous with dura mater)
what does the middle layer of the eye contain? (3)
- Iris
- Ciliary body
- Choroid (continuous with pia/arachnoid)
what does the inner layer of the eye contain? (1)
Retina (continuous with optic nerve and brain)
3 layers of tissue enclosing the eye to keep its shape?
- Sclera
Tough white fibrous tissue
Anterior portion is cornea - Choroid
Highly vascularized
Continuous with the iris and ciliary body
Opening in center of iris is pupil - Retina
Optic nerve exits retina at optic disk
No photo receptor at blind spot
iris
pupil dilator muscle, pupil sphincter muscle, and pigment cells
Ciliary body
suspension lens, ciliary muscle for near focus of lens, aqueous humor
Anterior vs posterior chamber
space between iris and cornea vs space between the lens and the iris
Aqueous humor
continuously made by the ciliary body, maintains intraocular pressure, drains via canals into the blood
Vitreous chamber
space between the lens and the retina filled with vitreous humor
vitreous humor
thick and gelatinous, can contains debris called floaters ⇒ helps the eyeball keep its shape
glaucoma
results if production and drainage are not in balance where fluid accumulates in the anterior chamber⇒ puts pressure on the eye
what is the path of light?
- Cornea: main focusing element
- Iris: regulates the amount of light - Anterior chamber
- Pupil: hole in the iris
- Posterior chamber
- Lens: fine focus/Ciliary body: suspends lens
- Vitreous chamber
- Retina
nearsighted
the cornea focuses the light in front of the retina
farsighted
the cornea focuses the light behind the retina
what are the layers of the retina from top down? (8)
- retinal pigment epithelium
- inner and outer segments (receptor apparatus)
- outer nuclear layer
- outer plexiform layer
- inner nuclear layer
- inner plexiform layer
- ganglion cell layer
- optic fiber layer (axons of ganglion cells)
pigment epithelial cells (RPE) of the retina
provides nutrients to the photoreceptors and also has melanin to keep the light from getting to the rest of the retina
- Contains small microvilli which come into the photoreceptors below (lose bond)
what is retinal detachment?
occurs when the retinal epithelial layer lift away from the rods and cones which starves the photoreceptor cells
Inner and outer segments of the retina
senses light for rods and cones
outer nuclear layer of the retina
photoreceptor neurons (rods and cones)
outer plexiform layer of the retina
many axons and dendrites here of the photoreceptors
inner nuclear layer of the retina
contains horizontal, bipolar, amacrine cells where rods and cones synapse before these cells synapse on the ganglion cell
inner plexiform layer of the retina
axons and dendrites
ganglion cell layer of the retina
axons forming the optic nerve
optic fiber layer of the retina
axons of retinal ganglion cells (along vitreous chamber)
what do rods do?
sensitive in low light and important for motion detection
- Rhodopsin is the light sensitive protein in rod cells
- needs vitamin A and zinc
what do cones do?
sensitive in bright light, color sensitive, and important for high acuity vision
- Different opsins are sensitive to different wavelengths of light
- 3 types of cone cells each with a different opsin and sensitive to a different wavelength
opsin
light sensitive proteins in photoreceptors; opsins bind retinal, which is a vitamin A derivative ⇒ also allow for fine details
when are photoreceptor cells depolarized and hyper polarized
depolarized in the dark and hyper polarized in the light
- Light reduces release of transmitter (glutamate) released from photoreceptors
bipolar cells
(interneuron) 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 rod vs cone cells connect to a single bipolar cell?
15-30 rods vs 1 cone cell
horizontal cells
synapse with photoreceptor and bipolar cells ⇒ talk to several rods and cones
- Enhance contrast through lateral interactions
Amacrine cells
synapse with bipolar and ganglion cells ⇒ talks to ganglion cells
- Helps adapt to changing light conditions
retinal ganglion cells
receive synapses from bipolar and amacrine cells
- Most receive information originating from rod and cone photoreceptor cells
- M and P 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 that receive information from many bipolar cells
Important for motion perception
fovea
specialized for high acuity vision
- only has cones while the rest of the retina has more rods than cones
- reading or identifying faces
Macula
the novae is in the center of the macula
what is an important function of the extra ocular muscles regarding looking at objects?
they move the eyes so the object of interest falls on the fovea
optic nerve head
the start of the optic nerve where there is no retina ⇒ blind spot
retinotopic organization receptive fields
neurons with receptive fields close together in visual space have cell bodies close together in the cortex
where does the optic nerve attach to the brain?
at the optic chasm
- Retinal axons from the nasal side of the retina cross in the optic chiasm
- The retinal axons continue in the optic tract
central visual pathway vs peripheral
- The center of the visual field goes to both eyes, the binocular zone
- The periphery of the visual field goes to only 1 eye, the monocular zone
binocular zone
the portion where both eyes see part of the visual field ⇒ nasal
- axons from these sides cross in the optic chiasm
monocular zone
where the lateral portions of the eye only see one part of the visual field (non nasal side) ⇒ temporal
primary visual pathway
axons in the optic tract synapse onto neurons of the lateral geniculate nucleus
- The neurons of the LGN will send their axon through the optic radiations to V1
- tract → LGN (thalamus) → optic radiations to primary visual cortex
V1
primary visual cortex in the occipital lobe and is on either side of the calcarine sulcus
what splits the visual pathways into upper and lower in the occipital lobe?
the calcarine sulcus
where do the right and left visual hemifields project to?
the right hemifield projects to the left side of the brain and the left hemifield projects to the right side of the brain
where do retinal axons synapse in the centers of the brain? (4)
- suprachiasmatic nucleus
- lateral geniculate nucleus
- pretectal nucleus
- superior colliculus
→ different ganglion cell axons go to different targets ⇒ no axon goes to all these visual centers
suprachiasmatic nucleus
in the hypothalamus for regulation of circadian rhythms (diencephalon)
lateral geniculate nucleus
in the thalamus for relay to visual cortex for conscious perception of vision
- Primary pathway
pretectal nucleus
in the midbrain for the pupillary light reflex and other reflexes ⇒ in front of SC
superior colliculus location and role
in the midbrain for oculomotor control
how many cell layers are in the lateral geniculate nucleus and which two types of cells are found there?
6 layers total
- M type ganglion in layers 1,2
- P type cells in layers 3-6
Magno cellular layers
the 2 M type ganglion cell layers in the LGN
Parvo cellular layers
the 4 P type ganglion cell layers in the LGN
how is retinotopic organization of cells done in the lateral geniculate nucleus?
they alternate between contralateral nasal hemiretina and ipsilateral temporal hemiretina
C: 1,4,6
I: 2,3,5
which 2 routes do neurons of the LGN send their axons to V1?
- temporal lobe: inferior retina (superior visual field) via meyers loop
- inferior to calcarine fissure - Parietal lobe: superior retina (inferior visual field)
- superior to calcarine fissure
columns purpose and location
the functional units of cortex => many are in the primary visual field
3 types of primary visual cortex columns?
- Orientation columns: the angle a shape is presented
- Ocular dominance columns: input from the one eye vs the other eye
- Color columns (blobs): detect color
how do orientation columns work?
depending on which line orientation you are looking at, certain columns will have neuronal activity
how do the ocular dominance columns work?
segregated into alternating stripes for each output of the eye and are cross correlated with the orientation columns which determine which type of line stimulus they respond to
which neocortex layer are the ocular dominance column?
layer 4 (IV)
how does visual experience influence cortex development?
- the axons carrying information from the two eyes overlap in layer IV ⇒ before the eyes are opened, ocular dominance is not set up yet
- as development progresses, visual function is required for segregation of the inputs to layer IV ⇒ the axons will project to the appropriate area of layer 4 and retract from inappropriate regions
strabismus (amblyopia)
both eyes do not line up in the same direction and results in all layers being monocular
- may not have vision in one eye if not corrected during development
where do neurons the primary and secondary visual cortex send their axons to?
primary send axons to secondary (V2; area 18) and secondary send axons to tertiary (area 19)
2 streams for axons from the primary visual cortex to the association cortex?
- Dorsal stream: motion, location
- Ventral stream: form, color
–> comes from the retina and then the LGN
dorsal stream visual pathway
into parietal lobe carrying information for motion and location analysis (M pathway)
ventral stream visual pathway
into temporal lobe carrying information for color and object recognition (P pathway)
suprachiasmatic nucleus
(pretectal nucleus) projects to other nuclei in the hypothalamus which in turn project to numerous centers that regulate circadian rhythms and sleep
- project to stellate ganglion
superior colliculus
(visual pathway) projects to the motor nuclei that control the extraocular muscles and neck muscles
- important for saccade eye movements
saccade
rapid, conjugate, eye movements that shift the center of gaze from one part of the visual field to another
- used for orientating gaze and makes you turn your head and neck (also recognition)
pupillary light reflex
(pretectal nuclei vision pathway) controls the parasympathetic system component of the oculomotor nerve ⇒ The pupils should constrict together
how does light in your eye work with the pupillary light reflex?
light –> retinal ganglion project to pretectal area –> project to EdingerWestphal nucleus (parasympathetic component of oculomotor nucleus) on both sides –> axons in the oculomotor nerves synapse cells of ciliary ganglion –> synapse on ciliary muscles causing pupil constriction
which eye muscles do CN 3 control?
- superior rectus => eye up
- medial rectus => inward side to side
- inferior oblique => inward and up
- inferior rectus => outward and down
which eye muscle does CN 4 control?
superior oblique => inward and down rotation
which eye muscle does CN 6 control?
lateral rectus => outward side to side
