Lateral line

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  • Created by: Sarah
  • Created on: 23-05-19 11:17
where is the lateral line located?
on the surface of the entire body
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what does the lateral line sense?
water movement
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is it just ZF that have a lateral line?
no the ability to sense water movement so it's present in all aquatic vertebrates such as fish but also amphibians such as frogs before metamorphosis
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why have the lateral line?
escape predation, oritentation and schooling = crucial for survival
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why is the lateral line one of the first systems functional in the ZF?
its crucial for survival- they won't be able to escape predators and won't be able to feed
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what can it detect specifically?
is both an auditory and vestibular system- can detect moving objects around the fish, sound waves and pressure gradients in the water
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when is the lateral line functional in the ZF?
48 hours post fertilisation-
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how is the development timing different to higher vertebrates?
development really quick for ZF 48 hours post-fertilisation, in mice we're talking days and months in humans
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why is ZF a good model to udnertsand the development of an organ system?
develops quickly os don't have to wait and is less complicated, has transgenic ability
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why is it good that mice have a transgenic ability?
have a specific mutation in a human coniditon you can find out why the lateral line or hair cell doesn't work by making the same mutation
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is the ZF a mammal?
no its non mammalian
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when does the development of the lateral line start?
18-20 hours post fertilisation
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when is the lateral line fully functional?
48 hours post fertilisation
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what is a primordium?
an organ, structure or tissue in the earliest stage of development
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the primordium travels from the trunk of the ZF and travels over a period of time, what does it does as it travels?
depoists a group of cells
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what are the group of cells the primoridum is depositing as it moves along?
these are the cells that will form the most important unit of the lateral line- the neuromaster
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what is in the neuromaster of the lateral line?
the sensory cells
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what is different about the the deposits the primordium makes from the mammalian system?
the primordium deposits not only hair cells but also the neurons- neurons and hair cells go together in the LL not the case in the mammalian system
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what are the hair cells in the deposits?
unit of the LL called the neuromast
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what can be seen in the neuromast
a lot of protein or skin cells around and hair cells in the middle
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what are hair cells surrounded by in the neuromast?
non sensory cells-
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what are the sensory hair cells innervated by in the neuromast?
afferent and efferent system
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what is the difference between the LL and mammalian inner ear (vestibular and cochlea)?
inner ear is highly protected in a bow case within the temporal bone and in the LL it's on the surface
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why is the inner ear arranged differently in mammalians and ZF?
inner ear in mammalians is protected, LL stimulated directly because they can regenerate cells int he fish, can't damage mammalian as won't regenerate
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why do we think the cochlea in mammals can't regenerate?
the inner ear is highly sensitive and specialised, with high specialisation comes a cost- they lose the ability to regenersate
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why is it iportant that the cochlea is sensitive?
in order to be really sensitive they need to amplify signals and amplification produced by other structures like the inner ear and BM - increases complexity of sensory system why it needs protecting
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what has a simpler version of the hair cell?
the hair cells in the LL is a simple version of the hair cells in the cochlea
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what is in mammals but not in ZF?
a high level of specialisation
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why are the sensory cells on the surface of the fish?
less sensitive- fish needs to know where to escape a predator or where food is have to have a quick response so are on surface but get damaged on surface so kept their ability to regenerate
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what is different about the scaling of the sensory organ to the size of an animal?
cochlea of elephant is not different from ours is NOT scaled to an animal
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is the lateral line scaled to the fish?
lateral line is scaled to the fish
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why is the LL scaled to the fish?
needs to cover the entire length of the fish so if you have a big shark you need them all way along it, need to sense predator coming from any direction
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are the hair cells the same size in a ZF and shark?
not larger hair cells just more of them the neuromasts are the same but just cover the entire surface of the fish
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similarities between neuromast and cochlea?
kinocilium is present in ZF neuromast and mammalian vestibula system but not in the cochlea
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are all the bundles going in the same directional polarity in the mamallian cochlea and vestibula system?
yes
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do the neuromasts show directional polarity?
yes
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the directional polarity (cells within the neuromast respond in one way on onse dside and other side responds in the opposite way applies to what axis in the neuromast?
anterior-posterior dorsal-ventral
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why does the neuromast need directional polarity in AP and DV axis, why be sensitive in both directions?
water movement- need to know if predator is coming from above or below to know what direction of motor movement to go in
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why do you get only one set of fibres excited whilst the other ones inhibited?
one afferent fibre will only innervate one polarity- stimulus coming from head bundle will be excited towards kinocilium or taller sterocilia all these cells excited and these cells inhibited but one afferent fibre innervates one polarity
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can each fibre contact several neuromasts
yes one fibre can contact several neuromasts but only contacts the cell with the same polarity = polarity specific afferent innervation
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is this the same with IHCs in the cochlea?
no 1-1 connctions with the IHC. one presynaptic and one postsynaptic afferent fibres don't branch but IHCs can have multiple up to 30 afferent but 1-1
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how is the OHC innervation different?
not 1-1, type 2 afferent fibre only 5% innervates the cochlea- they are very weakly activated so they need the activation and excitation of up to 15-20 OHCs. One type 2 fibre innervates 15-20 OHcs
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how is the lateral line afferent innervation similar to OHCs in the cochlea?
one type 2 fibre innervates several OHCs so similar to LL as one fibre receives input from several cells
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what has a similar structure in the evstibula system (mammals) and in the LL?
stereocilia- structure of stereociliary bundle
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what is the difference in size of hair cell in the vestibular system and LL?
10-20 um in vestibular system = very long hair cell but in ZF are tiny tiny 1.5 um
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why do you need a kiniocilium? why not make longer stereocilia?
very long stereocilia in ZF, at the bottom of the stereocilia are able to pivot- the M gets thinner so sterocilia pivot and don't bend, long stereocilia will bend because less stiff, more floppy
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why is there a physical limit to the stereocilia length?
to ensure they move efficiently with high sensitivity- don't them floppy or they won't be sensitive
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Why do ZF need a kinocilium instead of having a longer stereocilia?
if stereocilia too long they lose their sensitivity as they become floppy
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do the tip links have a similar structure in the LL and in the cochlea?
yes similar molecules
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what is there more of in the mammalian hair cells?
wider range of proteins- more specialised and complex in the cochlea
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what molecules are present in the tip links of LL and mammalian?
Myosin 7a (important for tension), cadherin 23 and protocadherin similar organisation, clarin 1 (usher in mammals), same MET chANNEL- tmc1/2 proteins and TMIE- proteins important for mechanotransduction
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why is ZF used to study hearing loss and deafness in humans?
has all the important proteins for mechanotransduction
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major difference between tip link archeticture?
TMC1/2 there in LL and vestibular system but in the cochlear you lose TMC2 in development after the onset of hearing
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why are mechanotransducers currents much smaller in ZF?
they have a smaller bundle with much less stereocilia
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what is different with ribbon synapses?
they are round like in the vestibular system and mature cochlear so they don't become elongated and each of the cells have 4-5 ribbons compared to 20-30 in the mouse
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why don't you need so many ribbon synapses in the mouse?
because they intergate a large number of hair cells so don't need a lot of stimulation from each individual cell
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Card 2

Front

what does the lateral line sense?

Back

water movement

Card 3

Front

is it just ZF that have a lateral line?

Back

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Card 4

Front

why have the lateral line?

Back

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Card 5

Front

why is the lateral line one of the first systems functional in the ZF?

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