4/16/15 – Lecture 23 – the Psychoneuroendocrinology of Stress- Goal – to define stress and understand how it affects the brain and the body- Stress – a stimulus that challenges the body’s homeostasis and triggers arousal (can be physical or psychological)o Physical Stressors Threat from predators Exposure to extreme heat or cold Lack of sleep Injury, chronic pain, chronic disease Strenuous exercises Starvation or dehydrationo Acute Psychological Stressors Taking/failing an exam Job interview Work deadlines Losing a job Minor car accident Stuck in traffic Asked to speak in front of a group Arguments with significant other Pregnancyo Chronic Psychological Stressors Caring for an ailing parent or spouse Poverty or persistent financial worries High pressure job Being bullied Daily commutingo Extreme Psychological Stressors Being in a natural disaster Being in war in any way Sexual/physical abuseo KEY POINTS about stress Stress is not always bad!- It produces adaptive changes that help an animal or person respond to the current stressor and to future stressors Chronic/sever stress, however, often produces maladaptive changes to the brain and body Whether a particular stimulus is stressful or not depends upon a person’s interpretation of the stimulus, their coping abilities, and their support system- Neuroendocrine Response to Stresso Sympathetic Nervous System – the “rapid” neural response that increases bodily arousalo The Locus Coeruleus – part of the reticular activating system, neural response that increases cognitive arousalo The hypothalamic/pituitary/adrenal (HPA) axis – more long-term hormonal response Neuroendocrine responses to stress start in the emotional circuit of the brain How does the Hypothalamus Sense Stress- Sensory information is received from the outside world (the smell of smoke, the sight of a bear, the roar of a mountain lion)- This information is sent to the amygdala and to the PFC and the CC which also provide feedback to the amygdala- Amygdala neurons send their axons to the hypothalamus- The hypothalamus the activates the locus coeruleus (LC), SNS, and the HPA pathways that produce a physiological stress response The Sympathetic Nervous System- Stress it perceived by the hypothalamus- Hypothalamic neurons project to the spinal cord where neurons of the autonomic nervous system are found- Sympathetic neurons are activated which produce effects throughout the body- Sympathetic nerves also stimulate the adrenal medulla, which release the stress hormone epinephrine and norepinephrine into the bloodo Effects of Sympathetic Activation Breathing rate increases Heart rate increases Blood vessels vasoconstrict to non-muscle areas like the gut Pupils dilate Mobilization of fats and sugars increase- Primarily concerned with allowing the organism to escape an immediate threat The HPA axis- Stress ie perceived by the hypothalamus- Hypothalamic neurons release corticotropin releasing hormone (CRH) onto endocrine cells of the anterior pituitary gland- Pituitary cells secrete the hormone adrenocorticotropic hormone (ACTH) into the blood stream- ACTH circulates into the adrenal glands and causes cells in the adrenal cortex to secrete cortisol- Cortisol enters the blood stream and has effects through out the bodyo Effects of the Acute HPA Axis Breakdown of muscle protein for amino acids Increased uptake of amino acids and gluconeogenesis inliver Breakdown of stored fats in adipose Suppression of immune system Suppression of bone and muscle growth Suppression of reproductive functions- Primarily concerned with mobilizing and conserving energy stores in order to battle a prolonged stress (like lack of food) The Locus Coeruleus- Cluster of neurons in the reticular activating system- LC neurons release norepinephrine (NE) on neurons throughout the forebrain when activated- NE release increases alertness and attention – important when dealing with potential threatso 6 Key factors modulating the magnitude of the stress response Novelty – a new stressor is often more stressful than an old one Lack of Predictability – stressor(s) are random and irregular are worse Perception of Things Worsening – if stress seems to be increasing rather than decreasing or remaining the same Lack of Control – can be the belief of control rather than the control itself Outlet for Frustration – exercise, catharsis, misplaced aggression Perception of Low Social Support – from family, spouse, friends, communityo Inactivating the HPA axis Cortisol binds to receptors on the hypothalamus and decreases their firing and release of CRF Cortisol binds to receptors on the pituitary and decreases its release of ACTH Cortisol binds to hippocampal neurons and increases their inhibitory firing to