Stress Response and Allostasis

Stress Response

• The body initiates a stress response upon exposure to "stressors."
• Stress is a physiological and psychological experience when demands surpass coping abilities.
• The stress response includes the hypothalamic-pituitary-adrenal (HPA) axis, autonomic nervous system (ANS), and immune system (IS).
• The alarm stage involves secretion of hormones and catecholamines to prepare the body to fight or flee.
• The resistance stage mobilizes body resources like cortisol and adrenaline to cope with a sustained challenge.
• The exhaustion stage occurs when body resources are depleted, and the immune system can no longer cope, leading to psychosomatic, physical, and mental disorders.
• Allostasis is "stability through change," where the brain monitors parameters to anticipate HPA and ANS requirements.
• Allostatic overload is chronic overactivation of adaptive regulatory physiologic systems, potentially leading to pathophysiology and disease.
• The adrenal medulla releases significant amounts of epinephrine and small amounts of norepinephrine.
• Cortisol is released from the adrenal cortex and stimulated by adrenocorticotropic hormone (ACTH) from the anterior pituitary.

Neurotransmission

• Neurotransmitters released into the synaptic cleft bind with receptors, acting as excitatory, inhibitory, or modulatory signals.
• Neurotransmitters are removed from the synaptic cleft via diffusion, enzymatic digestion, or reuptake.
• The noradrenergic system (mood, arousal), serotonergic system (sleep-wake cycle, emotional tone), and dopaminergic system (excitatory neurotransmitter, precursor to norepinephrine) are key neurotransmitter systems involved in mental health

Neural Plasticity

• Neurons can form new connections or strengthen existing ones during learning and memory.
• New neurons can be produced in areas like the hippocampus.
• Neurons can adapt to lost functions and reroute functions in case of brain injury.

Mental Illness

• Mental illnesses involve alterations in thinking, mood, or behavior, causing significant distress and impaired functioning.
• Pathogenesis can involve excessive excitatory neurotransmitters, increased sensitivity of excitatory receptors, insufficient inhibitory neurotransmitters, or decreased sensitivity of inhibitory receptors.
• 10-20% of Canadian youth experience mental illness or disorder.

Mood Disorders

• Mood disorders are defined by a sustained emotional state.

Depressive Disorders

• Depressive disorders involve prominent and uncontrollable emotional states, such as sadness.
• The monoamine hypothesis suggests major depression results from decreased norepinephrine, serotonin, and/or dopamine levels.
• Major depression patients may exhibit altered serotonin receptor expression, changes in cerebral blood flow, and elevated cortisol levels.
• The hypothalamic-pituitary-adrenal (HPA) system is overactivated.

Bipolar Disorders

• Bipolar disorders involve variable depression and mania.
• Manic episodes may result from elevated norepinephrine, dopamine, and/or serotonin levels.
• Increased ventricular volume and reduced prefrontal cortex volume can be observed.
• Clinical depression is characterized by persistent sadness and loss of interest, changes in appetite, fatigue, and difficulty concentrating.
• Bipolar I disorder features major depression periods followed by mania, which includes grandiosity, increased energy, rapid speech, racing thoughts, poor judgment, and sometimes delusions or hallucinations.

Anxiety Disorders

• Anxiety can arise secondary to drug reactions or physical illness.
• Panic disorder may be linked to a more sensitive autonomic nervous system and reduced benzodiazepine receptors.
• Generalized anxiety disorder may have genetic components.
• Obsessive-compulsive disorder (OCD) might involve abnormal communication between the basal ganglia and prefrontal cortex, increased activity in the prefrontal cortex, and decreased serotonin synthesis.
• Social anxiety disorder (SAD) involves increased activity in limbic and frontal cortical areas with abnormal connections between the prefrontal cortex and amygdala, along with a possible reduction in the serotonin 5-HT1A-binding protein.
• Fear is the emotional response to a real or perceived threat and is associated with autonomic activity.
• The limbic system regulates autonomic and endocrine functions and sets arousal levels.
• Dysregulation of the HPA axis and ANS contributes to anxiety disorders.

Thought Disorders: Schizophrenia

• Schizophrenia is characterized by disorganized thoughts, hallucinations, delusions, and cognitive defects.
• Negative symptoms are characterized by the absence of expected behaviors, such as affective flattening, anhedonia, alogia, and avolition, and are associated with decreased activity in the dorsolateral prefrontal cortex.
• Schizophrenia involves neurodevelopmental defects during fetal life, including neuroanatomic alterations like enlargement of the lateral and third ventricles and loss of cortical gray matter.
• Neurotransmitter alterations include decreased GABA production in the dorsolateral prefrontal cortex, resulting in impaired synaptic performance and decreased activity in the area.
• The dopamine hypothesis suggests altered brain dopamine pathways, with reduced dopaminergic neurotransmission in the mesocortical pathway and hyperdopaminergic secretion in the mesolimbic regions.
• The mesolimbic system, with dopaminergic neurons innervating the nucleus accumbens, hippocampus, and amygdala, is involved in memory and motivating behaviors.

Habituation and Addiction

• Drugs of abuse activate brain reward pathways, increasing dopamine in the synaptic cleft.
• High dopamine promotes dopamine receptor desensitization.

Feeding and Eating Disorders

• Eating disorders involve aberrant eating behavior and weight regulation, disturbed attitudes about body weight and shape, and resistance to treatment.
• Anorexia nervosa is defined by weight loss resulting in body weights