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S2 Neuroscience > Neuroplasticity > Flashcards

Flashcards in Neuroplasticity Deck (65):

models of nervous system function
-have historically influenced...
-what are they?

have historically influenced ideas about the system's ability to reorganize
Hierarchical Control Model
Distributed Systems Model


Hierarchical Control Model
-what is it?
-2 specific ideas

higher brain centers control primitive behaviors in lower brain centers
localization of function
-specific brain areas control specific functions
no regeneration in CNS because of inability of central axons to regenerate following lesions


distributed systems model
-what is it?
-3 specific ideas

numerous reciprocal connections between and within levels of CNS
information and motor commands flow in all directions
function is a cooperative effort among regions of the CNS
control site depends on the task to be executed
-voluntary movement - area 4 vs. automatic movement - area 6; both may be active


-what is it
-why does it happen
-eventually may result in...

decrease in a response due to a decrease in the synaptic effectiveness (decreased neurotransmitter released from presynaptic membrame)
eventually may result in decreased number of synaptic connections


-what is it
-may involves what synapses?

enhancement of synaptic transmission
experience with one type of stimulus (i.e. painful) enhances responsiveness to other stimuli (i.e. nonpainful)
may involve axo-axonal synapses (presynaptic)


-chemial reason for why it works

facilitating neurons, some of which are serotonergic, enhance transmitter release from the sensory neurons by increasing the amount of second messenger cAMP in the sensory neurons
these effects are short-term


-with repeated exposure to stimulus, what can happen?

long-term changes may occur that involve the synthesis of new protein and gene activation (mRNA)


long term potentiation
-what is it?

cellular mechanism proposed for formation or consolidation of memories through hippocampal formation


long term potentiation
-how does it occur
-the effects of the LTP are specific to...

cooperative and associative activation of numerous neurons in the hippocampal formation increases the amplitude of EPSPs (increased depolarization) on a receptive cell
the effects of the LTP are specific to those synapses that are activated by the stimulus


long term depression
-what circuitry?

cerebellar cortical circuitry proposed to be responsible for motor learning


long term depression
-essential process required for this to occur

the persistent desensitization of selective glutamate receptors that mediate mossy fiber --> parallel fiber --> Purkinje cell transmission


long term depression
-role of climbing fibers

play a leading role in induction of LTD
monitor the performance of a system in which the cerebellar circuitry plays a role and informs Purkinje cells about control errors due to misperformance of the plan


long term depression
-classic example

change in gain of VOR


neuroplasticity development
-thought to serve as...

a process template for lateral neuroplastic changes


development: radial glial cells

guidance system for neuronal migration in neural tube


development: process growth
-what is it

the axons and dendrites extend outward from the soma, the axon first process in vivo
in vitro (petri dish), undetermined neurite outgrowth occurs until a "guiding signal" is recognized that determines axon vs. dendrite


development: guidance of the process (axon and dendrites) formation is governed and directed by...

a number of external signals


development: growth cone
-importance of the enlarged tip

has multiple filopodia or lamellipodia
-contain organelles and cytoskeleton necessary for growth and addition of neuron membrane as well as movement proteins
-the membrane is rich in receptors responding to directing signals


development: directing signals
-what are the various signals?

contact inhibition
growth factors
GAP 43


development: adhesion different dependent upon...

extracellular matrix


contact inhibition
-can be...

recognition of neurotransmitters


growth factors
-nerve growth factor function
what other growth factors may play a role?

nerve growth factor supports and directs process outgrowth
other growth factors
-epidermal growth factor (EGF)
-fibroblast growth factor (FGF)
-cytokines and hormones


-how does it work?
-too much may result in...
-what other role of calcium is useful to remember when thinking about this concept

modify growth cone mitility
thought to act by facilitating depolarizing currents as the neurite grows
too much may result in hyperpolarization, effectively slowing down growth
Ca++ has a role on terminal activity specific to neurotransmitter release


GAP 43
-found in...

growth cones of axons, not dendrites


synaptogenesis and pathfinding
-contact guidance

membrane molecule mediated (neural cell adhesion molecule, laminin, neural cadherin)


synaptogenesis and pathfinding: chemotropism
-specific to...
-evidence has been noted in...

neurotransmitter specific, region specific
-the growth of individual neuronal cell axons in response to extra-cellular signals, which guide the developing axon to innervate the correct target tissue
-evidence of chemotropism has been noted in neuronal regeneration, where chemotropic substances guide the ganglionic neurites towards the degenerated neuronal stump


synaptogenesis and pathfinding: galvanotropism
-growth toward...
-what substance is thought to be a factor in neurite outgrowth?

negative pole in voltage variable environment


synaptogenesis and pathfinding: neurotransmitter-specific

postsynaptic excitability, presynaptic site formed first then postsynaptic site modifies position by becoming localized


synaptogenesis and pathfinding: adjustments
-2 examples

apoptosis (programmed cell death)
exuberant axons (multiple axons develop and then are reduced to a single functional axon)


synaptogenesis and pathfinding: competition

spatial and chemospecific
-functional validation of "the best suited wins"
this may be spatial on any given neuron


synaptic changes after injury: recovery of synaptic effectiveness
-neurons at site of injury may be temporarily affected by...

neurons at site of lesion may be temporarily affected by swelling, free radical presence, loss of blood supply, neurotoxic chemicals released in response to trauma


synaptic changes after injury: synaptic hypereffectiveness
-where is the change
-what happens

change in presynaptic event
-more neurotransmitter released


synaptic changes after injury: denervation hypersensitivity
-in response to...
-what happens

in response to vacated synapses, adaptive changes occur to other synapses in the area
increased receptor density in postsynaptic membrane is evidenced in mammalian NS


synaptic changes after injury: denervation hypersensitivity
-originally found in...
-in denervated muscle...

originally found in PNS
in denervated muscles, Ach receptors increased in density in entire length of muscle, not just motor endplate


synaptic changes after injury: denervation hypersensitivity
-where else can it happen apart from PNS
--in what condition
--how does it occur?

also known to happen in basal ganglia with Parkinson's disease
cells in the striatum deprived of DA input from substantia nigra
-some receptors will increase in density in postsynaptic membrane


synaptic changes after injury: unmasking of silent synapses
-what are silent synapses
-what happens with this unmasking
-potential reason why it works

some synapses exist on dendrites that are "silent" (don't release neurotransmitter)
these normally ineffective synapses become effective
may consist of strengthening dormant synapses of remaining input to a cell


synaptic changes after injury: unmasking of silent synapses
-kitten study example

one eye of kitten was sewn shut for 4 months
when the eye was opened, only 10% of the cortical cells responsed to light (normally 80% would - most cells are binocular)
the remaining good eye was surgically removed
-immediately 40% of the neurons in the cortex receiving connections from the previously sutured eye now responses to light
-this suggests that the pathways were present but not being used


axon reorganization: axonal regeneration
-what is it?
-may connect with...

sprouts from injured axons start growing out within several days of injury
may connect with nearer cell bodies, scarring a problem


axon reorganization: axonal regeneration
-possibility in human CNS
-possibility in PNS

not a strong possibility in human CNS
occurs in PNS


axon reorganization: axonal regeneration
-rate in PNS
-process is similar to...

rate of 1 mm/day
scarring can still be a problem
this process is similar to axon outgrowth during development using similar signals such as growth factor giudance


axon reorganization: collateral sprouting
-what is it?

surviving neurons that innervated the same target organ are somehow stimulated (postsynaptic hypersensitivity) to send out collateral branches from their axons to reinnervate denervated target cells


axon reorganization: collateral sprouting
-when does it begin?
-where does it occur?

begins 4-5 days post-injury
first identified in PNS, but now confirmed in CNS


axon reorganization: collateral sprouting
-specificity of sprouts

not randon
new input closely related to original function (use of same neurotransmitter, although not necessarily same afferent system)


axon reorganization: collateral sprouting
-advantage and disadvantage

-may prevent dendritic atrophy and maintain functional level of excitability (but not necessarily the same function)
-may create abnormal connections - SCI - may be responsible for spasticity


activity-dependent functional reorganization
-what are 2 ways you can change the cortical representation of digits?

apply spinning disc with sensory information to tip of finger


what percentage of fibers needed to be spared in a SCI to recover walking?



propriospinal system: propriospinal neurons
-what are they
-what do they do?
-important for...

interneurons whose cell bodies are located intrinsically in the spinal cord
these neurons ascend and descend throughout the cord, and they integrate both sensory and motor information
propriospinal neurons are important for synchronizing activity in spinal motor circuits


propriospinal system: short propriospinal neurons

span 6 vertebral segnents
organized in columns through the spinal cord
-more medial neurons innervate axial trunk muscle
-more lateral neurons innervate distal limb muscles
some cross, some ipsi


propriospinal system: long propriospinal neurons

connect cervical and lumbar enlargements
involved with the patterned motor activity seen in walking
some cross, some ipsi


staggered hemisection
-what is it

researchers initially lesion one half of the spinal cord, wait a few weeks, and then lesion the other half of the spinal cord at a different level


staggered hemisection
-what is it

researchers initially lesion one half of the spinal cord, wait a few weeks, and then lesion the other half of the spinal cord at a different level


staggered hemisection

following the hemisection injury to the corticospinal tract, transected fibers sprout into cervical gray matter to communicate with propriospinal interneurons, which then relay the motor command to its distal target
the motor command coming from the brain can now use this new corticopropriospinal pathway to carry out its mission


how can the corticopropriospinal connection be enhanced

locomotor treadmill training


effect of aging on neuroplasticity
-primary thing that occurs

decrease in brain weight and volume


aging: what areas of the brain decrease?

frontal and temporal lobe
hippocampus and amygdala vs. primary sensory and motor regions


aging: what increases?

increase ventricle size


aging: two mechanisms

cell loss
neuronal atrophy


aging: axonal death
-loss of collaterals may explain...

decrease in ability to "multitask"


aging: effect of neuronal atrophy on excitability of neuron

decreased input - increased time for summation - increased processing time


what else apart from aging can lead to atrophy and cell death?



stem cells
-where are they present?

layer I and at other places such as the hippocampal formation


stem cells
-responsible for...

continued CNS mitotic growth well into our 20s


stem cells
-can be turned on by...

trauma such as ischemia or traumatic denervation


stem cells
-response to trauma

generate new neurons


stem cells
-the problem

as it exists now (current technology), we don't know how to "encourage" this growth in a positive way or direct migration of new cells to area of need
the increase in new neuron number does not predict that axonal growth can or does occur