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Biological Psychology > Synapses and Networks > Flashcards

Synapses and Networks Flashcards

1
Q

HISTORY OF NEUROSCIENCE

A
  • early theories on brain organisation diffuse reticular syncytium of neural matter
    GOLGI (1843-1926)
  • historical silver neuron stains (bathing tissue in potassium chromate/silver nitrate solution)
    RAMON Y CAJAL (1853-1934)
  • “father of neuroscience”
  • bril neuroanatomist; artist; drew microscopic brain structures
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2
Q

THE NEURON DOCTRINE

A
  1. Brains are composed of separate neurons/other cells.
  2. Cells are independent.
  3. Neurons are polarised cells.
  4. Info is transmitted from cell to cell across tiny gaps.
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3
Q

SIGNAL GENERATION/TRANSMISSION DETERMINED VIA ION CHANNEL NATURES

A 
- gen ion channel locations (in varying numbers/densities):
VOLTAGE-GATED CHANNELS
- axonal hillock (integration zone of axon)/axon (conduction zone)
LEAK CHANNELS/ION PUMPS
- entire neural membrane
VOLTAGE-GATED CA2+ CHANNELS
- axon terminals (output zone)
LIGAND-GATED CHANNELS
- dendrites/soma (input zone)
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4
Q

SIGNALS TRANSMITTED OVER SYNAPSE TO NEURONS/TISSUES UNDER DIRECT NEURONAL CONTROL (MUSCLES/GLANDS)

A

PRESYNAPTIC CELL
- cell body -> axon -> synapse
POSTSYNAPTIC CELL
- synapse -> axon -> another neuron/muscle

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5
Q

SYNAPTIC PROCESS LOCATIONS

A 
TYPICAL 
- axo-dendritic 
- axo-somatic
- axo-axonic 
RARE 
- dendro-dendritic
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6
Q

SERIAL ELECTRON MICROSCOPY RECONSTRUCTION

A
  • focused on axonal inputs (various colours) onto a small segment of apical dendrite
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7
Q

GOLGI-IMPREGNATED PYRAMIDAL CELL

A
  • in hippocampal area CA1

- have soma/apical/basal dendrites

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8
Q

DEPOLARISATION

A
  • graded potential in input zone

- when presynaptic neuron = excited by incoming signal (neurotransmitter)

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9
Q

ACTION POTENTIALS

A
  • spikes
  • generated in integration zone if depolarisation passes threshold
  • signal transmission continues towards output zone
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10
Q

SIGNAL TRANSMISSION TO NEXT NEURON

A
  • when action potentials reach output zone

- neurotransmitter released into synaptic cleft (chemical synapse)

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11
Q

SIGNAL TRANSMISSION ACHIEVED

A
  • achieved if neurotransmitter leads to graded potential (depolarisation/hyperpolarisation) in input zone of postsynaptic neuron
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12
Q

PRESYNAPTIC NEURON

A
  • depolarisation of axonal terminal membrane opens Ca2+ channels; Ca2+ ions enter terminal
  • Ca2+ concentration increase stimulates release of neurotransmitter stored in vesicles
  • when vesicles fuse w/presynaptic membrane, neurotransmitter diffuses into synaptic cleft
  • neurotransmitter either crosses synaptic cleft; interacts w/ionotropic receptors embedded in membrane of dendrite/soma of postsynaptic neuron
  • neurotransmitter can also interact w/metabotropic receptors
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13
Q

IONOTROPIC RECEPTORS = LIGAND-GATED ION CHANNELS

A
  • ligand-gated ion channels open when bound by neurotransmitter molecules
  • dif types of iontropic receptors; vary in affinity for particular neurotransmitter/drug
  • reuptake = transmitter taken up to presynaptic cell
  • some neurotransmitter molecules don’t close cleft; bind to auto-receptors that inform presynaptic cell about net
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14
Q

METABOTROPIC RECEPERS

A
  • slower; control ion channels indirectly
  • coupled to G protein (guanine nucleotide-binding) consisting of 3 subunits (therefore also known as GPCRs (G protein-coupled receptors))
  • when activated by conformational change of GPCR (shape change), G protein (alpha-unit bound to GTP (guanosin triphosphate)) can interact directly w/ion channel or control it via second messenger molecules release inside postsynaptic cell (ie. cAMP (cyclic adenosine monophosphate)/PIP2 (phosphatidynositol 4, 5-bisphosphate)
  • neurotransmitters synthesised; stored in vesicles in neuron’s output zone
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15
Q

IONOTROPIC RECEPTORS

A 
- fast/signal transmission; ie.
AMINS
- acetylcholin (nicotinic/nACh receptors/serotonin (5-HT)
AMINO ACIDS
- glutamate (NMDA/AMPA receptors)
- gamma-aminobutyric acid (GABA A)
- glycine
- aspartate
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16
Q

METABOTROPIC RECEPTORS

A 
- slow/long-lasting; more varied effects; neuronal modulation; ie. 
AMINS
- acetylcholic (muscarinic) 
- dopamine/serotonin
- norepinephrin
- octopamine
AMINO ACIDS
- glutamate 
- GABA B
- glycine
NEUROACTIVE PEPTIDES
- vasopressin (antidiuretic hormone ADH)
- oxytocin
17
Q

GAP JUNCTIONS CONNECT CYTOPLASMS OF 2 NEURONS

A
  • instantaneous current flow (v fast electric signal transmission across connexons producing coupling effect ie. virtually no time delays)
  • gap junction (membrane gap) small as 20-40nm
  • found where fast responses/activity synchronisation required
  • fast action = commanding escape responses (crayfish/fish)
  • synchronised activity = inhibitory neurons in mammalian brain; eye-moving muscles
18
Q

NEURAL SIGNALS OVER DISTANCE

A
  • spiking neurons w/long axons transmit signal via action potentials along axon
  • signal sustained effectively via voltage-gated ion channel pop in axonal membrane
  • non-spiking neurons w/short/thin/no axons don’t generate action potentials; signal spreads passively to output zone
19
Q

SIGNAL STRENGTH OVER DISTANCE

A
  • weakens the longer it travels
  • longer distance = stronger attenuation
  • solutions to reduce signal transmission costs include:
    1. long neurons have thick axons (ie. squid/invertabrates)
    2. white matter = myelinisation of axons in spiking neurons (vertebrates)
20
Q

NEUROLOGIA CELLS

A 
SCHWANN CELLS/OLIODENDROCYTES
- assist signal propagation
ASTROCYTES 
- provide nutrients to neurons
MICROGLIA 
- clear debris
- mediate immune response
21
Q

AXON MYELINSATION W/SALTATORY TRASMISSION GAPS

A
  • gaps for saltatory transmission of action potentials
  • neural membrane exposed at nodes of Ranvier for ion conductance via voltage-gated channels
  • saltatory conduction of action potentials increases transmission speed
22
Q

CONDUCTION VELOCITY ^ W/^ OF DIAMETER/AXON MYELINISATION

A
  • myelinated neurons w/thin axons can reach similar conduction velocities as those w/unmyelinated thick axons
23
Q

EACH NEURON FORMS MANY SYNAPSES

A
  • neurons collect info from few -> hundreds of others
  • when/which signal is picked up depends on:
    1. synapse type (excitatory/inhibitory); associated neurotransmitter
    2. synapse number; spatial position on dendrites/soma of input zone
    3. duration/synchrony of neurotransmitter release from dif synapses
24
Q

NEUROTRANSMITTER TYPE/RECEPTOR DEFINES POSTSYNAPTIC POTENTIAL TYPE

A 
EXCITATORY 
- glutamate 
- aspartate 
- nicotinic acetylcholine (nACh)
INHIBITORY 
- GABA
- glycine
- muscarinic acetylcholine
25
Q

NEUROTRANSMITTER/RECEPTOR REACTION AT POSTSYNAPTIC MEMBRANE

A

DEPOLARISATION
- EPSP (excitatory postsynaptic potentials)
HYPERPOLARISATION
- IPSP (inhibitory postsynaptic potentials)

26
Q

TEMPORAL SUMATION

A
  • if neurotransmitter released for longer into synaptic cleft, postsynaptic potential = stronger
27
Q

MULTIPLE SYNAPSE ACTIVATION EXAMPLE

A
  • imagine 2 excitatory & inhibitory synapses activated simultaneously by 2 dif stimuli
  • spatial summation = if postsynaptic potentials arrive together in integration they’re summed up
  • spiking neurons = if membrane at integration zone depolarised above threshold, action potential generated; the more excitatory input arrives, the stronger the output signal
  • at integration zone, EPSPs/IPSPs arriving simultaneously/within small window = summed up
  • the more inhibitory input arrives, the weaker the output signal; neuron may not even transmit output signal
28
Q

NEURAL LANGUAGE VOCAB

A
  • when neuron receives info from single neuron, it responds in binary code (ie. yes/no)
  • YES = signal gets transmitted to output zone; neurotransmitter released
  • NO = signal doesn’t reach output zone SO neurotransmitter not released
29
Q

NLV: WHEN NEURON RECEIVES INFO FROM MANY NEURONS

A
  • w/synapses neurons can only use simple arithmetics:
    1. sum (temporal/spatial summation)
    2. multiply
  • summing up (local operator “and”) = YES
  • if both EPSPs (1/2) present simultaneously & sum up to depolarisation that surpasses determined threshold THEN action potential generated/signal transmitted
  • summing up inhibitory input of sufficient strength (logical operator “not”) = NO
  • if IPSPs (3/4) present simultaneously as EPSPs (1/2) THEN action potential NOT generated/signal not transmitted
  • whether signal transmitted/not depends on sum of relative EPSPs/IPSPs strengths that arrive at integration zone in given time window
30
Q

INFO CODED IN NEURAL NETWORKS

A
  • spatial/temporal summation at synapses determine how signal travels through network
  • connectivity of network determines when/where signal travels faster/slower = amplified/reduced/muted
  • in feedforward circuits, signal distributed to many neurons through divergent connections OR determined via collecting signals from many converging neurons
  • divergence = neuron broadcasts to many others
  • convergence = neuron listens to many others; has high sensitivity; gatekeeper/decision-maker
  • feedback loops (positive/negative) provide direct/indirect input influencing signals, thus info
  • signal amplified soon after reaching network (positive loop/excitatory feedback synapse)/reduced (negative loop/inhibitory feedback synapse)
31
Q

COMPUTATIONAL NEURAL NETWORK MODELS

A
  • simple neural language rules (summation/multiplication) & binary (0/1) code
  • complexity of neural language comes w/number of connections/layers/connectivity types between neurons in networks
    CONNECTIONIST MODEL
  • ANNs (artificial neural networks) for modelling/understanding cog/brain
    DEEP LEARNING
  • ANNs for solving AI problems (ie. object recognition in images/speech recognition); may not require reference to cog mechanisms/neurobiological circuits; don’t aim to explain details on brain function
32
Q

SUMMARY

A
  • neurons communicate via electric signals
  • dif ion channel types gen located in dif neuron parts
  • neuron doctrine = brains composed of separate neurons & other independent cells; neurons = polarised; info transmitted cell -> cell across synapses
  • synapses = electric (rare/fastest)/chemical (most frequent)
  • ionotropic (ligand-gated ion channels)/metabotropic (coupled to G-protein) receptors
  • signal transmission over long distances requires modifications for loss of signal (axon diameter/myelinisation)
  • saltatory signal conduction in myelinised neurons

Biological Psychology (21 decks)

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