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51 Cards in this Set
- Front
- Back
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What is phototaxis? Give two examples |
Directional swimming towards the light. Used in diurnal vertical migration and in marine plankton (larvae) |
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How do larvae swim? |
In a helical fashion rotating about the anterior posterior axis. This means the dorsal size is always at the helix of the axis. |
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What is Tropism theory and who is it by? |
Jacques Loed. "Bilateral body plans allow animals to extract spatial information through sensation of external forces acting asymmetrically on symmetric body halves" |
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What is a good example of a model organism with a simple visual system |
Platynereis dumerilii - a polychaete worm |
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What is the eyespots in Platynereis dumerilii? |
The simplest animal eyes have a single photoreceptor and a pigmented shading cell. This gives broad spectral sensitivity. The dorsal eye sports have differential sensitivity to directions of light. There is no comparison between each sport - they work independently. (tropism theory) |
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What are the photoreceptors in Platynereis dumerilii? |
They have rhabdomeric photoreceptors that have folded apical membrances to conduct light activation of rhodopsin pigments via the IP3 pathway.
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What are ciliary receptors in Platynereis dumerilii? |
They have folded cilia and conduct via the cDMP signalling pathway. |
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How does the swimming work in Platynereis dumerilii? |
Due to light stimulation of the photoreceptor this directly influences ciliary beating because the photoreceptor is a cholingergic sensory motor neuron.
The eyesport activates and so the ACh modulates beat frequency on that side, therefor the animal turns.
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Give an example of an ACh agonist and what it does? |
alpha - bungarotoxin from snakes abolishes phototaxis. |
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What happens when fruit fly larvae are exposed to light? |
They move away from it. The turn frequency increases at the dark:light boundry more. The head sweep assessed the light environment as it causes a change in intensity at the photoreceptors. |
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What organ senses light in fly larvae? |
Bolwigs organ. The photosensors are in the opaque cuticular pocket and only recieve light from a given angle. The head movement enables the animal to detect light direction. Bolwigs organ has 12 photoreceptor cells. |
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What neurons in fruit flies mediates orientation and what else does it do? |
The 5th lateral neurons. These are 4 of the 12 photoreceptors in the Bolwigs organ and are sensetive to blue light because they express a blue light sensitive pigment rhodopsin5 (Rh5) and cause the head turns and pausing.
They synapse in the region of the lateral neurons in the larval brain and lateral neuron 5 is shown to be the main relay of photic information. |
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What is a more complicated model organism that is genetically and behaviourally tractable? |
Danio rerio (zebra fish) |
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What happens when you shine light on larval danio rerio? |
They show positive phototaxis to weak light, and negative phototaxis to strong light. This is shown by slow movement (scoots) and turns. |
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What are bipolar retinal ganglion cells? |
They are ON/OFF cells. On cells are depolorised by light, and OFF cells are hyperpolorised by light. On mediates positive taxis, and off mediates turns away from dark.
If fish lack ON cells, they do not scoot towards light. If they have only one eye, the one eye that works mediates a turn away from the dark. |
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What mediates locomotor activity and what happens when there is an antagonist? What does this say about the ON cells? |
The 5HT. 5HT antagonists abolish increased scoots. Thus ON pathway is driven by serotenergic system. |
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Give an example of geotaxis? |
Jellyfish maintain their optimal attitude in water column by corrective tilting. It is dependent on ELECTRICAL SYNAPSES. |
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What are electrical synapses? |
They are junctions that depend upon there being a gap to allow the electrical signal to pass directly from cell to cell. (gap junctions) These gap junctions are protein molecules that form hollow cylinders which bridge the membranes separating cells allowing electrical signals to be conducted. |
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What is good about electrical synapses? What are two types? and give three examples. |
Transmission is rapid (0.4ms)
One or both direction
Ommatidia in insect eye Neurosecretory cells Neurons with giant fibres. |
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What are 4 things about Cnidarian nerve nets? |
They are 2 dimensional.
Activity spreads from point of stimulus
They conduct very fast (0.1-1ms-1)
They are either conduct through electrical or chemical synapses
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How do the nerve nets do geotaxis? |
They detect that they are tilting through statocysts in the base of tenticles, when they tilt, the statocyst is stimulated, neurons active and muscles contract, righting the organism. |
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Two examples of migration? |
Birds and Turtles |
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What is the difference between navigation and orientation? |
True navigation necessitates the knowledge of current position as when as bearing required to reach target
Orientation requires only a fixed bearing and a distance to be travelled. |
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Example of navigation vs orientation. |
Thorup et al 2007 showed that adults who have a prior knowledge use navigation. Juventiles only fly using orientation. |
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What are two things needed for migration? |
Internal compass and internal map.
Compass - solar, skylight, stellar, lunar and magnetic. |
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What are examples of solar navigation and what does an animal need to have to do this? |
Butterflies, birds and fish all use the suns position to aid nagivation. They need an internal clock that can compensate for the suns movements. |
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Example of bird sun compasses? |
Kramer 1950s studied starlings. They attempted to fly in migratory direction. Cloud cover reduced attempts. Mirrors altered escape direction. Photic regime shifts affected flight direction. |
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My favourite example of solar cued movement? |
Talitrids emerge at dusk to move downshore and forage and mate. If the sun is shifted by 6 hours, they move in a different direction. |
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What happens to solar navigation when its cloudy? |
The monarch butterfly has a dorsal rim outside its retina that detects polarised light. |
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How does the dorsal rim work? |
The neurons in the optic lobe receive inputs from the dorsal rim area (DRA), and this is sent to the brain and the central complex. The neurons in the central complex are spatially organised in such a way that suggest they serve as an internal compass. |
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Example of stellar navigation? |
1950s Emlen showed that the bearing of restless birds in affected by the sky because he developed the ink blot funnel cage. Used indigo bunting. The bunting was shown to learn the patterns of the sky that rotated the least. |
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What is magnetoreception? |
The ability to migrate using the mangetic fields from the poles. |
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Give evidence for magnetoreception? |
Walcott attached electric coils to the heads of pigeons. If the field was revesed, the pigeon flew in the opposite direction. |
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What happens to turtles with magnets on their head? |
They are unable to migrate properly. |
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What causes avian magnetoreceptor? |
The N cluster in the avian brain is responsible as it shows increased activity when flying at night.
Also a magnetite in a birds upper beak also is related to the N cluster in the brain. |
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Migration vs. homing? |
Turtles, pigeons and salmon show homing. It is precise and spans different temporal and spacial scales. |
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Details about Salmon homing |
Disdromous teleost fish spawn in natal steams. Young fish transform into smolts and migrate to the sea. They return to their natal stream to spawn after 18-24 months |
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How have Olfactory Cues been proven to affect salmon homing? |
Fish transplanted before smoltification return to river of release.
Fish transplanted after moltification return to natal tributary. (1950, Hasler)
This learning of the river features takes place in a small temporal window and is irreversable. FILIAL IMPRINTING |
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What mechanism controls this olfactory homing in salmon? |
Thyroid hormones are involved in neural development. |
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How do fish tell their natal stream? |
Using olfactory senses. They have highly folded epithelium packed with chemoreceptors. Each natal stream is predicted to have a unique odor. - Haslers Theory (Hasler and Wisby 1951) |
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How is this proven? |
Lake michigan experiment. Smolts from same place were imprinted with two different chemicals, morpholine or beta phenlyethly alcohol.
They returned to the river perfused by that odourant. |
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What mechanism controls this detection of odourants? |
The olfactory bulb electroencephalogram |
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In pigeons, other than sun compass, and magnetoreceptors, what else do they use? And where is this stored in the brain? |
They use olfactory cues on approaching the loft, and use landmarks. This is stored in the hippocampus. |
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What is a biological clock? |
It is a rhythmic activity that is synchronised to cyclic stumulus
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Give examples of biological clocks? |
Circadian clock (day) circatidal (tides) circalunar (moons) |
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Who needs a biological clock? |
Every organism. To anticipate regular changes in environment, prepare for an activity and coordinate internal events. |
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How do clocks work? |
An environmental change happens, this goes to clock cells, this outputs a phenotype e.g behaviour, physiology or biochemistry. |
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What happens when clocks go wrong? |
Death, loss in productivity, cancer, heart disease, mental health problems, inappropriate behaviour etc. |
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What is a phase response curve? |
A graph plotted about how a clock responses to light at different phases of the cycle. |
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What is the monarch butterflies clocks? |
2 cryptochrones. The antennae - required for time compensation and sun compass orientation. |
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What is special about the antennae of monarch butterflies? |
They are rhythmic and selfsustaining. They continue to tick along and go in cycles even when removed from the butterflies head. |
