OF HATHA YOGA. ANATOMY OF HATHA YOGA A Manual for Students, Teachers, and Practitioners by. H. David Coulter Foreword by. Timothy McCall, M. D. Anatomy of Hatha Yoga: A Manual for Students, Teachers, and Practitioners Author: H. David Coulter | Timothy McCall Iniciandonos En Hatha Yoga. Editorial Reviews. From the Back Cover. Anatomy of Hatha Yoga now revised and in full four color reproduction, remains the most authoritative source.
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Anatomy of Hatha Yoga: A Manual for Students. Teachers and Practitioners By H. David Coulter di -Author-. *Scarica il pdf | ePub | DOC | audiobook | ebooks. title: download free: anatomy of hatha yoga a manual for students teachers and practitioners by david coulter pdf ebooks at cabs4u anatomy of hatha. byCoulter, H. David (Herbert David), Publication date Topics Buddhism, Yoga for exercise, Human anatomy, Hatha yoga, Health & Fitness, Consumer Health, Borrow this book to access EPUB and PDF files.
Ive not seen it, but it would hardly be surprising, and I have to admit that I would look carefully before not downloading it. Given human differences, the many schools of hatha yoga approach even the most basic postures with differing expectations, and yoga teachers find themselves facing a spectrum of students that ranges from accomplished dancers and gymnasts to nursing home residents who are afraid to lie down on the floor for fear they wont be able to get back up.
Thats fine; its not a problem to transcend such differences, because for everyone, no matter what their age or level of expertise, the most important issue in hatha yoga is not flexibility and the ability to do difficult postures, but awarenessawareness of the body and the breath, and for those who read this book, awareness of the anatomical and physiological principles that underlie each posture. From this awareness comes control, and from control comes grace and beauty.
Even postures approximated by beginning students can carry the germ of poise and elegance. How to accomplish these goals is another matter, and we often see disagreement over how the poses should be approached and taught. Therefore, the guidelines that follow are not set in stone; their purpose is to provide a common point of reference from which we can discuss the anatomy and physiology of hatha yoga.
Lock your attention within the body. You can hold your concentration on breathing, on tissues that are being stretched, on joints that are being stressed, on the speed of your movements, or on the relationships between breathing and stretching.
You can also concentrate on your options as you move in and out of postures. Practicing with total attention within the body is advanced yoga, no matter how easy the posture; practicing with your attention scattered is the practice of a beginner, no matter how difficult the posture.
Hatha yoga trains the mind as well as the body, so focus your attention without lapse. Well see in chapters 27 that inhalations lift you more fully into many postures and create a healthy internal tension and stability in the torso. You can test this by lying prone on the floor and noticing that lifting up higher in the cobra posture fig.
Paradoxically, however, exhalations rather than inhalations carry you further into many other postures. You can test this by settling into a sitting forward bend and noticing that exhalation allows you to draw your chest down closer to your thighs fig. But in either case you get two benefits: While doing postures, as a general rule keep the airway wide open, breathe only through the nose,.
Never hold the breath at the glottis or make noise as you breathe except as required or suggested by specific practices. As you do each asana, analyze its foundation in the body and pinpoint the key muscles that assist in maintaining that foundation: Focus your attention accordingly on the pertinent regional anatomy, both to prevent injury and to refine your understanding of the posture.
Then there is another kind of foundation, more general than what we appreciate from the point of view of regional anatomythe foundation of connective tissues throughout the body, especially those that bind the musculoskeletal system together. The connective tissues are like steel reinforcing rods in concrete; they are hidden but intrinsic to the integrity of the whole.
To strengthen these tissues in preparation for more demanding work with postures, concentrate at first on toughening up joint capsules, tendons, ligaments, and the fascial sheathes that envelop muscles.
The practical method for accomplishing these aims is to build strength, and to do this from the inside out, starting with the central muscles of the torso and then moving from there to the extremities.
Aches and pains frequently develop if you attempt extreme stretches before you have first developed the strength and skill to protect the allimportant joints. Unless you are already a weightlifter or body builder, stretching and becoming flexible should be a secondary concern.
Only as your practice matures should your emphasis be changed to cultivate a greater range of motion around the joints. Being in a state of silence when you have come into a posture is soothing and even magical, but you cannot connect with that state except by knowing how you got there and knowing where youre going.
If you jerk from posture to posture you cannot enjoy the journey, and the journey is just as important as the destination. So move into and out of postures slowly and consciously. As you move, survey the body from head to toe: You will soon develop awareness of how the body functions as a unit and notice quirks and discontinuities in your practice which you can then smooth out.
Finally, as you learn to move more gracefully, the final posture will seem less difficult. Do you honor or ignore messages from aches and pains? If you have back pain, do you adjust your posture and activities to minimize it, or do you just tough it out?
And do you keep a deferential eye on your body, or do you find that you get so wrapped up in some challenge that you forget about it? If you do not listen to messages from your body you will be a candidate for pulled muscles, tendinitis, pinched nerves, and ruptured intervertebral disks. To avoid injury in hatha yoga you have to develop a selfrespecting awareness.
Begin your program of hatha yoga with a resolution to avoid pain. Unless you have had years of experience and know exactly what you are doing, pushing yourself into a painful stretch will not only court injury, it will also create a state of fear and anxiety, and your nervous system will store those memories and thwart your efforts to recreate the posture. Pain is a gift; it tells us that some problem has developed. Analyze the nature of the problem instead of pushing ahead mindlessly.
With self-awareness. Try to practice at the same time and in the same place every day. Such habits will make it easier to analyze day-to-day changes. Mornings are best for improving healthstiffness in the early morning tells you where you need the most careful work and attention. Later in the day, you lose that sensitivity and incur the risk of injury.
Cultivate a frolicsome enthusiasm in the morning to counter stiffness, and cautiousness in the evening to avoid hurting yourself. And at any time, if you start feeling uncommonly strong, flexible, and frisky, be careful.
Thats when it is easy to go too far. Study with knowledgeable teachers, but at the same time take responsibility for your own decisions and actions.
Your instructor may be strong and vigorous, and may urge you on, but you have to be the final arbiter of what you are capable of doing. Because many hatha yoga postures make use of unnatural positions, they expose weaknesses in the body, and it is up to you to decide how and whether to proceed. One criterion is to make sure you not only feel fine an hour after your practice, but twenty-four hours later as well.
Finally, honor the contraindications for each posture and each class of postures; if in doubt, consult with a medical practitioner who has had experience with hatha yoga. Learn from the tortoise. Cultivate the patience to move forward steadily, no matter how slow your progress. Remember as well that the benefits of hatha yoga go beyond getting stronger and more flexible, and that if you are monitoring only that realm, you may be disappointed. For any kind of beneficial result you have to be patient.
The main culprit is thinking that you should be able to accomplish something without making consistent effort. That attitude has two unfortunate side effects: So resolve to practice being with your experience in the present moment, enjoy yourself no matter what, and let go of expectations.
The trouble is I do not know which half. The future is a rough taskmaster. Nevertheless, a herd instinct often grips the imaginations of scientists. Like lemmings, we are prone to charge over cliffs when a large enough pack of us moves in that direction. Michael Gershon, in The Second Brain, p.
The first organizing principle underlying human movement and posture is our existence in a gravitational field. Imagine its absence in a spacecraft, where astronauts float unless they are strapped in place, and where outside the vessel little backpack rockets propel them from one work site to another. To get exercise, which is crucial for preventing loss of bone calcium on long voyages, they must work out on machines bolted to the floor.
They cant do the three things that most of us depend on: If they tried to partner up for workouts, all they could do is jerk one another back and forth. And even hatha yoga postures would be valueless; they would involve little more than relaxing and squirming around. Back on earth, it is helpful to keep recalling how the force of gravity dominates our practice of hatha yoga.
We tend to overlook it, forgetting that it keeps us grounded in the most literal possible sense. When we lift up into the cobra, the locust, or the bow postures, we lift parts of the body away from the ground against the force of gravity. In the shoulderstand the force of gravity holds the shoulders against the floor. In a standing posture we would collapse if we did not either keep antigravity muscles active or lock joints to remain erect.
And even lying supine, without the need either to balance or to activate the antigravity muscles, we make use of gravity in other creative ways, as when we grasp our knees, pull them toward the chest, roll from side to side, and allow our body weight to massage the back muscles against the floor.
Keeping in mind that the earths gravitational field influences every movement we make, well turn our attention in the rest of this chapter to the mechanisms that make movement and posture possible. First well look at how the skeletal muscles move the body, then well discuss the way the nervous system controls the operation of the skeletal muscles, and then well examine how connective tissues restrict movement.
If we understand how these three function together within the field of gravity, we can begin to understand some of the principles underlying hatha yoga. Finally, well put it all together in a discussion of three postures. Well begin with the role of skeletal muscles. And in the practice of hatha yoga, it is plainly the musculoskeletal system that enables.
Nevertheless, we are subtly deceived if we think that is the end of the story. Just as we see munchkins sing and dance in The Wizard of Oz and do not learn that they are not autonomous until the end of the story, well find that muscles, like munchkins, do not operate in isolation.
And just as Dorothy found that the wizard kept a tether on everything going on in his realm, so well see that the nervous system keeps an absolute rein on the musculoskeletal system. The two systems combined form a neuro-musculoskeletal system that unifies all aspects of our actions and activities.
To illustrate how the nervous system manages posture, lets say you are standing and decide to sit. First your nervous system commands the flexor muscles muscles that fold the limbs and bend the spine forward to pull the upper part of the trunk forward and to initiate bending at the hips, knees, and ankles. A bare moment after you initiate that movement, gravity takes center stage and starts to pull you toward the sitting position. And at the same timeaccompanying the action of gravitythe nervous system commands the extensor muscles those that resist folding the limbs to counteract gravity and keep you from falling in a heap.
Finally, as soon as you are settled in a secure seated position, the nervous system permits the extensor muscles and the body as a whole to relax. The musculoskeletal system does more than move the body, it also serves as a movable container for the internal organs.
Just as a robot houses and protects its hidden supporting elements power plant, integrated circuits, programmable computers, self-repairing components, and enough fuel to function for a reasonable length of time , so does the musculoskeletal system house and protect the delicate internal organs. Hatha yoga postures teach us to control both the muscles that operate the extremities and the muscles that form the container. The term muscle technically includes both its central fleshy part, the belly of the muscle, and its tendons.
The belly of a muscle is composed of individual muscle fibers muscle cells which are surrounded by connective tissue fibers that run into a tendon. The tendon in turn connects the belly of the muscle to a bone. Under ordinary circumstances muscle cells contract, or shorten, only because nerve impulses signal them to do so. When many nerve impulses per second travel to most of the individual fibers in a muscle, it pulls strongly on the tendon; if only a few nerve impulses per second travel to a smaller population of fibers within the muscle, it pulls weakly on the tendon; and if nerve impulses are totally absent the muscle is totally relaxed.
One of the most persistent misconceptions doggedly surviving in the biomedical community is that all muscles, even those at rest, always keep receiving at least some nerve impulses.
Fifty years of electromyography with fine-wire needle electrodes is at odds with this belief, documenting from the s on that its not necessarily true, and that with biofeedback training we can learn to relax most of our skeletal muscles completely. A muscle usually operates on a movable joint such as a hinge or a ball and socket, and when a muscle is stimulated to contract by the nervous system, the resulting tension is imparted to the bones on both sides of the fulcrum of the joint.
In the case of a hinge such as the elbow that opens to about l80, any muscle situated on the face of the hinge that can close will decrease the angle between the two bones, and any muscle situated on the back side of the hinge will open it up from a closed or partially closed position.
For example, the biceps brachii muscle lies on the inside of the hinge, so it acts to flex the forearm by definition, the segment of the upper extremity between the wrist and the elbow , pulling the hand toward the shoulder. The triceps brachii is situated on the back side of the arm the segment of. We use the words origin and insertion to indicate where muscles are attached to bones in relation to the most common movement at a joint.
The origin of a muscle is on the bone that is relatively or usually stationary, and the insertion of a muscle is on the bone that is most generally moved. Flexion of the elbow is again a good example. Since ordinarily the arm is fixed and the forearm is moved, at least in relative terms, we say that the biceps brachii and triceps brachii take origin from the arm and shoulder, and that they insert on the forearm fig.
The origins and insertions of a muscle can be functionally reversed. When the latissimus dorsi muscle figs. But when we do a chin-up the arm is the relatively stable origin, and the lower back and pelvis become the insertion for lifting the body as a whole. In the coming chapters well see many examples of how working origins and insertions are reversed. The muscles surrounding a joint act cooperatively, but one of themthe agonistordinarily serves as the prime mover, assisted in its role by functionally related muscles called synergists.
While the agonist and its synergists are acting on one side of the joint, muscles on the opposite side act as antagonists. As suggested by the name, antagonists monitor, smooth, and even retard the movement in question. For example, when the biceps brachii and the brachialis in the arm the agonist and one of its synergists shorten to flex the elbow, the triceps brachii on the opposite side of the arm resists flexion antagonistically while incidentally holding the joint surfaces in correct apposition fig.
Muscles also act in relation to the force of gravity. In the lower extremities extensor muscles act as antigravity muscles to keep you upright and resist crumpling to the floor. Flexor muscles are antagonists to the extensors. They can act in two ways. They often aid gravity, as when you settle into a standing forward bend and then pull yourself down more insistently with your hip flexorsthe iliopsoas muscles figs.
But they also act to oppose gravity: Even so, the flexor muscles in the lower extremities are not classified as antigravity muscles, because under ordinary postural circumstances they are antagonists to the muscles that are supporting the body weight as a whole. For the upper extremities the situation is different, because unless you are doing something unusual like taking a walk in a handstand with slightly bent elbows which necessitates a strong commitment from the triceps brachii muscles , the extensor muscles do not support the weight of the body.
In most practical circumstances, it is likely to be the flexors rather than extensors that act as antigravity muscles in the upper extremities, as when you flex an elbow to lift a package or complete a chin-up.
Throughout this book, in order to keep terminology simple and yet precise, Ill stick with strict anatomical definitions of. The same goes for the careless use of the term arm to encompass an undetermined portion of the upper extremity and the careless use of the term leg to encompass an undetermined portion of the lower extremity.
Figure 1. View of the right scapula, arm, and upper part of the forearm from behind and the side from Sappey; see Acknowledgements for discussion of credits regarding drawings, illustrations, and other visual materials.
Just to avoid confusion, Ill not use the word flex except in regard to the opposite of extend. Everyone knows what a first grader means by saying look at me flex my muscles, but beyond this childhood expression, it can lead to ambiguity. For example, having someone flex their biceps results in flexion of the forearm, but flexing the gluteal musclesthe glutsresults not in flexion but in extension of the hips.
For describing yoga postures its better just to avoid the usage altogether. Until getting used to terminology for movements of body parts, it is often a puzzle whether its better to refer to moving a joint through some range of motion, or to moving the body part on the far side of the joint.
For example, the choice might be between saying: Even though the two usages are roughly equivalent, the context usually makes one or the other seem more sensible. For example, sometimes we refer specifically to the joint, as in flex the wrist. In that case, saying flex the hand would be ambiguous because it could mean any one of three things: On the other hand, referring to the body part is often more self-explanatory, as in flex the arm forward Although the alternativeflex the shoulder joint 90isnt nonsensical, its a little arcane for the non-professional.
To understand how the musculoskeletal system operates in hatha yoga we must look at how individual muscles contribute to whole-body activity. The simplest situation, concentric contraction, or concentric shortening, is one in which muscle fibers are stimulated by nerve impulses and the entire muscle responds by shortening, as when the biceps brachii muscle in the arm shortens concentrically to lift a book.
When we want to put the book down the picture is more complicated. We do not ordinarily drop an object we have just liftedwe set it down carefully by slowly extending the elbow, and we accomplish that by allowing the muscle as a whole to become longer while keeping some of its muscle fibers in a state of contraction.
Whenever this happenswhenever a muscle increases in length under tension while resisting gravitythe movement is called eccentric lengthening. We see concentric shortening and eccentric lengthening in most natural activities. When you walk up a flight of stairs, the muscles that are lifting you up are shortening concentrically; when you walk back down the stairs, the same muscles are lengthening eccentrically to control your descent.
And when you haul yourself up a climbing rope hand over hand, muscles of the upper extremities shorten concentrically every time you pull yourself up; as you come back down, the same muscles lengthen eccentrically.
In hatha yoga we see concentric shortening and eccentric lengthening in hundreds of situations. The simplest is when a single muscle or muscle group opposes gravity, as when the back muscles shorten concentrically to lift the torso up from a standing forward bend.
Then as you slowly lower back down into the bend, the back muscles resist the force of gravity that is pulling you forward, lengthening eccentrically to smooth your descent. Most readers are already familiar with the terms isotonic and isometric. Strictly speaking, the term isotonic refers solely to shortening of a muscle under a constant load, but this never happens in reality except in the case of vanishingly small ranges of motion.
Over time, however, the term isotonic has become corrupted to apply generally to exercise that involves movement, usually under conditions of moderate or minimal resistance. Isometric exercise, on the other hand, refers to something more precise holding still, often under conditions of substantial or maximum resistance. Raising and lowering a book repetitively is an isotonic exercise for the biceps brachii and its synergists, and holding it still, neither allowing it to fall nor raising it, is an isometric exercise for the same muscles.
Most athletic endeavors involve isotonic exercise because they involve movement. Japanese sumo wrestling between equally matched, tightly gripped, and momentarily immobile opponents is one obvious exception.
And isometric exercise is also exemplified by any and every hatha yoga posture which you are holding steadily with muscular effort. If few or no nerve impulses are impinging on muscle fibers, the muscle tissue will be relaxed, as when you are in the corpse posture fig. But if a relaxed muscle is stretched, the situation becomes more complex. Working with a partner can make this plain.
If you lie down and lift your hands straight overhead, and then ask someone to stretch you gently by pulling on your wrists, you will notice that you can easily go with the stretch provided you have good flexibility. But if your partner pulls too suddenly or if there is any appreciable pain, the nervous system will resist relaxation and keep the muscles tense; or at the least, you will sense them tightening up to resist the stretch.
Finally, if you allow yourself to remain near your limit of passive but comfortable stretch for a while longer, you may feel the muscles relax again, allowing your partner to pull more insistently.
Many of these same responses are apparent if you set up similar conditions of stretching on your own, as when you place your hands overhead against a wall and stretch the underside of the arms.
This is more demanding of your concentration than relaxing into someone elses work, however, because you are concentrating on two tasks at the same time: But the same rules apply. If you go too far and too quickly, pain inhibits lengthening, prevents relaxation, and spoils the work. To discover for yourself how skeletal muscles operate in hatha yoga, try a warrior posture warrior I with the feet spread wide apart, the hands stretched overhead, and the palms together figs.
Feel what happens as you slowly pull the arms to the rear and lower your weight. To pull the arms up and back, the muscles facing the rear have to shorten concentrically, while antagonist muscles facing the front passively resist the stretch and possibly completion of the posture. As you lower your weight the quadriceps femoris muscle on the front of the flexed thigh resists gravity and lengthens eccentrically.
Finally, as you hold still in the posture, muscles throughout the body will be in a state of isometric contraction. Several important principles of musculoskeletal activity cannot be addressed until we have considered the nervous system and the connective tissues in detail. For now, it is enough to realize that all muscular activity, whether it be contraction of individual cells, isotonic or isometric exercise, agonist or antagonist activity, concentric shortening, or eccentric lengthening, takes place strictly under the guidance of the nervous system.
THE NERVOUS SYSTEM We experience allor at least everything pertaining to the material worldthrough the agency of specialized, irreplaceable cells called neurons, billion of them in the brain alone, that channel information throughout the body and within the vast supporting cellular milieu of the central nervous system the brain and spinal cord.
This is all accomplished by only three kinds of neurons: The sensory information is carried into the dorsal horn of the spinal cord by way of dorsal roots, and the motor information is carried out of the ventral horn of the spinal cord by way of ventral roots.
The dorsal and ventral roots join to form mixed motor and sensory spinal nerves that in turn innervate structures throughout the body figs. Because this is a book correlating biomedical science with yoga, which many consider to be a science of mind, a few comments are required on a subject of perennial, although possibly overworked, philosophical interestthe nature of mind vis-a-vis the nervous system. Speaking for neuroscientists, I think I can say that most of us accept as axiomatic that neurons are collectively responsible for all of our thinking, cognition, emotions, and other activities of mind, and that the totality of mind is inherent in the nervous system.
But I also have to say as a practicing yogi that according to that tradition, the principle of mind is separate from and more subtle than the nervous system, and is considered to be a life principle that extends even beyond the body. They are topics that are not usually taken seriously by working scientists, who usually consider it a waste of time to ponder non-testable propositions, which are by definition propositions that cannot possibly be proven wrong.
Such statements abound in new age commentaries, and are a source of mild embarrassment to those of us who are trying to examine older traditions using techniques of modern science. This says nothing about the accuracy of such proposals.
It may be true, for example, that life cannot continue in the absence of prana. The problem is that short of developing a definition and assay for prana, such a statement can not be testedit can only be accepted, denied, or argued ad infinitum.
It simply stipulates that you must always ask yourself if the nature and content of a statement make it potentially refutable with an experimental approach. To give the benefit of the doubt to the purveyors of such statements, its rare that they are outright fabrications.
On the other hand, one should always keep in mind that all of us including scientists have a huge capacity for deceiving ourselves when it comes to defending our ideas and innovations. The problem is that its often impossible to distinguish fantasy, wishful thinking, mild exaggeration, and imprecise language from out-and-out fraud.
What to do? In the end its a waste of time to make a career of ferreting out errorsone cant get rid of bad ideas by pointing them out. On the other hand, if we turn our attention to propositions that can be tested, the creative attention this requires sometimes brings inspiration and better ideas, which in turn disposes of bad ideas by displacing them.
Lavoisier discredited the theory of phlogiston by pointing to brilliant experiments many of them carried out by others , not by crafting cunning arguments. More than likely, the idea wasnt presented in a straightforward manner, and it usually happens that this masks one or more fatal flaws in the putative reasoning. One dependable test of a concept is whether you can convincingly explain it, along with the mechanics of how it operates, to a third party.
If you find yourself getting your explanation garbled, or if your listener does not comprehend your arguement or is unpersuaded, please examine and research the idea more critically, and if it still does not pass muster, either discard it or put it on the back burner.
I invite the reader to hold me to these standards. To honor them, Ill limit inquiries to what we can appraise and discuss in the realm of modern biomedical science, and to refine and improve my presentation, I ask for your written input and cordial criticism. Microscopic section of dorsal root ganglion above , and three-dimensional view of the first lumbar segment L1 of the spinal cord, showing paired dorsal and ventral roots and mixed motor and sensory spinal nerves from Quain.
Returning to our immediate concerns, it is plain that neurons channel our mindful intentions to the muscles, but we still need working definitions for will and volition. In this book Im arbitrarily defining will as the decision-making process associated with mind, and Im defining volition as the actual initiation of the on and off commands from the cerebral cortex and other regions of the central nervous system that are responsible for commanding our actions.
So will is a black box, the contents of which are still largely unknown and at best marginally accessible to experimentation. The nature and content of volition, by contrast, can be explored with established methods of neuroscience. The neuron is the basic structural and functional unit of the nervous system. Although there are other cell types in the nervous system, namely the neuroglia, or nerve glue cells, which outnumber neurons So the neuron is our main interest.
It has several components: The cellular processes are of two types: Picture an octopus hooked on a fishing line. Its eight arms are the dendrites, and the fishing line is the axon. A typical motor neuron contains many dendrites that branch off the cell body. Its single axonthe fishing linemay extend anywhere from a fraction of an inch away from the cell body to four feet in the case of a motor neuron whose cell body is in the spinal cord and whose terminal ends in a muscle of the foot, or even fifteen feet long in the case of similar neurons in a giraffe.
The axon may have branches that come off the main trunk of the axon near the cell body axon collaterals , and all branches, including the main trunk, subdivide profusely as they near their targets. Dendrites are specialized to receive information from the environment or from other neurons, and. Dendrites of sensory neurons are in the skin, joints, muscles, and internal organs; their cell bodies are in dorsal root ganglia, which are located alongside the spine, and their axons carry sensory information into the spinal cord figs.
Dendrites of motor neurons are located in the central nervous system, and axons of motor neurons fan out from there in peripheral nerves to innervate muscle cells and glands throughout the body. Between the sensory and motor neurons are the association neurons, or interneurons, whose dendrites receive information from sensory neurons and whose axons contact other interneurons or motor neurons that innervate muscles fig.
As a class, the interneurons comprise most of the neurons within the brain and spinal cord, including secondary and tertiary linking neurons that relay sensory signals to the cerebrum, projection neurons that relay motor signals from the cerebrum and cerebellum to intermediary neurons that eventually contact motor neurons of the spinal cord, and commissural neurons that connect the right and left cerebral hemispheresthat is, the right brain and the left brain.
Interneurons put it all together. You sense and ultimately do, and between sensing and doing are the integrating activities of the interneurons. Its true, as the first-grade reader suggests, that you can think and do, but more often you sense, think, and do. To operate the entire organism, neurons form networks and chains that contact and influence one another at sites called synapses. Synaptic terminals of axons at such sites release chemical transmitter substances that affect the dendrite of the next neuron in the chain fig.
The first neuron is the presynaptic neuron, and the neuron affected is the post-synaptic neuron. The pre-synaptic axon terminal transmits to the post-synaptic dendritenot the other way around; its a one-way street.
Two types of transmitter substances are released at the synapse: Thousands of axon terminals may synapse on the dendrites of one post-synaptic neuron, and the level of activity of the recipient neuron depends on its pre-synaptic input. More facilitation yields more activity in the post-synaptic neuron in the form of increasing numbers of nerve impulses that travel down its axon; more inhibition yields diminished activity. For example, the pre-synaptic input of association neurons to motor neurons either facilitates the activity of motor neurons, causing them to fire more nerve impulses per second to skeletal muscles, or it inhibits their activity, causing them to fire fewer nerve impulses per second.
The peacock posture fig. On the other hand, muscular relaxation in the corpse posture fig. Cross-section of the fifth lumbar segment L5 of the spinal cord, with sensory input from a joint receptor, a generic interneuron, and motor output to a skeletal muscle cell.
The small arrows indicate the direction of nerve impulses and pre- to post-synaptic interneuronal relationships. The long heavy arrows indicate the locations of the generic interneuron in the spinal cord dorsal horn and of the motor neuron in the spinal cord ventral horn.
Exercising our volition to create active voluntary movement involves dozens of well-known circuits of association neurons whose dendrites and cell bodies are in the cerebrum, cerebellum, and other portions of the brain, and whose axons terminate on motor neurons. A small but important subset of projection neurons, the subset whose cell bodies are located in the cerebral cortex and whose axons terminate on motor neurons in the spinal cord, are known as upper motor neurons because they are important in controlling willed activity.
These are differentiated from the main class of motor neurons, the lower motor neurons, whose cell bodies are located in the spinal cord. Collectively, the lower motor neurons are called the final common pathway because it is their axons that directly innervate skeletal muscles.
In common parlance, if someone refers simply to motor neurons, they are invariably thinking of lower motor neurons fig. The best way to understand how the motor pathways of the nervous system operate is to examine the.
Well start with one of the most famous: Anyone who grew up in the s and early s will remember the dread of this disease. And then a miraclethe Salk vaccinecame in , putting an end to the fear. Poliomyelitis can be devastating because it destroys the lower motor neurons and deprives the muscles of nerve impulses from the spinal cord, and this results in muscular paralysis.
Our power of volition in the cerebral cortex has been disconnected from the pathway of action out of the spinal cord because the final common pathway has been destroyed. In its most extreme form the resulting paralysis causes muscles to become completely flaccid, and this accounts for its medical name: The same thing happens in a less global fashion when a peripheral nerve is severed or crushed.
Destruction of the lower motor neurons or their axons at any site in the spinal cord or peripheral nerves causes paralysis of all their muscular targets. Will, volition, and active voluntary movement are totally frustrated.
When the upper motor neurons or their axons are destroyed as in an injury or stroke the interruption of blood supply to the brain that destroys the motor region of the cerebral cortex, we lose much of our voluntary control of the lower motor neurons, especially on the side opposite to the site of the injury. Our will can no longer be expressed actively and smoothly.
The ultimate result of this, at least in severe cases in which a vascular mishap occurs at a site where the axons of other motor systems are interrupted along with those of the upper motor neurons, is not flaccid paralysis but spastic paralysis, in which the muscles are rigid and not easily controlled. A semblance of motor function remains because other parts of the nervous system, parts that have been spared injury, also send axon terminals to the lower motor neurons and affect motor function.
The problem is that these supplemental sources of input cannot be controlled accurately, and some of them facilitate the lower motor neurons to such an extent that skeletal muscles are driven into strong and uncontrolled states of contraction. Although most of the time the condition does not result in total dysfunction, severe spastic paralysis is only mildly less devastating than flaccid paralysis; some active voluntary movements are possible, but they are poorly coordinated, especially those that make use of the distal muscles of the extremities fig.
Upper and lower motor neurons. The cell body of an upper motor neuron is shown above in the left cerebral cortex, and its targetthe cell body of a motor neuron whose axon is destined to innervate the right quadriceps femoris muscleis on the right side of the spinal cord.
If the entire spinal cord is severed or severely damaged at some specific level, there are two main problems. First, sensory information that comes into the spinal cord from below the level of the injury cannot get to the cerebral cortex and thereby to conscious awareness. The patient is not aware of touch, pressure, pain, or temperature from the affected region of the body. Second, motor commands from the brain cannot get to the lower motor neurons that are located below the injury.
Spinal cord injuries at different levels illustrate these conditions: Injuries such as these are usually the result of either automobile or sports accidents. REFLEXES So far our discussion has focused on neuronal connections from the top downfrom our intention, to the cerebral cortex, to upper motor neurons, lower motor neurons, and skeletal muscles.
But there is. In this context reflexes have nothing at all to do with the lightning-fast reactions fast reflexes that are needed for expertise in video games or quick-draw artistry.
These reactions refer to unconscious responses carried out at the spinal level. A hypothetical scheme illustrating how injury to a small region of the brain could interrupt pathways important for the precise control of skeletal muscular activity and cause spastic paralysis.
The dotted line represents the systems that have been interrupted, and the solid line represents the remaining systems that cannot control muscular activity accurately by themselves.
Reflexes are simple. That is why they are called reflexes. They always include four elements: More explicitly, the sensory neurons carry nerve impulses from a muscle, tendon, ligament, joint, or the skin to an integrating center in the spinal cord. This integrating center might be as simple as one synapse between the sensory and motor neuron, or it might involve one or more interneurons. The motor neuron, in its turn, innervates muscle cells that complete the action.
By definition, the reflex bypasses higher centers of consciousness. Awareness of the accompanying sensation gets to the cerebral cortex after the fact and only because it is carried there independently by other circuits. There are dozens of well-known reflexes. Well examine three, all of which are important in hatha yoga.
The myotatic stretch reflex, familiar to everyone as the kneejerk, is actually found throughout the body, but is especially active in antigravity muscles fig.
You can test it in the thigh. Cross your knees so that one foot can bounce up and down freely, and then tap the patellar tendon just below the kneecap with the edge of your hand. Find just the right spot, and the big set of quadriceps femoris muscles on the front of the thigh will contract reflexly and cause the foot to fly up. You have to remain relaxed, however, because it is possible to override the reflex with a willed effort to hold the leg in place. The receptors for the myotatic stretch reflex are located in the belly of the muscle, where the dendrites of sensory neurons are in contact with muscle spindlesspecialized receptors barely large enough to be visible with the naked eye.
Named for their shapes, each of these muscle spindles contains a spindle-shaped collection of specialized muscle fibers that are loaded with sensory receptors fig. The reflex works this way: When you tap the patellar tendon to activate the reflex at the knee joint, the impact stretches muscle spindles in the quadriceps femoris muscle on the front of the thigh.
This stretch is as fast as an eyeblink, but it nevertheless stimulates the specific sensory neurons whose dendrites end in the muscle spindles and whose axons terminate directly on motor neurons back in the spinal cord. Those axon terminals strongly facilitate the cell bodies of the motor neurons whose axon terminals stimulate the quadriceps femoris muscle, causing it to shorten and jerk the foot up.
The myotatic stretch reflex is specific in that it feeds back only to the muscle in which the spindle is located.
As with all reflexes, this one takes place a fraction of a second before you are aware of it consciously. You feel it happen after the fact, after the reflex has already completed its circuit. And you notice the sensation consciously only because separate receptors for the modality of touch send messages to the cerebral cortex and thus into the conscious mind. The myotatic stretch reflex. A 3-foot vertical jump momentarily stretches muscle spindles in all the extensor anti-gravity muscles of the lower extremities.
You can feel the myotatic stretch reflex in operation in many sports in which your muscles absorb dynamic shocks. For example, when you are water skiing on rough water outside the wake of a boat, the muscle spindles in the knee extensors of the thighs are stretched by the impact of hitting each wave, and absorbing one bump after another would quickly collapse your posture were it not for the myotatic stretch reflex.
Instead, what happens is that each impact activates the reflex for the quadriceps femoris muscles in a few milliseconds, thus stabilizing the body in an upright position. You can also feel the reflex when you attack moguls aggressively on a ski slope, run down the boulder field of a mountain fig. The reflex is therefore a major contributor to what we interpret as strength in our dynamic interactions with gravity.
Athletes depend on it far more than most of them realize. Stimulating myotatic stretch reflexes repetitively has another important effect: We can see this most obviously in jogging, which only mildly engages the reflexes each time your front foot hits the ground, but engages them thousands of times in a halfhour. This can cause problems if taken to an extreme, and if you tend to be tight you should always do prolonged slow stretching after a run.
On the other hand, if the muscles, tendons, and ligaments are overly loose from too much stretching and too few repetitive movements, joints can become destabilized, and in such cases an activity that tightens everything down is one of the best things you. In hatha yoga we usually want to minimize the effects of the myotatic stretch reflex because even moderately dynamic movements will fire the receptors, stimulate the motor neurons, shorten the muscles, and thereby limit stretch.
Any dynamic movement in hatha yoga activates the myotatic stretch reflexbouncy sun salutations, jumping in and out of standing postures, and joints and glands exercises carried off with flair and toss. These are all fine, especially as warm-ups, but if you wish to lengthen muscles and increase flexibility it is better to move into postures slowly.
The clasp knife reflex acts like the blade of a pocket knife when it resists closure up to a certain point and then suddenly snaps into its folded position.
It is another stretch reflex, but this one causes the targeted muscle to relax rather than contract. The stimulus for the reflex is not dynamic stretch of a muscle spindle, but contractile tension on a sensory receptor in a tendon.
This tension reflexly causes the muscle attached to that tendon to relax and the joint to buckle fig. The sensory receptor for the clasp knife reflex is the Golgi tendon organ. Most of the receptors are actually located near musculotendinous junctions, where they link small slips of connective tissue with their associated muscle fibers.
The Golgi tendon organ is therefore activated by the contraction of muscles cells that are in line in series with the receptor.
Recent studies have clarified that the Golgi tendon organ is relatively insensitive to passive stretch, but that it begins to fire nerve impulses back to the spinal cord as soon as muscle fibers start tugging on it. And then what happens? This is the main idea: If you stimulate the receptor, the reflex relaxes the muscle fig.
It is a precise feedback loop in which the contraction of muscle fibers shuts down their own activity. This feedback loop works something like a thermostat that shuts off the heat when the temperature rises. Anecdotal reports of superhuman strength in which a parent is able to lift an automobile off her child might be due to a massive central nervous system inhibition of this reflex, like a thermostat that stops working and overheats a house. In ordinary life we see the clasp knife reflex in action, at least in a gross form, when two unequally matched arm wrestlers hold their positions for a few seconds, and suddenly the weaker of the two gives way fig.
Whether intentional or not, we constantly make use of the clasp knife reflex while we are practicing hatha yoga. To see it most effectively and to begin to gain awareness of its utility, measure roughly how far you can come into a forward bend with your knees straight, preferably the first thing in the morning.
Then bend the knees enough to flatten the torso against the thighs. Hold that position firmly, keeping the arms tightly wrapped around the thighs to stabilize the back in a comfortable position in relation to the pelvis. Then try to straighten the knees while keeping the chest tightly in place, and hold that position in an intense isometric pull for 30 seconds.
This is the hamstringsquadriceps thigh pull fig. Release the pose and then check to see how much further you can come into a forward bend with the knees straight.
The difference will be a measure of how much the Golgi tendon organs stimulated the hamstring muscles to relax by way of the clasp knife reflex. The Golgi tendon organs are sensitive to manual stimulation as well as to muscular tension. If you manipulate any musculotendinous junction in the body vigorously, its Golgi tendon organs will reflexly cause their associated muscle fibers to relax. This is one of the reasons why deep massage is relaxing.
This is also why body therapists wanting to reduce tension in a specific muscle will work directly on its. Its an old chiropractic trickmanual stimulation stimulates the clasp knife reflex almost as efficiently as contractile tension. Surprisingly, the results last for a day or two, during which time the recipient of the work has a chance to correct the offending musculoskeletal habit that gave rise to the excess tension in the first place. Although you can test the effects of manual stimulation on tendons anywhere in the body, lets experiment with the adductor muscles on the inside of the thighs because tight adductors, more than any other muscles, limit your ability to sit straight and comfortably in the classic yoga sitting postures.
First test your ability to sit in either the auspicious or accomplished posture figs. Then release the pose and lie with the hips butted up firmly against a wall with the knees extended and the thighs spread out as much as possible for an adductor stretch. With the help of a partner to hold your thighs abducted, try to pull the thighs together isometrically, engaging the adductors as much as possible, and at the same time stimulate the Golgi tendon organs in the adductor muscles with vigorous rubbing.
Some of the adductor tendons are the cordlike structures in the inner thighs near the genitals. Others are more flattened and are located further to the rear. All of them take origin from a pair of bones, the inferior pubic rami fig. As you massage the adductors for a minute or so while keeping them under tension, you will feel them gradually release, as evidenced by being able to abduct the thighs more completely.
Then sit up and check for improvement in your sitting posture. The combination of massaging the adductor tendons plus making an isometric effort with stretched adductors powerfully inhibits the motor neurons that innervate these muscles, and this allows them to release and permits you to sit straighter and more comfortably.
The hamstrings-quadriceps thigh pull and the adductor massage give us obvious examples of how the clasp knife reflex operates. It is also invoked in a milder form any time you are able to stay comfortable in an active posture for more than seconds, which is what we often do in hatha yoga.
In this case dont bounce unless you want to induce the myotatic stretch reflex, and dont take a posture into the discomfort zone unless you are prepared to trigger flexion reflexes, which well discuss next. The clasp knife reflex. Final result is relaxation of the muscle, or in this case, loss of the armwrestling match Sappey. The flexion reflexes fig. If you inadvertently touch a hot skillet you jerk your hand back reflexly.
You dont have to think about it, it just happens. As with the other reflexes, awareness comes a moment later.
Flexion reflexes are more complex than stretch reflexes, but they are easier to comprehend because pain is such an obvious part of everyones conscious experience.
Even if it is no more than a feeling of stretch that went too far while you were gardening, a pain in the knee or hip that developed after a strenuous hike, or a neck problem you didnt notice until you started to turn too far in a certain direction, with rare exceptions your automatic response will be flexion.
You may be only vaguely aware of the reflex itself, but you will certainly be aware of the fear and tension that accompanies it. The sensory neurons including their axons that carry the modalities of pain and temperature conduct their nerve impulses more slowly than those that activate the myotatic stretch reflex.
What is more, flexion reflexes are polysynapticthat is, they involve one or more interneurons in addition to the sensory and motor neuronsand each synapse in the chain of neurons slows down the speed of the reaction. You can estimate the conduction time for temperature by licking your finger and touching a. It will take almost a second for the sensation to reach consciousness from a finger, well over a second from a big toe, and, for the adventuresome, about a tenth of a second from the tip of the nose.
Such slow conduction times from the extremities would not serve the myotatic stretch reflex. If, for that reflex, it took a full second for nerve impulses to reach the spinal cord, you would be in serious trouble jumping off a platform onto the floor with bent kneesyou would collapse and shatter your kneecaps before the extensor muscles could react enough to support your weight.
Like the two stretch reflexes we have just considered, the motor reflexes for flexion are spinal, not cerebral. So even if the spinal cord were cut off from the brain, the flexion reflex would still withdraw a foot from a toxic stimulus. A handbook for students and practitioners.
Manual of Smoking Cessation: A Guide for Counsellors and Practitioners. Yoga Anatomy-2nd Edition. Functional Neurology for Practitioners of Manual Therapy. Developing Organizational Simulations: A Guide for Practitioners and Students. Character Recognition Systems: A Guide for Students and Practitioners. The CISG: A New Textbook for Students and Practitioners. Ecosystems and Human Well-Being: A Manual for Assessment Practitioners. Accounting for Non-Accountants: A Manual for Managers and Students.
Scholastic Sanskrit: A Manual for Students. Accounting for Non-accountants: Gray's Anatomy for Students, 2nd Edition. Recommend Documents. Hatha yoga pradipika Yoga Swami Svatmarama. Hatha yoga pradipika Table of Contents Yoga Swami Breviar practic Hatha Yoga A Manual for Students, Teachers, and Practitioners".