Physiology

Yoga & the Nervous System

You might wonder why after a challenging and sweaty session, stretching muscles in places you didn’t know existed, and testing your limits of focus and concentration, you can yet feel so deeply relaxed! Many of yoga’s benefits relate to its relationship with the nervous system. Here we explain how and why…

Nervous system 101

So the human nervous system has two main branches: Central (CNS), consisting of the brain and spinal chord; and Peripheral, linking the structures of the body, organs and limbs with the CNS. From the spine originate motor nerves, directing our movement, while sensory nerves lead back and forth to the brain, accomplishing appropriate responses to our outer and inner environments.

“The spine and brain are the altars of god”Paramahamsa Yogananda

Hence a practise which aims at self realisation must certainly treat these areas of the body as sacred. Movement in yoga is always initiated from the spine, in its optimal 8 directions. Asana not only conditions the surrounding spinal muscles and vertebral discs but maintains healthy cerebro spinal fluid. While the brain was once thought to be a fixed entity, science now understands its neuroplasticity; it can be remodelled by the practise of meditation and mindfulness. The cerebral cortex, associated with higher levels of thinking, is strengthened. We find that samskaras (grooves of past experience) can be re-written; as new neural pathways are created, influencing conscious behaviour and learning.

Peripheral Nervous System: NeuronA hand drawn sketch by Dr. Christensen from the University of Michigan Medical School
Peripheral Nervous System: Neuron
A hand drawn sketch by Dr. Christensen from the University of Michigan Medical School

Brake & accelerator

A peek at the workings of the Autonomic nervous system (ANS) gives us an understanding of how yoga boosts our ability to cope with stress off the mat. This looping communication network allows us to evaluate and make the appropriate psychological and physiological responses to the sensory inputs of inner and outer worlds.

The ANS consists of two complementary branches: Parasympathetic (PSNS) and Sympathetic (SNS); or the ‘brake’ and ‘accelerator’ respectively. In a state of natural balance, ‘homeostasis’, the PSNS dominates, with the SNS ready to come to the fore when we need to respond to a threat. In evolutionary terms this would have allowed us to run away from a predator or protect our families from threat.

Burn out

Have you ever kept on working and working, fuelled by coffee and deadlines, and felt invincible; yet when you took a week’s holiday there was a massive crash? With the SNS raised the adrenal glands secrete stress hormones; muscles tense, our pulse races and our pupils dilate; energy moves from functions such as digestion to the need for ‘fight or flight’. The mind is sharp and tense.

But in the modern day, the type of ‘threats’ we face tend to be psychological and sustained, like pressure at work or mounting bills. So the accelerator may remain active and dominant, perceiving and responding to constant stress; eventually creating burn out.

While running from a tiger would require tense muscles and a faster heart rate, today’s threats are better faced with a calm and rational mind. Which is more the domain of the PSNS. Often this is called ‘rest and digest’ as muscles relax, the heart slows and energy moves back to maintenance of the body’s systems, immunity and repair. Our mind becomes quieter, expansive and rational.

Photo: Fotolia
Photo: Fotolia

Postures held with ease and stillness

Stretching can lower the nervous system and yoga gives us a unique way to stretch; through asana. If posture is practised as intended by Sage Patanjali in the Yoga Sutras (‘sthirum sukham asanam’) – mindfully, with ease and with the breath – we can offload the samskaras of stress held muscularly. Hence that deep corpse-like release into shavasana at the end of class.

Yoga practises which alternate between dynamic and resting movement, or fast and slow breaths help us to build a resilient nervous system through understanding how to effectively operate the brake and accelerator!

The longest cranial nerve, the vagus, connects the brain with the major abdominal organs and heart. It may be that particular postures, like back bends, and Ujjayi breathing tone this nerve and contribute to an improved sense of wellness and ease.

Breath & consciousness

The nervous system functions largely out-with our conscious control, but of course yoga is primarily about consciousness. In the 1970’s Swami Rama proved, in front of astonished doctors and scientists, that highly adept yogis could control their heart rate at will.

Not many of us will reach this stage of mastery but we do know that when we our mind is disturbed our breath rate changes, our heart races and our body tenses! So it follows that when we guide our breath into a steady pattern, the rest of the body follows into relaxation. Creating a feedback to the mind to become calmer.

The yogis knew 5,000 years ago that the breath was the primary means to induce stillness. Hence a whole host of yogic technology for the relationship between body, breath and mind: Pranayama. As Sri Ramana Maharishi said: ‘through breath control, the mind becomes like a bird in a cage’.

SavasanaPhoto by Géraldine Warland
Savasana
Photo by Géraldine Warland

The subtle nerves

The yogis dived deeper into their breath, discovering subtler layers of existence. The life force (prana) and the pranic nerves (nadis) are invisible to the eye but may be experienced in deep states of meditation. Over 72,000 energy channels are said to exist in the subtle body but three are considered vital for the practise of yoga: ida (the moon), pingalla (the sun) and sushumna.

As a flame creates heat in the glass lamp that surrounds it, the subtle can affect the physical. Ida dominates the left side of the body and the right brain and correlates to the PSNS. Pingala dominates the right side of the body and left brain, correlating to the SNS. Practises such as anuloma viloma (alternate nostril breath) harness these inner flows until the central channel sushumna (CNS – remember those ‘altars of god’?)) becomes active – and consciousness flows, uninterrupted by the movements of mind.

“Yoga is the stilling of the fluctuations of consciousness”Patanjali

‘Yogas chitta vritti Nirodah’ said Sage Patanjali. Yoga is a practise of union, of coming into the centre from the extremes of life, the pairs of opposites. Whether we approach the nervous system from the realm of physical or subtle, it sheds light on how the balancing of body, mind and breath may spiral inwards to our true state of stillness.




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