1. Chapter 6
The Muscular System

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. 600+ Skeletal Muscles 5 Golden Rules of Muscle Activity
With a few exceptions, all muscles cross at least one joint
The bulk of the muscle lies proximal to the join crossed
All muscles have at least two attachments; the origin and the insertion
Muscles can only pull; they never push
During contraction, the muscle insertion moves toward the orgin

4. 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
Skeletal muscle must be stimulated by a nerve impulse to contract
Brachialis
flexes forearm

5. 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

6. 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

7. Antagonists of the Forearm

8. Antagonists of the Thigh

9. Antagonists of the Foot

10. 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

11. Functional Roles of Skeletal Muscles
Group Actions: most movements need several muscles working together
While the prime movers (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

12. 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

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

14. Naming Skeletal Muscles
Shape:
deltoid (triangle)
trapezius (trapezoid)
serratus (saw-toothed)
rhomboideus (rhomboid)
orbicularis and sphincters (circular)
Rhomboideus
major

15. Muscles Named by Size Psoas minor maximus (largest) minimis (smallest)
longus (longest)
brevis (short)
major (large)
minor (small)
Psoas major

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

17. Muscles Named for Number of Origins
biceps (2)
triceps (3)
quadriceps (4)
Biceps brachii

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

19. 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

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

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

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

23. 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

24. 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 opposing movement
Effort: the force exerted to achieve action

25. Levers A lever is acted upon at 2 different points by:
resistance or load
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)

26. 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.

27. 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

28. 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

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

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

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

32. Skeletal Muscles You will need to know all of these!