l2- neurons n cortex Flashcards
1
Q
Electrochemical Neuronal Signalling
electrical signals
A
- within a neuron
2
Q
Electrochemical Neuronal Signalling
chemical signals
A
- between neurons at synapses
3
Q
neuronal signalling
A
- process of transmitting info in the nervous system
4
Q
information
A
- =signal= any change in:
- membrane potential (diff in electrical charges inside/outside neuron)- postsynaptic (input) and action (output) potentials
- neurotransmitter quantity (chemical signal between neurons)
5
Q
Electrical neuronal signalling within a neuron
neuron mebrane
A
- seperates inside (intercellular) from outside (extracellular)
- has 3 types of transmembrane proteins: Na+/k+ ion pump, Na+ and K+ voltage-gated ion channels
6
Q
electrical neuronal signalling within a neuron
ion pump (Na+/K+ pump)
A
- continously moves Na+ out n K+ in- keeps a voltage difference
7
Q
electrical neuronal signalling within a neuron
volateg gated ion channels
A
- open/close based on membrane voltage
- only let specific ions (Na+ or K+) through
- closed at rest, open during signalling
8
Q
Resting Membrane Potential
Resting Potential
A
- the normal voltage across the membrane at rest (~ -70 mV)
- Created by the Na+/K+ pump (3 Na+ out, 2 K+ in = more positive outside).
- voltage gated channels stay closed below -55mV
- input from other neurons can change this voltage
9
Q
post synaptic potentials
A
- small voltage changes due to input from other neurons
- PSPs can add up:
- if enough EPSPs- reach -55mV= trigger action potential.
- IPSPs make it harder to reach threshold
10
Q
PSPs
excitatory psp
A
- makes membrane less negative then -70mV
- depolarisation
11
Q
psps
inhibitory
A
- makes membrane more negative
- hyperolarisation
12
Q
action potential
A
- triggers at -55mV: all or nothing event
- phases:
1. depolarisation- Na+ channels open → Na+ enters → inside becomes positive (up to +40 mV).
2. Repolarisation: K+ channels open → K+ exits → voltage drops. (from +40 mV to -70 mV)
3. Hyperpolarisation: Becomes more negative than resting (~ -80 mV). - Na+/K+ pump restores original state.
- Takes ~2 ms.
13
Q
actional potential propagation
A
- ap starts at axon hillock
- depolarisation spreads- triggers AP in next part of axon- continues forward
- refractory period: after firing, a section of the axon cant fire again immediately- ensures one way travel
14
Q
APP
refactory period
A
- after firing, a section of the axon cant immediately fire again- esures one way travel
15
Q
myelination
A
- speeds up AP transmission
- aps only occurs at gaps between myelin= nodes of ranvier
- ap ‘jumps’ between nodes- saltatory conduction
- myelin= found in white matter
- w/out myelin, signals would be too slow
16
Q
myelination
myelin sheath
A
- fatty insulation speeds up AP transmission
- theyre protrusions from oligodendrocytes, a type of glial cell
17
Q
properties of action potentials
all or nothing
A
- once an ap is triggered, same ap process always ensues
- fully happens or nothing at all
18
Q
properties of action potentials
self-propagation
A
- once triggered keeps going
19
Q
properties of action potentials
unidirectional
A
- moves one way thanks to refactory period
20
Q
properties of action potentials
does not dissipate
A
- ap keeps the same strength (+40 mV) as it travels along the axon
21
Q
Chemical communication between neurons at the synapse
chemical signalling between neurons
A
- happens at snypases
- ap arrives at axon terminal- causes neurotransmitter release
- NT crosses synaptic cleft- binds to receptos on next neuron
- triggers PSP
22
Q
Chemical communication between neurons at the synapse
signal conversion at synpase
A
- electrical (AP) arrives
- triggers chemical release (NT)
- causes electrical response in next neuron (PSP)
23
Q
Post-synaptic potential (PSP)
neurotransmitter action at synpase
A
- NT receptors r linked to ion channels
- bindning opens channels, which either:
1. hyperpolarises membrane potential=IPSP
2. depolarises membrane potential= EPSP
24
Q
properties of PSP
A
- local (near post synpatic dendrite)
- dissipate (weaken as travel)
- graded (not AoN)
- smaller in amplitude than aps (up to 5mv)
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PSPs to action potentials
- sum at axon hillock
- if total= -55mv-triggers ap
- if too many IPSPs- ap=blocked
- this= neuronal intergration
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neuronal coding
- the represenation of stimulus intensity by the rate of AP firing\
- NTs-more input- more released (graded)
- PSPs: stronger input - stronger psp (graded)
- APs:
- always same size
- stronger input- more aps fired-higher firing rate
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# neuronal coding
firing rate
- number of APs fired per second, increases w stronger stimulation
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# neurotransmitters
amino acid NTs:
glutamate
- main excitatory NT- leads to ESPS
(20% of CNS synpases)
- too much causes excito-toxicity- neurons overexcite n die
- involved in epilepsy: reduced firing threshold leads to overactivation
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# neurotransmitters
amino acid NTs:
GABA
- main inhibitory NT- leads to IPSPS
(40% of CNS synpases)
- prevents excessive excitation
- key for fine tuning of activation patterns
- alcohol enhances GABA receptor sensitivity- sedative + anxiolytic effects
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# neurotransmitter
system NTs
(specific brain circuits)
- **acetylcholine**- cholinergic system
- **serotonin**- serotonergic system
- **noradrenaline**- noradrenergic system
- **dopamine**- dopaminergic system
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the cerebal cortez
- divided through: lesion studies, neuroimaging/stimulation, animal electrophysiology
- 3 types: sensory, motor, association
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# sensory n motor cortex
primary sensory cortex
- recieves input from sensory organs
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# sensory n motor cortex
secondary sensory cortex
- processes inputs from cortex
not direct sensory organs- higher level processing
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# sensory n motor cortex
primary motor cortex
- sends commands to mucles
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# sensory n motor cortex
premotor cortex
- plans motor actions
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# sensory n motor cortex
brodmann areas (BA)
- BA17 = visual (V1)
BA22 = auditory
BA1,2,3 = somatosensory
BA4 = motor
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cortical maps
- cortex contains maps of body/senses:
- somatosensory+motor: body parts- disorted based on sensitivty/dexeterity
- visual:maps of visual field
- aduitory: maps of sound frequencies
- olfactory+gustary: unclear
- Contralateral representation: left hemisphere = right body/field and vice versa.
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motor and somatosensory cortical maps
- diff parts of MC control diff muscles
- diff parts of SSC recieve tactile info from skin (pain/pressure etc)
- more dexterous/sensitive parts=maginified
-maps=contralateral
- homunculus man
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visual cortical maps
- diff locs in primary VC correpsond to diff locs in visual field
- vsiual fields= contralateral
- centre=magnified
-secondary visual cortex=more maps
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auditory cortical maps
- cochlea in inner ear breaks down sound into frequencies
- PAC= maps
- ear sends info bilaterally to auditory cortex
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association cortex
- handles non-sensory n non-motor processing (so everything else):
- intergrates multisensory info
- supports compex cogniton (recogintion, memory etc)
- in frontal, partial n temporal lobes
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frontal lobe
- prefrontal cortex: lateral, orbital n medial parts
- functions:
- executive control (planning, prediction)
- working memory
- language
- decision making + error monitoring
- emotional processing
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parietal lobe
- specialised in:
- spatial awareness n attention
- multisensory integration (perception n memory action)
- object localisation n spatial relationships
- spatial-motor translation
- reading+writing
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temporal lobe
1. medial side:
- memory (hippocampus)
- emotion (amygdala)
2. lateral side
- visual object recogntion (ventral temporal)
- auditory object recognition (superior temporal)
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localisation vs distributed networks
- localisationsim: brain regions have specific functions
- BUT functions= distributed across networks
- connections r as important as regions themselves
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white matter tracts
- connect cortical regions
- **tracts**= bundles of axons (white matter highways)
- major egs;
- corpus callosum: connects hemispheres
- superior longtudinal fasciculus: connects frontal to parietal/occipital (attention, exec. control)
- arcuate fasciculus : connects frontal to temporal (language)
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NT systems
- brain circuits driven by specific NTs
- theyre made in subcortical/brainstem nuclei, projected widely
- each system supports multiple behaviours
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cholinergic system
- NT:acetylcholine
- made in basal forebrain nucleus
- projects to most cortex
- *functions*: cortical arousal/excitability, selective attention, memory (via hippocampus projections from pons/midbrain)
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noradrenergic system
- NT: noradrenaline
- made in locus coeruleus (pons), medulla
- projects to: thalamus, hypothalamus, cortex (esp PFC)
- functions: sleep+arousal, attention+vigialnce, emotional memory
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serotoninergic system
- NT: serotonin
- made in raphe nuclei (brainstem)
- projects to hypothalamus, hippocampus, amygdala, cerebellum, thalamus
- functions: homeostasis behaviours (sleep, sex, appetite), mood regulation, long term memory
- low serotonin- linked to depression
- SSRIs (eg antidepressants) affects sleep, sex, appetite
- MDMA damages serotengic neurons- LT memory deficits
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dopaminergic system
- NT: dopamine
- made in substantia nigra, ventral tegmental area, nucleus accumbens
3 subsystems:
1. ***nigrostriatal***: substantia nigra → basal ganglia
→ movement initiation & stopping
2. ***Mesolimbic***: VTA → limbic system
→ reward & reinforcement
3. ***Mesocortical***: VTA → prefrontal cortex
→ planning, working memory, problem solving
- dopamine in nucleus accumbens increases w: natural rewards (food), drugs, abstract rewards (money)
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