physiological organisation + control III Flashcards
how are bilatarian nervous systems organised
two neurones with paired ganglia. they are joined by connectives longitudinally and commissures laterally
how do leeches move
they have 5 locomotion behaviours. their sensory input is controlled by touch (6), pressure (4) and noxious (4) receptors
how do leeches achieve bending behaviour
antagonistic contraction eg when there is dorsal stimulation the dorsal side will contract and the ventral will relax to bend away from the stimulus. small relay to neighbouring segments allows for a smooth bend
how do leeches achieve shortening behaviour
when an end of the leech is touched it retracts. this is due to receptors innervating L2 neurones which cause the longitudinal muscle to contract. touch receptors also innervate C2 neurones which facilitates intersegment flow via S cells
describe habituation
reaction to a stimulus diminishes with repeated exposure to the same stimulus
describe sensitisation
increased response when a new stimulus is applied simultaneously with the original repeated stimulus
what is 5 HT
serotonin, a neuromodulator. it delays habituation and increases S cell excitation for more intersegment flow
what is a central pattern generator CPG
a collection of inter neurones which oscillate in activity for rhythmic behaviours such as swimming and breathing
how are CPGs altered
higher control centres or neuromodulators can alter the frequency or phase of the oscillations
how is swimming behaviour initiated in leeches
it is episodic, not continuous, and is stimulated eg by touch or waves which could indicate a predator or prey
how are touch/ wave stimuli detected in leeches
they are detected by sensillar movement receptors which are tiny hairs. signals from them are transduced to initiate a cascade
how does the cascade cause swimming in leeches
it is initiated by SMRs and cause CPGs to initiate oscillation where longitudinal and flattener waves contract out of phase to propel the body forward
what are pacemakers
an alternative to CPGs. they are controlled by cAMP, Ca2+ and negative feedback
why are Aplysia a model organism
their cells are large and easily identifiable. they also have a simple nervous system affected by neuromodulation and memory
what is the gill withdrawal reflex
the gills withdraw when siphon is touches as a defence mechanism. it undergoes habituation due to decreased levels of glutamate unless sensitisation occurs
