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Chapter 11

The Muscular System

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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

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• 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

Fascicle Arrangement

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• 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)

Fascicle Arrangement

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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

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• 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

How Muscles Produce Movement

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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