neurotransmitatori 1 Flashcards
what are neurotransmitters
chemicals that allow the communication between cells
releasing cell - neurone
target cell - neurone, gland cell or muscle cell
they have excitatory or inhibitory effect
why are NT important
important for activities that regulate our behaviour, cognition and emotions
where are NT stored
nt are contained in synaptic vesicles in the pre synaptic neurone
where are NT released
following action potential they are released into the synaptic cleft which is a small space between neurone and target cell
how do they reach the target cell
the act by binding onto the receptor of the post synaptic cell
summarise the action of a nT
in response to an action potential, NT is released at pre-synaptic terminal
NT moves across the synapse and binds with receptors in the post synaptic neurone, causing change in the membrane potential
Binding of NT may influence the post synaptic neurone in either an inhibitory or excitatory way
what is an excitatory action
contributes to trigger an action potential
what is an inhibitory signal
action that prevents action potential
why does a NT need to be stopped
bc it might become inappropriate or too time consuming
what are the four mechanisms a NT can be stopped
Diffusion
Enzymatic degradation
Glial cells
Reuptake
what is diffusion
when a NT moves away from the synaptic cleft where it can no longer act on a receptor
what is enzymatic degradation
then NT change their chemical structure by the action of enzymes so that they are no longer recognised by the receptors on the post synaptic cell and can no longer exert action
what is the mechanism of glial cells
NT can be moved away from the synaptic cell by glia cells
astrocytes remove NT from the synaptic cleft
what is re-uptake
recycling on NT
taking NT that has not been used back from the synaptic cleft
back into the presynaptic cell
nT is taken by a transporter
re-uptaking or failing to re-uptake is the basis of certain pathologies and addiction
summary of nT
production of NT which occurs in the cell body, the axon or the axon terminal
NT are stores in vesicles in the axon terminal
then released in synaptic cleft following an action potential
bind to receptors on post synaptic cell
NT is deactivated by diffusion, change due to action of enzyme, or re-uptaken into the pre-synaptic neurone
why do we focus on NT that are dominant
we look at NT that is more strongly present at the axon terminal
then a neurone and its dominant NT can be related to a function or behaviour
what are the 4 main NT systems in the central nervous system
dopaminergic system - dopamine
serotonergic system - serotonin
noradrenergic system - noradrenaline
cholinergic system - acetylcholine
what is the dopaminergic system
dopamine is produced in nerve cells mainly originating in the midbrain - substantial nigra and ventral tegmental areas VTA
where do neurones in subtantia nigra and VTA send their axons ?
from the substantial nigra and VTA, the system branches in 3 different directions that represent 3 different circuits
mesocortical
nigrostriatal
mesolimbic
what is the mesocortical system
starting from VTA across the cortex
important for cognition, memory, attention, emotional behaviour, learning
what is migrostriatal system
VTA to subcortical areas
important in movement, sensory information
Parkinson’s disease characterised by difficulty in movement due to malfunctioning of dopamine in this circuit
what is the mesolimbic system
from VTA to areas of the brain that deal with emotional stimuli and important for processing of reward, pleasure, seeking behaviours, addiction, emotion, perception
what is the role of dopamine in reward
dopa is important in maintaining and processing stimuli that generate sense of pleasure and reward
reward is associated with certain activities that are important for survival
bc of the importance of these functions, its critical to have sense of pleasure associated with them so that we are more inclined to look for these stimuli
what is study on how dopamine is important for survival
dopamine levels increase when animals or humans are exposed to survival activities (food or sexual stimulation)
how did dopamine levels increase in animals or humans
areas of the brain engaged in reward related activities are stimulated electrically resulting in an increase in rewarding effect
lesions to these parts of the brain will result in modification of preferences towards rewarding stimuli
what else is reward important for
rewarded activities are pleasurable, provide validation, social affirmation and connection
what is dopamine’s function as a predictor of reward
it is important to have a system in place that allow us to be engaged in activities that are likely to result in a sense of pleasure
we need to anticipate when a certain activity is likely to be linked to reward
2 distinct components to reward processing:
1. consumatory component
2. anticipatory component
what is the consumatory component
when we receive a reward
what is anticipatory component
activities we engage with based on past experiences we are likely to expect a reward that is not yet present
what are the different areas associated with reward vs reward anticipation
reward - greater activation of areas such as insula and frontal operculum SO frontal part of the brain
reward anticipation - greater activation of areas like amygdala, hypothalamus, striatum
why is reward important for learning
The skill to predict an award is important bc it’s important for learning
learning occurs when actual outcome is different from predicted outcome, resulting in prediction error
prediction error= failure to anticipate some expected event to occur
learning allows us to adjust future predictions to match the outcome more closely
how does the brain detect prediction mistakes
dopamine is released when predictions errors are made
this is shown in increased activity in striatum
in SZ there is inability to make predictions- and SZ patients have problems with dopamine
what is random reward
random rewards keep individuals responding for longer and repeatedly
this is why u stay in a rship when the person responds randomly
what is dopamine and memory
the hippocampus encodes memories for new events or episodes
hippocampal activity corresponds to dopamine released to keep memory of new events
what is a study to test the role of dopamine in memory
it is possible to improve duration of episodic memory by manipulating dopamine artificially
ppts took dopamine 1h and a half before experiment
low
medium
high dosage
looked at images in fMRI scanner
imaged depicted indoor or outdoor scenes
half images associated with reward, half not
then 1 hour or 3 hours after they were presented with same images mixed up with new images and indicate if they seen image before or not
RESULTS
performance improved especially for those who received dopamine in the middle dosage
hippocampus more activated for remembered than forgotten items
so dopamine is critical for episodic memory consolidation
what is the serotonergic system
based on serotonin- feel good chemical
regulates: sleep, appetite, mood balance, social behaviour, inhibition
what happens when serotonin is downregulated
depression, aggression, over-eating, suicide , SZ
What is the role of serotonin in moral judgement
moral judgement - certain behaviours aren’t morally appropriate
serotonin is a key player in this ability
what are the 2 hypothesis of how to test the role of serotonin in moral judgment
harm aversion
emotion regulation
what is harm aversion
serotonin controls certain impulses
serotonin promotes pro social behaviour and discourages antisocial behaviour
what is emotion regulation
serotonin promotes the control of violent impulses or down regulation of emotional reactions to provocation
how was role of serotonin in moral judgement studies
Ppts took a drug or a palcebo
Ppts were either taking a drug that amplified action of serotonin or amplified action of noradrenaline (linked to executive functions)
Drugs acted on re-uptaking
so NT remains available in synaptic cleft and effect of NT can be amplified
ppts addressed issues related to moral dilemmas
RESULTS
ppts found dilemmas that involved personal harm as less acceptable
boosting serotonin made personal situations less plausible than boosting noradrenaline
so serotonin enhances aversive emotional reactions to harm
what about serotonin and antisocial behaviour
serotonin has been linked to callous unemotional traits:
- lack of shame
- lack of empathy and understanding of other’s feelings
- psychopathic personality
ppts who scored low callous unemotional traits had higher levels of serotonin
so serotonin is linked to cognitive and emotional deficits in people with high levels of CU traits
what’s the role of serotonin in impulsivity
impulsivity is behaviour that occurs without foresight
serotonin is involved in psychopathology
low serotonin is linked to behavioural disinhibition leading to aggression
what is the noradrenergic system
adrenaline based
originates in brain stem structures - locus ceruleus and medulla
what are the 2 branches of the noradrenergic system
from the brainstem:
1. dorsal ascending system - covering neocortex and hippocampus
- ventral system - hypothalamus and limbic system - therefore involved in processing emotions
what are the main functions of the noradrenergic system
arousal
processing novelty
sensation seeking behaviour
too much novelty may cause stress
whats the rship between noradrenaline and sensation seeking behaviour
high sensation seeking - increased risk of addiction and negative behaviours
ppts divided into high and low sensation seeking behaviour
ppts in fMRI looked at images which could be high (nudity or violence) or low level of arousal (objects or people)
RESULTS
High sensation seeking activated brain areas involved in arousal more than low - especially for stimuli high in arousal
low sensation seekers: activated brain areas involved in emotional regulation - especially for stimuli high in arousal level - so they need to keep this stimuli under control and downregulate the emotions that this stimuli provoked
what is the cholinergic system
system regulated by acetylcholine
2 branches:
1 covers neocortex and hippocampus - important for a form of arousal called vigilance which has an impact on attention, memory encoding, and working memory processes
1 branch covers brain stem and important for regulation of sleep waking cycle
