Now study this diagram showing how the body responds to stressful stimuli. Notice that short-term stress follows one signaling pathway that begins in the brain, travels out the spinal cord, and directly to the adrenal glands. Many organs of the body will receive direct stress response messages using this pathway as well. When the adrenal glands receive the signal from this pathway, they release a stress hormone that signals many systems in the body to prepare to either run away from the stressor (such as a predator or an oncoming vehicle, for example), or fight. The part of the nervous system that activates this response to acute stress is called the sympathetic nervous system. After the stressful stimulus has passed, the parasympathetic (nicknamed the “rest and digest” response) calms the nervous system and restores the normal function of the body systems, maintaining homeostasis.
The Sympathetic vs. Parasympathetic Nervous Systems
These two divisions of the nervous system counteract each other to allow the body to receive the resources it needs to respond to a life-threatening situation (more glucose to the brain to enhance thinking ability, more oxygen and sugars to the muscles to run, etc.), and then return to a relaxed state. As you saw in the diagram, the sympathetic response begins when a stressful situation is detected by your sensory nerves, which make up the peripheral nervous system, or PNS. The sensory nerve endings can deliver this message directly to the brain through cranial nerves, which gather the information we need to give us the senses of smell, sight, hearing, and taste. Stress stimuli can also be detected by peripheral nerve endings throughout the body and delivered to the brain via the spinal cord. The brain and the spinal cord make up the central nervous system, or CNS.
View this diagram to review the anatomy of the sympathetic and parasympathetic nervous systems.
Notice that the “rest and digest” (parasympathetic) message is delivered through cranial nerves that originate in the brain stem, and sacral nerves that originate in the sacrum at the end of the spinal cord. The “fight or flight” (sympathetic) response originates from the spinal cord. These nerve impulses are delivered by the CNS to the effector organs responsible for reacting to the situation by either simulating the organ to take action, or calming (inhibiting) the organ to return homeostasis. In this situation, the nervous system sends a signal to the endocrine system to handle acute, or short-term stress.
When the body is faced with long-term, or chronic stress, the endocrine system predominantly responds by releasing hormones such as cortisol. You will learn more about cortisol in the next module.
Read Understanding the Stress Response in Harvard Health Publications, published by the Harvard Medical School.
From your reading address the following:
- Define acute and chronic stress. Provide examples.
- What region of the brain detects stress and interprets the stimulus as dangerous? What is its function, and where does it relay the signal that conveys the danger? What format is the signal in? What is the role of the region of the brain that receives the stress alert?
- What is a hormone? What hormones are involved in the stress response? When are hormones released in the stress response?
- What is the HPA and what role does it play in the stress response?
- What recommendations are given to counter stress?
Expert Solution Preview
Stress is a natural physiological response of the body that can be triggered by a variety of stimuli. In this assignment, we will explore the concepts of acute and chronic stress, the brain’s response to stress, and the role of hormones in the stress response. We will also discuss the HPA axis and recommended strategies to combat stress.
1. Define acute and chronic stress. Provide examples.
Acute stress is a short-term physiological response of the body to a perceived threat or challenge. Examples include being in a car accident, preparing for an important presentation, or encountering a dangerous animal. Chronic stress, on the other hand, is a prolonged and ongoing response to stressors that can have negative effects on physical and mental health. Examples include financial difficulties, ongoing relationship problems, or a high-pressure work environment.
2. What region of the brain detects stress and interprets the stimulus as dangerous? What is its function, and where does it relay the signal that conveys the danger? What format is the signal in? What is the role of the region of the brain that receives the stress alert?
The amygdala is the region of the brain that detects stress and interprets the stimulus as dangerous. Its function is to prepare the body for a fight-or-flight response. The amygdala then relays the danger signal to the hypothalamus through neural pathways in the brainstem in the form of electrical impulses. The role of the hypothalamus is to activate the HPA axis and trigger the release of stress hormones.
3. What is a hormone? What hormones are involved in the stress response? When are hormones released in the stress response?
A hormone is a chemical messenger that travels through the bloodstream to various organs and tissues to regulate physiological functions. Hormones involved in the stress response include adrenaline, noradrenaline, and cortisol. Adrenaline and noradrenaline are released during the acute stress response, while cortisol is released during the prolonged stress response.
4. What is the HPA and what role does it play in the stress response?
The HPA (hypothalamic-pituitary-adrenal) axis is a complex feedback system that regulates the release of cortisol in response to stress. The hypothalamus activates the HPA axis by releasing corticotropin-releasing hormone (CRH), which then triggers the release of adrenocorticotropic hormone (ACTH) from the pituitary gland. ACTH stimulates the adrenal glands to release cortisol, which prepares the body for the stress response.
5. What recommendations are given to counter stress?
There are several strategies to counter stress, including practicing relaxation techniques such as deep breathing, yoga, and meditation, engaging in regular physical activity, maintaining social connections with family and friends, getting adequate sleep, and seeking professional help if necessary. It is also important to maintain a healthy diet and prioritize self-care activities such as reading, listening to music, or engaging in creative pursuits.
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