Transcript Chapter 3
Chapter 11 The Muscular System 1 How Muscles Produce Movement • Produce movement by exerting force on tendons which in turn pull on bones – Generally cross one joint & are attached to bones of joint – One bone remains stationary & other moves – Attachment sites • Origin = attachmt of muscle tendon to stationary bone • Insertion = attachmt of tendon to movable bone • Insertion moves toward origin – Belly of muscle = fleshy portion between tendons – Actions = movements occurring when muscle is contracted 2 Fascicle Arrangement • Effects of fascicle arrangement – Fibers within fascicles are parallel to each other – Fascicles within muscles arranged in 1 of 5 patterns • Parallel – fascicles parallel to long axis of muscle – terminate in tendons @ either end of muscle – ex: stylohyoid • Fusiform – fascicles nearly parallel to long axis – taper toward tendons – ex: digastric muscle • Circular – fascicles arranged in concentric circles – ex: orbicularis oris 3 Fascicle Arrangement • Effects of fascicle arrgmt (ct’d) • triangular – spread over broad area & converge @ thick, central tendon – ex: pectoralis major • pennate – short fascicles; tendon extends entire length of muscle – 3 subcategories » unipennate = fascicles on one side of tendon (extensor digitorum longus) » bipennate = fascicles on both sides of centrally positioned tendon (rectus femoris) » multipennate = fascicles attached obliquely from a # of directions to several tendons (deltoid) 4 Fascicle Arrangements • A contracting muscle shortens to about 70% of its length • Fascicular arrangement represents a compromise between force of contraction (power) and range of motion – muscles w/ longer fibers have greater range of motion – short fiber can contract as forcefully as a long one 5 How Muscles Produce Movement • Coordination within muscle groups – movement = result of antagonistic muscle pairs @ joints – prime mover (agonist) = muscle that contracts to cause action – antagonist stretches & yields to prime mover – within a pair of muscles, roles of antagonist/prime mover switch with movement produced • ex: biceps/triceps brachii in flexion/extension of elbow 6 Naming Skeletal Muscles • Names of most skeletal muscles are based on several types of characteristics • Characteristics may be reflected in name of muscle – direction of fibers – size of muscle • major = large pectoralis major • minimus = smallest gluteus minimus – shape of muscle • delt = triangular deltoid • rhomb = diamond rhomboid – action of muscle • Adduction of thigh adductor longus – number/site of origins • biceps brachii/femoris: 2 sites of origin • triceps brachii: 3 sites of origin • quadriceps femoris: 4 sites of origin 7