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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. Muscle Structure Review. Muscle fiber = muscle cell

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mechanics of movement ii muscle action across joints

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
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
Muscle Origin and Insertion
  • Origin
    • Proximal
    • Fixed
  • Insertion
    • Distal
    • Moves
  • (usually!!)

Fig. 10.3

Frolich, Human Anatomy, Mechanics of Movement

mechanics of contraction
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
Visualizing muscle contraction

How actin-myosin complex (sarcomere)

shorten muscle

Fig. 10.7

Frolich, Human Anatomy, Mechanics of Movement

summary of muscle organization function
Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement

summary of muscle organization function7
Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement

summary of muscle organization function8
Summary of Muscle Organization/Function

Frolich, Human Anatomy, Mechanics of Movement

slide9

Levels of Muscle Organization

Table 10.2

Frolich, Human Anatomy, Mechanics of Movement

muscle physics principle i
Muscle Physics: Principle I
  • Cross sectional area is proportional to Force of muscle

Frolich, Human Anatomy, Mechanics of Movement

muscle physics principle ii
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
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
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
Muscle movement across joints is like lever system

Fig. 11.1

Frolich, Human Anatomy, Mechanics of Movement

first class lever
First-class lever

Fig. 11.2

Frolich, Human Anatomy, Mechanics of Movement

second class lever
Second-class lever

Fig. 11.2

Frolich, Human Anatomy, Mechanics of Movement

third class lever
Third-class lever

Fig. 11.2

Frolich, Human Anatomy, Mechanics of Movement

stabilization and control around joint
Stabilization and Control Around Joint
  • 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
Agonist/Antagonist

Frolich, Human Anatomy, Mechanics of Movement

relation between muscle contraction or firing and shortening
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