Health Psychology Stress & Stressors (Part III)

The Physiology of Stress

Introduction to Stress Physiology

  • Walter Cannon: Introduced the concept of the Fight-or-Flight Reaction.

    • Describes an outpouring of hormones (epinephrine, cortisol) that prepare an organism to defend against threats.

    • This response was adaptive for our ancestors.

    • In modern times, may lead to stress-related illnesses.

  • Robert Sapolsky: Highlighted that humans and other primates experience more stress-related diseases than other animals.

Role of the Brain and Nervous System

  • The body's overall reaction to stress is regulated by the central nervous system.

The Brain

  1. Brainstem

    • The oldest part of the brain, located at the base where the spinal cord enters the skull.

    • Responsible for automatic survival functions.

      • Medulla:

        • Base of the brainstem, controls heartbeat and breathing.

      • Pons:

        • Thick stalks linked to the cerebellum, regulating sleep, breathing, swallowing, bladder control, and other functions.

      • Reticular Formation:

        • A nerve network within the brainstem, vital for controlling arousal and alertness.

  2. Thalamus

    • Acts as the brain's sensory switchboard, located atop the brainstem.

    • Directs sensory messages to the cerebral cortex's sensory receiving areas.

  3. Cerebellum (little brain)

    • Located at the rear of the brain.

    • Coordinates voluntary movement and balance, possibly contributing to specialized brain regions.

The Limbic System

  • Comprises neural structures bordering the brainstem and cerebral hemispheres, associated with emotions (aggression, fear) and drives (food, sex).

    • Hippocampus:

      • Linked to memory within the limbic system.

    • Amygdala:

      • Neural clusters linked to emotion.

    • Hypothalamus:

      • Located below the thalamus, directs maintenance activities (eating, drinking, body temperature) and governs the endocrine system via the pituitary gland.

The Cerebral Cortex

  • Composed of interconnected neural cells covering the cerebral hemispheres; serves as the body's ultimate control and information-processing center.

Regions of the Cerebral Cortex

  • Frontal Lobes:

    • Located just behind the forehead; involved in muscle movements, planning, and judgments.

  • Parietal Lobes:

    • Located in the center of the cortex; includes the sensory cortex which receives information from the skin and body.

  • Occipital Lobes:

    • Located at the back of the cortex; contains visual areas receiving input from the opposite visual field.

  • Temporal Lobes:

    • Located behind the ears; includes auditory areas.

The Process of Stress Response

  • External event triggers a reaction through:

    • Sensory organs

    • Reticular formation: activates alertness.

    • Thalamus: sorts information.

    • Hypothalamus: initiates responses.

    • Cerebral Cortex: interprets meaning.

    • Results in organ, muscle, and gland responses mediated by the Sympathetic Nervous System (SNS) to prepare for defensive action.

The Endocrine System

  • Comprises glands secreting hormones regulating bodily functions.

  • Hormones are chemical messengers released into the bloodstream affecting distant organs.

Glands of the Endocrine System

  1. Adrenal Glands:

    • Located above the kidneys.

    • Secrete epinephrine (adrenaline), norepinephrine (noradrenaline), and cortisol which arouse the body during stress.

  2. Pituitary Gland:

    • Regulated by the hypothalamus, controls growth and other endocrine glands.

  3. Thyroid Gland:

    • Regulates growth and metabolism.

    • Hormones secreted help maintain calcium levels in the body.

  4. The Pancreas:

    • Secretes glucagon (increases blood glucose) and insulin (controls sugar and carbohydrates energy conversion).

The Role of the Endocrine System in Stress

  • Sympatho-Adreno-Medullary (SAM) Axis:

    • The body’s initial, rapid response to stress through SNS and adrenal medulla interaction.

    • Involves immediate release of epinephrine and norepinephrine, responsible for the fight-or-flight response (Carlton et al., 2021).

  • Hypothalamic-Pituitary-Adrenocortical (HPA) Axis:

    • Represents the body's delayed response to stress through secretion of corticosteroid hormones from the adrenal cortex.

    • Corticotropin-Releasing Hormone (CRH):

    • Stimulates the production of Adrenocorticotropic Hormone (ACTH) by the pituitary gland, activating the adrenal cortex to secrete corticosteroids.

Sex Differences in Stress Response

  • Women:

    • Experience lower and more variable HPA and autonomic nervous system reactions to stress from puberty to menopause.

    • More likely to engage in tend-and-befriend responses during stress.

  • Men:

    • Exhibit greater increases in cortisol and HPA reactivity when faced with psychological stress.