Simple animals Flashcards
Trichoplax
Multicellular - 2 layers (epithelia + cylindrical ciliated)
Glides along surfaces propelled by beating cilia - finds food, stops beating + secretes peptides
When Trichoplax pauses - induces neighbours to pause as well - not in direct contact/no synapses/diffusion is too slow
Peptide-induced-peptide-secretion forms a propagation wave
Genes in trichoplax:
* Same proteins found in mammalian synapses, but do not function as synapses in trichoplax
PAX6 gene
* Family provides instructions for transcription factors
* Humans: activate genes involved in the formation of the pancreas + the CNS (embryonic development)
* Trichoplax: located in a cell layer responsible for movements associated with feeding
PAX6 genes - humans
Encodes transcription factors involved in embryonic development of the pancreas + the CNS
Aglantha digitale
Jellyfish
Eating copepoda
Slow foraging swimming sequence
Pacemakers in the CNS produce repetitive swimming processes
Reaches height, turns over, sinks + traps food
Slow swimming = Ca2+ spikes (approx. 80ms)
Fast, escape swimming + Na+ spikes (approx. 4ms)
Na+ threshold above peak of Ca2+ spike - can exist in same axon w/out both being activated
Nerve ring, 8 giant motor axons controlling radial muscles to manubrium
Protozoa
Paramecium
Single celled creature
Hit nose - calcium spike, 1micromole, reverse cilia beating
Hit rear - depolarisation, acceleration
Sponge
Similar to Chanoflagellates?
Beating flagella which trap bacteria + small planktonic organisms
Sponge
Similar to Protozoa (Paramecium)?
Rise in internal calcium causes cessation of cilia beating
Cobalt is a calcium channel blocker - blocks cessation of cilia beating
Mutant: Pawn protozoa
Missing calcium channel
No backing off response when nose hit by stimulus
Mutant: Pantophobic protozoa
Exaggerated backing off response
No calcium-activated-K+-channels
The K+ channels are coupled to calmodulin which can bind 4xCa molecules - act as a receptor for the channel
K+ channels contribute to depolarisation of cell - mutant has extended calcium spikes, longer influx, longer time to pump out
Choanoflagellates
Single-celled organisms
Can be multi celled - formation of aggregate/colony if bacteria which they are feeding off release a lipid
Have same proteins found in higher functioning organisms - different role
HOMER Neurones: Associates with Shank Found in the cell membrane Act as a post-synaptic scaffolding protein for receptors at the PSD Involved in cell signalling
Choanoflagellates:
Not associated with Shank
Associated with Flotillin
Found in the nucleus - forms a component of lipid rafts
Sea pansy
Eggs have electrogenic properties - prevent polyspermy from occuring
Stimulus depolarises cell - immediate outward fast transient K+ current, followed by calcium spikes
Important - only want a prolonged stimulus (sperm penetrating) to produce change of internal concentration (Ca does this) - do not want slight outer stimulus to create a sperm-block - if prolonged, cell will still depolarise after transient K+ outward current
Remove K+ current with 4-aminopyridine
(Or by holding membrane at more +ve voltage)
See a chain of Ca spikes start immediately after the depolarising stimulus
Aplysia californica
Inking - a defensive response to crabs
Limited reservoir of ink - has to be a strong stimulus to release ink
Depolarisation - transient outward K+ channel which inactivates with prolonged stimulation, allowing inking to occur
Aglantha digitale
Jellyfish
Use: Polyorchis
Feeding inhibits swimming
Escape inhibits feeding
Larger pacemaker neurones than Aglantha - easier to record from
Pacemaker cells in ring/ganglion - electrically coupled to each other
If stimulate nerves in manubrium, inhibit swimming movements
AP from manubrium = IPSP
Plot inactivation curve of pacemaker cells - see it has K+, Ca + Na+ currents
IPSP mainly effects K+ currents
Box jellyfish
Courtship + mating behaviour
4 tentacles, 6 eyes
Both animals swimming, tentacles extended
Tentacles make contact, females tentacles contract to bring the two bells into contact
Male releases a strand of sperm - transfers to one of males tentacles
Female inserts the strand into her manubrium
Sperm = partially digested, nuclei released onto the surface of female gonad, fertilisation occurs
Female regurgitates the fertilised eggs, incubates in the bell
Chelophyes
Large train of tentacles
Swimming = streamlined, reduce drag
Not swimming = extended, maximise collection of water
Streamlined Dispersed
Size of APs ~ strength of contraction
Early on in swim sequence, tentacles being reconfigured to streamlined, therefore smaller contractions
Once streamlined, stronger contractions
How?
Depolarising transient K+ gets progressively weaker with repeated APs
Inactivating current
Muggiaea
Delays swimming until all tentacles have been withdrawn
Each swim is equal length/contraction
Due to:
Non-inactivating K+ channel
Transient K+ channel
