Neurochemistry

By Electra, Aimee and Zubiya

Neurotransmitters and Synapses

A nerve impulse travels along a neuron and when it reaches the end of the neuron, a chemical transmitter called a neurotransmitter is released.
These travel through the space between neurons called synapses.
They carry the message of the nerve impulse from one neuron to another, and this is how brain activity is stimulated.
Excitatory neurotransmitters - Stimulates brain activity (for example, dopamine)
Inhibitory neurotransmitters - Slow brain activity (for example, serotonin)

Hormones

Hormones are chemicals produced by endocrine glands, such as the pituitary glands. These glands release hormones directly into the bloodstream.

They travel to 'target cells' and act as messengers to affect our behaviour.

Specific hormones only affect these specific target cells, but they can affect them in different ways as these cells carry the organelles necessary to create varying responses.

Hormones enter directly into the bloodstream so thus they take longer to produce changes in behaviour than neurotransmitters.

Especially in animals, hormones can act to coordinate behaviour and physiology (like maturing gametes and starting mating behaviour)

DOpamine

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Dopamine is a neurotransmitter released by the brain that plays a number of roles in humans and other animals.

Dopamine helps control the brain's reward and pleasure centers. It also helps regulate movement and emotional responses, and it enables us not only to see rewards, but to take action to move toward them.

It is released during pleasurable situations and stimulates one to seek out the pleasurable activity or occupation. (Operant conditioning)

Dopamine deficiency can result in Parkinson's Disease, and people with low dopamine activity may be more prone to addiction.

Examples on behaviour

Experiment: Carrè et al (2006)
Study of a Canadian ice hockey team over the course of a season that found evidence of a surge of testosterone when the team played in their own stadium.

The influence of Neurotransmitters

Level of neurotransmitters can affect mood and behaviour in individuals Eg: The dopamine hypothesis suggests that schizophrenia results from an excess of dopamine. This causes the neurons to fire more often and transmits too many messages. These messages overload and produce many of the symptoms of schizophrenia.

A more recent explanations suggests that someone may have too many dopamine receptors, rather than too much dopamine the end result is the same.

Examples on behaviour

Richard Depue (1996)
Using personality tests, Depue found that how reactive someone is to dopamine highly correlates with high scores on positive emotionality. People who responded easily to the drug Ritalin and showed an increase in spontaneous eye blinks had a more active dopamine system in general and, Depue suspects, feel happier than others in response to incentives.

Schacter and Singer (1962)

Conducted research on the effect of the hormone adrenaline. 184 males were injected with adrenaline but were told it was Suproxin. There were two conditions, within both some of the participants were not told the affects of what they had been injected with and were asked to perform tasks (playing games or being asked questions - with confederates). Those who had no reason for any heightened emotion showed higher changes of emotion overall. Researchers concluded that emotion occurs by a process of cognitive labelling: the interpretation of physiological cues is combined with contextual cues to construct a person's subjective experience of emotion and therefore horomones can affect human emotions.

ocd

Abnormal levels of neurotransmitters:

High dopamine levels are thought to be associated with OCD

Based on animal studies – Szechtman et al (1998) found increasing levels of dopamine induced movements typically associated with OCD.

Low levels of serotonin are also associated with OCD.

Antidepressant drugs which increase serotonin levels found to reduce OCD symptoms – Pigott et al (1990)

ocd

Abnormal brain circuits (The Worry Circuit):

The Orbitofrontal cortex (OFC) sends ‘worry’ signals to the thalamus.
These are normally suppressed by the Caudate nucleus.
If the Caudate nucleus is damaged – the thalamus is alerted of these ‘worry’ signals, and confirms the worry to the OFC.

Creates a worry circuit which is found in people with OCD – i.e. germ phobic people.