Stress Response: Selye & Nervous System

• The stress-response is initiated by both physical and psychological stressors

Hans Selye's Discovery

• Hans Selye, a pioneer in stress physiology, identified the stress-response
• Selye's experiment with ovarian extract injections on rats led to the discovery
• Rats, when subjected to frequent injections, developed peptic ulcers, enlarged adrenal glands, and shrunken immune tissues
• Both the control group (saline injections) and the experimental group showed same symptoms
• Selye concluded these symptoms were a non-specific response to unpleasantness

Voluntary vs Autonomic Nervous System

• The brain communicates with the body through nerves
• The voluntary nervous system controls conscious movements
• The autonomic nervous system controls involuntary functions like blushing or gooseflesh
• Biofeedback and potty training are examples of gaining conscious control over autonomic functions

Sympathetic Nervous System

• The autonomic nervous system is what controls reactions to stress
• The sympathetic nervous system activates during stress
• Triggers physiological responses in emergencies
• Sympathetic projections extend from the brain to organs, blood vessels, and sweat glands
• It mediates vigilance, arousal, activation, and mobilization, exemplified by either fight, flight, fright, or sex
• Adrenaline is released, causing effects like stomach clenching
• American terminology epinephrine and norepinephrine
• Epinephrine comes from the adrenal glands, and norepinephrinefrom sympathetic nerve endings

Parasympathetic Nervous System

• The parasympathetic system opposes sympathetic
• Controls activities like growth, energy storage, and rest
• The autonomic system balances sympathetic and parasympathetic functions
• Sympathetic speeds up the heart rate, while parasympathetic slows it down
• The sympathetic system diverts blood flow to muscles, while parasympathetic goes opposite
• Simultaneous activation of both systems is counterproductive
• The brain typically inhibits one branch when activating the other

Neural and Hormonal Responses to Stress

• The brain responds to stress through nerves and hormones
• Neurotransmitters are chemical messengers between neurons
• Bladders are unidirectional and don't aid in stressful emergencies
• Stressful emergencies requires the bladder to be emptied

Cardiovascular Responses During Stress

• During stress, blood volume and force increase, ensuring efficient delivery
• Vigilance requires a different response as opposed to running: heart rate and blood flow slow down, vascular resistance increases
• Stress responses vary depending on needs
• After stress, the parasympathetic nervous system slows down the heart via the vagus nerve
• Chronically high blood pressure is caused by the stress response turning off slowly
• High blood pressure creates ventricular hypertrophy, increasing cardiac risk
• Hypertension damages blood vessels, especially at bifurcation points
• The sympathetic nervous system increases blood viscosity during stress
• Damaged cardiovascular systems are sensitive to stressors
• Failure to deactivate the cardiovascular system increases the sympathetic nervous system activity
• Slow recovery after stress indicates the vagus nerve is not slowing the cardiovascular system
• Heart rate variability during breathing reflects parasympathetic tone
• Low variability indicates difficulty in deactivating the cardiovascular stress-response

Sudden Cardiac Death

• Chronic stress gradually damages the cardiovascular system
• Cardiac arrest often occurs during a stressor

Explore the stress response, initiated by physical and psychological stressors. Learn about Hans Selye's discovery of the stress-response through experiments with rats, and understand the roles of the voluntary and autonomic nervous systems in this response.