1. The Muscular System HOW SKELETAL MUSCLES PRODUCE MOVEMENT
Chapter 11
The Muscular System
HOW SKELETAL MUSCLES PRODUCE MOVEMENT

2. Muscle Attachment Sites: Origin and Insertion
Skeletal muscles shorten & pull on the bones they are attached to
Origin is the bone that does not move when muscle shortens (normally proximal)
Insertion is the movable bone
Fleshy portion of the muscle in between attachment sites = belly
Principles of Human Anatomy and Physiology, 11e

3. Lever Systems and Leverage
Muscle acts on rigid rod (bone) that moves around a fixed point called a fulcrum
Resistance is weight of body part & perhaps an object
Effort or load is work done by muscle contraction
Mechanical advantage
the muscle whose attachment is farther from the joint will produce the most force
the muscle attaching closer to the joint has the greater range of motion and the faster the speed it can produce
Principles of Human Anatomy and Physiology, 11e

4. First - Class Lever
Can produce mechanical advantage or not depending on location of effort & resistance
if effort is further from fulcrum than resistance, then a strong resistance can be moved
Head resting on vertebral column
weight of face is the resistance
joint between skull & atlas is fulcrum
posterior neck muscles provide effort
Principles of Human Anatomy and Physiology, 11e

5. Second - Class Lever Similar to a wheelbarrow
Always produce mechanical advantage
resistance is always closer to fulcrum than the effort
Sacrifice of speed for force
Raising up on your toes
resistance is body weight
fulcrum is ball of foot
effort is contraction of calf muscles which pull heel up off of floor
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6. Third - Class Lever Most common levers in the body
Always produce a mechanical disadvantage
effort is always closer to fulcrum than resistance
Favors speed and range of motion over force
Flexor muscles at the elbow
resistance is weight in hand
fulcrum is elbow joint
effort is contraction of biceps brachii muscle
Principles of Human Anatomy and Physiology, 11e

7. Coordination Within Muscle Groups
Most movement is the result of several muscle working at the same time
Most muscles are arranged in opposing pairs at joints
prime mover or agonist contracts to cause the desired action
antagonist stretches and yields to prime mover
synergists contract to stabilize nearby joints
fixators stabilize the origin of the prime mover
scapula held steady so deltoid can raise arm
Principles of Human Anatomy and Physiology, 11e

8. HOW SKELETAL MUSCLES ARE NAMED
The most important characteristics include the direction in which the muscle fibers run, the size, shape, action, numbers of origins, and location of the muscle, and the sites of origin and insertion of the muscle
Examples from Table 11.2
triceps brachii -- 3 sites of origin
quadratus femoris -- square shape
serratus anterior -- saw-toothed edge
Principles of Human Anatomy and Physiology, 11e

9. Muscles of Facial Expression
Orbicularis oculi closes the eye
Orbicularis oris puckers the mouth
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10. Muscles that Move the Mandible
Masseter, temporalis Arise from skull & insert on mandible
Protracts, elevates or retracts mandible
Temporalis & Masseter elevate the mandible (biting)
Principles of Human Anatomy and Physiology, 11e

11. Muscles that Move the Head
Sternocleidomastoid muscle
arises from sternum & clavicle & inserts onto mastoid process of skull
contraction of one, laterally flexes the neck and rotates face in opposite direction
Principles of Human Anatomy and Physiology, 11e

12. Muscles of Abdominal Wall
Principles of Human Anatomy and Physiology, 11e

13. Muscles of Abdominal Wall
sheetlike muscles
rectus abdominis = vertically oriented
external & internal obliques
wrap around body to form anterior body wall
Principles of Human Anatomy and Physiology, 11e

14. Muscles Used in Breathing
Breathing requires a change in size of the thorax
During inspiration, thoracic cavity increases in size
external intercostal lift the ribs
diaphragm contracts & dome is flattened
During expiration, thoracic cavity decreases in size
internal intercostal used in forced expiration
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15. Stabilizing the Pectoral Girdle
Anterior thoracic muscles
Subclavius extends from 1st rib to clavicle
Pectoralis minor extends from ribs to coracoid process
Serratus anterior extends from ribs to inner surface of scapula
Posterior thoracic muscle
Trapezius extends from skull & vertebrae to clavicle & scapula
Rhomboideus extends from thoracic vertebrae to vertebral border of scapula
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16. Axial Muscles that Move the Arm
Pectoralis major & Latissimus dorsi extend from body wall to humerus.
Principles of Human Anatomy and Physiology, 11e

17. Muscles that Move the Arm
Deltoid arises from acromion & spine of scapula & inserts on arm
abducts, flexes & extends arm
Rotator cuff muscles extend from scapula posterior to shoulder joint to attach to the humerus
supraspinatus & infraspinatus: above & below spine of scapula
subscapularis on inner surface of scapula
Principles of Human Anatomy and Physiology, 11e

18. Flexors of the Forearm (elbow)
Biceps brachii
scapula to radial tuberosity
flexes shoulder and elbow & supinates hand
Brachialis
humerus to ulna
flexion of elbow
Principles of Human Anatomy and Physiology, 11e

19. Extensors of the Forearm (elbow)
Triceps brachii
long head arises scapula
medial & lateral heads from humerus
inserts on ulna
extends elbow & shoulder joints
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20. Muscle that Pronate & Flex
Flexor carpi muscles
radialis
ulnaris
Flexor digitorum muscles
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21. Muscles that Supinate & Extend
Extensors of wrist and fingers
extensor carpi
extensor digitorum
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22. Muscles Crossing the Hip Joint
Quadriceps femoris has 4 heads
Rectus femoris crosses hip
3 heads arise from femur
Vastus lateralis, intermedius and medialis
all act to extend the knee
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23. Adductor Muscles of the Thigh
Adductor group of muscle extends from pelvis to linea aspera on posterior surface of femur
adductor longus
gracilis
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24. Muscles of the Butt & Thigh
Gluteus muscles
maximus, medius & minimus
maximus extends hip
medius & minimus abduct
Hamstring muscles
semimembranosus (medial)
semitendinosus (medial)
biceps femoris (lateral)
extend hip & flex knee
Principles of Human Anatomy and Physiology, 11e

25. Muscles of the Calf (posterior leg)
muscles insert onto calcaneus
gastrocnemius arises femur
flexes knee and ankle
soleus arise from leg
flexes ankle
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26. Muscles of the Leg and Foot
Anterior compartment of leg
extensors of ankle & toes
tibialis anterior
extensor digitorum longus
Shinsplints syndrome
pain or soreness on anterior tibia
running on hard surfaces
Principles of Human Anatomy and Physiology, 11e