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Kinesiology Lecture 3: Muscle Structure and Function
Terms in this set (39)
Contribute to mobility and stability.
-Can have rotary (mobility) function by producing or controlling the movement of a bony lever around a joint axis.
-Can have a stability function through translatory movement of the bones in the joint, which is joint compression or joint approximation, and by resisting movement.
Skeletal Muscles Help:
To move the joints into and out of close-packed and loose-packed positions.
When a joint is in a close-packed position:
The stability role of the muscles is decreased because the ligaments and joint capsule are taut and support the joint.
When a joint is in the loose-packed position:
The muscles have a larger role in providing stability because the passive supporting structures are slacker.
Describes the basic shape of a whole muscle. Two common shapes:
-Fibers run parallel.
-Examples: Biceps, Triceps, Pectoralis
-Fibers approach the central tendon obliquely
-Form a common angle with the tendon
-Examples: Rectus Femoris, Deltoids, Gastrocmenius
Muscle Fiber: Structure Unit of Muscle
-Range in thickness from about 10 to 100 micrometers
-Range in length from about 1 to 50 cm
-Each fiber is a cell with multiple nuclei
-Within muscle consists of fibers embedded in ground substance. Most fibers are collagen and the remaining are elastin.
-Three different connective tissues occur in muscle:
-Tough structure that surrounds the entire muscle belly
-Contains collagen fibers
-Highly resistive to stretch
-Lies under the epimysium and divides the muscle into fascicles that provide a conduit for blood vessels and nerves
-Tough/resistive to stretch
-Surrounds the individual muscle fibers
-Composed of dense collagen fibrils that are partly connected to the perimysium
-Conveys the contractile force to the tendon
Physiologic Cross-Sectional Area:
-Reflects the amount of contractile protein available to generate force.
-Cross sectional area of fusiform muscle is determined by dividing the muscle's volume by its length.
-A fusiform muscle with thick fibers has a greater cross sectional area.
-Maximal force potential of muscle is therefore proportional to the sum of the cross-sectional area of all the fibers.
-Refers to the angle of orientation between muscle fibers and tendon.
-If fibers are parallel to the tendon, the angle is 0.
-If the angle is greater than 0, then less force is transmitted to the tendon.
-30 degrees transmits 86% of force to the tendon.
-In general pennate muscles produce greater maximal force than fusiform muscle of similar size.
-Oblique arrangement fits more fibers into a given length of muscle.
-The most important characteristic of a muscle is its ability to develop tension and to exert force on the bony lever.
-Tension can be either active or passive and the total tension that a muscle can develop includes both active and passive components.
-Developed by the contractile elements of the muscle. Initiated by the cross bridge formation of movement of the actin and myosin.
-Tension may be increased by increasing the firing of a motor units that are firing
-Recruitment occurs when the muscle is stressed by increasing the load or speed requirements of a movement or when the muscle begins to tire
-Muscle fibers of repeatedly recruited motor units hypertrophy in response to increased resistance or load, thereby increasing strength
-Developed in the non-contractile components of muscle (connective tissue: tendon)
-Connective tissues are slightly elastic and like a rubber band, generate a resistive force when elongated
-Stretching of a muscle elongates both generating a spring-like resistance. This resistance is passive tension.
Parallel Elastic Component:
Connective tissues that surround or lie parallel to the contractile proteins that cause a muscle to contract.
Series Elastic Component:
Connective tissues within the tendon.
Direct relationship between tension development in a muscle and the length of muscle.
Optimal length for developing tension is approximately:
The resting length of a muscle (length when detached from bone)
-This is the length where the actin and myosin filaments are positioned so the maximum number of cross bridges can be formed.
-If the muscle is lengthened or shortened beyond optimal length, the amount of tension that the muscle is able to generate diminishes.
The body unconsciously learns to place muscles at:
Their optimal length for maximum tension development.
Muscles are able to generate:
Moderate tension in the lengthened range, maximum tension in the middle of the contractile range and minimal tension in the shortened range during a concentric or active shortening contraction.
-The diminished ability of a muscle to produce or maintain active tension.
-Usually occurs when the muscle is shortened to a point at which no further sliding of the filaments can take place. The muscle is on slack.
-Muscles that cross more than one joint may reach maximum elongation or shortening prior to attainment of full ROM at all of the joints crossed by the muscle.
Active insufficiency is most commonly encountered when:
Full ROM is attempted simultaneously at all joints crossed by a 2 or multijoint muscle.
Occurs when an inactive, potentially antagonistic muscle is of insufficient length to permit completion of the full ROM available at the joints crossed by the passive muscle.
-Usually occurs at two-joint or multijoint muscles.
-NOTE: Although both active and passive insufficiency are related to the length of a muscle, each state involves very different elements in the muscle.
-Passive insufficiency is due to the passive components of the muscle and active insufficiency is due to the active contractile components of the muscle.
Shortening contraction. The muscle pulls both ends, its attachments on the bones toward the center of the muscle belly.
-Constant length. There is no visible change in the length of the muscle and no movement of either bony attachment. There is a crossbridge formation to produce the tension in the muscle but there is no observable movement of bones because they are fixed in a still position.
Lengthening of the muscle while it is active or tense. The muscle acts as a brake and controls the movement of bones as the two attachments move further apart.
-Same or constant tension throughout the contraction.
-Some researchers assert that an exact equality of tension can only occur in detached muscles, dissected out from the body, lifting vertically against gravity.
-They claim that an isotonic contraction is unphysiological and does not occur in the live human body, because of the bony lever system and the changing torques form different joint angles.
-However, clinically, the term is often used to mean any muscle contraction that produces movement.
-Same or constant velocity. Occurs when the speed of movement of the bone is kept constant through the ROM by a mechanical device such as exercise equipment.
When an agonist is performing a desired motion the antagonist is inhibited or relaxed.
When the agonist and the antagonist contract simultaneously. Co-contraction of muscles around a joint can help provide stability for the joint and is a type of synergy that is helpful in certain situations.
Neutralizing or counteracting synergists, conjoint synergists, and stabilizing or fixating synergists.
Muscles may contract to prevent unwanted movements produced by the prime mover.
Two or more muscles may work together to produce the desired movement. The muscle contracting alone would be unable to produce movement.
Muscles may stabilize or fix a joint proximal to the moving joint to provide a stable base from which the distal moving segment can effectively work.
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