Lecture 17 - CNS Plasticity and Learning Flashcards
postnatal growth of the brain is guided by:
learning
what is the critical period for visual cortex development in humans?
6 months - 3 years
true or false: projections to the visual cortex are made randomly
false
eye closure for a couple of days during the critical period induces:
movement of spines as part of synaptic plasticity (use it or lose it)
act as the housekeepers of the nervous system by doing the actual synaptic pruning or enchantment
microglia with GABAb receptors
GABA neurons adjust the level of activity and guides:
anatomical plasticity
what is the effect of enhancing inhibitory GABA signalling on the critical period?
widens the critical period and increases plasticity
synaptic stabilization contributes to termination of critical period, and this may be due to:
- myelination (and associated nogo myelin), which occurs at the end of the critical period
- development of the adult perineuronal net (PNN)
- reduction in growth potential of adult neurons, compared to neonatal neurons
- reductions in growth factors like BDNF and neuromodulators like noradrenaline
what does “Nogo” do?
inhibits neuronal growth via axonal nogo receptors
a web of proteoglycans (CSPG) that wrap around certain neurons, especially inhibitory neurons
the perineuronal net (PNN)
the mature perineuronal net (PNN) inhibits ____ around GABA neurons
neuronal plasticity
true or false: critical periods occur for all skills and vary in duration
true
social deprivation in an orphanage increases:
cognitive dysfunction
children without social interaction in the critical period have:
a less related frontal cortex
critical period plasticity may be restored in adults by techniques used in:
spinal cord injury treatment
list six potential treatments that can be used to restore critical-period plasticity
1) blocking myelin inhibition of growth
2) degrading the perineuronal net (PNN) with chondroitinase
3) transplantation of immature GABAergic neurons
4) increasing neuromodulators via antidepressants
5) training or enriched environment to increase BDNF
6) microglial-neuronal communication increases GABA neuron plasticity
see slide 496
transplanted neurons woohoo
what are the effects of an enriched environment on the cerebral cortex?
- increases cortical thickness
- increases the size of neurons
- increases the number of spines/synapses
- increases BDNF
monocular deprivation results in:
enhanced somatosensory discrimination (other senses become heightened)
how is it possible for enhanced somatosensory discrimination to occur in the presence of monocular deprivation?
due to microglia phagocytosing inhibitory inputs to the visual cortex, which enables greater responses to somatosensory stimulation
____ strip off GABA inhibition to adapt to injury
microglia
ture or false: it is possible for sensation in the phantom limb to be evoked from face simulation 4 weeks after an amputation and cortical remapping
true (unused brain areas get taken over by neighbouring regions)
the _____ resists external distubances and can be readily studied in humans to examine plasticity and learning
monosynaptic stretch reflex (knee-jerk reaction)
is the monosynaptic stretch reflex excitatory or inhibitory?
excitatory (EPSP)
turns off antagonist motorneurons when making a movement
reciprocal inhibition
turns off reflex pathways when not needed by GABAb receptors on the terminal of sensory afferents
presynaptic inhibition
presynaptic inhibition allows learning of skilled movements by:
lowering unwanted reflexes and increasing sensation (ex: dancers or climbers)
list the two major points of Nashner’s experiment on the adaptation of postural stretch reflexes
- ankle extensor stretch reflexes reduce body sway if the foot is displaces horizontally –> the CNS augments the reflex in successive trials
- the same reflexes increase body sway in a toe-up rotation about the ankle joint –> the CNS attenuates them in successive trials
context-dependence and adaptation of reflexes may be controlled by:
the cerebellum and brainstem reticular formation
postural muscles are often activated involuntarily prior to _____ in order to compensate for the expected shifts in the centre of gravity
voluntary movement of limbs
delays in the stretch reflex can cause:
instability and tremor (especially in certain postures or with peripheral demyelination/spinal cord injury)
review slides 501-505
decent diagrams
with spinal cord injury, nerve injury, stroke, or cerbral palsy the reflex pathwyas are disrupted, leading to:
spasticity
when reciprocal inhibition of muscles is reduced there is co-contraction of the muscles, leading to:
stiffness
when presynaptic inhibition is reduced, this leads to:
exaggerated reflexes
after injury, sensory terminal sprouting and microglia plasticity can increase reflexes by:
making inappropriate connections
reduced reciprocal inhibition, reduced presynaptic inhibition, sensory terminal sprouting and microglia plasticity all lead to:
exaggerated reflexes and large reflex driven tremors (clonus)
in motorneurons, intrinsic voltage-dependent persistent Na+ and Ca++ currents increase with injury, leading to:
sustained muscle spasms
with inury, serotonin innervation of the spinal cord is ____, but 5-HT2 receptors on motorneurons become _____, which further augments _____
lost, constitutively active, spasms
what are treatments for muscle spasticity and tremors?
GABA agonists, 5-HT antagonists, botox, surgery, rehab
