Musculoskeletal:
The musculoskeletal system (also known as the locomotor system) is an organ system that gives animals the ability to move using the muscular and skeletal systems. The musculoskeletal system provides form, stability, and movement to the human body. It is made up of the body's bones (the skeleton), muscles, cartilage, tendons, ligaments, joints, and other connective tissue (described as the tissue that supports and binds tissues and organs together). The musculoskeletal system's primary functions include supporting the body, allowing motion, and protecting vital organs[1]. The skeletal portion of the system serves as the main storage system for calcium and phosphorus and contains critical components of the hematopoietic system[2]. There are, however, diseases and disorders that may render the function and overall effectiveness of the system. These diseases can be difficult to diagnose due to the close relation of the musculoskeletal system to other internal systems. The "common" musculoskeletal system refers to the system having its muscles attached to an internal skeletal system. However, hydrostatic musculoskeletal systems contain muscles attached to an external exoskeleton in order to function and maintain shape.
[edit] Structures in humans
[edit] Skeletal
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The human skeleton is a complex structure with two distinct divisions. The axial skeleton consists of the skull, vertebral column, and rib cage. The vertebral column is made up of 33 separate vertebrae separated by cartilaginous disks that allow movement. The ribs contain cartilage that allow the rib cage to flex during breathing. The appendicular skeleton is the remaining 126 bones that in the arms, legs and pelvis.[3]
[edit] Muscular
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There are three types of muscles - cardiac, skeletal, and smooth. Smooth muscles are used to control the flow of substances within the lumens of hollow organs, and are not consciously controlled. Skeletal and cardiac muscles are striated; due to the components within their cells, muscles appear striped (striated) when viewed with a microscope. Only skeletal and smooth muscles are part of the musculoskeletal system and only the skeletal muscles can move the body (cardiac muscles are found in the heart and are used exclusively to circulate blood; like the smooth muscles, these muscles are not under conscious control). Skeletal muscles are attached to bones and arranged in opposing groups around joints.[4] Muscles are innervated by nerves, which conduct electrical currents from the central nervous system and cause the muscles to contract.[5]
[edit] Contraction initiation
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In mammals, when a muscle contracts, a series of reactions occur. Muscle contraction is stimulated by the motor neuron sending a message to the muscles from the somatic nervous system. Depolarization of the motor neuron results in neurotransmitters being released from the nerve terminal. The space between the nerve terminal and the muscle cell is called the neuromuscular junction. These neurotransmitters diffuse across the synapse and bind to specific receptor sites on the cell membrane of the muscle fiber. When enough receptors are stimulated, an action potential is generated and the permeability of the sarcolemma is altered. This process is known as initiation.[6]
[edit] Joints
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Joints are structures that connect individual bones and may allow bones to move against each other to cause movement. There are two divisions of joints, diarthroses which allow extensive mobility between two or more articular heads, and false joints or synarthroses that allow little or no movement and are predominantly fibrous. Synovial joints are lubricated by a solution called synovia that is produced by the synovial membranes. This fluid lowers the friction between the articular surfaces and is kept within an articular capsule, binding the joint with its taut tissue.[3]
[edit] Tendons
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A tendon is a tough, flexible band of fibrous connective tissue that connects muscles to bones.[7] Muscles gradually become tendon as the cells become closer to the origins and insertions on bones, eventually becoming solid bands of tendon that merge into the periosteum of individual bones. As muscles contract, tendons transmit the forces to the rigid bones, pulling on them and causing movement.
[edit] Ligaments
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A ligament is a small band of dense, white, fibrous elastic tissue.[3] Ligaments connect the ends of bones together in order to form a joint. Most ligaments limit dislocation, or prevent certain movements that may cause breaks. Since they are only elastic they increasingly lengthen when under pressure. When this occurs the ligament may be susceptible to break resulting in an unstable joint.
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A bursa is a small fluid-filled sac made of white fibrous tissue and lined with synovial membrane. It provides a cushion between bones and tendons and/or muscles around a joint; bursae are filled with synovial fluid and are found around almost every major joint of the body.
[edit] Diseases and disorders
Because many other body systems, including the vascular, nervous, and integumentary systems, are interrelated, disorders of one of these systems may also affect the musculoskeletal system and complicate the diagnosis of the disorder's origin. Diseases of the musculoskeletal system mostly encompass functional disorders or motion discrepancies; the level of impairment depends specifically on the problem and its severity and articular (of or pertaining to the joints[8]) disorders are the most common. Although, primary muscular diseases, neurologic (related to the medical science that deals with the nervous system and disorders affecting it[9]) deficits, toxins, endocrine abnormalities, metabolic disorders, infectious diseases, blood and vascular disorders, and nutritional imbalances are diagnosed as well. Disorders of muscles from another body system can bring about irregularities such as: impairment of ocular motion and control, respiratory dysfunction, and bladder malfunction. Complete paralysis, paresis, or ataxia may be caused by primary muscular dysfunctions of infectious or toxic origin; however, the primary disorder is usually related to the nervous system, with the muscular system acting as the effector organ, an organ capable of responding to a stimulus, especially a nerve impulse.[2]
[edit] Carpal tunnel syndrome
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Carpal tunnel syndrome is a very common condition among the trapped nerve syndromes. It occurs when the median nerve at the wrist is pressured in the carpal tunnel region. This results in the relocation of the median nerve, tendons, and blood vessels, which pass through the carpal tunnel to the fingers and thumb. This compression may cause motor function issues in the hand.[10]
[edit] Osteoporosis
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Main article: osteoporosis
Osteoporosis is a bone disorder related to a change in metabolic rates within a certain bone. It occurs when the rate at which the bone breaks down, bone resorption, increases while formation of the bone decreases, resulting in a loss of bone mass. This condition causes the loss of calcium and phosphate which affects the entire skeletal system. If not treated the spine may curve and the ribs can fall on the pelvic rim.[10]
[edit] Hydrostatic musculoskeletal systems
Among others, cnidarians and annelids, have a hydrostatic skeleton consisting of fluid-filled chambers that use internal pressures generated by muscle contractions to move and maintain the shape of the animals. Animals such as the earthworm and the sea anemone use these hydrostatic skeletons to change their body shape as they move forward. The sea anemone has one set of longitudinal muscles in the outer layer of the body, and a layer of circular muscles in the inner layer of the body. The anemone can elongate or contract its body by contracting these different sets of muscles.[11] Most of these creatures can be considered arthropods, which have muscles attached to an exoskeleton rather than an interior skeletal structure.
- ^ Mooar, Pekka (2007). "Introduction". Merck Manual. Retrieved on 2008-11-12.
- ^ a b Kahn, Cynthia; Scott Line (2008). Musculoskeletal System Introduction: Introduction. NJ, USA: Merck & Co., Inc., http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/90100.htm.
- ^ a b c Gary, Farr (2002-06-25). "The Musculoskeletal System". Retrieved on 2008-11-18.
- ^ Mooar, Pekka (2007). "Muscles". The Merck Manuals Online Medical Library. Retrieved on 2008-11-16.
- ^ Bárány, Michael (2002). "SMOOTH MUSCLE". Retrieved on 2008-11-19.
- ^ "The Mechanism of Muscle Contraction". Principles of Meat Science (4th Edition). Retrieved on 2008-11-18.
- ^ Jonathan, Cluett (2008). "Tendons". Retrieved on 2008-11-19.
- ^ "articular". Random House Unabridged Dictionary. Random House, Inc. (2006). Retrieved on 2008-11-15.
- ^ "neurologic". The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company (2006). Retrieved on 2008-11-15.
- ^ a b Heiserman, David (2004). "The Musculoskeletal System". SweetHaven Publishing Services. Retrieved on 2008-11-18.
- ^ Farabee, M.J. (2001). "Muscular and Skeletal Systems". Retrieved on 2008-10-05.
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