Mechanics of Movement II: Muscle Action Across Joints Review muscle force generation Muscle Physics --force versus cross section --length versus strain Lever mechanics Stabilizing the joint—isometric and eccentric contraction Frolich, Human Anatomy, Mechanics of Movement

Muscle Structure Review Fig. 10.1 Muscle fiber = muscle cell Fibers lined up = direction of pull Tendon attaches to bone Muscle pulls on bone Frolich, Human Anatomy, Mechanics of Movement

Muscle Origin and Insertion Proximal Fixed Insertion Distal Moves (usually!!) Fig. 10.3 Frolich, Human Anatomy, Mechanics of Movement

Mechanics of Contraction Muscle cell is unit Role of actin/myosin Action potential or depolarization of membrane makes cell “contract” (motor neuron action potential stimulates muscle membrane depolarization) Fig. 10.4 Frolich, Human Anatomy, Mechanics of Movement

Visualizing muscle contraction How actin-myosin complex (sarcomere) shorten muscle Fig. 10.7 Frolich, Human Anatomy, Mechanics of Movement

Summary of Muscle Organization/Function Frolich, Human Anatomy, Mechanics of Movement

Summary of Muscle Organization/Function Frolich, Human Anatomy, Mechanics of Movement

Summary of Muscle Organization/Function Frolich, Human Anatomy, Mechanics of Movement

Frolich, Human Anatomy, Mechanics of Movement Levels of Muscle Organization Table 10.2 Frolich, Human Anatomy, Mechanics of Movement

Muscle Physics: Principle I Cross sectional area is proportional to Force of muscle Frolich, Human Anatomy, Mechanics of Movement

Muscle Physics: Principle II Length of muscle is proportional to ability to shorten (strain) Number of sarcomeres in series gives shortening ability Short, fat muscles Lots of force Less shortening range Long, skinny muscles Less force More shortening range Frolich, Human Anatomy, Mechanics of Movement

Muscle Physics: Principle III Force generation depends on current length of muscle or overlap in actin/myosin of sarcomeres Muscle force strongest between 80-120% of normal resting length—WHY? (don’t forget role of cross-bridges) Most muscles arranged to work in this range Frolich, Human Anatomy, Mechanics of Movement

Types of fascicle arrangements Affects length and cross section of muscle Thus affects force and shortening properties of muscle See Muscle Physics Principles I-III if this doesn’t make sense Fig. 11.3 Frolich, Human Anatomy, Mechanics of Movement

Muscle movement across joints is like lever system Fig. 11.1 Frolich, Human Anatomy, Mechanics of Movement

Frolich, Human Anatomy, Mechanics of Movement First-class lever Fig. 11.2 Frolich, Human Anatomy, Mechanics of Movement

Frolich, Human Anatomy, Mechanics of Movement Second-class lever Fig. 11.2 Frolich, Human Anatomy, Mechanics of Movement

Frolich, Human Anatomy, Mechanics of Movement Third-class lever Fig. 11.2 Frolich, Human Anatomy, Mechanics of Movement

Stabilization and Control Around Joint Agonist Main Mover E.g. biceps Antagonist Opposite motion E.g. triceps Synergist Aids agonist E.g. brachialis Antagonist often “fires” or contracts or is stimulated simultaneously with agonist to stabilize around joint during movement NOTE: Muscle “contraction” or stimulus to “fire” does not always result in muscle shortening Frolich, Human Anatomy, Mechanics of Movement

Frolich, Human Anatomy, Mechanics of Movement Agonist/Antagonist Frolich, Human Anatomy, Mechanics of Movement

Relation between muscle contraction (or “firing”) and shortening Concentric contraction—muscle contracts and shortens to cause movement across joint Isometric contraction—muscle contracts but stays same length to hold joint or body in same position Eccentric contraction—muscle contracts while lengthening to stabilize joint during movement (most common in antagonist to slow movement caused by agonist) Frolich, Human Anatomy, Mechanics of Movement