How good are we aware of the operations of systems and mechanisms that make us walk?

Costly research and development efforts are under way in centers throughout the world seeking to build walking robots by mimicking human mobility. After 14 years of research, automotive firms built Asimo, a robot which can walk bipedally and climb stairs like humans. Even though the moves Asimo could make matched those of a one year old baby, it was still considered a great success for the robot technology.

Hardships encountered during these research projects proved walking to be a great miracle, apart from normal habits of movement. We often become aware of how extraordinary movement is and that the moves we repeat hundreds of times, such as walking, running, bending, sitting and standing, are blessings granted to us only when we see someone who has lost some of their mobility.

That humans can walk bi-pedally is truly exceptional. Most organisms have a front leaning skeletal structure and walk on four extremities; they only stand upright when absolutely required to, since it is very difficult for them. Human ability to stand upright and walk on two legs truly signifies them as special amongst creatures, and sets them apart from all of creation. The lively, regal posture of dexterous bipedal humans constitutes very important evidence showing they are “the most superior of all creatures.”

The multifunctional, flexible nature of our skeletal system enables us to complete very simple moves automatically. Walking seems to be a very easy task, however, it occurs as a calculated outcome of many factors, such as determination of stepping distance, the toning of corresponding muscles of the same and opposite direction, relaxation and contraction levels, and relocation of the body’s gravity center.

Walking takes place via the coordinated works of the locomotor (musculoskeletal) system, motor control system, and balance-coordination system.

Locomotor (musculoskeletal) system

The framework of the human body is built together with 206 bones of variable hardness. With their strong nature and capacity to endure extra weights, bones takes up 20% of a body’s mass, and are the major load bearing part of the body’s structure.

The main part of our skeleton is the vertebral column. It consists of 33 small bones, known as vertebrae, positioned on top of each other. Wear-preventing discs are found in between vertebrae to protect against motion related wearing over time. As the vertebral column holds the weight of the upper body, it is created in a way to keep the body upright. The spinal cord inside the channel that is surrounded by the vertebral column is a very important signaling network providing coordination between the brain and other organs.

Joints and ligaments are among the moving parts of our body. The most important joints for walking are the hips, knees, and ankles. The curvy shape of the foot and its contact to the ground at three spots supports bones against body weight and helps with balance. This is why flat footed people struggle with walking and get tired easily. The curves of our spine at the neck, back and waist regions, and the hips, knee joints, and curvature of the foot, are perfectly shaped for standing upright and walking.

In order to move we need a muscle system along with the skeletal system. Muscles are made up of thousands of contractible muscle fibers. There are more than 6 billion muscle fiber motors in the human body. We walk, run, eat, breathe, talk and do many more moves by using ability granted to muscles. Approximately 35 muscles in each leg, and around 100 muscles in the whole body, function during walking.

Ligaments and tendons are links that secure bones and muscles together; they also help to stabilize joints, thus when standing, joints remain in place without muscles contracting.

Four different mechanisms are involved in walking:

1. Proper upright posture and maintenance of balance during walking
2. Forward motion of body via muscle power
3. Reduction of shock-impact effect while stepping
4. Maintenance of motion with the least amount of energy.

A series of movements is generated in the legs to provide a forward motion and these are constantly repeated. These constant repetitions are called the “walk cycle.” The “passing pose” is defined as the time frame when the leg is in the air, and the contact pose is the phase during ground contact. In the middle of the contact pose, even though body is in balance, because of the forward momentum of the body, balance is lost, thus the body leans forward. Balance is then restored by stepping on the ground with the leg in the air. As a result of this rhythmic loss and restoration of balance, the body moves forward.

In a person standing upright, the center of gravity is in front of the fifth vertebra. At the start of a walk, the body leans forward to carry the center of gravity towards the front; then the initiation of the motion via forward transfer of the power with toes and joints takes place, followed by the lifting of the heels, the bending of the knees, and the lifting of the foot, thus displacing the center of gravity of the forward leaning body towards the front.

Balance should be maintained when one leg is lifted in order to let the other leg carry the load of the body’s weight. The gravitational center of the body is located in the distance between the two legs since each leg is located on the side. Body balance is maintained by the contractions of dorsal muscles located across the side of the stepping foot, working in parallel to support and transfer body weight to the foot via the hip and femoral muscles. These events happen so quickly that we often do not even notice all the complicated processes.

The great Sufi figure Abdul-Qadir Gilani was often asked questions such as, “Master, show us a miracle.” He would stand up to walk three to five steps and sit back down. Everybody was confused, looking at each other. One person among them was heard saying, “Master, excuse us but we can all do that as well.” Gilani replied then, “Is there a greater miracle than walking? You see it, but do not understand.”

Motor control of walking

Bodily motions are controlled via the primary motor centers that are located on the side and cortex region of the brain. These centers are created in a way to prepare and organize motor programs involving body movements, and to integrate them with the proprioceptive memory. This synthesis of information enables the adaptation of motor commands to the present posture of the legs and arms regarding intended moves.

A desire to make a move is a necessary prerequisite for the stimulation of muscles pertaining to it. If we want to hold something, we can easily do it; when we want to raise our arm, our elbows bend; to run or walk, our leg muscles start to move and work. How do all of those moves happen? Is our desire enough to do so? Can the guidance of all the bones and muscles, working together towards the same target, happen by itself or occur via coincidences?

In order for muscles to move, our thoughts must be relayed to them and this is provided by the nervous system and nerve network. There is an amazing communication network present in our body. In case of an intended move, an electric signal is sent by the brain. During this journey, which seems to be complicated, the signal arrives at the spinal cord and then quickly diverts to the corresponding organ. Millions of motors that make up the muscle are stimulated by the electric signal, contracting the fibers instantly upon reception of the signal. In order to do a coordinated move, it is necessary to know the related body organs’ positions and their relations to each other. Millions of transmitters that provide this information have been placed throughout the body. This data come from the eyes, the inner ear’s balance and sensory organs, muscles, joints, and skin. There are billions of micro receptors located in muscles and joints programmed to send instantaneous positions of the body to the central nervous system. In every stage of a move, the positions of the muscles are reported instantly to the command center by these micro receptors inside the muscles. New commands are given to the muscles based on the assessments made here. This way, each second, billions of bits of information can be processed and assessed.

The cerebellum is another center that is in charge of functions such as maintenance of balance during walking and standing, carrying out proper and coordinated moves with visual control, providing coordination among muscle groups, promptly starting and stopping movements, and the maintenance and organization of normal muscle toning. The cerebellum is tasked primarily with hastened muscle activities like running, typing, and talking. Thus, fast moves necessary for the balance system are sustained properly and successively without abnormal oscillations.

Specific motion templates have been programmed in the spinal cord for all muscle-covered regions of the body. Rhythmic movements, such as forward and backward motion of the legs and arms, and coordinated activities of other body parts in tandem with walking, are controlled here. The task to control repeated moves like walking is assigned to the nerve network consisting of the spinal cord, brainstem and cerebellum.

Balance and coordination system

One of the requirements to walk and move is to stay in balance. Despite our advanced musculoskeletal system, without balance, this system of ours would be useless, or even dangerous.. Our balance system, which is in charge of the instantaneous control and fine adjustments regarding our body, is granted to us as a blessing of Divine compassion.

There are three systems that provide data involving the positions of the head and body: vestibular system (the apparatus of the inner ear), visual senses, proprioceptive senses

The vestibular structures are an essential part of the balance system. They are found in the inner ear, and are small and complicated systems. This 6.5 mm diameter wide system is composed of semicircular channels that contain specific fluid and ciliated sensory cells that cover the inner linings of the channels. This system constantly reports information involving our status in the outer world and instantaneous changes to the balance system.

When we move, the fluid inside the semicircular inner ear channels get displaced; this motion vibrates the cilia. This vibration causes an electric signal to generate in the cells. This electrical signal is then transmitted to the cerebellum; received information gets evaluated instantly in the cerebellum. This system is created to function autonomously without our will and control. When this system is impaired, balance disorders occur, such as dizziness.

Information regarding our position in the environment and the relative status of the environment according to us is sent to the cerebellum and brainstem via our visual senses.

Proprioceptive senses are formed via the activities of tension receptors built in muscle fibers, tendons and joint capsules. These are sensitive to motions and positions. These receptors regularly provide information to the central nervous system. The cerebellum receives information from all the muscles and joints of the body, including the eyes. These inputs are analyzed very promptly at the cerebellum, and the relative gravitational position of the body is finely calculated, thus the proper motions of muscles are determined. The resulting response is relayed towards muscles by nerves. These events take place in a time frame that does not even last for a hundredth of a second. We easily walk, run, and do complicated moves without feeling any of these activities happening inside us. Yet the calculations taking place in our body even for a single moment of those movements can fill thousands of pages.

To understand the fascinating side of our ordinary movements, let’s consider a person climbing up the stairs. First, the eyes scan the surroundings, then the three dimensional information of positions acquired from the materials and belongings in the environment are transmitted to the brain. Once received, the information is analyzed and the necessary commands are sent to the target organ from the motor centers of the brain. Commands passing through related tracks and centers finally arrive at the musculoskeletal system. Many factors, like the height of stair steps, length and depth of the foot step, center of gravity and position of the body, are calculated and determined almost instantly.

Proprioceptive signals constantly report the positions of organs, like the arms and legs, to the command center. Inner ear receptors are in charge of the prompt transmission of information necessary for balance, like motion, speed, and direction of the body. These inputs are calculated in milliseconds at corresponding centers in order to maintain the coordination and harmony of the entire body. A person who is running up the stairs may think to jump a couple of stairs. This change of command is rerouted to the locomotor system as a new and different command from the brain. All of these processes are completed in centiseconds. In the mean time, the head, shoulders, and arms are employed for rhythmic oscillations in order to adapt to the overall body momentum.

In conclusion, standing and walking are miraculous and take place via thousands of interrelated activities. Nonetheless, we usually do not notice any of the thousands of processes that are constantly taking place. One hopes that every blessing we have is seen through the window of thanksgiving and appreciation.

Kemal Serce is a professor of veterinary medicine in Bursa, Turkey.

They are tiny, and there are billions of them inside you. Tiny machines, one thousand times thinner than a hair strand but strong enough to carry all kinds of material within your cells. Yes, there is a complex army of tiny machines inside your body performing an amazing array of functions while you sit at home sipping your tea.

Your heart is beating. Its lifelong duty is to pump blood to tissues to deliver essential nutrients. Transportation of nutrients continues from blood vessels to cells and then into subcellular compartments. Inside of a cell, there is a need for sophisticated biomachines which are responsible for transport. Did you know that you were equipped with minuscule motors that transported cargos in your cells? Or about cellular highways where molecular cargos are transported?

There are various proteins called “motors” in the cell. They can convert chemical energy to mechanical energy to produce force and motion in the cellular highways.¹ Amazingly, molecular motors are much superior to man-made motors in terms of energetic efficiency by hydrolyzing ATP to fuel enzymatic reactions. These molecular motors include rotary motors, polymerization motors, nucleic acid motors and cytoskeletal motors.

Rotary motors

Bacterial flagellum, used for swimming, acts as a propeller and uses a rotary motor. It has been suggested that this motor is similar to Fo motor found in FoF1-ATP synthase. FoF1-ATP synthase takes part in the conversion of chemical energy in ATP to proton gradient, or vice versa. This chemical reaction involves mechanical rotation of parts of the complex.

Polymerization and nucleic acid motors

Polymerization motors take role in polymerizations and these polymerizations generate forces for repulsion (Actin or microtubule polymerization), or separation of clathrin buds from plasma membrane (Dynamin).

DNA and RNA synthesis also involves the use of molecular motors such as RNA polymerase (RNA synthesis from DNA), DNA polymerase (DNA synthesis), Helicases (separation of double stranded DNA prior to DNA or RNA synthesis), Topoisomerases (removal of supercoiling of DNA), RSC, SWI/SNF, and SMC proteins (Chromatin remodeling and chromosome condensation). Moreover, there are specific viral DNA packaging motors that pack tightly viral DNA into capsids. separation of double stranded DNA prior to DNA or RNA synthesis), Topoisomerases (removal of supercoiling of DNA), RSC, SWI/SNF, and SMC proteins (Chromatin remodeling and chromosome condensation). Moreover, there are specific viral DNA packaging motors that pack tightly viral DNA into capsids.

Cytoskeletal motors

Dyneins, kinesins and myosins denote the three major classes of molecular motor that moves along cytoskeletal structures. Myosin is among the most prominent of motor proteins that takes role in muscle contraction. Kinesin operates on microtubules (long tubes composed of dimers of the protein tubulin, arranged to form 13 parallel tracks) to move cargos inside the cells away from the nucleus (toward positive end of microtubules) and play essential roles in the formation of spindle apparatus and axonal transport. Dynein is also known to transport cargo but in the opposite direction to Kinesin, towards the cell nucleus (toward minus end of microtubules). In addition, dynein is required to beat cilia and flagella.

How molecular motors move

Myosin and kinesin are structurally similar in terms of being dimeric with two motor heads, two legs, and a common stalk. The head regions control the forward movement by binding itself to actin or microtubule filaments. Movement is facilitated by the consumption of ATP by ATPase sites. It is fascinating how these motors translate chemical energy into motion and still be different to the movement of cars. There are different proposals as to how molecular motors move, such as walking (hand-over-hand model), inchworm model, and biased diffusion model.

The-hand-over-hand model suggests that ATP binding induces a conformational change in the forward head movements and keeps fixed, thus leading to the movement of the rear head forward and vice versa. This model, which is also known as the walking model, is similar to upright walking where one foot moves forward while other stay fixed, and vice versa. On the other hand, the inchworm model suggests that only forward head movements use ATP and leads while the other head follows. Studies on the Myosin VI with shorter legs suggested a biased diffusion model. In the diffusion model, the motor moves randomly to the next binding site in a forward direction. In order to find out which mechanism used by molecular motors, scientists measured how much of the head moves following staining with a fluorescent dye. Since molecular motor movements are so small (5-10 nM), optical traps and cantilever probes (>100 μm) were not useful to watch head movements. By increasing both photostability and brightness of organic dyes, Dr. Yildiz at UC Berkeley was able to measure head movements down to 1.5nM scale.

Kinesin: A molecular motor that walks

Kinesins are among microtubule-based motors recently shown to walk like a mountain climber by swapping its two motor units (analogous to feet) in a hand-over-hand mechanism rather than an inchworm mechanism. This recent discovery sheds light on how kinesin moves its cargos such as membrane components, messenger RNA, signaling moleculers, and others along microtubules. In addition, as suggested by findings of Dr. Yildiz, kinesin demonstrates an asymmetric walking where motor heads alternate with slow and fast steps. Further studies using advanced microscopy techniques (called FIONA) which allow nano scale detection of movement down to 2nM resolution demonstrated delicately that processive kinesin motor takes about 8 nM steps (eight-billionths of a meter) for each ATP molecule consumption with alternating 16-nm and 0-nm steps. Furthermore, kinesin is attached to the microtubule while it waits for ATP between steps. Since kinesin is used for long distance cargo transport on relatively big highways of a cell, it elegantly demonstrates a processive motor that reliably travels in a coordinated manner. Of course, not all motors will be moving like kinesin.

Dynein moves through uncoordinated stepping of ring domains

Another motor protein involved in long distance cargo transport is dynein. Dynein is a staggering giant which is much bigger and complex than kinesin and myosin motors. There are about 15 types of dyneins known to take role in cilia and flagella movement and 2 cytoplasmic forms. Cytoplasmic dynein is a homodimeric AAA+ (ATPases associated with cellular activities) motor that transports toward the microtubule minus end, acting opposite to kinesin. FIONA assay demonstrated that the heads moving processively but independently. This mechanism is quite different from the hand-over-hand stepping of kinesin and myosin, for dynein’s steps are not strictly coordinated and highly variable. Most of the time, dynein heads move alternatively with variable head-to-head distance of about 5-50nM. Each head of dynein mostly does not pass each other.

Elegant design, efficiency in transportation and being part of the living system makes molecular motors in the cells superior to man-made motors. Molecular motors travel on cellular highways in the cellular microcosm in the manner of dutiful officials of a king traveling in his domain in security via the fastest modes of transportation and easily cross provincial boundaries, demonstrating more evidently that the Sovereignty of the Eternal King is limitless. Indeed, the signs of His Dominion are reflected by each and every entity from the microcosmic world to macrocosmic universe.

Note

1 Cellular highways are composed of microtubules, microfilaments and actin filaments. Myosin moves along microfilaments through interaction with actin, but dynein and kinesin move along microtubules through interaction with tubulin

References

• DeWitt MA et al. Cytoplasmic dynein moves through uncoordinated stepping of the AAA+ ring domains. Science. 2012 Jan 13;335(6065):221-5. Epub 2011 Dec 8.
• King SM. AAA domains and organization of the dynein motor unit. J Cell Sci. 2000 Jul;113 ( Pt 14):2521-6.
• Wilhelm J. Walter & Stefan Diez. A staggering giant. Nature. Vol 482. 2 February 2012.
• Molecular motors and Motor proteins. Retrieved from Wikipedia on 3/31/2012.
• Yildiz et al. Myosin V Walks Hand-Over-Hand: Single Fluorophore Imaging with 1.5-nm Localization. Science 27 June 2003:Vol. 300 no. 5628 pp. 2061-2065
• Yildiz et al. Kinesin Walks Hand-Over-Hand. Science 30 January 2004: Vol. 303 no. 5658 pp. 676-678

The Qur’an is not a book of sciences. But since sciences deal with nature and man and since sciences and technology constitute a very important aspect of man’s life and are themselves the product of man’s mind, the Qur’an, which contains ‘whatever is wet and dry’ either explicitly or implicitly or by allusion, certainly refers to sciences and scientific advancements. But, while sciences deal with nature and things for their own sake and concentrate on the question of ‘how?’, the Qur’an refers to them for the sake of God and for their most, fundamental purpose as signs of Divine Existence and Unity as the manifestations of Divine Names, and therefore as the means of obtaining knowledge of God. Second, the Qur’an seeks to guide people and inculcate in them belief and high standards of morality. The great majority of people do not have specialized knowledge about scientific facts or theories. It would be inappropriate for a book of guidance directed to all people in all ages to refer to things and natural events in the manner of sciences. If the Qur’an referred to, say, the sun as a heavenly body of such and such size, made up of gases composed of two thousand billion times billion tonnes of matter, with the remains of other elements and in which for every million atoms of hydrogen there are about 85,000 helium atoms, most people would be simply bewildered or indifferent. As the comprehensive and conclusive Revelation, the Qur’an addresses all levels of understanding and intends to be understood, with belief and action to follow understanding. Since most people judge according to their sense-impressions, the Qur’an uses the appropriate language and style. For example, while narrating the story of Dhu’l-Qarnayn, the Qur’an says that he reached the setting-place of the sun and found the sun setting in a fiery muddy spring (18.86). It is obvious that the sun does not set in a spring. But this verse, besides giving many clues to certain facts to be discovered later, considers ordinary sense-impressions. First of all, we understand from the verse that Dhu’l-Qarnayn went as far as the western end of a land adjoining water around which there was not another visible land. That is why most commentators of the Qur’an have concluded that it was the Atlantic Ocean. Second, the verse implicitly states that Dhu’l-Qarnayn did not reach the coasts of the land he conquered in the west but advanced only so far as the point from which he could see the ocean like a spring. Thirdly, when he reached that point, it was a fiery summer day and, most probably because of the vapours rising from the ocean and the marshy land adjoining the sea, it appeared from afar like a muddy spring. Fourthly, the verse contains a subtle and important point. The word translated here as spring also means eye and the sun. As the Qur’an, because of its elevated perspective, looks at the world from ‘on high’ and also there are innumerable eyes watching the world from on high, the ocean from that perspective, however large it may appear to the people in this world, appears no bigger than a spring. Further, there is a subtle allusion here to a time when those who believe in God will gain enough power and equipment to rule, at least, a considerable part of the world and, ascending the heavens, observe the world from on high.

The statement just discussed comprises only five words. All the statements of the Qur’an contain lots of information either explicitly or implicitly and allusively to satisfy all levels of understanding in all times until the Judgement Day. Another example is a statement of only four words: The sun moves (in its course) to a resting-place for it (36.38). Before elucidating other meanings and connotations of this statement, we should remember that in the past people, judging again by their sense-impressions, believed that the earth was motionless while the sun moved around it. Later developments in science and observations showed that the earth spins upon its own axis and orbits the sun which is, relatively, motionless. First of all, since people see the sun moving, the Qur’an mentions it as moving. Second, the Qur’an mentions the sun here as an illustration of the magnificent order prevailing throughout the universe as a sign of God’s Might and Knowledge, The context is as follows:

A sign for them is the night. We strip it of the day, and behold! they are in darkness. And the sun moves (in its course) to a resting-place for it. That is the measuring and ordaining of the All-Mighty, the All-Knowing. And for the moon We have appointed mansions till it returns like an old shrivelled palm-leaf. It is not for the sun to overtake the moon, nor does the night outstrip the day. They float, each in an orbit. (36.37-40)

We understand from the statement in its context that the sun has a vital function in the universal order. The Qur’an uses in the statement mustaqarr, meaning a fixed course to follow, stability and the place in which stability is secured. So, the statement can mean that the sun has a central position in the order of the universe. Second, the preposition used together with the word ‘stability1, li, has three meanings: for, to, and in. Therefore, the exact meaning of the statement comprising four words is: The sun moves following a route or course to a fixed place determined for it for the purpose of its (system’s) stability.

In recent decades, solar astronomers have been able to observe that the sun is not in fact motionless. It quivers and shakes and continually rings like a well-hit gong. These vibrations of the sun reveal vital information about the sun’s deep interior, its hidden layers, information which affects calculations of the age of the universe. Also, knowing exactly how the sun spins internally is important in testing Einstein’s theory of general relativity. Like so many other significant findings in astronomy, this discovery about the sun was totally unexpected. Having discovered the quivering and ringing sun, some astronomers have commented that it is as if the sun were a symphony orchestra, with all the instruments being played simultaneously. All the vibrations combine at times to produce a net oscillation on the solar surface that is thousands of times stronger than any individual vibration.

Commenting on the Qur’anic verse. The sun moves to a resting-place for it, several decades before this totally unexpected discovery in astronomy, Said Nursi had written:

As the word ‘moves’ points to a style, the phrase ‘in its course’ demonstrates a reality. The sun, like a vessel built of gold, travels and floats in the ocean of the heavens comprising ether and defined as a stretched and tightened wave. Although it quivers and shakes in its course or orbit, since people see it running, the Qur’an uses the word travel or float. However, since the origin of the force of gravity is movement, the sun moves and quivers in its orbit. Through this vibration, which is the wheel of its figurative movement, its satellites are attracted to it and preserved from falling and scattering. When a tree quivers, its fruits fall. But, when the sun quivers and shakes, its fruits-its satellites-are preserved from falling. Again, wisdom requires that the sun should move and travel on its mobile throne-its course or orbit-accompanied by its soldiers-its satellites. For the Divine Power has made everything moving and condemned nothing to absolute rest or motionlessness. Divine Mercy allows nothing to be condemned to inertia which is the cousin of death. So, the sun is free, it can travel provided it obeys the laws of God and does not disturb others’ freedom. So, it may actually be travelling, as its travelling may also be figurative. However, what is important according to the Qur’an is the universal order, the wheel of which is the sun and its movement. Through the sun, the stability and orderliness are ensured. [Muhakemat (Reasonings), Istanbul 1988, pp. 68-69.]

Recomended Reading

• BUCAILLE, M. (1987) The Bible, The Qur’an and Science, Taj Company, Delhi.
• JONES, B, (1992) The Night Sky, Salamander Books Ltd.
• NURBAKI, H. (1989) Verses from the Glorious Qur’an and the Facts of Science, T.D.V., Ankara.
• LEIBACHER, J., R. NOYES, J. TOOMRE & R. ULRICH (1985) ‘Helioseismology’, Scientific American (September), pp.48-57.
• BARTUSIAC, M, (1994) ‘Sounds of the Sun’, American Scientist (January-February), pp.61-68.