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Emotions and the autonomic nervous system
The topic of how to deal with emotions (vexations) is an important element of Zen and mindfulness, as described in ‘Zen, metacognition and AI’. In recent years, the main approach to emotion theory has been to recognise that emotions cannot be captured by philosophical or religious concepts in the mind alone, but are influenced by physiological factors, as described in ‘On Emotion Recognition, Buddhist Philosophy and AI’.
One such physiological factor of importance is the autonomic nervous system.
The autonomic nervous system is the nervous system that automatically regulates various functions of the body regardless of our will, specifically controlling heart rate, blood pressure, respiration, digestion and thermoregulation.
The autonomic nervous system is divided into two main categories
1. the sympathetic nervous system: acts mainly during times of stress and tension, preparing the body for a ‘fight or flight’ situation by increasing the heart rate, blood pressure and breathing.
2. parasympathetic: works mainly during relaxation and rest, lowering the heart rate, facilitating digestion and setting the body in a state of restoring energy.
These two nerves are in balance and constantly regulate the state of the body.
In this article, the autonomic nervous system will be discussed based on ‘The science of the autonomic nervous system: what it means to be “physically fit”’.
Signal transmission by neurons and neurotransmitters
First, nerves are fibre-like structures that connect the central nervous system, such as the brain and spinal cord, to parts of the body, and nerves serve to transmit electrical signals, which in turn transmit sensory and motor information. Nerves consist mainly of nerve cells (neurons), which receive signals and transmit them to other neurons and muscles. These neurons form the backbone model of modern AI technology, which is also discussed in ‘On deep learning’.
There are two main systems of nerves
1. central nervous system (brain and spinal cord): processes information, makes decisions and controls the entire body
2. the peripheral nervous system (all nerves outside the central nervous system): which
– Sensory nerves: transmit stimuli from the skin and sensory organs to the brain.
– Motor nerves: transmit commands from the brain to muscles and organs.
These enable us to sense information from our environment and to move our bodies.
The length of a neuron varies greatly from site to site, with the cell body, which is usually the main body of the neuron, being very small, measuring only a few tens of micrometres (around 0.01 mm). However, the axons (the long parts that carry signals) of neurons can grow very long, with the longest axons in the human body sometimes reaching more than one metre. In particular, nerves covering distances from the feet to the head may consist of a single long nerve cell (especially axons).
A single nerve contains many nerve fibres in bundles, which are made up of the axon of the nerve cell (neuron) and the myelin sheath (or non-myelinous Schwann cells, for example) that covers it.
Neuronal fibres are classified into several types, mainly according to their function and structure, and each type plays a different role, with different thicknesses and transmission rates. They are discussed below.
1. A fibres: A fibres are divided into four main subtypes, which are covered by a myelin sheath and have very high transmission speeds: Aα fibres are 13-20 µm thick and have transmission speeds of 70-120 m/s (max 432 km/h); Aβ fibres are 6-12 µm thick and have transmission speeds of 30 70 m/s (max 270 km/h), Aγ fibres are 5-8 µm thick and have a transmission speed of 15-30 m/s (max 108 km/h) and *Aδ fibres are 1-5 µm thick and have a transmission speed of 12-30 m/s, giving very fast signal propagation, comparable to the speed of a bullet train.
2. B fibres: B fibres are associated with the autonomic nervous system and are covered by a myelin sheath, but are slower than A fibres, with a thickness of 1-3 µm and a transmission speed of 3-15 m/s (around 50 kn/h: the speed equivalent of a car).
3. C fibres: C fibres are unmyelinated nerves without a myelin sheath and have the slowest transmission speed. They are involved in the transmission of pain and temperature sensation. They are 0.2-1.5 µm thick and have a transmission velocity of 0.5-2 m/s (the speed of a slow human walk).
In summary, A fibres are thick and have a high transmission speed and are involved in the transmission of movement, touch and sharp pain; B fibres are associated with the autonomic nervous system and have a medium transmission speed; and C fibres are the thinnest and have a slow transmission speed but transmit persistent pain and temperature sensations.
Thus, although relatively fast signal transmission takes place within neurons using electricity as the medium, there is no direct connection between neurons, and signal transmission takes place via chemicals in the space between them, as shown in the diagram below.
This chemical transmission creates non-linear signal transmission and enables complex signal processing.
These chemicals, called neurotransmitters, are released by neurons (nerve cells) to transmit signals across synapses to other neurons, muscle cells and gland cells, which then cross the synaptic cleft and bind to receptors to produce excitatory or inhibitory effects. The main neurotransmitter types and their roles are described below.
1. acetylcholine: Acetylcholine transmits signals from motoneurons to muscle cells, mainly at the neuromuscular junction, causing muscle contraction. It is also involved in the parasympathetic nervous system, reducing heart rate and stimulating digestive activity. In the central nervous system, it is involved in learning and memory, while in the peripheral nervous system, it promotes muscle contraction and regulates heart rate.
2. glutamate: the most abundant excitatory neurotransmitter in the central nervous system, which activates information transmission between neurons and is involved in learning and memory formation. Its role is to promote the activity of postsynaptic neurons and to carry excitatory signals that increase neural activity.
3. gamma-aminobutyric acid (GABA, Gamma-Aminobutyric Acid): Contrary to glutamate, GABA acts as an inhibitory neurotransmitter in the central nervous system, preventing overexcitation and maintaining stable neural activity by suppressing neural activity. Its role is to inhibit the activity of postsynaptic neurons and to carry out inhibitory signalling that reduces neural activity.
4. dopamine : dopamine is an important neurotransmitter involved in motor regulation, reward systems, motivation, pleasure and emotional control, with deficiency resulting in Parkinson’s disease and excess in schizophrenia. Its role includes motor control, such as coordination for smooth movement, and reward and motivation, which is involved in pleasure and reward sensation and influences learning and motivational processes.
5. serotonin : serotonin is involved in mood regulation, sleep, appetite and digestion and can cause depression and anxiety when serotonin is out of balance. Roles include mood regulation, such as maintaining mood stability and a sense of well-being, and sleep and wakefulness, such as regulating sleep cycles.
6. noradrenaline : Noradrenaline acts in the sympathetic nervous system and is associated with the stress response and fight-or-flight response. It is also involved in attention and concentration. Its roles include stress responses such as increased heart rate and blood pressure and increased energy supply, and attention and arousal such as increased alertness and vigilance.
7. endorphins: endorphins are analgesic substances produced by the body that relieve pain and cause pleasant sensations. They are secreted after exercise and during stress relief and are involved in the phenomenon known as ‘runner’s high’. Their roles include pain suppression, such as relieving pain and inducing pleasant sensations, and stress relief, such as providing a sense of relaxation and well-being.
These neurotransmitters can be broadly classified as excitatory and inhibitory and have a significant impact on our physical and mental state and are one of the key mechanisms for smooth control of movement, emotions, memory and pain.
Autonomic nervous system and its control
Of these nerves, those involved in the external environment are called the motor and sensory nerves, while those involved in the internal environment are called the autonomic nerves. homeostasis) of the internal environment.
The nervous systems involved in the external environment and the autonomic nervous system interact closely and regulate the body’s adaptations and reactions. Although these two nervous systems have different roles, they consistently co-operate in response to external stimuli, protecting and balancing the body.
Examples of the integrated action of the nervous and autonomic systems in relation to the external environment in external interactions include
1. reaction to perceived danger:
1. external stimuli (e.g. visual, auditory, tactile) are perceived by the somatic nervous system. For example, when a person touches something hot or perceives danger visually, the sensory nerves communicate this to the brain.
2. the sympathetic nervous system is activated and immediately regulates the body’s response. The heart rate increases, blood pressure rises and breathing speeds up. Blood flow also collects in the muscles, readying them for fight or flight (‘fight or flight response’).
3. at the same time, the somatic nervous system gives motor commands to retract the hand or flee from a dangerous situation. In this way, the somatic and autonomic nervous systems co-ordinate to enable a quick response to external danger.
2. post-meal reactions:
1. when eating, the somatic nervous system moves the muscles involved in the mouth and chewing to process the food
2. after eating, the parasympathetic nervous system becomes dominant towards digestion, which promotes the digestive system, increases blood flow to the gastrointestinal tract and maintains a relaxed state.
3. the somatic nervous system, on the other hand, reduces muscle activity and creates a quiet state to concentrate on digestion.
3. stress and emotional influences:
Changes in the external environment and emotional responses (e.g. stress, anxiety, fear) affect both the somatic and autonomic nervous systems. For example, when under intense stress, the somatic nervous system causes tension and the sympathetic nervous system correspondingly increases the heart rate and tenses the muscles. This causes the whole body to become tense; conversely, in a relaxed environment, the parasympathetic nervous system is activated and the muscles relax.
4. maintenance of homeostasis:
The autonomic nervous system is responsible for maintaining a constant internal environment in response to changes in the external environment. For example, when the temperature drops suddenly, the somatic nervous system senses the cold and the sympathetic nervous system contracts the blood vessels to maintain body temperature, causing shivering and producing heat. Conversely, when it is hot, blood vessels dilate and sweat to lower body temperature.
In this way, external stimuli cause the nervous system related to the external environment to operate, and furthermore, the autonomic nervous system can be triggered to change the state of the organism to a more stable one. This shows that the autonomic nervous system can be controlled not only by passive changes in the external environment, but also by active changes.
Active control of this autonomic nervous system includes the following.
1. breathing exercises: breathing is the most popular approach to controlling the autonomic nervous system, as described in ‘On breathing (relationship between Zen, cognitive activity and sport)’. Specific breathing techniques include
– Abdominal breathing: Slow, deep breathing with the abdomen activates the parasympathetic nervous system (the nervous system that works during relaxation). Specifically, the recommended rhythm is to inhale for 4 seconds, hold for 4 seconds and exhale over 8 seconds.
– 4-7-8 breathing: inhale for 4 seconds, hold the breath for 7 seconds and exhale over 8 seconds to promote relaxation of the body and mind.
2. meditation: meditation, which is also discussed in ‘Meditation, enlightenment (awareness) and problem solving’, is another important approach to controlling the autonomic nervous system. Meditation helps to calm the mind and increase the parasympathetic nervous system, and focusing on breathing and awareness can help to reduce stress and balance the autonomic nervous system.
3. exercise: light aerobic exercise, yoga and stretching also stimulate the parasympathetic nervous system and help stabilise the autonomic nervous system. Rhythmic exercise is particularly effective in balancing the autonomic nervous system.
4. regular lifestyle: the Shobogenzo, which preserves Dogen’s philosophy as described in ‘Zen Master Dogen’, contains many references to a regular lifestyle as part of Zen practice. A regular rhythmic lifestyle, adequate sleep and a balanced diet help to regulate the autonomic nervous system.
5. hot and cold baths: showering or bathing in alternating hot and cold water helps to stimulate and balance the autonomic nervous system. The recent popularity of sauna ‘regulating’ is attributed to the effects of hot and cold bathing. 6.
6. relaxation: consciously taking time out to relax is also important, and incorporating activities that help you to relax, such as listening to your favourite music, aromatherapy or reading, can help to keep your body and mind in balance.
Adopting these methods on a daily basis is expected to help control the autonomic nervous system, not only to reduce stress and fatigue, but also to improve the functioning of the digestive system and activate metabolism, as well as to improve immune function, stabilise emotions and improve performance in work and study.
Autonomic control is important in many aspects, from day-to-day stress management to maintaining physical and mental health and improving performance, and maintaining balanced autonomic function can help protect physical and mental health in the long term and improve quality of life.
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