Dr Jordi Dalmau i Carre. MD

The Chemistry of Fear

In medicine we use the term somatosensory system to indicate the system in charge of sensing the body, the soma. It is not one single system, but a combination of several subsystems, each one conveying signals to the brain about the state of the body at any given moment. The signals can follow nerve or chemical pathways. Emotions are one type of signal.

We can define emotions as a collection of responses outwardly directed and public, meaning they can be observed by others. Emotions belong to our homeostatic bio-regulatory devices and as such they are aimed at the organism’s survival.

In the process of sensing the engagement with life, emotions become a fundamental part for the body’s own regulation. Emotions can be caused by stimuli that come from the outward-event (i.e. something you see) or from the inward-image (i.e. a memory) or from the chemical profile of the internal medium (i.e. your level of blood sugar).

The innate set of brain devices which produce emotions can be engaged automatically. We have for every stimulus coming from the internal or external environment of the body a matching answer in the form of emotions. Emotion most of the time can be predicted when induced by a particular stimulus.

Emotions produce a change in the body internal medium accompanied by an endocrine-visceral and musculo-skeletal adaptation as well as modification in the operation of brain circuits. These changes collectively constitute the substrate for neural patterns that eventually becomes the feeling of the emotion.

The autonomic nervous system (ANS) is a part of the nervous system in charge of the automatic control of smooth muscle, cardiac muscle and glands – what is known as visceral control. These neural structures located in the brain stem, hypothalamus and limbic nuclei operate largely unconsciously and generally function independently of our will, in an autonomous mode. There are smooth muscles in every blood vessel anywhere in the body. These muscles can contract or dilate to regulate blood circulation and with it blood pressure and body temperature. Visceral organisation includes mechanisms such as reflexes and, at higher levels, drives and integrative processes that include mood and feeling states, motivation and emotion. The ANS is divided into two systems: the sympathetic and the parasympathetic nervous system.

When the whole sympathetic system is activated including the medulla of the adrenal gland, the response of the individual exhibits the characteristics of Anxiety or Stress leading to Anger or Fear. All these responses are part of the preparation of the individual for an action, fight or flight.

Immediately after sympathetic stimulation the heart rate increases, with elevated blood sugar, sweating, erection of the hair, dilation of the pupils. A generalised constriction of veins and small arteries reduces the pool of blood in the veins and raises the blood pressure.

The blood supply to voluntary muscles is increased by dilating the blood vessels. Mechanical and secretory activities of the stomach and intestines are inhibited and intestinal sphincters are constricted.

In the liver the activation of sympathetic fibers produces vasoconstriction and inhibits the contractions of the gall bladder, and in the spleen it causes splenic contraction, releasing red and white cells into the general circulation.

The release of epinephrine and norepinephrine from the medulla of the adrenal gland causes the destruction of glycogen and liberates glucose, augments glucagon output, inhibits insulin secretion, increases metabolic rate and reduces the blood clotting time.

There is a local release of acetylcholine (Ach) in the sweat glands producing perspiration in a rhythmic activity of every 6-7 minutes, showing areas of the skin with synchronous sweating bursts. Also axillary glands are activated by mental stress.

In the bladder the sympathic action produces relaxation of the wall and internal sphincter contraction. Most structures in the pelvic area undergo vasoconstriction, only the external sex organs experience vasodilation.

Emotions are a complicated collection of chemical and neural responses, with a regulatory role in assisting the organism in maintaining life by leading to the creation of circumstances advantageous for that organism.

The brain induces emotions from a remarkably small number of brain areas, most of them located below the cerebral cortex. One of these subcortical structures located in the depth of each temporal lobe is a nucleus called the amygdala, responsible for the recognition and expression of fear. There is a particular dysfunction involving an abnormal deposit of calcium in the amygdala that produces an impairment of those nuclei to sense and experience fear. This impairment alters the ability to make sound judgments based on previous experiences, putting at risk the welfare of the individual.

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