Frolich, Human Anatomy, Mechanics of Movement

Mechanics of Movement II: Muscle Action Across Joints

Review muscle force generationMuscle Physics

--force versus cross section--length versus strain

Lever mechanicsStabilizing the joint—isometric and eccentric contraction

Frolich, Human Anatomy, Mechanics of Movement

Muscle Structure Review

Muscle fiber = muscle cell Fibers lined up = direction of pull Tendon attaches to bone Muscle pulls on bone

Fig. 10.1

Frolich, Human Anatomy, Mechanics of Movement

Muscle Origin and Insertion

Origin 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

Fig. 10.7

How actin-myosin complex (sarcomere)shorten muscle

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

Table 10.2

Levels of Muscle Organization

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

First-class lever

Fig. 11.2

Frolich, Human Anatomy, Mechanics of Movement

Second-class lever

Fig. 11.2

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

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)