The Autonomic Nervous System (ANS)
Responsible for managing everything that keeps you alive without you even thinking about it - the autonomic nervous system (ANS) controls your heart rate and breathing, absorbing the nutrients from your food and coordinating your immune defences.
Autonomic balance is mediated via reflex systems in the hypothalamus and brainstem, where incoming sensory information triggers reflex outgoing impulses which are relayed via autonomic ganglia and peripheral fibres to their target organs.
Autonomic Divisions: Sympathetic and Parasympathetic
Most people can identify the sympathetic nervous system (SNS) as initiating our flight or fight response to perceived threat, and the parasympathetic nervous system (PSNS) as managing resting and digesting activities. These divisions work together to maintain our internal balance - or homeostasis, as we go about a diverse array of activities, situations and environments every day.
The PSNS and SNS fibres extend from the brainstem to exit via the Cranial, Cervical and Sacral Nerves (parasympathetic fibres), or Thoracic Spinal Nerves (sympathetic fibres). Afferent and efferent fibres synapse within peripheral ganglia, and terminal efferents travel to their target organ within the peripheral nerve sheath (epineurium).
Likewise, incoming sensory information is transferred via the peripheral ganglia to ascending pathways in the spinal cord, synapsing in the brainstem and hypothalamus in a continuous autonomic feedback loop.
The Enteric Nervous System
This post will discuss the interactive balance between the sympathetic and parasympathetic fibers to control blood and lymph flow, the role of parasympathetic innervation in the skin and subcutaneous tissues, and the local and systemic actions of MLD on autonomic balance.
However we also need to consider the Enteric Nervous System (ENS). Often referred to as our second brain, the ENS operates almost entirely within its own reflex systems.
Descending afferents from the PSNS and SNS synapse with local enteric fibres within enteric ganglion located in the abdominal cavity. The enteric system is the only location to have this tertiary level of autonomic nerves.
Sympathetic Nervous System
The sympathetic nerves all enter and exit the spinal column with the thoracic spinal nerves. Sympathetic ganglia near these thoracic exits extend to the cervical and sacral segments forming a chain of sympathetic ganglia known as the dorsal chain. Central sympathetic neurons synapse with peripheral SNS neurons in the Sympathetic ganglia and can transfer reflex sympathetic connections between upper and lower spinal segments and traverse the spinal cord across spinal segments to the opposing side. Some sympathetic fibres pass across the spinal cord without synapsing with interneurons in the grey matter (1).
The SNS regulates blood flow
Whenever a stressful situation is encountered, the body prepares to fight or flee. Both actions require increased mental awareness and skeletal muscle activity.
Blood flow is directed to the brain and muscles and away from non-lifesaving activities such as digestion. Blood vessels under the skin are constricted to prevent blood loss (in case you have to fight for your life) and immune reactions are put on hold. No point expending energy on wound healing and tissue repair if you don't survive the battle.
While modern life may not present us with actual physical battles, the emotional and mental stresses that we experience on a daily basis still initiate these physical responses as if we had to physically fight for survival. This means that whenever we feel stressed our skin, digestive system and immune system are suffering, not able to carry out rejuvenation or wound healing actions.
Para-sympathetic Nervous System
Named for its role in working alongside the SNS, the PSNS is often referred to as the housekeeping system, co-ordinating digestive and immune functions to maintain a health environment for cellular life. PSNS fibres exit the CNS with the cranial and sacral nerves.
There are four parasympathetic ganglia, all in the head where they synapse with peripheral PSNS fibres to control the pupils and salivary glands.
All other parasympathetic fibres synapse with their peripheral counterparts clos to or in the walls of their target organs. Almost 3/4 of parasympathetic fibres are in the Vagus Nerve, the central Autonomic trunk that innervates the heart lungs and digestive tract.
PSNS activity slows the heart rate and constricts the bronchi during rest, and is also responsible for many reproductive activities. Most PSNS fibres are therefore located in the thoracic and abdominal cavities, however there are PSNS fibres that innervate blood and lymph vessels in the peripheral system with the opposite action to SNS fibres, ie under sympathetic activation small blood and lymph vessels under the skin dilate, and immune activities are promoted (2).
The Autonomic Nervous System and MLD
Smooth muscle in the lymph vessels wall is auto-myogenic, which means that even when there is no other stimulus the lymphangion will contract every 10 seconds or so. This maintains a constant lymph flow and prevents lymph stasis.
Lymph vessels are also innervated by autonomic fibres, and under normal conditions the SNS and PSNS work together to maintain the optimal blood and lymph flow under the skin. When stress levels are high, sympathetic messages constrict the lymph collectors in the same way that subcutaneous blood vessels are constricted during the stress response.
Almost 50 years ago Prof. Dr. Paul Hutzschenreuter measured the effect of Dr Vodder's MLD on the sympathetic nervous system, noting a significant reduction in sympathetic activity within 5 minutes of beginning the MLD treatment. He coined the term sympatholytic which is now commonly used in lymphology.
This relaxation effect can also be achieved through massage. However, when when pressure or 'good pain' techniques are used to induce relaxation, the incoming sensory messages must first be processed by the limbic system for interpretation. The slow, light pressure techniques used to perform MLD bypass the limbic system, working directly with the autonomic pathways to induce the powerful sympatholysis observed by Hutzschenreuter.
The sympatholytic effect is essential to achieving good lymph drainage.
As sympathetic activity decreases, the precapillary sphincters responsible for regulating blood flow in superficial capillaries relax, allowing for an increased delivery of oxygen and nutrients to the tissues. It is crucial to understand that MLD does not raise capillary pressure, thereby preventing any excess fluid from entering the tissues. This stands in contrast to massage, which boosts blood flow along with an elevation in capillary pressure. This fundamental disparity explains why MLD is recommended for acute oedemas, while massage is not advised during this phase.
When sympathetic activity decreases, superficial lymph vessels dilate, enabling greater filling of the lymphangion. MLD also triggers sympathetic reflexes to enhance the speed and strength of lymphatic pumping. This effect is produced by the particular shear and stress forces exerted on the tissues during MLD, which activate sensory sympathetic fibres in the lymphangion wall.
While efferent parasympathetic fibres have a role in dilating blood and lymph vessels, there are no sensory fibres from the blood or lymph vessels or any organ in the subcutaneous compartment. Therefore the effect of MLD on autonomic tone is achieved through reducing sympathetic activity. This allows for increased parasympathetic function which in turn improves, digestion and promotes immune activity, tissue repair and wound healing.
Waxenbaum JA, Reddy V, Varacallo M: Anatomy, Autonomic Nervous System: StatPearls Publishing, Treasure Island (FL); 2023. https://europepmc-org.elibrary.jcu.edu.au/article/nbk/nbk539845#__NBK539845_dtls__
Bachmann SB, Gsponer D, Montoya-Zegarra JA, Schneider M, Scholkmann F, Tacconi C, Noerrelykke SF, Proulx ST, Detmar M: A distinct role of the autonomic nervous system in modulating the function of lymphatic vessels under physiological and tumor-draining conditions. Cell reports 2019, 27(11):3305-3314. e3313.
Birch R: The Peripheral Nervous System: Anatomy and Function. In: Peripheral Nerve Injuries: A Clinical Guide. edn. Edited by Birch R. London: Springer London; 2013: 1-67.
A great reminder . Thank you