1. J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
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 (straight)-parallel to long axis
Transverse
Oblique
Rectus
abdominis
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