Chapter 2: Neurotransmitters and behaviour Flashcards
Describe the structure of neurons and the function of the different parts
Dendrites: filament extruding from the soma, typically multiple - receiver
Soma: cell body
Axon: only one filament extruding from the soma - sends out signals
Synapse
Where the axon of one neuron approaches a dendrite or soma of another neuron. The connections between neurons. Each neuron, on average, has about 15000 synapses with other neurons.
Threshold of excitation
If the sum of the excitation from other neurons exceeds this threshold, the neuron ‘fires’ and generates action potential that travels along the axon to other neurons, passing on the excitation.
Note: this action is binary, either it fires or it does not
Neurotransmitter
Chemical messenger (about 100 of them). They are constantly synthesized in the neutron and moved to the axon terminal to be stored. A released neurotransmitter is available in the synapse for a short period during which it may be metabolized, pulled back through reuptake or reach the post-synaptic membrane (dendrite) and bind to one of the receptors on its surface. Neurotransmitters transmit through the synaptic cleft. Neurotransmitters are either excitatory or inhibitory (excitatory or inhibitory effects on the neuron, meaning they either increase or decrease the likelihood of action potential).
Antagonists (chemical)
Chemicals that counteract a neurotransmitter and so prevent a signal from being passed further. See: SSRIs (selective serotonin reuptake inhibitors)
Limitations for direct correlation between the level of a neurotransmitter (x) and the behaviour exhibited (z)
● X may function as an agonist for neurotransmitter
Y, which in turn may affect behaviour Z. In other words, the effects of neurotransmitters may be indirect, sometimes with many links between the “cause” and the “effect”.
● X may serve as a trigger for a long-lasting process of change in a system of interconnected variables. In other words, the effects of X on Z may be postponed.
● X is usually not the only factor affecting Z.
● X is never the only factor that changes. As you artificially increase the level of X, this may result in various side effects
Agonists
Chemicals that enhance the action of a neurotransmitter
Crockett et al (2010)
A: investigating the effect of serotonin on prosocial behaviour
M: An experiment with 30 healthy subjects. Repeated measures design with two conditions. It was counter-balanced and a double-blind study
P: Condition 1: participants were given an SSRI, boosting serotonin levels.
Condition 2: placebo. Then moral dilemmas were presented: a choice between a utilitarian outcome (practical) and averse harmful actions (killing a person in a personal or impersonal manner).
R: If the aversive harmful action was impersonal, there was no significant difference between the two conditions, but participants from condition one were less likely to personal aversive harmful action.
C: serotonin reduces acceptability of personal harm and in that way promotes prosocial behaviour.
E: limited by the used SSRI (citalopram) induced slight nausea. This might mean that participants could work out what condition they were in on that trial.
Fisher, Aron and Brown (2005)
A: investigating the neural mechanisms of romantic love
M: Self-selected sampling. fMRI of ten men and seven women who were ‘intensely in love’
P: Participants were shown photos of their love and later an emotionally neutral acquaintance with countdowns in between.
R: Pattern of activation in the ventral tegmental area and caudate nucleus (both rich in dopamine) in response to photos of loved ones. These dopamine-rich regions form the dopaminergic pathway, which increases dopamine activity in the brain.
C: Dopamine activity in the brain plays a role in romantic love, as dopaminergic activity is linked to motivation and pleasure.
E: What constitutes being ‘intensely in love?’
How acquainted where the ‘emotionally neutral acquaintances’?
Fatigue due to the procedure being repeated 6 times.
Freed et al (2001)
A: To study the role of dopamine in Parkinson’s disease
M: 40 patients between 34-75 who have had Parkinson’s for the mean of 14 years.
P: The sample was divided into two groups: the experimental group received a transplant of nerve cells and the control group underwent sham surgery. Both surgeries had tissue with dopamine-producing neurons from aborted embryos which were then drilled into the patients’ putamen. In the control group, the dura was not penetrated by the needles. The patients were observed and interviewed and received PET scans over the course of one year.
R: PET scans showed growth of dopamine-producing cells in the putamen. In the transplant group, a reduction of symptoms by 28% was found in patients younger than 60.
C: Transplantation of dopamine-producing neurons in the putamen of patients with severe Parkinson’s can be beneficial for younger patients.
E: Ethical considerations: drilling holes in patients while they were awake, as well as using brain tissue from aborted embryos. The ethics committee did approve.
The role of serotonin in depression
Serotonin has been shown to be involved in the symptoms of major depressive disorder. The hypothesis states that low levels of serotonin in the brain play a causal role in developing depression. Many studies have found this by clinical trials with two groups, where the experimental group is given a drug that affects levels of serotonin, and the control group was given a placebo. However, it has also been found that behavioral effects are not immediate, that drugs are not universally beneficial and therefore the link between serotonin and depression isn’t either, and that the explanation for depression can be caused by stress (and therefore damage to neurons in the hippocampus) or simply certain genes.
Neuron
Neurons are nerve cells and the basic building blocks of our entire nervous systems. The neurons act as sensors for all types of stimuli and communicate the stimuli throughout the body – they transfer information throughout the brain, which is communicated through chemical signals.
Myelin sheath
Myelin is a fatty substance that covers neurons in the nervous system. Around your neurons is a myelin sheath that helps increase the speed at which information can travel on the neurons – how fast it takes for a nerve to traverse an axon – and protects the nerves from other electrical impulses.
Endocrine system
The endocrine system works alongside the nervous system. It is a network of internal glands across the body that secrete hormones. Instead of using nerves (sensory and motor neurons) to transmit information, this system uses blood vessels.
Various neurotransmitters
Endorphins
Opiatelike; linked to pain control and pleasure.
Norepinephrine
Control alertness and arousal.
Glutamate
Learning and memory.
GABA
Inhibitory – reduces neural excitability.
Serotonin
Affects mood, hunger, and sleep. Low amounts are linked to depression.
Acetylcholine
Excitatory and inhibitory. Enables muscle action, learning, and memory.
Dopamine
Excitatory and inhibitory. Influences movement, learning, attention, and emotion. Motivation salience.
