THE EYE

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Last updated 7:03 AM on 11/21/22
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106 Terms

1
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a internal or external environmental change
what stimulates a response ?
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A chemical or physical change in the internal or external environment detected by receptors which evoke a response
What is a stimulus ?
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they perceive a specific form of energy (heat, force, kinetic) and then convert the stimulus energy into a chemical energy called a nervous impulse
What do receptor cells do
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converts stimulus energy into chemical energy in the form of an impulse
What is a transduction?
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biological transducers
what are receptors called
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term image
fill in
fill in
7
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Orbits in the skull (sockets with tiny hole at the end
where is the eye located?
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there are no bones in the eye rather it is supported via hydrostatic pressure created by the vitreous humour
how are the eyes supported
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—> Sclera & cornea
—> choroid, ciliary body, lens & iris
—> the retina
outer to inner most tissue layers of the eye
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they are external to the eye
Where are the ancillary structures located?
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eyebrows & eyelashes — protect from foreign objects, perspiration and sunlight

eyelid — retractable shade (baths eye by blinking)

Conjunctiva — transparent, mucous membrane (continuous with sclera and eyelids. Lubricates the eye surface by secreting mucilage. It secrets lysozyme (bacterial enzyme) and contains blood vessels.
what structures make up the ancillary structures and what are their functions?
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Lacrimal glands
Where are tear produced?
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above both eyes
where is the lacrimal gland located?
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water, salts, mucilage, oils (lipids), antibodies & lysozymes
what do tears consist of
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Lacrimal canaliculi, Lacrimal sac (surplus tears flow into nasal cavity)
where do tears drain?
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The outermost layer of the eye, which is tough and opaque with a yellowish-white surface due to collagen fibres
What is the sclera ?
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To protect the eye and support by maintaining shape
What is the function of the sclera ?
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it is a transparent dome covering the iris
What is the cornea?
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To refract light onto the retina, this is possible due to its curved surface. This function is aided by the aqueous humour found just behind the cornea as it increases the refracted index.
what is the cornea’s function?
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a circular muscular diaphragm, made of smooth muscle.
What is the Iris?
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it closes and opens the pupil controlling the amount of light which enters
what is the function of the iris?
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the pigment over the iris (the amount of melanin)
what determines the pigment of the iris?
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an opening in the iris, it looks black due to it absorbing light.
What is the pupil?
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when intense light reflects off of the choroid blood vessels inside.
what is the red pupil effect ?
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iris contracts (circular muscle contracts) therefore the pupil contracts and allows less light in
Closing of pupil:
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longitudinal muscle contracts, the pupil dilates, allowing more light in.
opening of pupil:
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The contraction and dilation of the pupil is a reflex, meaning that it is an involuntary movement in response to a stimulus
what is a reflex, give an example :
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the autonomic nervous system
What part of the NS controls the pupil ?
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—> It is rich in blood vessels to supply the retina
—> contains pigment cells which absorb light and prevent reflection of light (eye appears black)
Function of the choroid layer>
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ciliary body: marks the point where the sclera and cornea join, contains muscles and blood vessels as well as secretes aq humour.
ciliary muscle: smooth muscle, circular and longitudinal which bring about lens accommodation
ciliary ligaments: attaches ciliary body to lense
what make up the accommodation structures? and what are their functions?
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The ability to alter its shape and shift focus (forward backward) to form image on retina.
What is lens accommodation ?
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A plastic, transparent biconvex structure that focuses light via refraction.
What is the lens?
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composed on sensory tissue with receptor cells, cell bodies and axons of neurones
What is the retina?
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Rods: work best in low intensity light (convergence)
Cones: work best in high intensity light (visual acuity)
what are the two types of receptor cells ?
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The optic disc which is the blind spot
Where do all neurones lead to ?
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The most sensitive spot which contains the most cones, it is the point where most light focuses (sharpest vision)
What is the Fovea ?
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a clear salt solution that refracts light (secreted by the ciliary body and drains into the blood vessels (via the cabal of schlemm)
What is Aqueous humour ?
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Glaucoma
What happens if the canal of schlemm block up?
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it is a clear semi- solid gel that refracts light further and supports the eyeball via hydrostatic pressure.
what is vitreous humour?
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term image
knowt flashcard image
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Photoreceptor layers: contains the rods and cones, particularly embedded in choroid to stop light travelling further.
intermediate layer: contains bio polar neurones and synapses connecting the photoreceptors layer and internal layer.
internal layer: includes ganglion cells and dendrites & axons of the optic nerve
what are the 3 tissues layers the retina consists of ?
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—> outer segment : photosensitive region (flattened membranous vesicles containing pigment)

converts light energy into a generator potential (graded potential (may trigger an action potential)

—> A constriction: cytoplasm constricts due to pinch in outer membrane.
inner and outer segment connected via two cilia.

—> Inner segments: NUCLEUS (metabolically active part of the cell. MITOCHONDRIA (produces energy). POLYSOMES (protein synthesis — pigments and membranous vesicles)

—> Synaptic region: receptor synaptic connection with bipolar neurone.
what are the 4 main parts of cones and rods ?
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a change in the membrane potential that is proportional to the size of the stimulus.
Graded potential
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connect rods and integrate + regulate impulses
Horizontal cells
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horizontally connected across several bipolar neurones (link both rods and cones). Allow for some visual processing before the impulse leaves retina
Amacrine cells
Amacrine cells
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visual pigment — rods
rhodopsin
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rod-shaped light sensitive cells which lies on the most peripheral parts of the retina in the vertebrate eye
rods
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rod
outer segment is cylindrical
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rod
synaptic connection is a single knob
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rod
single type of cell
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rod
monochromatic vision
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several rods are interconnected to one horizontal cell
convergence
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rod
used for low vision light conditions
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rod
sensitive to scattered light
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rod
highly light sensitive
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rod
low visual acuity
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rod
absent in fovea
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rod
slower response to light
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rod
about 12 million
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rods
contain more pigments
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rods
stacks of membrane - enclosed discs are not attached directly
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rods
insufficiency of rhodopsin causes night blindness (black spots)
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cones
trichromatic
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cones
not sensitive to scattered light
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cones
not highly sensitive to light
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cones
around 6 million
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cones
concentrated in fovea
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cones
discs directly attached to outer membrane
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cones
insufficiency of iodopsin causes colourblindness
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cones
faster light response
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cones
contains fewer pigments
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cones
useful in bright light conditions
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cones
each is connected individually
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cones
3 types if cells (RBG)
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cones
synaptic connection is branched
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cones
outer segment is conical
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cones
Iodopsin is the visual pigment
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a type of photoreceptor in the retina which is responsible for colour vision in daylight.
cone
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when they are directly stared at as there is a concentration of cones in the fovea.
when do objects look sharpest and why ?
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they work in inverse sequence compared to general sensory stimuli.
how do light energy transductions work ?
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rods and cones work similarly:
—> absence of light = produce inhibitory neurotransmitter (glutamate)

—> glutamate — hyperpolarises the bipolar neurones (therefore wont excite ganglion cells)

—> presence of light — inhibitory neurotransmitter is inhibited

—> bipolar neurones exit ganglion cells and generate impulse leading to the brain.
mechanism of sensory transduction
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opsin (protein + light absorbing group)
isomers of retinal (💡all-trans retinal 🌚 11-cris retinal)
what does rhodopsin consist of?
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11-cis retinal + light photon = all-trans retinal
opsin breaks off from all-trans retinal
—> molecule losses sensitivity (BLEACHING)
Rhodopsin In light
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bleaching happens quickly in bright light — dark spots appear and disappear when rhodopsin is recharged.

(11- cis retinal spontaneous turn to all trans retinal and opsin rebonds to it as they are recharged)
explain bleaching
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when opsin is broken off and changes shape it triggers this effect.
what triggers the Na+ channels to close in the outer segment
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Na+ channel in the outer segment are open in the dark and so Na+ ions flow from inner segment ——> outer segment.

opsin present :
Cyclic Guanosine Monophosphate —> Guanosine Monophosphate

Cyclic Guanosine Monophosphate —> keep Na+ channels open
Dark current:
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light Na+ channels close therefore hyperpolarisation

Guanosine monophosphate closes channels
hyperpolarisation of photoreceptors
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hyperpolarised photoreceptors, which depolarises bipolar neurones and generate an Action Potential leading to a retinal ganglion cell Action potential sending an impulse to the brain
what stops the release of glutamate?
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1 photon inhibits over 1m Na+
what triggers hyperpolarisation of photoreceptors
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term image
knowt flashcard image
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having 3 types of cones each with a different opsin molecule (different opsin = absorb different ranges of visible spectrum).
It involves mixing RBG signals
Trichromatic vision
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blue region
S-cone
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green
M-cone
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red
L-cones
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dichromatic
most mammals are ____chromatic
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fish, turtles, birds
have extra cones so they see ultraviolet
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deficiency of one or more cones, linked to X-chromosome (sex linked)
colourblindness
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red-green
most common colourblindness
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> only rods (or few cones)
> pupils stretch far wider (allow more light in)
> Tapetum lucidum (reflects more light onto receptors)
> Disproportionately large eyes
> Reduced eye movement
> Rotational ability of the neck
> spherical lens and wide cornea —> increase refraction
Adaptations of nocturnal Animals (7)
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the ability to distinguish two ore more stimuli of equal intensity separately. SHARPNESS OF VISION
visual acuity