introduction
Stress, stressor, stress response… these are terms we often use interchangeably in our everyday lives. To understand a little more precisely what is going on in our bodies, let’s start with a little clarification.
stress – the body’s nonspecific response to any demand placed upon it (Selye, 1936).
This means that regardless of whether we are experiencing a physical stimulus (e.g. strenuous exercise) or an emotional stimulus (e.g. conflict with a partner), our body reacts in a similar way. These stimuli were later described by Selye as stressors.
stressor – any environmental stimulus capable of triggering a stress response.
A stressor can be a sports competition, a singing exam, a strict teacher’s opinion, a bad grade, a stomach ache, the presence of someone important to us in the audience, an unpleasant smell in the classroom, noise or inappropriate temperature.
stress response – the natural (physiological) reaction of the human body to stressors.
Selye (1976) also drew attention to the existence of so-called positive stress, which the researcher called eustress, and the phenomenon we know today as chronic stress.
This article will focus mainly on the stress response, i.e. the physiological reaction of the body. We will look at how the different structures of the brain behave after a stressor and how these reaction chains interact. To do this, we will first need some biology.
the nervous system
The human nervous system can be divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and the spinal cord.
The peripheral nervous system consists of a network of nerve cells and fibres that help the brain and spinal cord communicate with the rest of the body. It can be divided into two main parts: the somatic nervous system and the autonomic nervous system.
The somatic nervous system is responsible for voluntary movements (such as running or playing the piano).
The autonomic nervous system controls automatic functions such as breathing, heartbeat and digestion. The autonomic nervous system can be further divided into two groups:
The sympathetic nervous system (SNS) increases heart rate and blood pressure, preparing organs for the fight or flight response.
The parasympathetic nervous system (PNS), on the other hand, slows down the heartbeat and breathing and stimulates digestion, helping the body to relax.
the brain
The brain is the most important part of the central nervous system. The following parts are key to stress response:
The limbic system, located in the central, innermost part of the brain, plays a crucial role in instinctive behaviour and memorisation. Within it, a structure called the amygdala is primarily responsible for emotions, especially fear, anxiety and aggression. In contrast, the hippocampus plays an important role in the long-term storage of information and events.
The hypothalamus, located next to the limbic system, is responsible for both the autonomic nervous system and the endocrine system. Its nerve connections lead, among other organs, to the pituitary gland, which produces and releases a number of hormones.
The anterior part of the cerebral cortex, called the prefrontal cortex, plays an important role in thinking, decision making and emotion regulation.
stress response
When we sense a potential stressor, the amygdala kicks in and immediately sends an alarm signal to the hypothalamus.
The hypothalamus is a control centre: from there, further commands are sent to other systems.
Within one second, the autonomic nervous system triggers the release of adrenaline by nerve cells along the spine.
Certain organs are key in times of stress. There, adrenaline causes vasodilatation, resulting in a faster heartbeat, faster blood flow to the leg muscles and dilated pupils.
In the digestive or reproductive system, the effect of adrenaline is the opposite: blood vessels constrict and functions that could waste energy in a threatening situation slow down or stop.
After the fight or flight response has subsided, the hypothalamus triggers the so-called HPA (hypothalamic-pituitary-adrenal) axis.
Two seconds after the stressor is detected, the hypothalamus starts to release a hormone called corticoliberin. This triggers the production of corticotropin in the pituitary gland within ten seconds.
Approximately 30 seconds after the stressor is recorded, corticotropin releases cortisol in the adrenal glands.
The fast response of the autonomic nervous system and the slower, longer-lasting action of the HPA axis complement each other – the cortisol keeps the body on high alert. When the stressor passes, cortisol levels drop. The parasympathetic nervous system begins to blunt the stress response.
the effect of stress
It is important to distinguish between intense, short-term and chronic stress, as their effects on the body and brain structures are often different.
The effects of short-term, intense stress are beneficial: the adrenaline released stimulates the immune system, prepares the body for increased exertion(e.g. escape) and sharpens cognitive abilities (narrowing focus, increasing analytical and decision-making speed). Arousal levels rise.
The limbic system is particularly sensitive to the effects of cortisol. In its resting state, the amygdala is responsible for emotions, especially anxiety, while the hippocampus is responsible for memorisation. Under intense stress, these organs become interconnected. Under short-term stress, cortisol causes blood vessels to dilate and new neural connections to form, leading to more effective learning and memory, especially for the storage of information in memory.
During chronic stress, this effect is reversed. Nerve connections in the hippocampus slow down or disappear. This can mean difficulties with memory and learning. The amygdala works at an increased speed under prolonged stress, which can even physically overload the organ (as in post-traumatic stress disorder). The stress response becomes more frequent, with more stimuli (or even without stimuli) and possibly with greater intensity. This is what we call anxiety.
The bodily processes associated with stress are natural and fundamentally beneficial. Just because your hands sweat or your heart beats faster doesn’t necessarily mean you won’t perform well. If these symptoms reach a disturbing level, you may want to work on arousal-regulation techniques such as breathing techniques or autogenic training.
források
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Barlow, D. H. (2000). Unraveling the mysteries of anxiety and its disorders from the perspective of emotion theory. American Psychologist, 55(11), 1247–1263. https://doi.org/10.1037/0003-066X.55.11.1247
Selye, H. (1936). A Syndrome produced by Diverse Nocuous Agents. Nature, 138(3479), 32–32. https://doi.org/10.1038/138032a0
Selye, H. (1976). Stress in Health and Disease. Elsevier. https://doi.org/10.1016/C2013-0-06263-9
Spielberger, C. D. (1985). Anxiety, cognition and affect: A state-trait perspective. Anxiety and the anxiety disorders. Lawrence Erlbaum Associates, Inc.
Tafet, G. E. (2022). Neuroscience of Stress: From Neurobiology to Cognitive, Emotional and Behavioral Sciences. W Neuroscience of Stress: From Neurobiology to Cognitive, Emotional and Behavioral Sciences. Springer International Publishing. https://doi.org/10.1007/978-3-031-00864-1