Quiz #2 Flashcards
What processes occur during experimental phase of neural development?
- experience changes synapses from the time of birth throughout and individuals life
- wiring by firing = Hebb’s rule
What processes occur during the developmental phase of neural darwinism?
- genetics present before birth of child
- neural darwinism and apoptosis
What is Neural Darwinism?
- theory of neuronal group selection
What is Developmental Selection?
- genes generate a hugee population of neural and glial cells to select for network building (making network larger through life and death of neural and glial cells)
What is Experiential Selection?
- experience leads to changes in connection strength of synapses, which favour some pathways and weaken others
What are the 2 forms of Neural Darwinism?
- Developmental
- Experiential
What is the organization of the ocular dominance column?
the columns are found in layer 4 of the striate cortex (of the monkeys)
In ocular dominance column, what is the distribution of LGN and where do the zones appear?
- LGN serves one eeye
- zones appear in patches within layer 4 (zebra stripes if superficial 1-3 layers peeled away)
What do dark bands get information from? light bands?
dark bands - get information from one eye
light bands - get information from the other eye
* alternating stripes - ZEBRA LOOK
Input from the LGN serving the 2 eyes are intermingled in where? over time?
- layer 4
- over time - ocular dominance columns in layer 4
The zebra stripes begin to form due to what?
competition dominance
What is the critical period?
- if eye covered at birth then lose segregation and sending of information from that eye => lack of dominance and see black shapes (due to lack of information from the monocular eye development)
What does monocular input beginning at birth lead to?
complete eye dominance
When is the process of ocular dominance column formation?
complete by 6 week
What is monocular deprivation in the early stages post birth?
lose eye information and less striping in layer 4 of the cortex
What does deprivation at 2,3,6 weeks have on monocular deprivation?
weaker effect on the ocular dominance columns since they become more segregated with time
What is the Hebbs synaptic learning/plasticity rule for LTP and LTD?
when an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased
What is a Hebbs synapse?
- pre and post synaptic simultaneous/ concurrent activity
- produces increased synaptic transmission efficiency/strength
- initially signal is only strong enough so that A fires
What is an Anti-hebbian synaptic process?
- an unused connection decays
- triggered by non-concident pre and post synaptic activity
- produces a weakening r decrease in synaptic strength and efficiency, if depression is persistent (LTD)
- initially cell A or B doesnt fire (silent) => synapse A-B weakened
What does LTD stand for?
Long Term Depression
What does an inactivation of cell B do to an active cell A?
depression
What does an active cell B do to an active cell A?
potentiation
What does and inactive cell B do to an inactive cell A?
no change
What is Hebbs view?
chief mechanisms of learning and memory is simply the strengthening of synaptic connections between brain cells of an assembly
What are the different processing streams in neural circuits?
divergence
convergence
hierarchical
What is divergence?
one source cell can send info to multiple targets in the same area, or multiple targets in 2 different areas
What is convergence?
many sources converge onto one neuron. source signal can come from multiple neurons in one area or multiple neurons in different areas
What 4 types of processing occur in hierarchical circuits?
serial information processing
parallel information processing
reciprocal information processing
local circuit connections
What is serial information processing?
information handed from area to area in a sequence at each level processing is regulated by other kinds of local circuits
What are parallel information processing?
information flows through hierarchy in a side by side fashion
What is reciprocal information processing?
information may flow back and forth within circuits
what are local circuit connections?
- both feedforward and feedback as well as excitatory and inhibitory
- information alters the processing at each hierarchical stage determining the nature of information that will be sent to the next stage
What is feed forward excitation?
helps to sustain the excitatory discharge response over time
What is elicited inhibition?
produces on/off gating by the effected nerve cell
What are feedforward excitation and inhibition?
elicited excitation
elicited inhibition
What are feedback excitation and inhibition
recurrent excitation
recurrent inhibition
What is recurrent excitation?
accelerates the original outputs overtime - feedback amplification
What is recurrent inhibition?
feedback signal from post synaptic cell comes back to slowly suppress cell output over time
What is a disinhibition circuit?
inhibition of inhibition that leads to the release of excitation
Where are feedback inhibition, feedforward inhibition and dis-inhibitory connections found?
spinal cord motor circuitry
What are Principal cells?
pyramidal cell
spiny stellate cell
What are pyramidal cells?
converge multiple signals and then send one signal out to an excitatory cell
What are spiny stellate cells?
one neuron sends out to multiple signals
What are the features of principal cells
- ~80% circuit neurons
- Glutaminergic
- excitatory synaptic actions
- electrical synapses are absent
- local intrinsic and projection extrinsic targets
- reciprocal connection with other principal cells, interneurons and with themselves
- dendritic spines on both cell types
What is the electrophysiology of principal cells?
each type of principal “excitatory” neuron expresses a specific combination of membrane ion channels, produces certain numbers of each channel, uniquely modifies each channels molecular structure. And distributes signal in a characteristic pattern across the membrane surface to generate a specific type of electrical behav
What are special about glutamatergic principal cells?
can be modifies by experience = hebbian plasticity
What are the features of interneurons?
- GABAergic
- inhibitory synaptic actions: feedforward, feedback and recurrent
- interneuron subtypes: form reciprocal synaptic connections with other inhibitory interneurons and principal cells and with themselves
What are the subtypes of interneurons based upon?
- molecular diversity and related electrophysiology
- distinguished based on post synaptic targets, dendritic patterns and expression of key molecular markers
- distinct inhibit netweorks - exxist as a result of gap junctional electrical coupling
What do interneurons perform on principal cells?
disinhibition
What are the function of interneurons?
inhibitory interneurons produce rapid alterations in time windows of synaptic convergence in targeted cells that allows coincident time binding across large numbers of neurons constituting hebbiaan assembly/cognitive network.
What are the old views of brain function?
- brain structure is stable
- brain circuitry is hard wired
- cognitive functions and memory are localized
- brain activity is driven by excitatory sensory input
- information processing involves serial processing only
- functions vulnerable to single site injury/lesion
- limited clinical explanatory power
What are the new views of brain function?
- brain structure is changeable
- cognitive functions and memories are distributed
- info processing involves SP, PP, RP streams together at the same time
- brain activity is driven by internal intrinsic cycles
- functions resistant to degradation by single site injury
- excellent clinical explanatory power
What are the major nuclei of Ach?
nucleus basalis, pontopedunuclear-tegmental nuclei
What is the transmitter for Ach modulatory network?
Ach
What is the Ach synaptic action?
excitatory&inhibitory
What is the duration of Ach network?
fast/slow
What are the signal transduction for Ach?
nicotinic (iono (2))
muscarinic (metabo (5))
What does Ach control?
learning, memory, emotion, REM sleep
What are the major nuclei of NE network?
locus ceruleus of rostral pons
What is the transmitter of NE network?
norepinephrine
What is the synaptic action of NE?
excitatory & inhibitory
What is the duration of NE?
slow
What is the signal transduction of NE?
noradrenergic (metab (9r/c))
What does NE control?
attention, supports learning & memory, emotions and deep slow wave sleep
What are the major nuclei of DA network?
substantia nigra, ventral tegmental area, arcuate nuclei
What is the transmitter for DA network?
dopamine
What is the synaptic action of DA?
excitatory & inhibition
What is the duration of DA?
slow
What is the signal transduction of DA?
dopaminergic (metabo (5r/c))
What does DA control?
emotion, learning, memory, movement regulation, positive reward system
What are the major nuclei for 5HT (serotonin) network?
raphe nuclei
What is the transmitter for 5HT?
serotonin
What is the synaptic action of 5HT?
excitatory & inhibitory
What is the duration of 5HT?
fast & slow
What is the signal transduction for 5HT?
serotinergic (metabo (13r/c))
ionotropic (1r/c/)
What does 5HT control?
inhibition of behaviour, emotion, learning, memory, deep sleep
What are the major nuclei of HIS network?
tuberomammillary nuclei (MTn)
What is the transmitter for HIS?
histamine
What is the synaptic action of HIS?
excitatory
What is the duration of HIS?
slow
What are the signal transduction of HIS?
histaminergic (metabo (3r/c))
What does HIS ccontrol?
attention, body energy stores, stress, learning and memory
NE graph shows what when intern levels of arousal cognitive performance is the highest?
inverted U
What are drugs of abuse?
psycho-stimulants that act to rapidly and abnormally increase 3 modulatory squad transmitters NE, 5HT, DA
What are the short term effects of drug abuse?
euphoria, suppression of fatigue and appetite
What are withdrawal symptoms of drug abuse?
dysphoria, depression, anxiety, fear, fatigue, exhaustion, hyperphagia
What does cocaine do?
block dopamine uptake at synaptic cleft and increases potential dopamine transmission in nucleus accumbens
What does amphetamine do?
increase dopamine release from vesicles in presynaptic terminal
What does PCP do?
blocks input from other areas causing down regulation. blocks excitatory glutaminergic input to cortex decrease nucleus accumbens
What do opiates do?
inhibit GABA neuron, reducing tonic inhibition of DA, thus increasing their firing increasing nucleus accumbens
What does nicotine/alcohol do?
increase DA reward system within brain
What is the pre-synaptic site of action of addictive drugs acting on dopamine reward network?
- dis-inhibition action - heroin and THC decrease GABA release => increased VTA dopamine
- presynaptic facilitation - of glutamate release by nicotine => leads to VTA dopamine neuron spiking
What is ARAS?
Ascending reticular activating system
What does ARAS regulate?
arousal and sleep/wake transitions
What does ARAS relay input to?
relays sensory input to non specific areas of he brain (thalamus relays to specific areas)
What are the functions of ARAS?
- to alert/wake up cortex and prepare for more specific stimuli
- tells the entire cortex to pay attention
- brain stem ARAS makes diffuse connections to thalamic ARAS and cortex
- damage to ARAS would result in deep coma
What is the function of the thalamus?
- tells and isolated area about a specific stimuli
- makes connections to specific cortical projections
What type of input passes through the thalamus on its way to the cortex?
all sensory input except smell
What are the nuclei of the thalamic ARAS?
(see notes)
What is a cortical column?
information processing unit within a cortical module
What are the cortical columns comprised of?
narrow chain of neurons that extend vertically across cellular layers 2-4
What are the diameters of cortical columns?
sensory/motor = 100-500micrometers
association fibers = 200-500 micrometers
What are the related properties and selectivities that neurons within a column show?
- place - peripheral RF
- modality - nature of adequate stimuli that change discharge of cell
What is the EJ Jones Rule?
inputs to column layer 4, outputs to layers 2 and 3 to other cortical columns/layers 5 and 6 to subcortical targets
Can cortical columns be linked together?
yes. by short and long range horizontal intracortical synaptic connections to form larger groupings (modules)
What is the sleep induction hypothesis?
when glial cell glycogen stores are depleted by repeat n.t. release during wakefulness, adenosine is released from glia and initiates non REM sleep (NREM).
Increased adenosine binds to specific r/c in cortex, thalamus and brainstem where they promote sleep induction.
What is NREM?
deep or slow wave sleep
What does the anabolic nature of sleep suggest?
a rest and restorative function - sleep conservation of energy. repair of injury, isolation and immobility as a defence from predation
What is REM sleep?
dream sleep
What occurs during REM sleep with the brain?
consolidation of daytime info into long term memory.
this stage of sleep prevents interference in the consolidation process by suppressing further sensory input and motor input
What cortical area control working memory?
controlled by the prefrontal cortex
What is the relationship between working memory and attention?
(see notes)
What is working memory?
The ability to remember/retain certain “task” information and then recall it after a certain time period (delayed matching)
What are the stages of a working memory model?
- 1-cue period (10sec)- visual
- 2-delay period (2min) - auditory
- 3-response - visual motor
What is selective attention?
Attention is the cognitive process of selectively concentrating on one aspect of the environment while ignoring other things. Attention has also been referred to as the allocation of processing resources.
What is a STROOP test?
name the colours of the words, but do not read the words
What brain area controls selective attention?
cingulate gyrus
What brain areas regulate positive and negative emotions?
positive - ventral tegmental area
negative - locus ceruleus and nucleus raphe
What are the neuro-modulators of positive and negative emotions?
positive - increased nucleas accumbens, and decreased amygdala
negative - increased amygdala, decreased nucleus accumbens
What do we see with major depression?
- abnormally increased rCBF in prefrontal cortex
- abnormally increase of rCBF in amygdala
- abnormal decrease in rCBF in caudate nucleus
- these features relate to a patients excessive negative feelings and their inability to develop a strategy to escape from or solve the problem
What are some examples of antidepressant drugs?
MAOIs, tricyclics, SSRIs
What is the effects of MAOIs?
inhibitors enhance the action of NE and serotonin by preventing their enzymatic destruction
What are the action of tricyclics and serotonin?
blocking uptake
What is the effect of SSRIs?
selective for serotonin by preventing uptake
What is the Theory of the Mind?
the ability to infer what others are thinking and feeling, inferring motive or intention on the part of others
What are the features of TOM?
- sensitive to understand emotional state of others
- operates when you have positive emotion of love aand compassion for others, feelings of empathy
- only observable in humans and appears at age 4-5
- not working in autism or schizo or with sociopathic personalities
What modulatory network supports TOM?
anterior paracingulate cortex activated awareness of mental state of self (desire, emotion, thought) and social interaction
Where is the hippocampus located?
temporal lobe
Whats the function of the hippocampus?
transferring short term memories into long term memories
Specifically where does the hippocampus lie?
at the tail end of the fornix in the floor of the lateral ventricle
What is the mossy fiber pathway?
connects with the pyramidal cells in areas CA3, where CA3 cells project to pyramidal cells in CA1 by schaeffer collaterals
What happens when schaeffer collateral fibre pathway sends information from CA3 to CA1
see long term potentiation to CA1 region
What is the perforant pathway?
major excitatory pathway with granule cells that give rise to form the mossy fiber pathway
How can the features of hippocampal long term potentiation be demonstrated?
by stimulating two different fiber pathways converging onto a single CA1 pyramidal neuron
How does LTD conduction occur?
- glutamate binds to NMDA r/c
- post synaptic neuron is strongly depolarized releasing Mg block of the NMDA r/c allowing Ca to flow through the channel
- through Ca/calmodulin kinase and protein kinase see a retrograde messenger is triggered and causes increased glutamate release by presynaptic cell => enhance n.t. release
What does LTP result in?
multiplication of synapses
Where are most synapses located?
on dendritic spines
What is the mechanism of synaptic modifications supporting NMDA r/c mediated LTP?
- post synaptic density expands, perforates and splits into multiple densities
- the presynaptic active zone splits into corresponding regions
- perforated synapse further divides spine branches
- branched spine ultimately become two spines each cntaining a synaptic region
What are synaptic modifications supporting NMDA r/c mediated LTP in terms of AMPA r/cs?
strengthening individual synapses by increasing the number of AMPA r/c on the post synaptic membrane which increases the cells response to glutamate
- Ca activates CaMK enzyme
- 2nd messenger signal transduction pathways are activated - new AMPA r/c inserted into membrane
What is cooperativity?
tetanize the weak and strong inputs individually. the weak input does not potentiate but the strong input does
What is associativity?
tetanize the weak nd strong inputs simultaneous - both weak and strong inputs potentiate
What is specificity?
tetanize the strong input alone - the weak input doesnt potentiate but the strong input
What happens to the post synaptic activity when you inject EGTA?
no LTP
What happens to the post synaptic activity when you raise extracellular Ca?
see LTP increase
What happens to the post synaptic activity when prevent depolarization through intracellular hyperpolarization current inject?
no LTP
What happens to the post synaptic activity when pair weak input with intracellular depolarization current injection?
increases LTP
What does AVP do to LTP?
its an NMDA antagonist and blocks LTP
What happens to LTD with low freq stimulation?
- with small post synaptic depol
- not temporal summation of EPSPs
What happens to LTD with postsynaptic depolarization?
strong hyperpolarization = no LTD
What happens to LTD with a change in post synaptic Ca?
- inject BAPTA (Ca chelator) = no LTD
- lower extracellular Ca - induce LTD instead of LTP
Does AVP block LTD?
yes
How can you convert LTD to LTP by adjusting membrane potential of post synaptic cell?
by changing depolarization in extracellular fluid
What causes the conversion of LTD to LTP?
strong depol of post synaptic cell
What is a serial scheme?
a lesion at B prevents information from A to be transmitted to C,D,E
What is a Distribution scheme?
if a lesion at B, will have minimal impact on transfer of info from A to C,D,E
What does a distribution scheme tell us?
time, location, quality, and magnitude of signal
