Nervous system ↗Context is appraised
Sensory input, memory, expectation, body state, controllability, and social context influence whether and how strongly response networks engage.
BRAIN & NERVES / 04
Mobilize first.
Then regulate.
Stress biology is a coordinated response to challenge, not simply “too much cortisol.” Neural appraisal, autonomic output, adrenal catecholamines, the HPA axis, behavior, immune signals, and feedback act on different clocks.
Sympathetic patterns emerge
Hypothalamic and brainstem circuits change organ-specific sympathetic and parasympathetic output rather than issuing one uniform command.
Catecholamines extend the signal
Adrenal-medulla epinephrine and norepinephrine amplify cardiovascular, respiratory, metabolic, and attentional changes.
Fuel and flow reprioritize
Cardiac output, vascular tone, liver glucose output, adipose fuel release, airway state, and digestion can shift according to the challenge.
Hypothalamus releases CRH
Paraventricular hypothalamic neurons release corticotropin-releasing hormone into pituitary portal blood, with vasopressin as a context-dependent partner.
Pituitary releases ACTH
Anterior-pituitary corticotrophs respond by secreting adrenocorticotropic hormone into systemic circulation.
Adrenal cortex makes cortisol
ACTH stimulates glucocorticoid synthesis. Cortisol influences metabolism, cardiovascular responsiveness, immune signaling, cognition, and gene regulation.
Rhythms shape the concentration
Cortisol is secreted in pulses atop a circadian rhythm, so clock time, sleep, sampling method, medicines, illness, and the stressor matter.
Negative feedback engages
Glucocorticoid signaling at pituitary, hypothalamic, and other brain sites restrains further HPA output; feedback timing is distributed.
Safety cues update networks
Changed context, controllability, action completion, social signals, breathing, posture, and cognition can modify autonomic and behavioral state.
Organs restore context
Fuel handling, digestion, blood flow, temperature, immune activity, attention, and sleep pressure settle on different schedules.
Repeated stress changes regulation
Baseline, reactivity, recovery, sleep, behavior, and tissue exposure may adapt differently; chronic stress does not require persistently high cortisol.