Clinical Kinesiology and Anatomy, Chapter 6: Muscular System PDF

Book cover for Clinical Kinesiology and Anatomy, Seventh Edition. Chapter 6 Muscular System Copyright ©2023 F.A. Davis Company  Characteristics of Muscle  Normal resting length: the length of a...

Book cover for Clinical Kinesiology and Anatomy, Seventh Edition. Chapter 6 Muscular System Copyright ©2023 F.A. Davis Company  Characteristics of Muscle  Normal resting length: the length of a muscle when it is not shortened or lengthened by active contraction or the application of external force  Four properties of muscle Irritability Contractility Extensibility Elasticity Copyright ©2023 F.A. Davis Company  Irritability  Ability to respond to a stimulus, an impulse from a nerve or external stretch resulting in a contraction Copyright ©2023 F.A. Davis Company  Contractility  Ability to contract generating force when adequate stimulus is applied Concentric: shortening Eccentric: lengthening Isometric: no length change Copyright ©2023 F.A. Davis Company  Extensibility  Ability to lengthen when a force is applied Copyright ©2023 F.A. Davis Company  Elasticity  Ability to return to normal resting length when force is removed Return from lengthened or shortened position Copyright ©2023 F.A. Davis Company  Anatomy of a Muscle  A muscle is a collection of muscle fibers bound together into bundles termed fascicles.  Each muscle fiber is composed of smaller bundles termed myofibrils. Copyright ©2023 F.A. Davis Company  Anatomy of a Muscle (continued_1)  Myofibrils are divided into sarcomeres.  Sarcomeres is where length change occurs.  Sarcomeres contain two types of filaments: thin actin and thicker myosin.  Filaments are attached to z-lines. Copyright ©2023 F.A. Davis Company  Anatomy of a Muscle (continued_2)  Two actin filaments are on each side of a myosin filament.  Actin filaments do not extend into the middle of a sarcomere.  Projecting from myosin filaments are myosin heads, which contract and temporarily bind with actin filaments when muscle is activated. Copyright ©2023 F.A. Davis Company  Anatomy of a Muscle (continued_3) Copyright ©2023 F.A. Davis Company  Sliding Filament Theroy  Binding of myosin heads to actin is termed cross-bridges  When myosin heads bind with actin, the actin filament slides closer to or away from the actin filament on the other side of the gap Shortening contraction: actin filament moves toward the gap in the middle of the sarcomere Lengthening contraction: actin filaments move apart Copyright ©2023 F.A. Davis Company  Sliding Filament Theroy (continued)  The number of cross-bridges formed determines the force generated.  At resting length, the maximum number of cross-bridges can be formed.  When muscle length is greater or less than resting length decrease in formation of cross-bridges Copyright ©2023 F.A. Davis Company  Fiber Types  Type I: termed slow twitch or slow oxidative Smaller in diameter Slower to respond to stimulus Sustain longer periods of contraction Rich blood supply—red Use oxygen as energy source Characteristics mean type I fibers are better for endurance and low levels of force production Postural muscles Copyright ©2023 F.A. Davis Company  Fiber Types (continued)  Type II: termed fast twitch or fast glycolytic Larger in diameter Respond quickly to stimulation Relax quickly after stimulation, avoiding fatigue Less blood supply—pale (white) Use existing stores of glycogen as energy source Prone to fatigue Effective for short bursts of contraction: Copyright ©2023 F.A. Davis Company  Motor Units  Muscle fibers innervated by the same motor neuron  Fibers not all bundled together but are distributed among several fascicles  Number of muscle fibers in a motor unit varies Precision movements use motor units with fewer number of muscle fibers Power movement use motor units with greater number of muscle fibers Copyright ©2023 F.A. Davis Company  Motor Units (continued)  Gradation of number of motor units recruits based on force required  Musculotendinous junction: place where muscle joins tendon  Tenoperiosteal junction: place where tendon joins bone  Origin: proximal muscle attachment  Insertion: distal muscle attachment Copyright ©2023 F.A. Davis Company  Muscle Fiber Arrangement  Amount of force muscle can generate is directly proportional to the cross- sectional area of the muscle  Cross-sectional area is related to muscle fiber orientation  Parallel muscle fibers Fibers extend entire length of muscle Copyright ©2023 F.A. Davis Company  Muscle Fiber Arrangement (continued_1)  Oblique muscle fibers More cross-sectional area possible Shorter fibers Attach obliquely to tendon  Angle of insertion: angle at which a muscle attaches to a bone or other structure Changes through ROM  Line of pull: line drawn from origin to insertion of muscle accounting for twist and turns along the path Copyright ©2023 F.A. Davis Company  Muscle Fiber Arrangement (continued_2)  Angle of pennation: angle at which oblique fibers within a pennate or multipennate muscle attach to muscle tendons  Regardless of angle of insertion or angle of pennation, all muscle force generated contributes to the osteokinematic motion about a joint axis and the traction or compression force through a joint. Copyright ©2023 F.A. Davis Company  Muscle Shapes Copyright ©2023 F.A. Davis Company  Muscle Names  Location: anterior tibialis  Shape: quadratus lumborum  Action: flexor digitorum  Number of heads/divisions: biceps brachii  Attachments: sternocleidomastoid  Fiber orientation: external oblique  Size: extensor radialis longus Copyright ©2023 F.A. Davis Company  Roles of Muscles  Agonist: muscle responsible for desired motion Determined by size, location, line of pull, contractile ability  Antagonist: muscle that performs the opposite motion of the agonist  Co-contraction: simultaneous contraction of agonist and antagonist Copyright ©2023 F.A. Davis Company  Roles of Muscles (continued)  Synergist: two or more muscles contracting together to produce motion that neither can perform individually Copyright ©2023 F.A. Davis Company  Types of Muscle Contraction  Isometric contraction Force produced without change in muscle length  Concentric contraction Muscle attachments move toward each other Shortening contraction Generally overcoming the effect of gravity Open kinetic chain configuration: insertion moves toward origin Copyright ©2023 F.A. Davis Company  Types of Muscle Contraction (continued)  Eccentric contraction Muscle attachments move away from each other Lengthening contraction Open kinetic chain: insertion moves away from origin Generally slowing down the effect of gravity Copyright ©2023 F.A. Davis Company  Active Insufficiency Passive Insufficiency  Multi-joint muscles  Active insufficiency Unable to actively shorten simultaneously through full ROM at all joints spanned  Passive insufficiency Unable to lengthen simultaneously through full ROM at all joints spanned Copyright ©2023 F.A. Davis Company  Active Insufficiency Passive Insufficiency (continued)  Tenodesis: closing of fist through passive insufficiency Allows some grasp and release for those who cannot actively grasp and release Copyright ©2023 F.A. Davis Company  Adaptive Lengthening Adaptive Shortening  Muscle length changes when maintained in a lengthened or shortened position for prolonged periods Not necessarily stronger or weaker Point in ROM of greatest force production shifts Loss of sarcomeres: adaptive shortening Addition of sarcomeres: adaptive lengthening Copyright ©2023 F.A. Davis Company  Common Pathologies of Muscle and Tendon  Strain: overstretching  Rupture: complete tearing of a tendon  Trigger points: hyperirritable painful points in a muscle  Tendonitis: inflammation of a tendon Copyright ©2023 F.A. Davis Company