The human body and yoga

2.1 Introduction to the human body

The body, from one cell to one person

Two words first. Anatomy is the study of the body’s structure: what is where, and what it is made of. Physiology is the study of its functions: how each part works, and how the parts work together. Both came up on the first day of my class; see the notes of 6 September.

Levels of organisation

IGNOU’s physiology course counts seven levels, from the smallest up. Source

1. Atoms: carbon, hydrogen, oxygen, nitrogen, phosphorus, and traces of others such as sodium and calcium.
2. Molecules: atoms joined together, from water to glucose, proteins, fats and DNA.
3. Cells: the smallest unit that is alive, the structural and functional unit of the body. There are about 200 kinds of cell in the human body.
4. Tissues: cells of similar structure working as a team. There are four kinds: epithelial (coverings and linings), connective (bone, cartilage, blood and the tissue that binds organs), muscular and nervous.
5. Organs: several tissues arranged for one special job. The heart pumps; the stomach digests.
6. Organ systems: organs working together, such as the heart and blood vessels in the cardiovascular system.
7. Organism: all the systems in harmony, one living person.

My class notes write the same ladder in six steps, counting atoms and molecules together as the “chemical” level: chemical → cell → tissue → organ → organ system → organism. One organ can serve two systems. The pancreas makes digestive juice and also hormones, so it belongs to both the digestive and the endocrine system. Source

Regions and cavities

The body’s regions are the head, neck, trunk, upper limbs and lower limbs. The trunk has two parts, the chest (thorax) and the abdomen. Inside, the organs sit in protected spaces called cavities:

The diaphragm, a dome of muscle, separates the thoracic cavity from the abdominal cavity, and it is the main muscle of breathing. Source The cranium has 8 bones, and the spinal cord runs through the central canal of the vertebrae. Source

The eleven organ systems

My class listed eleven systems (notes of 6 September). The syllabus looks closely at six of them, in the next section.

The yogic view. The Taittirīya Upaniṣad (chapter 2) describes the person as five sheaths (kośas), one inside the other. The physical body is the outermost, the annamaya kośa, the sheath made of food; inside it lie the sheaths of prāṇa, mind, intellect and bliss. Source Everything on this page belongs to that first sheath, the one yoga starts with. See Pañcakośa on the concept map, and how yoga therapy uses the five sheaths.

2.2 Basic structure and functions of the body systems

Six systems at work

Musculoskeletal system

The adult skeleton has 206 bones and a few cartilages. Bone is a hard connective tissue, its matrix stiffened with calcium salts; cartilage is slightly pliable. The skeleton has two divisions: Source

• Axial skeleton, 80 bones, along the body’s axis: the skull (22 bones: 8 cranial and 14 facial), the vertebral column, the sternum and the ribs. The count includes the U-shaped hyoid in the throat and the three tiny ear ossicles (malleus, incus, stapes) in each middle ear.
• Appendicular skeleton, the other 126: the bones of the limbs and of the girdles that join them to the trunk.
• Vertebral column, 26 vertebrae: cervical 7, thoracic 12, lumbar 5, then the sacrum (1, fused) and the coccyx (1, fused). It protects the spinal cord and supports the head.
• Ribs, 12 pairs.
• Joints are of three kinds: fibrous (no movement, like the sutures of the skull), cartilaginous (a little movement, like the joints between vertebrae) and synovial (free movement, like the shoulder, hip and knee).

Muscle comes in three kinds: skeletal muscle (striped under the microscope, under our will, attached to bones), visceral or smooth muscle (not striped, not under our will, in the walls of hollow organs such as the gut and blood vessels) and cardiac muscle (striped but involuntary, found only in the heart). Source Āsana is skeletal-muscle work, from the loosening practices to the held postures on our āsana page.

Respiratory system

Air enters through the nostrils and passes the pharynx (a passage shared by food and air), the larynx (the cartilage box that makes sound) and the trachea, which divides into the bronchi, the bronchioles and at last the tiny air sacs, the alveoli. Bronchi, bronchioles and alveoli together make up the two lungs, each wrapped in a double membrane, the pleura. Source

• Breathing in starts when the diaphragm contracts and flattens; the external intercostal muscles lift the ribs. The chest grows and air flows in. Breathing out at rest is mostly those muscles relaxing.
• Gas exchange takes place in the alveoli, by diffusion: oxygen into the blood, carbon dioxide out of it.
• Rate: a healthy adult breathes about 12–16 times a minute at rest, moving about 500 mL of air in each quiet breath (the tidal volume), or 6–8 litres a minute. Source Textbooks differ a little: an IGNOU unit gives 14–18 a minute. Source

Why it matters for yoga: the diaphragm and the rib muscles are the very muscles that sectional breathing trains.

Cardiovascular system

The human heart has four chambers: two small upper atria and two larger lower ventricles, divided by walls (septa) and guarded by valves: the tricuspid valve on the right, the bicuspid (mitral) valve on the left, and the semilunar valves where blood leaves for the lungs and the body. Source

• Double circulation. The right ventricle pumps blood to the lungs (pulmonary circulation); it comes back, rich in oxygen, to the left atrium. The left ventricle pumps it to the whole body (systemic circulation); it comes back to the right atrium.
• Heart rate. A patch of special tissue, the sino-atrial node, is the pacemaker. The heart normally beats 70–75 times a minute, on average 72.
• Cardiac output, the blood each ventricle pumps in a minute, averages about 5 litres.
• Blood pressure. Normal is about 120/80 mm Hg: 120 is the systolic (pumping) pressure, 80 the diastolic (resting) pressure. Repeated readings of 140/90 or more mean hypertension. Source
• Control. The heart beats on its own, but a centre in the medulla oblongata adjusts it: sympathetic nerves speed it up, parasympathetic nerves slow it down.

Nervous system

The central nervous system (CNS) is the brain and the spinal cord. The peripheral nervous system is all the nerves that link them with the body. Its somatic part carries commands to the skeletal muscles; its autonomic part runs the involuntary organs and smooth muscle, and is itself divided into the sympathetic and parasympathetic systems. The unit of the whole system is the neuron, a cell with a cell body, branching dendrites and a long axon; one neuron passes its signal to the next across a gap, the synapse. Source

• Forebrain: the cerebrum (thinking, memory, the senses, voluntary movement), the thalamus (a relay centre) and the hypothalamus, which controls body temperature, hunger and thirst and links the brain with the hormones.
• Midbrain, between the forebrain and the hindbrain.
• Hindbrain: the pons; the cerebellum, which uses signals from the ear’s balance organs to keep you steady; and the medulla oblongata, with centres for breathing, heart and blood-vessel reflexes and gastric secretion. Source
• Nerves: 12 pairs of cranial nerves leave the brain Source, and 31 pairs of spinal nerves leave the spinal cord. Source

The two autonomic systems pull in opposite directions. The sympathetic system prepares the body for an emergency; the parasympathetic system restores normal conditions once it is over. Relaxation practices aim at the second state.

After NIOS Biology, lesson 17, table 17.1. Source

Digestive system

My class spent three weeks on digestion, so here is only the outline; the details are in the class notes.

• Two parts: the alimentary canal (mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum, anus) and the accessory glands (the salivary glands, the liver with the gall bladder, and the pancreas). Notes of 27 September
• Lengths: oesophagus about 25 cm; small intestine about 6–7.5 m; large intestine about 1.5 m; the whole canal about 8–10 m. Nutrients are absorbed through the villi of the small intestine. Notes of 4 October
• From the mouth to the small intestine: saliva starts on starch, the stomach on protein, and bile and pancreatic juice finish the work in the duodenum. Notes of 11 October

Endocrine system

Endocrine glands have no ducts: they release hormones straight into the blood, which carries them to their target organs. Source Hormones act more slowly than nerve signals, and their effects last longer.

After NCERT Biology Class XI, chapter 19. Source

Numbers to remember

2.3 Homeostasis

Homeostasis: the art of staying the same

The word is Greek: homoios, similar, and stasis, standing still. The body regulates its own functions to keep its internal conditions as stable as possible, because every cell needs the right temperature, the right chemistry and the right acidity around it to work. Source Steady does not mean fixed: each value moves a little around a normal level, its set point, and the body pulls it back.

The parts of a feedback loop

1. Stimulus: a change in something the body watches, such as a rise in body temperature.
2. Receptor (sensor): detects the change and reports it. For temperature, heat and cold receptors in the skin, and the hypothalamus itself, which senses the temperature of the blood.
3. Control centre (integrating centre): compares the report with the set point and sends commands. Usually a part of the brain; for temperature, the hypothalamus.
4. Effector: the muscle, gland or organ that carries out the command, such as the sweat glands.
5. Response: the result, which feeds back on the stimulus. In negative feedback it reverses it.

IGNOU names stimulus, receptor, control centre and effector Source; NIOS names set point, sensor, integrating centre and effectors. Source Same loop, different words: learn both.

Negative feedback: the body’s thermostat

Almost every loop in the body is negative feedback: the response reverses the change that set it off. NIOS puts it simply: negative feedback reverses a condition; positive feedback continues in the direction of the change. Source

Positive feedback: when the body wants more

Positive feedback is rare. Instead of reversing a change, it amplifies it, until some event ends the loop.

• Childbirth. The first contractions of labour push the baby against the cervix and stretch it. The signal reaches the brain, and the pituitary releases oxytocin, which makes the uterine muscle contract harder; that stretches the cervix more, which releases more oxytocin. The loop ends when the baby is born. Source NCERT calls the first mild contractions the foetal ejection reflex. Source
• Blood clotting. Each step of clotting triggers the next, faster and faster, until the clot plugs the cut. Source

Stress, and where yoga comes in

Stress pushes many loops at once. The hypothalamus starts two pathways: through the sympathetic nerves, the adrenal glands release adrenaline and noradrenaline (the fight-or-flight response); through the pituitary, the adrenal cortex releases cortisol, which raises the energy supply. Hans Selye, the scientist often called the father of stress research, described what happens when stress goes on and on, the general adaptation syndrome: an alarm reaction, a stage of resistance, and finally exhaustion, when the body’s resources run down and stress-related illness, such as high blood pressure, becomes more likely. Source

Yoga works on the other side of the balance. NCERT’s psychology textbook counts relaxation, deep breathing with muscle relaxation, and the yogic method of meditation among the techniques that reduce the symptoms of stress. Source The Common Yoga Protocol says Śavāsana relaxes the whole psycho-physiological system and is very useful in managing stress. Source In body language: slow breathing and deep rest shift the balance from the sympathetic toward the parasympathetic side, the “rest and digest” state in the table above. Yoga does not run the loops for you. It lowers the noise, so the body’s own controls can do their work. See relaxation techniques and yoga nidrā.

2.4 Sensory organs

The five senses, two maps

Sense organs are the organs through which we detect changes in the world outside. Each has special sensory cells that receive a stimulus and send impulses along a nerve to the brain or the spinal cord; the brain sorts the impulses, interprets them, and sends out the response. Humans have five: the eyes, ears, nose, tongue and skin. Source

The yogic view: five senses, five subtle elements

Indian philosophy draws a second map. The Sāṅkhya darśana, which the Yoga darśana shares (Swami Harshananda’s Ṣaḍdarśana explains both), counts five jñānendriyas, organs of knowledge; five tanmātras, subtle elements, the pure essences of sound, touch, form, taste and smell; and five mahābhūtas, gross elements. In Sāṅkhya the sense is not the physical organ but its power: not the ear, but the power of hearing in the ear. The tanmātras are too subtle to perceive; they are known by inference, and the five gross elements arise from them. Source

The order of the rows is the order of creation in the Taittirīya Upaniṣad (2.1): from the Self arose space; from space, air; from air, fire; from fire, water; from water, earth. Space, the first and subtlest, has sound as its quality. Source Patañjali puts the senses and the elements together as “what is seen”:

Light, activity and stability are the three guṇas: sattva, rajas and tamas. So the senses are not the enemy in yoga. They are instruments, given for experience and, used well, for freedom.

Pratyāhāra: turning the senses inward

Pratyāhāra is the fifth of the eight limbs, the hinge between outer practice and inner practice.

Pratyāhāra does not mean shutting the eyes tight or blocking the ears. The organs keep working; the attention stops running out after their objects and rests with the mind instead. You practise it whenever you move the attention from the noise around you to the breath, or around the body in yoga nidrā; ṣaṇmukhī mudrā, which closes the eyes, ears, nose and mouth with the fingers, makes it physical. It prepares the ground for dhāraṇā and dhyāna.

2.5 Impact of yogic practices on the body systems

What practice does to the body

The texts name the fruits first. The Haṭha Yoga Pradīpikā says why āsana comes first of all:

The Gheraṇḍa Saṁhitā (1.10–1.11) gives one fruit to each limb: ṣaṭkarma purifies, āsana makes the body firm, mudrā makes it steady, and prāṇāyāma brings lightness (see the haṭha texts). B.K.S. Iyengar’s Light on Yoga, one of the prescribed books, gives the effects of each posture beside its technique, and Swami Satyananda Saraswati’s Asana Pranayama Mudra Bandha (Bihar School of Yoga) gives the benefits and the contra-indications of each practice in the same way. Today’s government manuals say the same in the language of the body systems. The Common Yoga Protocol, in its summary of research, says yoga is beneficial for physical fitness, musculoskeletal functioning and cardiovascular health, and helps in managing respiratory disorders, hypertension and many lifestyle-related disorders. Source

Practice × system

What the Indian manuals say each group of practices does for three systems. Tap a practice name to go to its unit.

CYP: Ministry of Ayush, Common Yoga Protocol Source. NIOS: Physical Education and Yog, lessons 19 (ṣaṭkarma), 20 (āsana), 21 (prāṇāyāma), 22 (mudrā and bandha). NCERT: Health and Physical Education XI, chapter 6, and Biology XI, chapter 14. MDNIY: yogic practices for high blood pressure.

Reading these claims well

• “Supports”, not “cures”. Some older manuals use strong words. This page keeps to “helps” and “supports”, and so should a teacher. Where a manual says a practice is useful in asthma or diabetes, read it as: a practice that may help, alongside medical care.
• Slow calms, fast stimulates. Slow breathing and long exhalations lean toward the parasympathetic, “rest and digest” side of the nervous system; fast, forceful practices such as kapālabhāti and bhastrikā stimulate. That is why the same list of cautions keeps returning for high blood pressure and heart disease.
• Order matters. Loosening first, then āsana, then prāṇāyāma, then relaxation and meditation. The Haṭha Yoga Pradīpikā puts prāṇāyāma after a steady āsana (2.1), and ṣaṭkarma before prāṇāyāma for those who need it (2.21).

2.6 Introduction to psychology

Psychology, East and West

NCERT defines psychology as a science that studies mental processes, experiences and behaviour in different contexts. Mental processes are activities such as remembering, learning, perceiving and thinking. Experiences are subjective: only the person who has them can know them directly, like the pain of someone who is ill. Behaviour is what we do, from a blink to a decision, and much of it can be observed. Source

Branches of psychology

• Cognitive: attention, perception, memory, thinking, problem-solving.
• Biological: the links between behaviour and the brain, nervous system and hormones.
• Developmental: how we change from birth to old age.
• Social: how other people influence what we think, feel and do.
• Health: the role of psychology in health and illness; stress and coping.
• Clinical and counselling: causes, treatment and prevention of psychological disorders, and help with everyday problems.
• Educational: how people learn, and how to teach them; most useful to a yoga teacher.
• Industrial / organisational, environmental, sports, and more.

After NCERT Psychology XI, chapter 1. Source

Key concepts

Patañjali’s psychology

Citta is the whole field of the mind. In the Yoga darśana it covers the three inner organs of Sāṅkhya: buddhi, the intellect that decides; ahaṅkāra, the ego, the sense of “I”; and manas, the mind that receives the senses’ reports. Source Yoga’s definition is a definition in psychology:

Patañjali counts five vṛttis (YS 1.6) Source, and each has a modern counterpart:

Every vṛtti is either painful (kliṣṭa) or not painful (akliṣṭa) (YS 1.5). The painful ones are rooted in the five kleśas, the afflictions:

The third idea is the three guṇas, the qualities of nature. Sattva is clarity and light; rajas, activity and restlessness; tamas, inertia and dullness. They are present in every person in different degrees, and the one that dominates shapes behaviour, which is how NCERT’s textbook presents the guṇa typology of personality. Source The Gītā puts it this way:

The guṇas also mark the five states of the mind (citta bhūmis) that the commentators describe: kṣipta, restless, where rajas dominates; mūḍha, dull, where tamas dominates; vikṣipta, distracted, where sattva begins to prevail; ekāgra, one-pointed; and niruddha, fully stilled. Source See Citta bhūmi on the concept map.

Where the two meet. Modern psychology describes and measures the mind; Patañjali’s psychology adds a method to change it. Kriyā yoga (YS 2.1–2.2) weakens the kleśas, and their active forms are removed by meditation (dhyāna, YS 2.11). That is where this unit hands over to the meditation unit, and, for food and the guṇas, to sāttvika food.

Quick revision

Test yourself

Sources

Where this comes from

• Prescribed books: B.K.S. Iyengar, Light on Yoga (on what the postures do for the body); Swami Harshananda, Ṣaḍdarśana: the six systems of Hindu philosophy, Ramakrishna Math (the Sāṅkhya and Yoga darśanas: senses, tanmātras, elements, guṇas); Patañjali’s Yoga Sūtra; Hatha Yoga Pradipika, with commentary by Swami Muktibodhananda (Bihar School of Yoga / Yoga Publications Trust, Munger), whose verse numbering this page follows (HYP 1.17, 2.1, 2.21, 2.35); Swami Satyananda Saraswati, Asana Pranayama Mudra Bandha (Bihar School of Yoga / Yoga Publications Trust, Munger), on the benefits and contra-indications of āsana, prāṇāyāma, mudrā and bandha. Named, not quoted: explained here in my own words.
• Classical texts: Yoga Sūtra 1.2, 1.5–1.11, 2.1–2.9, 2.11, 2.18, 2.54; Bhagavad Gītā 2.58, 14.5; Haṭha Yoga Pradīpikā 1.17, 2.1, 2.21, 2.35 (Bihar School numbering); Gheraṇḍa Saṁhitā 1.10–1.11; Taittirīya Upaniṣad, chapter 2 (2.1, the order of the elements; the five kośas).
• Verse texts: IIT Kanpur Gita Supersite (Heritage IITK), YS 1.2, 1.6, 2.3, 2.18, 2.54; BG 2.58, 14.5.
• NCERT Biology, Class XI: ch. 14, Breathing and exchange of gases; ch. 15, Body fluids and circulation; ch. 17, Locomotion and movement; ch. 18, Neural control and coordination; ch. 19, Chemical coordination and integration. Class XII: ch. 2, Human reproduction (parturition).
• NCERT Science, Class X: ch. 6, Control and coordination; ch. 10, The human eye. NCERT Health and Physical Education, Class XI, ch. 6, Yoga.
• NCERT Psychology, Class XI: ch. 1, What is psychology?, ch. 4, Sensory, attentional and perceptual processes, ch. 6, Human memory, ch. 8, Motivation and emotion. Class XII: ch. 2, Self and personality; ch. 3, Meeting life challenges.
• NIOS Biology (314): lesson 17, Coordination and control (sense organs, nerves, autonomic system); lesson 18, Homeostasis. NIOS Physical Education and Yog (373): lessons 19, 20, 21, 22.
• IGNOU (eGyanKosh): Homeostasis and organisation of body fluid compartments (levels of organisation); Homeostatic control system (feedback loops, set points); Introduction to human body systems; Sāṅkhya philosophy; Yoga philosophy (citta, citta bhūmis, kleśas); Taittirīya Upaniṣad.
• SATHEE (IIT Kanpur, Ministry of Education), NCERT Biology XI, Neural control and coordination: chapter text (eye and ear) and exercises (cranial and spinal nerves).
• Ministry of Ayush, Common Yoga Protocol (English booklet, hosted by the Ministry of External Affairs). MDNIY, yogic practices for the management of high blood pressure.
• Class notes: 6 September (organisation, eleven systems), 20 September (memory), 27 September, 4 October and 11 October (digestion).