Functions of the Muscular System
Maintenance of posture
Production of body heat
Constriction of organs and vessels
ability of a muscle to shorten with force
capacity of muscle to respond to a stimulus
muscle can be stretched to its normal resting length and beyond to a limited degree
ability of muscle to recoil to original resting length after stretched
Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
Walls of hollow organs, blood vessels, eyes
Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow
Heart: major source of movement of blood
Skeletal Muscle Structure
Composed of muscle cells (fibers), connective tissue, blood vessels, nerves
Fibers are long, cylindrical, multinucleated
Tend to be smaller diameter in small muscles and larger in large muscles. 1 mm- 4 cm in length
Develop from myoblasts; numbers remain constant
Striated appearance due to light and dark banding
Loose C.T. with reticular fibers.
Delicate, reticular fibers. Surrounds sarcolemma (cell membrane of a muscle fiber)
Denser C.T. surrounding a group of muscle fibers. Each group called a fasciculus
C.T. that surrounds a whole muscle (many fascicles)
connective tissue sheet
Forms layer under the skin
Holds muscles together and separates them into functional groups.
Allows free movements of muscles.
Carries nerves (motor neurons, sensory neurons), blood vessels, and lymphatics.
Continuous with connective tissue of tendons and periosteum.
Nerves and Blood Vessel Supply
Motor neurons: stimulate muscle fibers to contract. Nerve cells with cell bodies in brain or spinal cord; axons extend to skeletal muscle fibers through nerves
Axons branch so that each muscle fiber is innervated
Capillary beds surround muscle fibers
Cell packed with myofibrils within cytoplasm
Composed of protein threads called myofilaments: thin (actin) and thick (myosin)
Sarcomeres: highly ordered repeating units of myofilaments