Chemical Messengers
Chemical Messengers
Chemical messengers are biological molecules that transmit signals within and between cells. In psychology, the most relevant chemical messengers are neurotransmitters, which carry signals between neurons across synaptic gaps, and hormones, which are released into the bloodstream and affect distant organs and tissues. Both systems regulate a wide range of physiological and psychological states.
Neurotransmitters
Neurotransmitters are released from presynaptic terminals and bind to receptors on the postsynaptic neuron, either exciting or inhibiting it. Key neurotransmitters include:
- Serotonin: regulates mood, sleep, appetite, and social behaviour. Low serotonin activity has been associated with depression, anxiety, and impulsive aggression. SSRIs target this system.
- Dopamine: Central to the brain's reward system, motivation, and motor control. It plays a key role in addiction -- drugs such as cocaine and amphetamines produce massive dopamine releases in the nucleus accumbens, the brain's primary reward centre, reinforcing drug-seeking behaviour through the same mechanisms that normally reinforce adaptive behaviours.
- GABA (Gamma-Aminobutyric Acid): the main inhibitory neurotransmitter. Reduces neural excitability and plays a role in anxiety. Benzodiazepines (anti-anxiety medications) enhance GABA activity.
- Noradrenaline (norepinephrine): involved in the fight-or-flight response, attention, and arousal. Elevated noradrenaline is associated with panic disorders.
- Acetylcholine: plays a key role in learning, memory, and muscle activation. Alzheimer's disease is associated with a significant loss of acetylcholine-producing neurons.
Hormones
Hormones are released by glands of the endocrine system and travel through the bloodstream to target organs. Cortisol, released by the adrenal cortex in response to stress, is closely studied in health psychology. While short-term cortisol elevation aids the stress response by mobilising energy, chronic cortisol elevation has damaging effects on the hippocampus, immune system, and cardiovascular health. Testosterone, estrogen, and oxytocin are also studied for their roles in aggression, social bonding, and mood.
Evaluation
Understanding chemical messengers has produced effective treatments and valuable insights into the biological substrates of behaviour. However, chemical messenger systems are highly complex and interactive. A simple model of 'too much' or 'too little' of any single neurotransmitter rarely captures the full picture. Serotonin affects dozens of receptor subtypes across multiple brain systems, meaning that manipulating it pharmacologically has wide-ranging effects. Reductionist explanations focused on single chemicals risk obscuring the importance of neural circuits, environmental context, and individual variation.
Practice Question
Question 2.2 — Short Answer
Outline the role of two chemical messengers in regulating psychological states and explain why a reductionist account of their role is considered limited.
Command term — "Outline" + "Explain": Give brief, accurate descriptions of two neurotransmitters/hormones (1 mark each) and then provide a reason why reducing psychological states to these chemicals is considered an oversimplification (2 marks).