The human cerebrum is divided into two hemispheres, the right and left. These sides are not identical to one another in structure or function. The right hemisphere is in charge of coordinating functions related to the left side of the body, and the left part of the brain controls the right side of the body. To date, science hasn’t been able to explain the reason for this split.

There are other differences between the hemispheres, including functions like speech and motor skills. For example, in 90% of people, speech and hand skills are centered in the left hemisphere. However, skills such as drawing, architecture, or sense of perspective – skills that are spatial and dimensional – are dominated by the right hemisphere. While the two hemispheres are employed for various tasks, they communicate with each other. For this to happen, a structure called the corpus callosum, which contains only axons as nerve extensions, is placed between the two hemispheres and enables the transfer of information. For instance, if a needle sticks your left hand, this is perceived by the right hemisphere. In patients where the corpus callosum is missing or disconnected, when an image of a red apple is shown with the left eye closed and again with the right eye shut, the patient will report having seen no apple.

The lack of a corpus callosum is rarely encountered as a birth defect (corpus callosum agenesis). In this instance, there is rarely a deficiency when it comes to movements and sensory receptions. Activities such as speaking, standing, balancing, walking and running are almost similar to normal levels.

In the case of epilepsy, an abnormal electric current is observed in the cerebrum. The corpus callosum can be cut by surgery, disconnecting the two hemispheres in order to prevent the dispersal and transfer of abnormal electricity to the other hemisphere of the brain.

These days, this surgery is not implemented unless necessary. Obviously, performing this surgery means communication between the two hemispheres is interrupted; the tasks that are assigned to the right brain remain only in the right and the ones assigned to the left brain stay in the left. This can complicate basic motor skills. For instance, if a person wants to write or throw a ball with two hands, this task is first planned in the left hemisphere, then it is transferred to the motor-skill regions found in both hemispheres via the corpus callosum. These skills are developed via both sides of the brain and our hands, and usually one hand is better in these skills than the other. Because the left brain is usually dominant, most people are right handed.

Schizophrenia is a permanent psychiatric disease that affects a person’s emotions, thoughts, and behaviors. It means being split-minded, or the separation of the mind (in Greek, schizo means split, or divided, and phrenos means mind). In schizophrenia, the coordination between the hemispheres is disrupted and the two hemispheres intervene simultaneously to solve the same problem. Briefly, it may not cause a problem if a specific task requires only one hemisphere to be in charge; however, complications arise when both hemispheres try to solve the same job. In schizophrenic patients, it has been reported that a problem exists in the corpus callosum; therefore, communications are hindered between them. This results in a disruption.

At this point, some questions may arise. Why is our body controlled by two brain regions that have different jobs? Why do these two hemispheres communicate? What would happen if our brain was not built in two parts?

It’s hard to give answers to these questions. Sometimes, we end up with nothing to say but, “if God creates in this way, then it must be in the most beautiful form.” There is nothing useless, extra and unnecessary in the human body. But the following can be hypothesized regarding the two sided functioning of the brain: cerebral hemorrhages always occur in only one side of the brain. Speech is lost if the left side is injured, and spatial and geometrical skills are lost when the right side is injured. Therefore, maybe while a function is lost on one side, the functions of the other side are conserved.

Though the different hemispheres of the brain are in charge of different functions, they successfully fulfill their duty to activate our bodily functions through constant communication. Despite continuing clinical studies, the full extent of the brain’s power remains mysterious. Its incredible design, which allows the body to function so perfectly, is a sign of humanity’s remarkable architecture.

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