Chapter 10

1. Chapter 10 The Muscular System J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.

2. The Muscular System Interactions of Skeletal Muscles in the Body • Muscles usually work in groups, i.e. perform “group actions” • Muscles are usually arranged in antagonistic pairs • flexor-extensor • abductor-adductor, etc.

3. How Skeletal Muscles Produce Movement • Muscles exert force on tendons that pull on bones • Muscles usually span a joint • Muscle contraction changes the angle or position of one bone relative to another Brachialis flexes forearm

4. How Skeletal Muscles Produce Movement origin • Origin: the attachment of the muscle to the bone that remains stationary • Insertion: the attachment of the muscle to the bone that moves • Belly: the fleshy part of the muscle between the tendons of origin and/or insertion belly insertion

5. Interactions of Skeletal Muscles in the Body • Prime Mover (agonist): the principle muscle that causes a movement • ex: biceps brachii, flexion of forearm • Antagonist: the principle muscle that causes the opposite movement • ex: triceps brachii, extension of forearm

6. Interactions of Skeletal Muscles in the Body • Synergists: muscles that assist the prime mover • ex: extensor carpi (wrist) muscles are synergists for the flexor digitorum muscles when you clench your fist • Fixators: synergists that stabilize the origin of a prime over • ex: several back muscles that stabilize scapula when the deltoid flexes the arm

7. Functional Roles of Skeletal Muscles • Group actions: most movements need several muscles working together While the prime mover (agonist) and synergists are contracting to provide the desired movement • other muscles (antagonists) are relaxing & being stretched out passively • agonist and antagonist change roles depending on the action • e.g., abduction versus adduction • Synergists and fixators become agonists and antagonists in different movements

8. Naming Skeletal Muscles • Location of the muscle • Shape of the muscle • Relative Size of the muscle • Direction/Orientation of the muscle fibers/cells • Number of Origins • Location of the Attachments • Action of the muscle Know the muscle names as described in Lab Guide 6!

9. Muscles Named by Location • Epicranius (around cranium) • Tibialis anterior (front of tibia) tibialis anterior

10. Naming Skeletal Muscles by Shape Trapezius • Deltoid (triangle) • Trapezius (trapezoid, 2 parallel sides) • Serratus (saw-toothed) • Rhomboideus (rhomboid, 4 parallel sides) • Orbicularis and sphincters (circular) Deltoid Rhomboideus major Serratus anterior

11. Muscles Named by Size Psoas minor • Maximus (largest) • Minimis (smallest) • Longus (longest) • Brevis (short) • Major (large) • Minor (small) Psoas major

12. Muscles Named by Direction of Fibers Rectus abdominis • Rectus (straight)-parallel to long axis • Transverse • Oblique External oblique

13. Muscles Named for Number of Origins • Biceps (2) • Triceps (3) • Quadriceps (4) Biceps brachii

14. Muscles Named for Origin and Insertion Sternocleidomastoid originates from sternum and clavicle and inserts on mastoid process of temporal bone insertion origins

15. Muscles Named for Action • Flexor carpi radialis (extensor carpi radialis) –flexes wrist • Abductor pollicis brevis (adductor pollicis) –flexes thumb • Abductor magnus – abducts thigh • Extensor digitorum – extends fingers Adductor magnus

16. Arrangement of Fascicles • Parallel (strap-like), ex: sartorius • Fusiform (spindle shaped), ex: biceps femoris

17. Arrangement of Fascicles • Pennate ("feather shaped"), ex: extensor digitorum longus • Bipennate, ex: rectus femoris • Multipennate, ex: deltoid

18. Arrangement of Fascicles • Convergent, ex: pectoralis major • Circular (sphincters), ex: orbicularis oris

19. Arrangement of Fascicles • Range of motion: depends on length of muscle fibers (fascicles); long fibers = large range of motion • parallel and fusiform muscles • Power: depends on total number of muscle fibers; many fibers = great power • convergent, pennate, bipennate, multipennate

20. Lever Systems and Leverage • Lever: i.e. bones, a rigid rod that moves on some fixed point • Fulcrum: i.e. joint, a fixed point • Resistance: • the force that opposes movement • the load or object (bone or tissue) to be moved • Effort: • the force exerted to achieve a movement • the effort is provided by muscle(s) • Motion is produced when the effort exceeds the resistance (isotonic contraction)

21. Lever Systems and Leverage • Leverage: the mechanical advantage gained by a lever • Power: muscle tension (effort) farther from joint (fulcrum) produces stronger contraction (opposes greater resistance) • Range of motion (ROM): muscle tension (effort) closer to joint (fulcrum) produces greater range of motion.

22. Mechanical Advantage • Load is near fulcrum, effort is far away • Only a small effort is required to move an object • Allows a heavy object to be moved with a small effort • Example: car jack

23. Mechanical Disadvantage • Load is far from the fulcrum, effort is near the fulcrum • a large effort is required to move the object • allows object to be moved rapidly, a “speed lever” • throwing a baseball

24. Lever Systems and Leverage • First-class lever: (EFR) Effort-Fulcrum-Resistance

25. Leverage Systems and Leverage • Second class lever: (FRE) Fulcrum-Resistance-Effort

26. Leverage Systems and Leverage • Third-class lever: (FER) Fulcrum-Effort-Resistance

27. Skeletal Muscles Know the muscles, their origins and insertions as described in your Lab Guide 6.

28. Additional Information • You do not need to memorize the details of the different leverage system types for Exam 3. • Slides with some examples of the naming of muscles can be found in the PowerPoint presentation for Lab 6.

29. End Chapter 10