The Muscular System

Contents: Muscle Cell Types  -  skeletal, smooth, cardiac Musculoskeletal System -  Tissues: bones, ligaments,  cartilage, muscles, tendons How We Move Muscles by Name Muscles by Function Motor Developmental Milestones To Learn More    The Muscular  System  (Musculoskeletal System)

Muscle Cell Types There are three types of muscle tissue: . skeletal (or voluntary/striated) muscle, the most abundant tissue in the human body, producing movement. Each skeletal-muscle fiber is roughly cylindrical, contains many nuclei, and is crossed by alternating light and dark bands called striations. Fibers bind together, via connective tissue, into bundles; and these bundles, in turn, bind together to form muscles. Thus, skeletal muscles are composite structures composed of many muscle fibers, nerves, blood vessels, and connective tissue. Skeletal muscles are controlled by the somatic nervous system (SNS). smooth (or visceral) muscle, forming the muscle layers in the walls of the digestive tract, bladder, various ducts, arteries and veins, and other internal organs. Smooth- muscle cells are elongated and thin, not striated, have only one nucleus, and interlace to form sheets rather than bundles of muscles. Smooth muscle is controlled by theautonomic nervous system (ANS). cardiac (or heart) muscle, a cross between the smooth and striated muscles, comprising the heart tissue. Like smooth muscle, it is innervated by the autonomic nervous system  (ANS). Each of more than 600 muscles is served by nerves which link the muscle to the brain and spinal cord.  Skeletal muscle Smooth muscle Cardiac muscle Musculoskeletal System The musculoskeletal system consists of the skeletal system -- bones and joints (union of two or more bones) --  and the skeletal muscle system (voluntary or striated muscles). These two systems work together to provide basic functions that are essential to life, including: Protection: protects the brain and internal organs Support: maintains upright posture Blood cell formation: hematopoiesis Mineral homeostasis Storage: stores fat and minerals. Leverage: A lever is a simple machine that magnifies speed of movement or force. The levers are mainly the long bones of the body and the axes are the joints where the bones meet. Tissues There are 5 basic tissues comprising the musculoskeletal system:  bones,  ligaments (attaching bone to bone)  cartilage (protective gel-like subtance lining the joints and intervertebral discs),  skeletal muscles, and  tendons (attaching muscle to bone).  Detail views: elbow  ligament view skeletal view muscular view Schematic representation of the typical arrangement of musculoskeletal tissues Each of these contains various combinations of 4 connective tissue building blocks: fibroblasts - the "mother" cell, producing the other 3 connective tissue components. collagen - the principal protein manufactured by the fibroblast. Organized into various configurations, these long, thin fibers intertwine to form very strong fibers which do NOT stretch. elastic fibers - highly elastic fibers, unlike collagen, particularly abundant in the walls of arteries. proteoglycans - the "ground substance," or "matrix," in which fibroblasts, collagen, and elastic fibers reside.  How We Move  Skeletal muscles, attached to bone by tendons, produce movement by bending the skeleton at movable joints. The connecting tendon closest to the body or head is called the proximal attachment: this is termed the origin of the muscle. The other end, the distal attachment, is called the insertion. During contraction, the origin remains stationary and the insertion moves.The force producing the bending is always exerted as a pull by contraction, thus making the muscle shorter: Muscles cannot actively push. Reversing the direction in which a joint bends is produced by contracting a different set of muscles. For example, when one group of muscles contracts, an antagonistic group stretches, exerting an opposing pull, ready to reverse the direction of movement. The contracting unit is the muscle fiber.  Muscle fibers consist of two main protein strands - actin and myosin. Where the strands overlap, the fiber appears dark. Where they do not overlap, the fiber appears light. These alternating bands of light and dark give skeletal muscle its characterisitc striated appearance.  The trigger which starts contraction comes from the motor nerve attached to each muscle fiber at the motor end plate. Acetylcholine is released at the motor end plate when the electrical impulse reaches the muscle fiber. As it binds to receptors on the surface of the muscle cells, it causes the electrical impulse to be transmitted in both directions along the fiber, activating the actin and myosin strands. The strands slide past each other to flex, or to shorten, the fiber, thus producing contraction.Muscles by Name Click on the body regions and front/back views to see greater detail    Graphics modified from: The InnerBody: Anatomy Tutorials - Muscle System.             (Front View)        (Back View) Muscle Regions (Master Muscle List) Back  Upper Limb Head and Neck  Thorax  Abdomen  Pelvis and Perineum  Lower Limb  Muscles Names Alphabetical Order Test yourself:  Interactive Tutorial Muscles by Function Each muscle has its own special name. Muscles, however, are also described by their function. Muscles that bend a limb are flexors; those which straighten a limb are extensors (e.g. elbow flexors and elbow extensors.) Muscles which move a limb to the side, away from the body, are abductors; those which move a limb sideways toward the body are adductors (e.g. hip abductors and hip adductors.) Other functional groups are elevators, depressors, rotators, doriflexors, planar flexors, and palmar flexors. Motions and Functions Available at Different Levels of Spinal Cord Injury Source: Class notes for UNCG's CSD 500 Diagnostic Procedures: Inquiry, Observation and Measurement: "Cognitive and Motor Development Screening"  With permission from Mariana Newton,  Instructor.  First Year Good head balance Reaches for object Transfers objects from hand to hand Sitting at 6 months Pulls to standing at 9-10 months Cruises furniture Takes first steps 18-24 months Opens a small box Marks with a pencil Seats self in small chair Points Feeds self with spoon Places square and circle in formboard  Builds a 3 block tower 24-36 months Turns pages of a book Scribbles with pencil Makes tower of 7 blocks Completes 3 piece formboard Kicks ball Walks and runs fairly well Toilet training, with assistance 3-4 years Imitates drawings of circle and cross Builds 10 block tower Imitates building of 4 block train Imitates 3 block bridge Achieving toilet independence Hand dominance Stands on one foot momentarily 4 years Stands heel to toe 15 sec., eyes closed Performs finger to nose well, eyes closed Hops in place on both feet 7/5 sec. 5 years Balances on tiptoe for 10 sec. Hops 15 feet on one foot Parts lips and clenches teeth, no overflow 6 years Balances on one foot for 10 sec. Hits target (10 sq. in.) with ball from 5 feet Jumps over rope 8 inches high 7 years Balances on tiptoes 10 sec., bending at hips Walks straight line, heel to toe for 6 feet 8 years Maintains crouched position on tiptoes for 10 sec., arms extended and eyes closed Touches fingertips of one hand successively with thumb starting with little finger and repeating in reverse order To Learn More Web resources: CID-David: Online Atlas of Human Anatomy - Muscles The InnerBody: Anatomy Tutorials -Muscles Maricopa: Muscular and Skeletal Systems Visible Human Project  See related: PATTS "Significant Body Systems" - Skeletal System PATTS "Significant Body Systems" - Nervous System Brain/Motor Interaction Nerve/Muscle Connection Acknowledgments:  Joel DeLisa and Walter C. Stolov, "Significant Body Systems," in: Handbook of Severe Disability, edited by Walter C. Stolov and Michael R. Clowers. US Department of Education, Rehabilitation Services Administration, 1981, pages 41-45. Catherine Parker Anthony and Gary A. Thibodeau, Textbook of Anatomy & Physiology. St. Louis: Mosby, 1983, pages 498-548. Mariana Newton, Professor emeritus, UNCG Department of Communication Science and Disorders Superficial Muscles Tutorial by Dr. J. Crimando, GateWay Community College, Phoenix, AZ.