1. 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

2. 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

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

4. 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

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

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

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

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

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

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

11. 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

12. Muscle Physics: Principle III
Force generation depends on current length of muscle or overlap in actin/myosin of sarcomeres
Muscle force strongest between % 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

13. 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

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

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

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

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

18. 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

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

20. 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