This article provides an overview of kinesiology, the study of human movement. This article describes the three major body systems that are involved in movement-the skeletal system, the muscle system and the nervous system. Kinesiology includes the study of how these body systems work, both individually and cooperatively to facilitate the full range of human motions. This article explains the basic components of the skeletal system, including the internal structure of bones, bone development and the major classifications of bones. The muscular system is also described. The muscular system includes various types of muscles that provide the ability to perform movement and exert force through the activation of various muscle groups throughout the body. The information system that connects and commands the various body systems and functions is the nervous system. This article describes the components of the central nervous system-including the brain, spinal cord and neurons-and the peripheral nervous system and motor unit. Finally, the article describes how kinesiology applies to various motor skills, such as the major motion patterns that are involved in the movement of external objects, the ability of the body to maintain balance and support itself and to stop the movement of objects. The following sections explain these concepts in more detail.
Keywords Anatomy; Balance; Bone; Equilibrium; Gravity; Muscle; Nervous System; Range of Motion
Every day, from the time we wake up in the morning until the time we lie down to sleep at night, our body is in motion. This motion may not be immediately obvious, but there are muscular contractions unseen to the human eye that are occurring at all times. Even during sleep, often thought to be a period of inactivity, respiration continues, the beating of the heart slows but never stops and the body changes positions during the course of sleep. Only in paralysis does muscular response cease to exist.
Kinesiology, at its most basic, is the study of movement. Kinesiology is not an isolated science. Instead, kinesiology involves the examination of many sciences as they relate to the human body and movement. This broad discipline brings together the fields of anatomy, physiology, physics and geometry, and examines their relationship to human movement. In addition, kinesiology includes the study of the interrelationship between the major body systems, including the skeletal, muscular and nervous systems. Kinesiology also examines how basic human movements are completed and supported through the cooperation of bone, muscle, neural transmissions and even thought. Thus, kinesiology is a broad field that includes the study of the human body in motion and the collaboration of the body systems that facilitate this process. The following sections provide a more in-depth explanation of these concepts.
Role of the Skeleton in Movement
The human skeleton is the framework of the body. Bones vary in size according to gender and ethnicity, and among individuals within these groups. It is the bones that primarily determine the characteristics of body build. For instance, bone development will determine whether a person will be tall or short, will have thick limbs or slender or whether their hands and feet will be stocky and wide or small and delicate. The bone structure also has a significant impact on the movements of the individual. Certain bone structures are ideal for performing short, quick motions while these same movements would tend to cause imbalance in other bone structures.
In addition to determining body structure, bones serve a number of important purposes. First, bones play a significant role in a person's movement and work. Bones provide not only the dimension of the levers for work in the length of the bones themselves, but also the axes on which these levers turn in the form of joints. Each bone must be rigid and strong to withstand both the force of the muscles which pull upon it, called tension forces, and also the stress of the load which the lever bears, known as compression forces. Likewise, bones must be dense and solid to protect other vulnerable organs and tissues such as the vascular centers within long bones or the heart and lungs enclosed by the thorax. Although all bones play a similar role in framing the body and facilitating movement, the structure and classification of bones vary significantly.
Internal Structure of Bone
The internal structure of bones are made up of two different forms of material—compact bone and cancellous bone.
• Compact bone is the dense, hard exterior of the bone. It has the color and texture of ivory and is exceptionally strong. Holes and channels are intertwined through it to carry blood vessels and nerves from the periosteum - the bone’s membrane covering - to its inner elements.
• Cancellous bone has the appearance of a sponge and develops inside the compact bone. It is comprised of a mesh-like network of miniscule pieces of bone called trabeculae, with marrow filling in the spaces between.
Bones are living tissue and contain various layers. The center of bones consists of a tiny canal known as the Haversian canal through which extends a supply of tiny blood vessels that transport blood and fluids for metabolic needs. Around this central canal lie concentric rings of calcification that also contain canals for tiny capillaries. These layers do not fit together perfectly, and the spaces between are filled with layers of deposits so that the compact bone appears uniform and solid. The cancellous bone shows the same basic system of calcium deposits around circulatory canals, but these layers are not as parallel in arrangement.
Both compact and cancellous bone responds to the pressure and tension forces acting on the bone. The compact bone generally provides strength and protection. The cancellous bone is designed to provide strength while still being lightweight. If stress on a bone is great, the bones become substantial and the holes are smaller and more widely spaced. As stress diminishes, the bones will become less dense over time.
The human body contains 206 bones that support and connect muscles and protect vital organs. At the center of the human skeletal system is the spine and vertebral column, made up of 25 bones that support upright carriage and enable movements such as standing, walking, running, sitting and engaging in all large-muscle movements. In addition, human hands and feet contain slender, finer bones that enable the performance of intricate tasks. Each hand contains 27 bones, including an opposable thumb that provides the ability to perform a wide range of movements such as maneuvering tools, performing meticulous actions or playing musical instruments.
As bones develop, they first emerge as cartilage and are similar in shape and proportion to the ossified, adult bone. The bone changes from this state as a result of ossification. Ossification is the process whereby cartilage is gives way in favor of hard deposits of calcium phosphate and stretchy collagen, which are the two major components of bone. This process is started before birth and is gradually continued until a person reaches the early to mid-30s. In longer bones, the process of ossification takes longer and thus these bones are the last to calcify.
Once bones develop and are calcified, they still remain dynamic and living tissue that can adapt to stress, heal from injury and repair from fractures. The repair process occurs when the cracks or separated ends of a fractured bone first fill in with cartilage and begin bonding together. Over time, they are transformed into a stronger bone than before the facture. This healing process requires the steady supply of blood. The blood supply to both the marrow and the bone itself is profuse, supported by an ample supply of capillaries and blood vessels that transport nutrients for metabolism, bone absorption and replacement and the production of red cells. Through their development and repair process, the bones reveal a great deal about an individual's growth process, reflecting nutritional deficiencies, general health status and even age.
Classification of Bones
Bones are classified according to shape and proportion. Long bones consist of a shaft of compact bone filled with marrow that fills in the spaces between the sections of the cancellous portion. Muscles and tendons attach directly into the membrane that covers bone ends, and in some cases the fibers of tendons reach deep into the bone. Short bones are of irregular shape but are generally equivalent in diameter. They too have cartilage inside and a membrane that covers the outside. Short bones are mostly cancellous bones with a thin outer layer of compact tissue.
Irregular bones vary greatly in their shape, with different parts or projections depending on their purpose. They always contain compact bone as a shell and are filled with cancellous bone if they are of any thickness. Finally, although flat bones are thin, they are seldom flat. The ribs and cranial bones are considered flat bones, but are actually thin and curved. Flat bones are usually made up of outer layers of compact bone or plates of compact bone with a cancellous layer in between for strength. The cross section of flat bones resembles that of a cardboard box, with corrugated layers in between sheets of paper.
Role of the Muscular System in Movement
All movements of the segments of the body are the result of muscle contraction or muscle tension, or of the application of some external force, such as gravity. In muscle contraction, energy is expended to create movement. In muscle tension, the movement is passive and the energy cost of this form of movement is different than muscle contraction. Whenever there is nervous stimulation, it causes contraction or causes the muscle to resist relaxation. This results in muscular tension, which tends to increase the resistance offered to antagonistic muscles, and to slow up or actually check movement. The muscles of the body are a vast and intricate system of cooperation and harmony. There are a number of important muscle groups that are engaged during movement.
Types of Muscles
There are three types of muscles-cardiac, smooth and skeletal or striated-which vary in accordance with their function. Cardiac and smooth muscles have similar functions and are also similar in structure. They both surround hollow organs. Cardiac muscle is the muscle of the heart, and smooth muscle is the power unit of blood vessels, the digestive tract and certain other organs of the viscera. Cardiac and smooth muscles contract slowly, rhythmically and involuntarily. Skeletal muscles are quite different. They contract voluntarily as well as reflexively, and their fibers contract with great rapidity. Skeletal muscles are also usually attached to bones and cartilages. Under an ordinary microscope, skeletal muscles appear to be crossed with striations, whereas the smooth muscles have no such striations.
Movement is produced when some of the over 600 muscles constituting 40% of the human body weight shorten, thereby exerting a pull on the bones to which they are connected. In addition, muscles usually do not produce movements by working individually, but rather by participating with as many as 20 or 30 other muscles. When some muscles contract, muscles on the reverse sides of the joints involved must relax if movement is to be produced. There are approximately 75 pairs of muscles that are directly involved in working in coordination to move the bones to maintain posture, exert force or activate movement.
Muscular contraction can be classified generally into three types: concentric, eccentric and static.
• Concentric contraction occurs when a muscle develops sufficient tension to overcome a resistance and shortens, such as when an individual picks up an object such as a glass. In such a movement, some of the muscles of the arm-the biceps, for instance-shorten as the glass is lifted and moved.
• Eccentric contractions occur when muscles are used to oppose a movement but not to stop it, as in the action of the bicep in lowering the arm gradually after curling a free weight. The main characteristic is that the muscle lengthens during the action. Concentric and eccentric contractions are both called isotonic because the muscle changes length during the movement.
• A static contraction occurs when a muscle that contracts is unable to move the load and retains its original length. The effort exerted by the muscle is insufficient to move the load it is opposing, either because the load is too heavy or because the opposing muscles also contract, thus preventing movement. This type of static muscle contraction is termed isometric because the muscle develops tension without changing length.
Muscles are capable of generating significant force. To do so, muscles are powered by energy, which comes from ingested food that is transformed by the digestive system into chemical energy through a complex metabolic process that requires oxygen for its completion. The primary source of energy for muscles is in the form of glycogen, a carbohydrate that the muscles store in limited quantities and which must be replaced if activity is maintained for a long time. Thus, physical activity is made possible by the action of the heart as it moves oxygenated blood through the circulatory system and by metabolic processes that convert food into energy.
Muscles of the Head
Humans have skilled muscles in the face that allow for a wide variety of facial expressions. Because the muscles are used to express a wide range of emotions, they are an important way to convey meaning in a nonverbal manner. The muscles that are activated in the formation of facial expressions include frontalis, orbicularis oris, laris oculi, buccinator, and zygomaticus. In addition, there are four pairs of muscles...
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