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The Skeletal Muscle System Chapter 10 • • • • • • • Organization of the Muscular System Functions of Muscles Connective Tissues of Muscles Parts and Shapes of Muscles Actions of Muscles Intrinsic and Extrinsic Muscles Innervation of Muscles Organization of the Muscular System • There are about 600 human skeletal muscles • Muscles are organized and named by: – shapes of muscles – actions of muscles – innervation of muscles Functions of Skeletal Muscles • Movement: – of body parts including bones and non-bony structures like the lips and eyelids – of organ contents during respiration, circulation, digestion, defecation, urination, and childbirth. • Stability: muscles are used to: – maintain posture against gravity – prevent unwanted movement as in resisting wind – hold some articulating bones together such as the humerus and scapula • Communication - speech, hand writing, facial expressions, hand gestures • Control of body openings and passages with ring-like sphincter muscles as around the eyes, mouth, urethra, stomach, intestines. • 85% of body heat production results from skeletal muscle metabolism. Series Elastic Components of the Musculoskeletal System • Connective tissue layers of skeletal muscle tissue are continuous with the connective tissue of bones. • Connective Tissue is extensible and elastic which means that it stretches under tension and recoils when released • Series-elastic Components are all of the interconnected connective tissues in muscle that are attached to the bone membranes – epimysiumperimysiumendomysiumtendon periosteum – adds significantly to power output and efficiency of muscles – help return muscles to their resting lengths Connective Tissues of Muscle • Epimysium – connective tissue sheet that covers a whole muscle – blends into tendons at the ends of the muscles that attach to the periosteum of bone – epimysium is also called the deep fascia – deep fascia is covered with superficial fascia (also called the hypodermis) which is adipose tissue between muscles and skin – epimysium contains blood vessels and nerves • Perimysium – layer of connective tissue surrounding a muscle fascicle (a bundle of muscle cells) – perimysium contains blood vessels and nerves • Endomysium – thin layer of areolar connective tissue surrounding each muscle fiber (muscle fibers = muscle cells) – endomysium contains capillaries and nerves Connective Tissues of Muscle and Bone Tendon Deep Fascia Epimysium Perimysium Endomysium Periosteum Superficial Fascia and Deep Fascia • Superficial Fascia (same as the hypodermis) – found between skin and muscles – adipose tissue with vessels and nerves • Deep Fascia (grades onto the epimysium) – surrounds muscles and neurovascular bundles Skin (epidermis and dermis) Superficial Fascia (hypodermis) Neurovascular Bundle Individual Muscle with Fascicles Deep Fascia Fascicles, Perimysium, Endomysium Endomysium Fascicles, c.s. General Parts of a Skeletal Muscle • Origin – attachment to the more stationary end of a muscle • Belly – thick, middle region of a muscle • Insertion – attachment to the more mobile end of muscle Example: biceps brachii origin is scapula and insertion is radius Muscle Attachments • Connective tissue fibers of a muscle merge with the connective tissue of bone (periosteum). • At the ends of a muscle, the fibers of the Epimysium may form a cable-like tendon or a sheet-like aponeurosis – Tendons merge with the bone periosteum and they are connected by extremely strong Perforating Fibers (Sharpey’s fibers). Stress will tear the tendon before pulling the tendon loose from either muscle or bone – Aponeuroses are flat sheet-like tendons as under the scalp, palm, foot and other areas that attach muscle to the collagen fibers of the dermis. example: palmaris longus tendon fans out to become the palmar aponeurosis Skeletal Muscle Shapes • Fusiform Muscles – thick in middle and tapered at ends – biceps brachii m. • Convergent Muscle – broad at origin and tapering to a narrower insertion – pectoralis major m. • Parallel Muscles – long, uniform,parallel fascicles – shorten more than other muscles – rectus abdominis m. Skeletal Muscle Shapes • Circular Muscles – act as sphincters – ring around body openings – orbicularis oris m. and orbicularis occuli m. • Pennate Muscles – fascicles insert obliquely on a tendon – rectus femoris m. Coordinated Muscle Actions • Agonist is the Prime Mover – produces most of the force • Synergist aids the agonist – stabilizes the nearby joint – modifies the direction of movement that occurs • Antagonist opposes the prime mover – prevents excessive movement and injury • Fixator prevents movement of the bone that the prime mover is attached to Muscle Actions during Elbow Flexion • Agonist = biceps brachii m. • Synergist = brachialis m. • Antagonist = triceps brachii m. • Fixator = rhomboideus major m. that holds the scapula in place Intrinsic and Extrinsic Muscles • Intrinsic Muscles are entirely contained (both origin and insertion) within a region such as the hand like the lumbrical muscles • Extrinsic muscles move the fingers but origin is outside of the hand like the flexor digitorum profundus m.
