Which part of the brain holds muscle tone

How the brain and hormones control the stress response (2/4)

In the early evolutionary times from which the stress response originated, it was often about dangers to life and limb. Today other dangers are at the fore in many societies. For example, people experience stress when their self-worth is threatened, when they are afraid of failure, or when they are separated from other important people. Or sometimes quite simply, when something doesn't go the way you want it to. But no matter what the cause, the stress response still follows the same old pattern - even if you just imagine the stressful situation.

Then different regions of our brain become active. As with a good team, these regions work together to make us fit for fight or flight. Some parts of the brain are more "responsible" for emotional processing, others for planning and thinking. Still others ensure that the processes are set in motion that are necessary for the stress hormones to be released. And before that, other parts of the brain analyzed the sensory stimuli and passed the information on.


The brain is the organ that decides which experiences are stressful.
Bruce McEwen, Neuroscientist, Rockefeller University, New York

Amygdala - "fear center" of the brain

A very important brain region for our experience of stress and anxiety is the amygdala, a small, almond-shaped complex of nerve cells in the lower part of the brain. It is part of the so-called limbic system. This is a combination of different brain structures inside the brain that play a major role in the processing of emotions.

The amygdala controls - together with other brain regions - our psychological and physical reactions to stress- and fear-inducing situations. If she receives signals that require greater attention, for example when something is new or dangerous, her nerve cells fire. We become more alert and more attentive. This happens even before we consciously recognize the danger. Above a certain threshold of nerve activity, the amygdala sets the stress response in motion and thus activates the fight and flight response.

Two ways of responding to stress

The amygdala uses two routes to trigger the fight and flight response. The faster way is via the so-called sympathetic nervous system, which prepares the body for activity. The route via the hypothalamus is a little slower. The hypothalamus is a complex structure in the diencephalon that controls the basic functions of our body. He sets a whole cascade of hormones in motion for the stress reaction.

The quick way: the sympathetic nervous system

The information "danger" reaches the marrow of the adrenal gland via the nerve cords of the sympathetic nervous system in the spinal cord. There adrenaline and - to a lesser extent - noradrenaline are released. These hormones are also called catecholamines. For example, they increase the heartbeat and blood pressure, make the muscles more tense and cause more blood sugar to be released so that the muscle cells can be better supplied.

The "slow" route via the hypothalamus

At the same time, the amygdala informs the hypothalamus that danger is imminent. The hypothalamus releases hormonal messenger substances, including the corticotropin-releasing hormone. This hormone acts on the pituitary gland in the brain - also called the pituitary gland. It ensures that they release another hormone, adrenocorticotropin, or ACTH for short. It reaches the cortex of the adrenal gland in the blood and causes it to release the stress hormone cortisol. Cortisol is a vital glucocorticoid that has many other functions in the body as well. However, if it is in excess, it can also damage the body.

Together, the hormones and the sympathetic nervous system ensure that our body gets more oxygen and energy to act quickly. Some other hormones, messenger substances and the body's own proteins, the so-called cytokines, are also involved in the stress response.

What the hormones do

  • The breath accelerates
  • Heart rate and blood pressure rise
  • The liver produces more blood sugar
  • The spleen flushes out more red blood cells, which carry oxygen to the muscles
  • The veins in the muscles widen. This means that the muscles are better supplied with blood
  • The muscle tone increases. This often leads to tension. Trembling, rocking of the feet and gnashing of teeth are also related to it
  • The blood coagulates faster. This protects the body against blood loss
  • The cells produce messenger substances that are important for the immune system
  • Digestion and sexual functions decline. That saves energy

Stress and memory

The amygdala not only sets the stress response in motion. It also causes an important memory region in the brain, the nearby hippocampus, to remember the stress-inducing situation. In this way we learn to be wary of the stressor. If we get into such a situation again, the stress reaction runs even faster.

Research has shown that chronic stress can damage the cell processes in the hippocampus. They are part of the nerve cell and important for the reception of information. If they shrink, it has a negative effect on memory.

Thinking and stress

The amygdala is also closely connected with the "thinking" part of the brain, especially with a phylogenetically younger part of our brain, the frontal lobe. It is important for controlling emotions. As the name suggests, it sits behind the forehead. It is also called the prefrontal cortex. With its help, we can influence our emotions through logical analysis and thinking. It plays a big role in assessing whether we consider a stressor manageable or not, and in our behavior in the stressful situation. Chronic stress, however, can alter the prefrontal cortex, making it harder to make meaningful decisions.

Built-in stress brake

Fortunately, we usually cool down again after stress. A built-in stress brake helps. If the stress hormone cortisol is present in sufficient quantities in the blood, this is noticed by certain receptors in the glandular system and in the brain, the glucocorticoid receptors. The adrenal cortex then stops producing more cortisol. The parasympathetic nervous system - the part of the nervous system that allows our body to rest - becomes active. We become calmer again and relax.

When hormones get out of hand

The situation is different if the interaction of the hormones does not work optimally. For example, when there aren't enough receptors that might sense that there is enough cortisol. Or when the existing receptors are not working properly. Then the axis of hypothalamus, pituitary gland and adrenal gland becomes too active. It produces too much cortisol.

In bad cases, this can lead to thought disorders, tissue atrophy in the brain and disorders of the immune system. The development of depression is also attributed to this influence, as well as metabolic disorders that promote diabetes.

Early traumatic experiences influence the stress response

Intense stress in early childhood can affect the functioning of genes involved in the stress response in such a way that stress hormones are released faster and more intensely. Neuroscientists from the Max Planck Institute for Psychiatry in Munich have demonstrated this on animals. This effect lasts for life. Under certain genetic conditions, similar results appear to be found in people who have experienced trauma, for example from a natural disaster, from abuse or from violence. The scientists believe that such people are particularly susceptible to stress throughout their lives and, as a result, to depression and anxiety disorders.