Muscles of the Body

PowerPoint® Lecture Slides prepared by Leslie HendonUniversity of Alabama, Birmingham

C H A P T E R

Copyright © 2011 Pearson Education, Inc.

Part 1

11Muscles of the Body


Muscles of the Body

• Skeletal muscles• Produce movements• Blinking of eye, standing on tiptoe,

swallowing food, etc.• General principles of leverage• Muscles act with or against each other • Criteria used in naming muscles


Arrangement of Fascicles in Muscles

• Skeletal muscles—consist of fascicles• Fascicles—arranged in different patterns• Fascicle arrangement—tells about action of a

muscle



• Types of fascicle arrangement• Parallel—fascicles run parallel to the long

axis of the muscle• Strap-like—sternocleidomastoid• Fusiform—biceps brachii



• Types of fascicle arrangement• Convergent • Origin of the muscle is broad• Fascicles converge toward the tendon of

insertion• Example—pectoralis major



• Types of fascicle arrangement• Pennate• Unipennate—fascicles insert into one side

of the tendon• Bipennate—fascicles insert into the tendon

from both sides• Multipennate—fascicles insert into one

large tendon from all sides



• Circular• Fascicles are arranged in concentric rings • Surround external body openings• Sphincter—general name for a circular

muscle• Examples• Orbicularis oris and orbicularis oculi


(f) Bipennate (rectus femoris)

(a)

(b)(c)

(f)

(g)

(e)

(d)

(a) Circular (orbicularis oris)

(b) Convergent (pectoralis major)

(d) Parallel (sartorius)

(c) Fusiform (biceps brachii)

(g) Unipennate (extensor digitorum longus)

(e) Multipennate (deltoid)


Figure 11.1


Lever Systems: Bone-Muscle Relationships

• Movement of skeletal muscles involves leverage• Lever—a rigid bar that moves • Fulcrum—a fixed point• Effort—applied force• Load—resistance


Lever Systems

Figure 11.2a

Load

Effort

Load

Effort

10kg

1000 kg

Fulcrum

10 x 25 = 1000 x 0.25 250 = 250

Effort x length of effort arm = load x length of load arm (force x distance) = (resistance x distance)

(a) Mechanical advantage with a power lever

Fulcrum

25 cm

0.25 cm


Lever Systems

Figure 11.2b

LoadEffort

Fulcrum

Load

Effort

100 kg

50 kg

Fulcrum

100 x 25 = 50 x 50 2500 = 2500

(b) Mechanical disadvantage with a speed lever

25 cm

50 cm



• Bones—act as levers• Joints—act as fulcrums• Muscle contraction—provides effort• Applies force where muscle attaches to bone

• Load—bone, overlying tissue, and anything lifted



• Levers allow a given effort to• Move a heavier load• Move a load farther

• Mechanical advantage • Moves a large load over small distances

• Mechanical disadvantage• Allows a load to be moved over a large

distance



• First-class lever• Effort applied at one end• Load is at the opposite end• Fulcrum is located between load and effort



• Examples—seesaws, scissors, and lifting your head off your chest

Figure 11.3a

(a) First-class lever

Arrangement of the elements isload-fulcrum-effort.

L

L

Example: scissors

Load

Fulcrum

Load Effort

Effort

Fulcrum

(a) First-class lever

Arrangement of the elements isload-fulcrum-effort.

In the body: A first-class lever systemraises your head off your chest. Theposterior neck muscles provide the effort;the atlanto-occipital joint is the fulcrum;and the weight to be lifted is the facialskeleton.

Load

Fulcrum

Effort



• Second-class lever• Effort applied at one end • Fulcrum is at the opposite end• Load is between the effort and fulcrum• Examples—wheelbarrow or standing on tiptoe• An uncommon type of lever in the body

• Work at a mechanical advantage



Figure 11.3b

(b) Second-class leverArrangement of the elements is

fulcrum-load-effort.

L

L

Example: wheelbarrow

Load

Effort

Fulcrum

Effort

Load

Fulcrum

(b) Second-class leverArrangement of the elements is

fulcrum-load-effort.

In the body: Second-class leverage isexerted when you stand on tip-toe. Theeffort is exerted by the calf musclespulling upward on the heel; the joints ofthe ball of the foot are the fulcrum; andthe weight of the body is the load.

Load

Effort

Fulcrum



• Third-class lever• Effort is applied between the load and the

fulcrum• Work speedily• Always at a mechanical disadvantage

Figure 11.3c

(c) Third-class lever

Arrangement of the elements isload-effort-fulcrum.

L

L

Example: tweezers or forceps

Fulcrum

Load

Load

Effort

Effort

Fulcrum

(c) Third-class lever

Arrangement of the elements isload-effort-fulcrum.

In the body: Flexing the forearm by thebiceps brachii muscle exemplifiesthird-class leverage. The effort is exertedon the proximal radius of the forearm; thefulcrum is the elbow joint; and the load isthe hand and distal end of the forearm.

Load

Effort

Fulcrum



• Most skeletal muscles are third-class levers• Example—biceps brachii• Fulcrum—the elbow joint• Force—exerted on the proximal region of

the radius• Load—the distal part of the forearm


Muscle Actions and Interactions

• A muscle cannot reverse the movement it produces

• Another muscle must undo the action• Muscles with opposite actions lie on opposite

sides of a joint



• Prime mover (agonist)• Has major responsibility for a certain movement

• Antagonist• Opposes or reverses a movement

• Synergist—helps the prime mover • By adding extra force • By reducing undesirable movements • Fixator• A type of synergist that holds a bone firmly in place



Example:Pectoralis major(anterior view)

(a) A muscle that crosses on the anterior side of a joint produces flexion*

*These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.

Example:Latissimus dorsi(posterior view)

(b) A muscle that crosses on the posterior side of a joint produces extension*

*These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.

Figure 11.5a, b



Example:Teres major(posterolateral view)

(d) A muscle that crosses on the medial side of a joint produces adduction

Example:Medial deltoid(anterolateral view)

(c) A muscle that crosses on the lateral side of a joint produces abduction

Figure 11.5c, d


Muscle Compartments of the Limbs

• Dense fibrous connective tissue divides limb muscles into compartments

• Muscles in opposing compartments are• Agonist and antagonist pairs

• Each compartment is innervated by a single nerve


Muscle Compartments of the Thigh

• Posterior compartment muscles • Extend the hip and flex the knee• Innervation is the tibial branch of the sciatic

nerve• Anterior compartment muscles• Flex the hip and extend the knee• Innervation is the femoral nerve

• Medial compartment• Adduct the thigh• Innervation is the obturator nerve


Adductors

Vastuslateralis

Hamstrings

Posterior compartment ofthigh (flexes leg and extends thigh); innervation: tibial nerve (portion of sciatic nerve)

Medial compartment(adducts thigh); innervation:obturator nerve

Anterior compartment (extends leg); innervated by femoral nerve

Vastusintermedius

Rectus femoris

Femur

Vastus medialis

(a)

(a) Muscles of the thigh

Posterior compartmentmusclesAnterior compartmentmusclesMedial compartmentmuscles of thigh and lateral compartment muscles of leg

Muscle Compartments of the Thigh and Leg

Figure 11.7a


Naming the Skeletal Muscles

• Location• Example—the brachialis is located on the arm

• Shape• Example—the deltoid is triangular

• Relative size• Maximus, minimus, and longus indicate size• Example—gluteus maximus and gluteus

minimus



• Direction of fascicles and muscle fibers• Name tells direction in which fibers run• Example—rectus abdominis and transversus

abdominis • Location of attachments—name reveals

point of origin and insertion• Example—brachioradialis



• Number of origins• Two, three, or four origins • Indicated by the words biceps, triceps, and

quadriceps• Action• The action is part of the muscle’s name• Indicates type of muscle movement• Flexor, extensor, adductor, or abductor

Muscles of the Body

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