Stress

Stress can be defined as a response or reaction to particular events, situations, or stimuli that disrupt an existing state of balance or equilibrium. This disruption can manifest in various forms, including psychological and ecological, depending on the triggering factor.

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Notes

Psychological Stress: This occurs when an individual perceives a situation or event as threatening or demanding, triggering a series of physiological reactions, often termed the "fight or flight" response. Prolonged or chronic psychological stress can lead to a range of health problems.

Ecological Stress: In an ecological context, stress refers to the negative impact or strain that environmental changes or factors impose on an organism or an ecosystem, disrupting its balance and potentially causing significant changes or even extinction.

Stress, regardless of age, provokes a series of changes within the brain and the body, mainly revolving around the HPA (Hypothalamic-Pituitary-Adrenal) axis. The HPA access includes the following structures

1. Hypothalamus: The hypothalamus is a region of the brain responsible for the production of several releasing and inhibiting hormones, which control the release of hormones from the pituitary gland. One of these is corticotropin-releasing hormone (CRH), which initiates the stress response.
2. Pituitary gland: In response to CRH from the hypothalamus, the pituitary gland releases adrenocorticotropic hormone (ACTH). The pituitary is a pea-sized gland located at the base of the brain, and it plays a major role in regulating vital body functions and general wellbeing.
3. Adrenal glands: Upon receiving ACTH, the adrenal glands, located atop the kidneys, release cortisol, the body's main stress hormone. Cortisol prepares the body to respond to stressful situations by altering immune system responses and suppressing the digestive system, the reproductive system, and growth processes. This complex natural alarm system also communicates with regions of the brain that control mood, motivation, and fear.

The HPA access regulates many of the body's processes, including reactions to stress, mood and emotions, energy storage, and immune responses. Although stress can sometimes be beneficial, for instance, as a motivator to overcome challenges, chronic or ongoing stress can have detrimental effects. These effects vary based on the severity of stress (low, moderate, high) and the developmental stage (childhood, adolescence, adulthood).

Hindbrain

1. Medulla Oblongata: The medulla oblongata sits at the base of the brain, directly connected to the spinal cord. It is responsible for managing several physiological functions including heart rate (how quickly or slowly the heart beats), blood pressure, and respiration. When a person is startled or scared, it's the medulla oblongata that triggers the heart to beat faster. The medulla also oversees functions such as swallowing (for example, when a person swallows food), vomiting (like when someone is ill), and sneezing (as a response to an irritant in the nose).
2. Pons: Located above the medulla oblongata and below the midbrain, the pons acts as a message station between various areas of the brain, particularly between the cerebral cortex and the cerebellum. It also helps control functions like sleep (for instance, it aids in transitioning between sleep and wakefulness), respiration (it helps regulate the pace of breathing), and bladder control. It is also involved in auditory processes (like hearing a song), maintaining equilibrium (like keeping balance while walking on a narrow path), taste, eye movement, facial expressions, and posture.
3. Cerebellum: Positioned behind the brainstem, the cerebellum plays a key role in functions related to movement and motor skills. These include coordination, precision (like when painting a delicate picture), and timing (as required when playing a musical instrument). The cerebellum is also crucial in motor learning (like learning to ride a bike). More recent research suggests that the cerebellum may also be involved in certain cognitive processes, such as focusing attention, language abilities (like when learning a new language), understanding music, and processing other sensory temporal information.

Reticular Formation

The reticular formation is a complex network of interconnected neurons that are spread throughout the brainstem, reaching from the medulla to the midbrain, passing through the pons. It plays a key role in maintaining behavioral arousal and consciousness, making it essential for the regulation of the sleep-wake cycle. Key functions include:

1. Arousal and Sleep-Wake Transitions: The reticular formation contains the reticular activating system (RAS), which plays a crucial role in maintaining alertness and consciousness. It receives input from multiple sources and projects it to widespread areas in the cortex. Activation of the RAS results in arousal, enhancing wakefulness and attention. On the other hand, inhibition of the RAS promotes sleep.
2. Motor Control: The reticular formation also plays a role in motor control, specifically in maintaining muscle tone and controlling voluntary movements. It contributes to the balance and posture by integrating sensory and motor pathways.
3. Pain Modulation: The reticular formation is part of the neural circuitry that modulates the transmission of pain signals to the cerebral cortex, affecting the perception of pain.
4. Cardiac and Respiratory Control: Through its connections to the medulla, the reticular formation plays a role in autonomic control, helping regulate functions such as heart rate and respiration.
5. Habituation: This is a process in which the brain learns to ignore repetitive, meaningless stimuli while remaining sensitive to others. The reticular formation plays a significant role in this ability to selectively ignore certain inputs.

When the reticular formation is exposed to chronic stress, several behavioral, psychological, and emotional changes can occur.

Behavioral Changes: Prolonged stress can disrupt the normal functioning of the reticular formation, leading to alterations in sleep patterns. People may experience insomnia, difficulties falling asleep, or interrupted sleep. This can lead to daytime fatigue and decreased performance in daily tasks. In a study by Meerlo et al. (2008), chronic stress was found to induce changes in sleep patterns, particularly a reduction in rapid eye movement (REM) sleep, which is believed to be crucial for emotional regulation and memory consolidation.

Psychological Changes: The reticular formation's role in mediating overall arousal can be affected by chronic stress. People may experience heightened arousal and hypervigilance, which can manifest as an increased startle response, restlessness, and difficulties in concentrating. Chronic stress can also lead to an increase in the filtering of sensory stimuli, resulting in reduced sensory perception and potentially leading to feelings of disconnection or dissociation (Maren & Holmes, 2016).

Emotional Changes: Changes in sleep and arousal can have significant effects on emotional wellbeing. Insufficient or poor-quality sleep can exacerbate feelings of stress, anxiety, and depression (Goldstein & Walker, 2014). Likewise, the heightened arousal and hypervigilance associated with chronic stress can contribute to feelings of anxiety and tension.

It's important to note that the effects of chronic stress can vary widely among individuals, influenced by factors such as genetics, environment, and lifestyle. Also, the precise mechanisms through which chronic stress affects the reticular formation and other parts of the brain are complex and not fully understood.