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PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
11
HUMAN
ANATOMY
PART 1
Muscles of
the Body
fifth edition
MARIEB | MALLATT | WILHELM
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Lever Systems
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.1a
Lever Systems
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Figure 11.1b
Lever Systems: Bone-Muscle Relationships



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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Lever Systems: Bone-Muscle Relationships

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Lever Systems: Bone-Muscle Relationships

First-class lever
 Effort applied at one end
 Load is at the opposite end
 Fulcrum is located between load and effort
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Lever Systems: Bone-Muscle Relationships
 Examples – seesaws, scissors, and lifting your head
off your chest
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.2a
Lever Systems: Bone-Muscle Relationships

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Lever Systems: Bone-Muscle Relationships
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.2b
Lever Systems: Bone-Muscle Relationships

Third-class lever
 Effort is applied between the load and the fulcrum
 Work speedily
 Always at a mechanical disadvantage
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.2c
Lever Systems: Bone-Muscle Relationships

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Arrangement of Fascicles in Muscles

Skeletal muscles – consist of fascicles
 Fascicles – arranged in different patterns
 Fascicle arrangement – tells about action of a
muscle
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Arrangement of Fascicles in Muscles

Types of fascicle arrangement
 Parallel – fascicles run parallel to the long axis of
the muscle
 Strap-like – sternocleidomastoid
 Fusiform – biceps brachii
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Arrangement of Fascicles in Muscles

Types of fascicle arrangement
 Convergent
 Origin of the muscle is broad
 Fascicles converge toward the tendon of insertion
 Example – pectoralis major
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Arrangement of Fascicles in Muscles

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Arrangement of Fascicles in Muscles

Circular
 Fascicles are arranged in concentric rings
 Surround external body openings
 Sphincter – general name for a circular muscle
 Examples
 Orbicularis oris and orbicularis oculi
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Arrangement of Fascicles in Muscles
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.3
Organization Scheme Based on Embryonic Development

Overview based upon
 Embryonic origin
 General function

Muscles develop from mesoderm
 Myotomes
 Somitomeres
 The first seven myotomes of the head
 Splanchnic mesoderm
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Development and Basic Organization of the Muscles
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Figure 11.4a, b
Organization Scheme Based on Embryonic Development

Muscles organized into four groups
 Musculature of the visceral organs
 Pharyngeal arch muscles
 Axial muscles
 Limb muscles
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Organization Scheme Based on Embryonic Development

Musculature of the visceral organs
 Includes – smooth and cardiac muscle
 Develops from splanchnic mesoderm

Pharyngeal arch muscles
 Includes
 Skeletal muscles of the pharynx
 Muscles of the head and neck
 Develop from the fourth to seventh somitomeres
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Pharyngeal Arch Muscles
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Figure 11.4c
Axial Muscles


Lie anterior and posterior to the body axis
Muscles of the
 Thorax, abdomen, and pelvis

Many muscles of the
 Neck and some of the head

Function to move the trunk and maintain posture
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Axial Muscles

Develop from myotomes and some somitomeres
 Dorsal regions of myotomes – deep muscles of the
back
 Ventral regions of myotomes – muscles of the trunk
and neck
 Respiratory muscles
 Anterior abdominal wall muscles
 Muscles of the pelvic floor
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Axial Muscles
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.4d
Limb Muscles


Limb muscles arise from lateral parts of nearby
myotomes
Extensors
 Muscle mass dorsal to limb bones

Flexors
 Muscle mass ventral to limb bones
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Limb Muscles
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Figure 11.4e
Interactions of Skeletal Muscles in the Body



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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Muscles Classified into Several Functional Groups

Prime mover (agonist)

Antagonist

Synergist – helps the prime mover
 Has major responsibility for a certain movement
 Opposes or reverses a movement
 By adding extra force
 By reducing undesirable movements
 Fixator
 A type of synergist that holds a bone firmly in place
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
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
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Muscle Compartments of Arm and Forearm

The upper limb has anterior and posterior
compartments
 Anterior arm compartment muscles
 Flex the shoulder or arm
 Innervation is the musculocutaneous nerve
 Anterior forearm compartment muscles
 Flex the wrist and digits
 Innervation is the median or ulnar nerve
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Compartments of the Arm and Forearm
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.5a
Muscle Compartments of the Arm and Forearm
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.5b
Muscle Compartments of the Thigh

Posterior compartment muscles

Anterior compartment muscles

Medial compartment
 Extend the hip and flex the knee
 Innervation is the tibial branch of the sciatic nerve
 Flex the hip and extend the knee
 Innervation is the femoral nerve
 Adduct the thigh
 Innervation is the obturator nerve
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Compartments of the Leg

Posterior compartment muscles

Anterior compartment muscles

Lateral compartment muscles
 Contains digital and plantar flexors
 Innervation is the tibial nerve
 Contains digital extensors and dorsiflexors
 Innervation is the deep fibular nerve
 Plantar flex and evert the foot
 Innervation is the superficial fibular nerve
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle Compartments of the Thigh and Leg
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.6a
Muscle Compartments of the Thigh and Leg
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 11.6b
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
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Naming the Skeletal Muscles

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Naming the Skeletal Muscles

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
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings