Animal phys. topic 12
How do the camera eyes of an animal such as an octopus differ from the camera eyes of vertebrates?
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Since most animals have the ability to respond to light, how do they accomplish this when they occur in a variety of environments and have very different body forms?
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What are the major features of the compound eyes possessed by insects and other arthropods?
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________ have the highest visual acuity and light reaches them without passing through bipolar and other cells
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how do rods and cones differ with respect to sensory processing of light?
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how do the visual capacities of different types of animals match their environments?
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how does the retina process light?
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what are the major functional components of the retina?
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what are the major functional components of the vertebrate eye?
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what are the major structural differences associated with seeing through air and seeing through water? with seeing under dim light conditions?
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where are visual impulses that originated in the retinal ganglion cells transmitted and how are the various aspects of visual information processed?
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light adaptation
Pupils constrict; Rhodopsin rapidly breaks down; Decreased sensitivity of rods to light
dark adaptation
Pupils dilate; Photopigments broken down during light exposure gradually regenerate; Increased sensitivity of rods to light; Night blindness is caused by dietary deficiency of vitamin A (retinene is a derivative of vitamin A)
tapetum lucidum
a layer of reflecting material enhances vision in dim light in some species
in the presence of light
a retinene molecule absorbs a photon; retinine changes shape from cis to trans conformation; triggers enzymatic activity of opsin; activates a G protein called transduction; Phosphodiesterase degrades cyclic GMP, causing Na+ channels to close; Hyperpolarizing receptor potential reduces glutamate release
Adjustments in lens focusing power for near vision in mammals is called
accommodation and are accomplished by the ciliary muscle.
Rods
are more abundant in nocturnal animals because they have greater light sensitivity; might function as tiny lenses; numerous activate one bipolar cell/ganglion cell combination, decreasing visual acuity at night; "burned out" by bright light; shades of gray;
cones
are present in concentrated retinal areas in diurnal animals. one activates one bipolar cell/ganglion cell combination, greatly increasing visual acuity during the day; three types (trichromatic) respond maximally to different light wavelengths
Retina may be
avascular (some reptiles), moderately vascularized (mammals) or have specialized oxygen-delivery structures called pectens (birds)
region where optic nerve exits the eye (optic disc) is the
blind spot
"visual streak"
broadens the region of high visual acuity
detachment of avascular retina
can lead to impaired vision
as an extension of the brain, the modified neurons in the retina
carry out preliminary processing of the light from the visual field before being transmitted by the optic nerve; This includes differential activation of on-center and off-center ganglion cells and lateral inhibition of nearby receptive fields.
some annelids alter the distance between the lens and photoreceptors by
changing the fluid volume of the optic chamber
Most animals have means of detecting light, there are two types of photoreceptors
ciliary and rhabdomeric
curvature of the lens is adjusted by the
ciliary muscles
vertebrates have ___________ with an outer fibrous layer (cornea and sclera), middle vascular layer (choroid, ciliary body, iris) and an inner lining of modified neurons (retina)
complex camera eyes
circular muscle
constricts pupil in response to light
inner segment
contains the metabolic machinery of the cell
autonomic nervous system
controls the iris muscles
in the absence of light
cyclic GMP concetration is hight in photoreceptors; Na+ channels are OPEN -> depolarization; Ca2+ channels in synaptic terminal remain open; glutamate is released
compound eye
densely packed units (ommatidia), each having its own lens and photoreceptors; arthropods
outer segment
detects the light stimulus
Different populations of cortical cells are
devoted to depth perception, form/movement, or color.
Light ________ depolarizes rhabdomeric photoreceptors (cf. with vertebrates, in which rods and cones stop releasing an inhibitory neurotransmitter in response to light).
directly
as in vertebrates, mechanisms for lateral inhibition
enhance visual contrast
at the optic chiasm
fibers from the medial half of each retina cross over, wile fibers from the lateral half remain on the same side
specific cone types respond to light of specific
frequencies
light must pass through the ______ and _______ layers before reaching the photoreceptors
ganglion and bipolar
cephalopod eyes
have cornea, lens, and retina
sensing polarized light helps
honeybees compute the location of food sources and butterflies to find a mate
visual development is regulated by the
hox gene known as Pax6
light moves
in the opposite direction of neural information flow in vertebrate eyes, which would not seem to be the best arrangment
Nocturnal arthropods possess superposition eyes,
in which visual info from separate ommatidia blend to some extent, increasing light sensitivity.
radial muscle
increases pupil size in dim light
Focusing of an image on the retina in air-seeing vertebrates involves
initial primary focus by the cornea, blocking out extraneous light by the iris, and fine focus adjustment by the lens.
parasympathetic
innervate circular muscle
sympathetic
innervate radial muscle
the result of separate transduction unites (rhabdomeric photoreceptors)
is a mosaic rather than a continuous image
optic tracts project to the
lateral geniculate nucleus of the thalamus
light rays from the _______ of the visual field fall on the right half of the retina
left half
Conversely, in fish the _______ is primarily responsible for focus.
lens
camera eye
lens enhances light-gathering power; many phyla, including vertebrates and cephalopods
eyespots
less than 100 photoreceptor cells lining an open cup; permits animal to locate a light source
synaptic terminal
lies closet to the eye's interior
phototransduction
light energy causes an isomerization reaction linked to neuron depolarization
three layers of
neurons
fibers terminate the visual cortex in the
occipital lobe
individual _____________ transduce light separately from each other and have their own individual visual fields
ommatidia
information from ach half of the visual field is brought together on the
opposite side of the brain
almost all of the visual systems employ pigments composed of
opsin and retinene.
axons of ganglion cells form the
optic nerve
The visual fields of some animals __________ to a significant extent (binocular vision, allowing depth perception) while in others they _____________ at all (monocular vision).
overlap , do not overlap
three retinal layers in the vertebrate eye, moving inward
photoreceptors (rods and cones); modified neurons (bipolar, amacrine, and horizontal cells); and ganglion cells
The eyes of cephalopod molluscs possess what seems to be a more "sensible" arrangement in which the
photoreceptors are in front of the neurons. Otherwise they are similar, with a cornea, iris, lens, etc. (see Fig. 6-42).
iris
pigmented ring of smooth muscle; controls the amount of light entering the eye
_________ of reticular cells contain the photopigment rhodopsin
rhabdoeres
when dark,
rods release an inhibitory neurotransmitter (glutamate) that hyper polarizes and bipolar cells
when light,
rods stop releasing glutamate and bipolar cells are allowed to depolarize
pupil
round central opening
pinhole eye
size of cup aperture is reduced; permits formation of an image
Not all retinal ganglion cell axon impulses are dedicated to perception of visual images:
some set the biological clock in the hypothalamus, others maintain cortical alertness.
some animals use ultraviolet light for
spatial orientation and prey detection, among other things
in nocturnal animals, the ________ _________ apparently reflects light throughout he retina a second time
tapetum lucidium
convex surfaces of the cornea and lens determine
the eye's refractive ability
Visual information flows from
the optic nerve to the lateral geniculate nucleus (LGN of thalamus). Axons of neurons originating in the LGN give rise to the optic radiations -> cerebral cortex.
fovea
the point of greatest visual acuity
image detected on the retina is
upside down and backwards
the number and distribution of cones depends on
where an animal lives
