Sympathomedullary Pathway

The sympathomedullary pathway (SAM) is the body’s response to acute stress (short-term stress).

The SAM responds rapidly to stressors, meaning a person can react quickly if they come under a threat. SAM was essential for our ancestors, who had to quickly respond in life-threatening situations such as coming across a lion.

Let us first define the sympathomedullary pathway stages to later on show evidence and evaluate it.

Let us first identify the sympathomedullary pathway stages before presenting and evaluating evidence.

What are the sympathomedullary pathway stages?

If a situation is stressful, the brain activates the fight or flight response via the SAM. Let’s have a look at a SAM pathway diagram, which shows the stages of this stress response:

SAM pathway diagram, Tyler Smith - StudySmarter Originals

1. The hypothalamus (part of the brain in charge of the stress response) activates if a situation is stressful.

2. The autonomic nervous system (regulates physiological processes such as heart rate, blood pressure, respiration, and digestion), which includes the sympathetic nervous system, is aroused, and heart rate and blood pressure increase.

3. The sympathetic nervous system signals the adrenal medulla (located inside the adrenal cortex, in the centre of an adrenal gland) to release adrenaline and noradrenaline.

Adrenaline effects: adrenaline boosts the supply of oxygen and sugar to help the body respond to the stressor quickly and stops non-emergency processes, such as digestion.

Noradrenaline effects: Noradrenaline raises physiological arousal, preparing the body for ‘fight or flight’.

4. Adrenaline and noradrenaline activate the fight or flight response. The fight or flight response is when you either stay and deal with a threat (fight) or run away (flight).

5. After the threat is over, the parasympathetic nervous system brings the body back into a balanced state.

Evidence for the sympathomedullary pathway

• Taylor et al. (2000) found that acute stress produces the fight or flight response in men, but the tend-to-befriend response in women.

  The tend-to-befriend response involves the protection of offspring (tend) and reaching out to the social network for help and support (befriend). This response occurs because women produce more oxytocin, a chemical that promotes relaxation and nurturing.

  Also, female stress responses that increased the survival of offspring were more likely to have been passed on through natural selection. It seems there are gender differences in the way people respond to acute stressors.

• Age also affects a person’s physiological response to stress. McCarty (1981) subjected rats of various ages to one minute of electric shocks to the feet (acute stressor). Before the electric shocks, their blood plasma levels of adrenaline and noradrenaline were the same. After the electric shocks, the older rats had lower levels of adrenaline and noradrenaline than the younger rats. This finding implies older animals have diminished responsiveness of the sympathomedullary pathway, which leads to reduced capacity to adjust to stressful situations.

• Horwatt et al. (1988) found that if animals are exposed to the same stressful stimulus every day for weeks, several adaptive changes occur in the SAM. If these animals are then exposed to a new stressful situation, they display an exaggerated response of the SAM, compared to animals without this conditioning. This finding suggests that acute stress responses develop differently according to previous stress experiences.

Evaluating sympathomedullary pathway

• It seems there are gender differences in the way people respond to acute stressors. Thus, the acute stress response is different for each person; we should not assume everyone will react in the same way physiologically. The fight-or-flight response may be a male-centric (focused or centred on men) viewpoint.

• Lots of research into the acute stress response has focused on animals. Humans are physiologically different; therefore, animal responses to acute stress and human responses are incomparable. Humans also have a cognitive element to their stress response.

• Lazarus (1999) argued that a physiological account alone could not explain how people respond to stressors. How we perceive the potential stressor (the demands of the stressor and our ability to cope with it) also determines our response.

• Speisman et al. (1964) provided evidence for this argument. The researchers asked students to watch a gruesome medical procedure while measuring their heart rates. When the video became traumatic for the students to watch, their heart rates would increase, indicating the stress response. However, their heart rates decreased if they interpreted the procedure as a voluntary and joyful rite of passage, which researchers suggested to them at the start of the study.

• Mason (1975) measured the levels of adrenaline produced by different people under the same stressors. The same stressors produced different adrenaline levels depending on how people interpreted the stress.