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advantage of specialised behaviours

learning- animals programmed to do it
coincidence detectors- 1 thing occurs then so may another
ability to change is a fundamental neuronal property



relate changes in cellular properties to changes in behaviour
identify where changes happen


triggers for behaviour change

hormonally mediated cycles
learning new association between sensory stimulus and motor program- a memory
includes changes in neuronal excitability and strengths of synapses
over longer term first protein manufacture then later gene to make new branches on synapse


Kandel- study of aplysia gill withdrawal

large well laid out ganglia that contain very large nerve cells
kandel exploited the abdominal ganglion to do a number of experiments
Groove at top of animal that contains gull- water goes over gill and expelled over siphon
gill protect it by fleshy flaps that can be moved to increase or decrease level of protection
if stimuli is persistent it will expel purple ink



reduction in strength of a specific behaviour evoked by a particular repeated stimulus



repeated administration of a stimulus results in the progressive amplification of a response
short term and long term memory


Study of aplysia

in almost intact animal
in isolated abdominal ganglion
removed from the ganglion, placed on culture dish and allowed to make synaptic connections with each other

24 sensory neurons associated with skin of siphon
small number of motor neurons that control muscles that control contraction of gill- direct synapse between the 2


Aplysia habituation

repeatedly touching the siphon- progressive decrease in response
specific to one stimulus and response; distinct from sensory adaptation or fatigue
electrode between sensory and motor neurons can produce an excitation but not a spike, however if you do it again not longer after the PSPs get progressively smaller- synaptic depression
straight forward pathway but not only one- interneurons also pass message to motor neuron


Aplysia sensitisation

stimulate tail neuron- originates in different ganglion- restores synapse strength also underlies sensitization
stimulation of tail neuron makes spike in sensory neuron longer
mimic this by applying serotonin (NT)
longer lasting spikes means greater release of NT
cAMP important


How can cAMP make cells electrically more excitable?

-spikes activate calcium channels and allow the cell to take it in (calcium allows vesicle to bind to cell membrane and release NT- exocytosis)
-cAMP 2nd messenger carries message from serotonin which binds to surface of cell
-makes cAMP which activates PKA by phosphorylatiion
-subunits of PKA split and catalytic subunit closes K channels and makes Ca more likely to remain open
-enhanced release of NT


PKA enhances

excitability of neuron synaptic terminals
availability of neurotransmitter


Protein Kinases

family of enzymes that modify activity by phosphorylation
important metabolic regulators
associated with association


Long term memory

prolonged training- behaviour can persist for days
sensory neurons will sprout new terminals which synapse with motor neurons so number of synapses increases which increases the overall


PKA and long term memory

repeated shock activates whole process more persistently
now PKA does 2 jobs- some encourages vesicles to synapse
rest move into nucleus where it activates the trancription factor CREB-1 which binds to CRE gene when phosphorylated
these genes encourage the growth of new synapses


Is PKA cycle unique to aplysia?

aplysia large neurons allow detailed examination
similar experiments in leech demonstrate preS mechanism
genetic techniques in flies- similar conclusion


Post-synaptic mechanisms

AMPA receptors- open when glutamate binds and excites post S neuron
NDMA receptors- require 2 factors to open- glutamate and electrical excitation of membrane they sit in (which comes from AMPA)
NMDA respond to coincidences
Another neuron could excite or AMPA could excite excitation
post S makes more AMPA
signals travels back to preS terminal and enhances transmitter release
since 2000, good evidence both pre an post S changes involved in long term changes in aplysia gill withdrawal
likely to include NMDA receptors