MPBD summary psychiatric disorders

What does the term plasticity mean?

Answer: Plasticity is the brain’s capacity to adapt or to change over time by creating new neurons and building new networks.

What does the term heritability mean?

Answer: This is the proportion of variance in symptoms that are explained by the variance in genetic factors (twin studies).

What does the classic theory entail?

Answer: This theory states that a single abnormal gene leads to an abnormal gene product, which leads to neuronal malfunction and mental illness.

What is the stress-diathesis model?

Answer: This model is based on the fact that predisposition of genes + environmental stress can lead to disease. The hypothesis states: mental conditions are caused by multiple small contributions from several genes, all interacting with environmental stressors. A complex set of risk factors can bias a person towards mental illness, but does not cause them. You can inherit the risk but not the disease itself.

What does the term endophenotype mean?

Answer: These are variables that could measure the link between the genotype and the phenotype/inheritance and disease.

What are the two types of endophenotypes?

Answer: 1) Biological endophenotype 2) Symptom/system endophenotype

What is a biological endophenotype?

Answer: These are closer to the genotype and measure biological phenomena such as electrophysiological responses, neuroimaging, etc. Exaple: depression is linked to an overative amygdala.

What are symptom/system endophenotypes?

Answer: These are closer to the phenotype side and are associated with symptoms in certain conditions. Exaple: insomnia, executive dysfunction, anhedonia.

How does the stress system work?

Answer: There are two pathways, the fast- and the slow-acting pathway. The fast acting pathway works via the hypothalamus that sends a message through the spinal cord, which activates the sympathetic nervous system. This stimulates the medulla of the adrenal gland, which releases (nor)epinephrine into the circulatory system. Long-term stress actives the slow-acting pathway. This pathway starts with the release of corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) by the hypothalamus. This in turn triggers the release of ACTH from the pituitary gland that leads to the production of cortisol by the adrenal cortex (HPA-axis).

How can the HPA stress system be shut down?

Answer: This happens when cortisol itself binds to glucocorticoid receptors (GR) in the brain, which shuts the system down by a negative feedback loop. Cortisol does this by altering gene expression/transcription.