Over the course of my recent writings to you concerning the subject of human anxiety, i.e. what it is; and how to manage it; I have had occasion to make brief reference to the human body’s Autonomic Nervous System (ANS) and to the central and complex role which it plays in mood and behaviour- related experience. Accordingly (and before proceeding further) I have decided to provide a brief review of the ANS for any who might be interested enough to read it. If however, this doesn’t include you, then quite simply pass on to the very next posting on this subject matter of Anxiety.
The Autonomic Nervous System (ANS) forms part of the body’s overall nervous system. Its ‘hardware’ consisting of two rows of nervous ganglia sited on either side of the spinal column. From here, bodily functions which are not subject to conscious control, i.e. heart and respiration rate, gastro-intestinal motility, salivation, sweating etc. are regulated and controlled. The ANS also incorporates the body’s on-board, so-called “fight or flight” mechanism, which is made up of two groupings of the said ganglia and known as the “sympathetic” and “parasympathetic” divisions. Sympathetic nerves connect with the middle section of the spinal cord, whilst those of the parasympathetic send messages to and from the brain and lower spinal cord. The heart, smooth (involuntary) muscle and most glands receive nerve fibres of both kinds and from both sources.

It is the sympathetic division that deals with and responds to those situations and circumstances in life which alert us to an emergency and need for action. Examples might be auditory cues (disturbing news) or visual cues (sudden awareness of a bull in a field in which we happen to be standing). In such cases there takes place what is known as an “all or nothing” response. An “all” response means that nerve fibres from the sympathetic division produce, for example, an immediate increase in heart and pulse rate, together with the dilation (expansion) of blood vessels: this in order to, in an instant, supply more blood to the peripheries (limbs etc.) for ‘fight or flight’. Further, an “all” response results in an instant change in respiration rate, i.e. breathing becomes more rapid and shallow; gastro-intestinal activity is inhibited, all for similar reasons. A “nothing” response simply means that the status quo is maintained.

In instances of parasympathetic activity, the converse response is the goal to be attained, i.e. that of “calming down”. However, due to a different configuration of nerve fibres from parasympathetic ganglia to organs and other vicera, the ensuing relaxed and tranquil state is more slowly and less dramatically achieved. What should now be clear is that it is this interplay of sympathetic and parasympathetic activity that governs and controls mood/emotional state and ensuing behavioural activity at any given time.

For those who are interested and desirous of taking things further, the following will provide a brief account of the ANS’s mode of operation. Information/signals monitored by one (or more) of the primary senses, e.g. vision, hearing, smell etc. enters a relay station in the limbic (or mammalian brain) known as the “thalamus” (Gk for “room”). Some of that signal may well take the short route to an important structure (also situated in the middle brain) known as the “amygdala”, which, in reality, is the brain’s ‘emotional computer’. (The amygdala also plays a complex role in our overall fear response. For further information see footnote•). The amygdala –aided by input from another key structure in this part of the brain, namely the “hippocampus,•• also sends signals to the neo-cortex or new brain. It is at this point that the decision is taken whether or not to alert the ANS.

Let us suppose that for some reason the alert is in fact raised, e.g. the expectation or reception of bad news, or the awareness of a bull in a field in which we happen to be standing. (Note that if whilst witnessing our “bull in a field” we also catch a glance of a handy nearby exit, e.g. a gate,, then the new brain will decide not to refer it on and a “nothing” response will ensue. However, where it is so referred, e.g. no available gate is apparent, messages will be instantly dispatched to the adrenal glands and to other structures deep within the old, i.e. reptilian brain or brainstem. In an instant, the sympathetic division of the ANS will drive up blood pressure and heart, pulse and respiration rate, together with levels of adrenaline and cortisol, i.e. the stress hormone will rise in the readiness for “fight or flight”.

In certain extreme circumstances, e.g. engine failure or irregular activity on-board an airplane during flight, signals will go directly into the hypothalamus (Greek for lower room or basement) and situated below the thalamus in the brain; sometimes referred to as “the brain of the brain”). Unlike responses requiring some form of decision to be made, this response will bypass the neo-cortex in order that direct and immediate action can ensue. The hypothalamus also appears to direct and regulate the release of a substance known as Corticotrophin-Releasing Factor (CRF), which heightens vigilance and makes further contact with the adrenals via the pituitary gland at the base of the brain (the body’s master gland) concerning further release of adrenalin and cortisol.