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Lecture Presentation by
Steven Bassett
Southeast Community College
Chapter 9
The Muscular
System
Skeletal Muscle
Tissue and Muscle
Organization
© 2015 Pearson Education, Inc.
Introduction
• Humans rely on muscles for:
• Many of our physiological processes
• Virtually all our dynamic interactions with the
environment
• Skeletal muscles consist of:
• Elongated cells called fibers (muscle fibers)
• These fibers contract along their longitudinal axis
© 2015 Pearson Education, Inc.
Introduction
• There are three types of muscle tissue
• Skeletal muscle
• Pulls on skeletal bones
• Voluntary contraction
• Cardiac muscle
• Pushes blood through arteries and veins
• Rhythmic contractions
• Smooth muscle
• Pushes fluids and solids along the digestive tract,
for example
• Involuntary contraction
© 2015 Pearson Education, Inc.
Introduction
• Muscle tissues share four basic properties
• Excitability
• The ability to respond to stimuli
• Contractility
• The ability to shorten and exert a pull or tension
• Extensibility
• The ability to continue to contract over a range of
resting lengths
• Elasticity
• The ability to rebound toward its original length
© 2015 Pearson Education, Inc.
Functions of Skeletal Muscles
• Skeletal muscles perform the following functions:
• Produce skeletal movement
• Pull on tendons to move the bones
• Maintain posture and body position
• Stabilize the joints to aid in posture
• Support soft tissue
• Support the weight of the visceral organs
© 2015 Pearson Education, Inc.
Functions of Skeletal Muscles
• Skeletal muscles perform the following
functions (continued):
• Regulate entering and exiting of material
• Voluntary control over swallowing, defecation, and
urination
• Maintain body temperature
• Some of the energy used for contraction is
converted to heat
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Gross anatomy is the study of:
• Overall organization of muscles
• Connective tissue associated with muscles
• Nerves associated with muscles
• Blood vessels associated with muscles
• Microscopic anatomy is the study of:
• Myofibrils
• Myofilaments
• Sarcomeres
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Gross Anatomy
• Connective tissue of muscle
• Epimysium: dense tissue that surrounds the entire
muscle
• Perimysium: dense tissue that divides the muscle
into parallel compartments of fascicles
• Endomysium: dense tissue that surrounds
individual muscle fibers
© 2015 Pearson Education, Inc.
Figure 9.1 Structural Organization of Skeletal Muscle
© 2015 Pearson Education, Inc.
Tendon
Perimysium
Muscle fascicle
Endomysium
Perimysium
Nerve
Muscle fibers
Blood vessels
SKELETAL MUSCLE
(organ)
Perimysium
Muscle fiber
Endomysium
MUSCLE FASCICLE(bundle of cells)
Epimysium
Blood vessels
and nerves
Endomysium
CapillaryMitochondria
SarcolemmaEndomysium
Myofibril
Myosatellite
cell
AxonNucleusSarcoplasm
MUSCLE FIBER
(cell)
Epimysium
Anatomy of Skeletal Muscles
• Connective Tissue of Muscle
• Tendons and aponeuroses
• Epimysium, perimysium, and endomysium
converge to form tendons
• Tendons connect a muscle to a bone
• Aponeuroses connect a muscle to a muscle
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Gross Anatomy
• Nerves and blood vessels
• Nerves innervate the muscle by penetrating the
epimysium
• There is a chemical communication between a
nerve and a muscle
• The chemical is released into the neuromuscular
synapse (neuromuscular junction)
© 2015 Pearson Education, Inc.
Figure 9.2 Skeletal Muscle Innervation
© 2015 Pearson Education, Inc.
Neuromuscular
synapse
Skeletal
muscle
fiber
Axon
Nerve
A neuromuscular synapse as seen
on a muscle fiber of this fascicleColorized SEM of a neuromuscular
synapse
LM x 230 SEM x 400
ba
Anatomy of Skeletal Muscles
• Gross Anatomy
• Nerves and blood vessels (continued)
• Blood vessels often parallel the nerves that
innervate the muscle
• They then branch to form coiled networks to
accommodate flexion and extension of the muscle
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Microanatomy of Skeletal Muscle Fibers
• Sarcolemma
• Membrane that surrounds the muscle cell
• Sarcoplasm
• The cytosol of the muscle cell
• Muscle fiber (same thing as a muscle cell)
• Can be 30–40 cm in length
• Multinucleate (each muscle cell has hundreds of
nuclei)
• Nuclei are located just deep to the sarcolemma
© 2015 Pearson Education, Inc.
Figure 9.3ab The Formation and Structure of a Skeletal Muscle Fiber
© 2015 Pearson Education, Inc.
Myoblasts
Muscle fibers develop
through the fusion of
mesodermal cells
called myoblasts.
Myosatellite cell
Development of a
skeletal muscle fiber.
Nuclei
Immature
muscle fiber
External appearance
and histological view.
a
b
Anatomy of Skeletal Muscles
• Myofibrils and Myofilaments
• The sarcoplasm contains myofibrils
• Myofibrils are responsible for the contraction of
muscles
• Myofibrils are attached to the sarcolemma at each
end of the muscle cell
• Surrounding each myofibril is the sarcoplasmic
reticulum
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Myofibrils and Myofilaments
• Myofibrils are made of myofilaments
• Actin
• Thin protein filaments
• Myosin
• Thick protein filaments
© 2015 Pearson Education, Inc.
Figure 9.3b-d The Formation and Structure of a Skeletal Muscle Fiber
© 2015 Pearson Education, Inc.
Nuclei
MUSCLE FIBERSarcoplasm
Myofibril
Sarcolemma
Terminal cisterna
Sarcolemma
Sarcoplasm
Myofibrils
Mitochondria
Sarcolemma
T tubulesSarcoplasmic
reticulum
Triad
Thick filament
Thin filament
Myofibril
External appearance
and histological view.
The external organization
of a muscle fiber.
Internal organization of a muscle fiber.
Note the relationships among myofibrils,
sarcoplasmic reticulum, mitochondria,
triads, and thick and thin filaments.
b
c
d
Anatomy of Skeletal Muscles
• Sarcomere Organization
• Myosin (thick filament)
• Actin (thin filament)
• Both are arranged in repeating units called
sarcomeres
• All the myofilaments are arranged parallel to the
long axis of the cell
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Sarcomere Organization
• Sarcomere
• Main functioning unit of muscle fibers
• Approximately 10,000 per myofibril
• Consists of overlapping actin and myosin
• This overlapping creates the striations that give the
skeletal muscle its identifiable characteristic
© 2015 Pearson Education, Inc.
Anatomy of Skeletal Muscles
• Sarcomere Organization
• Each sarcomere consists of:
• Z line (Z disc)
• I band
• A band (overlapping A bands create striations)
• H band
• M line
© 2015 Pearson Education, Inc.
Figure 9.4b Sarcomere Structure
© 2015 Pearson Education, Inc.
I band A band
H band Z line Titin
Thick
filament
Thin
filamentZone of overlap M line
Sarcomere
I band A band
H band Z line
TEM x 64,000M line
Sarcomere
Zone of overlapZ line
b A corresponding view of a sarcomere in a myofibril in
the gastrocnemius muscle of the calf and a diagram
showing the various components of this sarcomere
Anatomy of Skeletal Muscles
• Sarcomere Organization
• Skeletal muscles consist of muscle fascicles
• Muscle fascicles consist of muscle fibers
• Muscle fibers consist of myofibrils
• Myofibrils consist of sarcomeres
• Sarcomeres consist of myofilaments
• Myofilaments are made of actin and myosin
© 2015 Pearson Education, Inc.
Figure 9.5 Levels of Functional Organization in a Skeletal Muscle Fiber
© 2015 Pearson Education, Inc.
SKELETAL MUSCLE
MUSCLE FASCICLE
MUSCLE FIBER
Surrounded by:Epimysium
Contains:Muscle fascicles
Surrounded by:Perimysium
Contains:Muscle fibers
MYOFIBRIL
Surrounded by:Endomysium
Contains:Myofibrils
Surrounded by:Sarcoplasmic reticulum
Consists of:Sarcomeres (Z line to Z line)
SARCOMERE
I band A band
Contains:Thick filaments
Thin filaments
Z line M line
H band
Titin Z line
Anatomy of Skeletal Muscles
• Thin Filaments (Actin)
• Consists of:
• Twisted filaments of :
• F actin strands
• G actin globular molecules
• G actin molecules consist of an active site (binding
site)
• Tropomyosin: A protein that covers the binding
sites when the muscle is relaxed
• Troponin: Holds tropomyosin in position
© 2015 Pearson Education, Inc.
Figure 9.6ab Thin and Thick Filaments
© 2015 Pearson Education, Inc.
Actinin Z line Titin
Troponin Active site Nebulin Tropomyosin G actin molecules
F actin
strand
The attachmentof thin filamentsto the Z line
Sarcomere
H band
Myofibril
Z lineM line
The detailed structure of a thin filament showing
the organization of G actin, troponin, and
tropomyosin
a
b
Anatomy of Skeletal Muscles
• Thick Filaments (Myosin)
• Myosin filaments consist of an elongated tail and a
globular head (cross-bridges)
• Myosin is a stationary molecule. It is held in place
by:
• Protein forming the M line
• A core of titin connecting to the Z lines
• Myosin heads project toward the actin filaments
© 2015 Pearson Education, Inc.
Figure 9.6cd Thin and Thick Filaments
© 2015 Pearson Education, Inc.
Sarcomere
H band
Myofibril
Z lineM line
The structure of
thick filaments
c
M line
Titin
Myosin head
HingeMyosin tail
A single myosin molecule detailing the structure and
movement of the myosin head after cross-bridge
binding occurs
d
Muscle Contraction
• A contracting muscle shortens in length
• Contraction is caused by interactions between
thick and thin filaments within the sarcomere
• Contraction is triggered by the presence of
calcium ions
• Muscle contraction requires the presence of ATP
• When a muscle contracts, actin filaments slide
toward each other
• This sliding action is called the sliding filament
theory
© 2015 Pearson Education, Inc.
Muscle Contraction
• The Sliding Filament Theory
• Upon contraction:
• The H band and I band get smaller
• The zone of overlap gets larger
• The Z lines move closer together
• The width of the A band remains constant
throughout the contraction
© 2015 Pearson Education, Inc.
Figure 9.7 Sliding Filament Theory (1 of 11)
© 2015 Pearson Education, Inc.
Resting SarcomereA resting sarcomere showing the locations of the
I band, A band, H band, M, and Z lines.
I band A band M line
Z line H band Z line
Resting myofibril
Contracted SarcomereAfter repeated cycles of “bind, pivot, detach, and reactivate”
the entire muscle completes its contraction.
Contracted myofibril
I band A band M line
Z line H band Z line
In a contracting sarcomere the A band stays the same width,
but the Z lines move closer together and the H band and the
I bands get smaller
Muscle Contraction
• The Neural Control of Muscle Fiber Contraction
• An impulse travels down the axon of a nerve
• Acetylcholine is released from the end of the
axon into the neuromuscular synapse
• This ultimately causes the sarcoplasmic reticulum
to release its stored calcium ions
• This begins the actual contraction of the muscle
© 2015 Pearson Education, Inc.
Figure 9.8 The Neuromuscular Synapse
© 2015 Pearson Education, Inc.
Arriving action
potential
Synaptic
cleft
ACh receptor
site
Sarcolemma of
motor end plate
AChE molecules
Junctional fold
Synaptic
vesicles
ACh
Glial cell
b Detailed view of a terminal, synaptic cleft,
and motor end plate. See also Figure 9.2.
Motor
neuron
Path of action
potentialAxon
Synaptic
terminal
Muscle FiberMyofibril
Motor end plate
Myofibril
Sarcolemma
Mitochondrion
A diagrammatic view of a
neuromuscular synapse.
a
Muscle Contraction
• Muscle Contraction: A Summary
• The nerve impulse ultimately causes the release
of a neurotransmitter (ACh), which comes in
contact with the sarcoplasmic reticulum
• This neurotransmitter causes the sarcoplasmic
reticulum to release its stored calcium ions
• Calcium ions bind to troponin
© 2015 Pearson Education, Inc.
Figure 9.7 Sliding Filament Theory (2 of 11)
© 2015 Pearson Education, Inc.
Contraction Cycle Begins
Active-Site Exposure
1
2
Ca2+
Actin
Ca2+
Tropomyosin
Activesite
The contraction cycle involves a series of
interrelated steps. The cycle begins with
electrical events in the sarcolemma that
trigger the release of calcium from the
terminal cisternae of the sarcoplasmic
reticulum (SR). These calcium ions enter
the zone of overlap.
Calcium ions bind to troponin in the
troponin– tropomyosin complex. The
tropomyosin molecule then rolls away
from the active sites on the actin
molecules of the thin filaments.
Muscle Contraction
• Muscle Contraction: A Summary (continued)
• The bound calcium ions cause the tropomyosin
molecule to roll so that it exposes the active sites
on actin
• The myosin heads now extend and bind to the
exposed active sites on actin
• Once the myosin heads bind to the active sites,
they pivot in the direction of the M line
© 2015 Pearson Education, Inc.
Figure 9.7 Sliding Filament Theory (3 of 11)
© 2015 Pearson Education, Inc.
Cross-Bridge Formation
Myosin Head Pivoting
3
4
Myosin head
Cross-bridgeOnce the active sites are exposed, the
myosin heads of adjacent thick
filaments bind to them, forming
cross-bridges.
After cross-bridge formation, energy is
released as the myosin heads pivot
toward the M line.
Muscle Contraction
• Muscle Contraction: A Summary (continued)
• Upon pivoting of the myosin heads, the actin
filament slides toward the M line
• ATP binds to the myosin heads causing them to
release their attachment and return to their original
position to start over again
© 2015 Pearson Education, Inc.
Figure 9.7 Sliding Filament Theory (4 of 11)
© 2015 Pearson Education, Inc.
Cross-Bridge Detachment
Myosin Reactivation
ATP
ATP
ATP then binds to the myosin heads,
breaking the cross-bridges between the
myosin heads and the actin molecules.
ATP provides the energy to reactivate
the myosin heads and return them to
their original positions. Now the entire
cycle can be repeated as long as
calcium ion concentrations remain
elevated and ATP reserves are
sufficient.
5
6
Muscle Contraction
• Muscle Contraction: A Summary (continued)
• Upon contraction:
• I bands get smaller
• H bands get smaller
• Z lines get closer together
© 2015 Pearson Education, Inc.
Figure 9.7 Sliding Filament Theory
© 2015 Pearson Education, Inc.
Figure 9.9 The Events in Muscle Contraction
© 2015 Pearson Education, Inc.
STEPS IN INITIATING MUSCLE CONTRACTION STEPS IN MUSCLE RELAXATION
Synaptic
terminal
Motor
end plate T tubule Sarcolemma
ACh released, binding
to receptors
Action
potential
reaches
T tubule
Sarcoplasmic
reticulum
releases Ca2+
Ca2+
Actin
Myosin
Active-site
exposure,
cross-bridge
formation
Contraction
begins
12
3
4
5
6
7
8
9
10
ACh removed by AChE
Sarcoplasmic
reticulum
recaptures Ca2+
Active sites
covered, no
cross-bridge
interaction
Contraction
ends
Relaxation occurs,
passive return to
resting length
Motor Units and Muscle Control
• Motor Units (Motor Neurons Controlling Muscle
Fibers)
• Precise control
• A motor neuron controlling two or three muscle
fibers
• Example: the control over the eye muscles
• Less precise control
• A motor neuron controlling perhaps 2000 muscle
fibers
• Example: the control over the leg muscles
© 2015 Pearson Education, Inc.
Figure 9.10 The Arrangement of Motor Units in a Skeletal Muscle
© 2015 Pearson Education, Inc.
Muscle fibers
Motor
nerve
Axons of
motor neurons
Motor Units and Muscle Control
• Muscle tension depends on:
• The frequency of stimulation
• A typical example is a muscle twitch
• The number of motor units involved
• Complete contraction or no contraction at all (all or
none principle)
• The amount of force of contraction depends on the
number of motor units activated
© 2015 Pearson Education, Inc.
Motor Units and Muscle Control
• Muscle Tone
• The tension of a muscle when it is relaxed
• Stabilizes the position of bones and joints
• Example: the amount of muscle involvement that
results in normal body posture
• Muscle Spindles
• These are specialized muscle cells that are
monitored by sensory nerves to control muscle
tone
© 2015 Pearson Education, Inc.
Motor Units and Muscle Control
• Muscle Hypertrophy
• Enlargement of the muscle
• Exercise causes:
• An increase in the number of mitochondria
• An increase in the activity of muscle spindles
• An increase in the concentration of glycolytic
enzymes
• An increase in the glycogen reserves
• An increase in the number of myofibrils
• The net effect is an enlargement of the muscle
© 2015 Pearson Education, Inc.
Motor Units and Muscle Control
• Muscle Atrophy
• Discontinued use of a muscle
• Disuse causes:
• A decrease in muscle size
• A decrease in muscle tone
• Physical therapy helps to reduce the effects
of atrophy
© 2015 Pearson Education, Inc.
Types of Skeletal Muscle Fibers
• Three Major Types of Muscle Fibers
• Fast fibers (white fibers)
• Associated with eye muscles (fast contractions)
• Intermediate fibers (pink fibers)
• Slow fibers (red fibers)
• Associated with leg muscles (slow contractions)
© 2015 Pearson Education, Inc.
Figure 9.11a Types of Skeletal Muscle Fibers
© 2015 Pearson Education, Inc.
Slow fibers
Fast fibers
Smaller diameter,
darker color due to
myoglobin; fatigue
resistant
Larger diameter,
paler color;
easily fatigued
LM x 170
LM x 170
Note the difference in the size of
slow muscle fibers (above) and
fast muscle fibers (below).
a
Types of Skeletal Muscle Fibers
• Features of Fast Fibers
• Large in diameter
• Large glycogen reserves
• Relatively few mitochondria
• Muscles contract using anaerobic metabolism
• Fatigue easily
• Can contract in 0.01 second or less after
stimulation
• Produce powerful contractions
© 2015 Pearson Education, Inc.
Types of Skeletal Muscle Fibers
• Features of Slow Fibers
• Half the diameter of fast fibers
• Take three times longer to contract after
stimulation
• Can contract for extended periods of time
• Contain abundant myoglobin (creates the red
color)
• Muscles contract using aerobic metabolism
• Have a large network of capillaries
© 2015 Pearson Education, Inc.
Types of Skeletal Muscle Fibers
• Features of Intermediate Fibers
• Similar to fast fibers
• Have low myoglobin content
• Have high glycolytic enzyme concentration
• Contract using anaerobic metabolism
• Similar to slow fibers
• Have lots of mitochondria
• Have a greater capillary supply
• Resist fatigue
© 2015 Pearson Education, Inc.
Table 9.1 Properties of Skeletal Muscle Fiber Types
© 2015 Pearson Education, Inc.
Types of Skeletal Muscle Fibers
• Distribution of Fast, Slow, and Intermediate
Fibers
• Fast fibers
• High density associated with eye and hand
muscles
• Sprinters have a high concentration of fast fibers
• Repeated intense workouts increase the fast fibers
© 2015 Pearson Education, Inc.
Types of Skeletal Muscle Fibers
• Distribution of Fast, Slow, and Intermediate
Fibers (continued)
• Slow and intermediate fibers
• None are associated with the eyes or hands
• Found in high density in the back and leg muscles
• Marathon runners have a high amount
• Training for long distance running increases the
proportion of intermediate fibers
© 2015 Pearson Education, Inc.
Organization of Skeletal Muscle Fibers
• Muscles can be classified based on shape or
by the arrangement of the fibers
• Parallel muscle fibers
• Convergent muscle fibers
• Pennate muscle fibers
• Unipennate muscle fibers
• Bipennate muscle fibers
• Multipennate muscle fibers
• Circular muscle fibers
© 2015 Pearson Education, Inc.
Organization of Skeletal Muscle Fibers
• Parallel Muscle Fibers
• Muscle fascicles are parallel to the longitudinal
axis
• Examples: biceps brachii and rectus abdominis
© 2015 Pearson Education, Inc.
Figure 9.12ab Skeletal Muscle Fiber Organization
© 2015 Pearson Education, Inc.
(h)
(d)
(g)
(a)
(b)
(e)
(c)
Parallel Muscles
Parallel muscle
(Biceps brachii muscle)
a b Parallel muscle with
tendinous bands
(Rectus abdominis
muscle)
Fascicle
Body
(belly)
Cross section
(f)
Organization of Skeletal Muscle Fibers
• Convergent Muscle Fibers
• Muscle fibers form a broad area but come
together at a common point
• Example: pectoralis major
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Figure 9.12d Skeletal Muscle Fiber Organization
© 2015 Pearson Education, Inc.
Convergent Muscles
d Convergent muscle
(Pectoralis muscles)
Tendon
Base of
muscle
Cross
section
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Organization of Skeletal Muscle Fibers
• Pennate Muscle Fibers (Unipennate)
• Muscle fibers form an oblique angle to the tendon
of the muscle
• An example is unipennate
• All the muscle fibers are on the same side of the
tendon
• Example: extensor digitorum
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Figure 9.12e Skeletal Muscle Fiber Organization
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Pennate Muscles
e Unipennate
muscle (Extensor
digitorum muscle)
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Extended
tendon
Organization of Skeletal Muscle Fibers
• Pennate Muscle Fibers (Bipennate)
• Muscle fibers form an oblique angle to the tendon
of the muscle
• An example is bipennate
• Muscle fibers are on both sides of the tendon
• Example: rectus femoris
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Figure 9.12f Skeletal Muscle Fiber Organization
© 2015 Pearson Education, Inc.
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Pennate Muscles
f Bipennate
muscle
(Rectus femoris
muscle)
Organization of Skeletal Muscle Fibers
• Pennate Muscle Fibers (Multipennate)
• Muscle fibers form an oblique angle to the tendon
of the muscle
• An example is multipennate
• The tendon branches within the muscle
• Example: deltoid muscle
© 2015 Pearson Education, Inc.
Figure 9.12g Skeletal Muscle Fiber Organization
© 2015 Pearson Education, Inc.
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Pennate Muscles
g Multipennate muscle
(Deltoid muscle)
Tendons
Cross section
Organization of Skeletal Muscle Fibers
• Circular Muscle Fibers
• Muscle fibers form concentric rings
• Also known as sphincter muscles
• Examples: orbicularis oris and orbicularis oculi
© 2015 Pearson Education, Inc.
Figure 9.12h Skeletal Muscle Fiber Organization
© 2015 Pearson Education, Inc.
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Circular Muscles
Circular muscleh
(Orbicularis oris muscle)
Contracted
Relaxed
Muscle Terminology
• Origins and Insertions
• Origin
• Point of muscle attachment that remains stationary
• Insertion
• Point of muscle attachment that is movable
• Actions
• The function of the muscle upon contraction
© 2015 Pearson Education, Inc.
Muscle Terminology
• There are two methods of describing
muscle actions
• The first makes reference to the bone region the
muscle is associated with
• The biceps brachii muscle causes “flexion of the
forearm”
• The second makes reference to a specific joint the
muscle is associated with
• The biceps brachii muscle causes “flexion at the
elbow”
© 2015 Pearson Education, Inc.
Muscle Terminology
• Muscles can be grouped according to
their primary actions into four types
• Prime movers (agonists)
• Responsible for producing a particular movement
• Antagonists
• Actions oppose the action of the agonist
• Synergists
• Assist the prime mover in performing an action
• Fixators
• Agonist and antagonist muscles contracting at the
same time to stabilize a joint
© 2015 Pearson Education, Inc.
Muscle Terminology
• Prime Movers example:
• Biceps brachii – flexes the lower arm
• Antagonists example:
• Triceps brachii – extends the lower arm
• Synergists example:
• Latissimus dorsi and teres major – contract to
move the arm medially over the posterior body
• Fixators example:
• Flexor and extensor muscles contract at the same
time to stabilize an outstretched hand
© 2015 Pearson Education, Inc.
Muscle Terminology
• Most muscle names provide clues to their
identification or location
• Muscles can be named for:
• Specific body regions or location
• Shape of the muscle
• Orientation of the muscle fibers
• Specific or unusual features
• Its origin and insertion points
• Primary function
• References to occupational or habitual action
© 2015 Pearson Education, Inc.
Muscle Terminology
• Examples of muscle names related to:
• Specific body regions or locations
• Brachialis: associated with the brachium of the
arm
• Tibialis anterior: associated with the anterior tibia
• Shape of the muscle
• Trapezius: trapezoid shape
• Deltoid: triangular shape
© 2015 Pearson Education, Inc.
Muscle Terminology
• Examples of muscle names related to:
• Orientation of the muscle fibers
• Rectus femoris: straight muscle of the leg
• External oblique: muscle on outside that is
oriented with the fibers at an angle
• Specific or unusual features
• Biceps brachii: two origins
• Teres major: long, big, rounded muscle
© 2015 Pearson Education, Inc.
Muscle Terminology
• Examples of muscle names related to:
• Origin and insertion points
• Sternocleidomastoid: points of attachment are
sternum, clavicle, and mastoid process
• Genioglossus: points of attachment are chin and
tongue
• Primary functions
• Flexor carpi radialis: a muscle that is near the
radius and flexes the wrist
• Adductor longus: a long muscle that adducts the
leg
© 2015 Pearson Education, Inc.
Muscle Terminology
• Examples of muscle names related to:
• References to occupational or habitual actions
• Buccinator (means “trumpet player”): the
buccinator area moves when playing a trumpet
• Sartorius: derived from the Latin term (sartor),
which is in reference to “tailors.” Tailors used to
cross their legs to form a table when sewing
material
© 2015 Pearson Education, Inc.
Levers and Pulleys: A Systems Design for Movement
• Most of the time, upon contraction, a muscle
causes action
• This action is applied to a lever (a bone)
• This lever moves on a fixed point called the
fulcrum (joint)
• The action of the lever is opposed by a force
acting in the opposite direction
© 2015 Pearson Education, Inc.
Levers and Pulleys: A Systems Design for Movement
• There are three classes of levers
• First class, second class, third class
• First class
• The fulcrum (joint) lies between the applied force
and the resistance force (opposed force)
• Example: tilting the head forward and backward
© 2015 Pearson Education, Inc.
Figure 9.13 Levers and Pulleys (2 of 6)
© 2015 Pearson Education, Inc.
First-Class Lever
In a first-class lever, the applied force and the
resistance are on opposite sides of the
fulcrum. This lever can change the amount of
force transmitted to the resistance and alter the
direction and speed of movement. There are
very few first-class levers in the human body.
R
F
AF
R
F
AF
Resistance Fulcrum Applied force
Movement
completed
Levers and Pulleys: A Systems Design for Movement
• Classes of Levers
• Second class
• The resistance is located between the applied force
and the fulcrum (joint)
• Example: standing on your tiptoes
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Figure 9.13 Levers and Pulleys (3 of 6)
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Second-Class Lever
In a second-class lever, the resistance lies
between the applied force and the fulcrum.
This arrangement
magnifies force at the
expense of distanceand speed; the direction
of movement remains
unchanged. There are
very few second-class
levers in the body.
AF
R
F
F
R
AF
Movement
completed
Levers and Pulleys: A Systems Design for Movement
• Classes of Levers
• Third class
• The force is applied between the resistance and
fulcrum (joint)
• Example: flexing the lower arm
© 2015 Pearson Education, Inc.
Figure 9.13 Levers and Pulleys (4 of 6)
© 2015 Pearson Education, Inc.
Third-Class Lever
In a third-class lever, which is the most
common lever in the body, the applied force
is between the resistance and the fulcrum.
This arrangement increases speed and
distance moved but requires a larger
applied force.
R
F
F
AF
R
Movement
completed
Levers and Pulleys: A Systems Design for Movement
• Sometimes, a tendon may loop around a bony
projection
• This bony projection could be called a pulley
• Example: lateral malleolus and trochlea of the eye
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Figure 9.13 Levers and Pulleys (5 of 6)
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The Lateral Malleolus
as an Anatomical Pulley
Plantar flexion of the foot
Pulley
Fibularis
longus
Lateral
malleolus
The lateral malleolus of the fibula is an
example of an anatomical pulley. The
tendon of insertion for the fibularis longus
muscle does not follow a direct path.
Instead, it curves around the posterior
margin of the lateral malleolus of the
fibula. This redirection of the contractile
force is essential to the normal function
of the fibularis longus in producing
plantar flexion at the ankle.
Figure 9.13 Levers and Pulleys (6 of 6)
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The Patella as an
Anatomical
Pulley
Pulley
Quadriceps muscles
Quadriceps tendon
Patella
Patellar
ligament
Extension
of the leg
The patella is another
example of an anatomical
pulley. The quadricepsfemoris is a group of four
muscles that form the anterior musculature of the
thigh. These four muscles attach to the patella by the
quadriceps tendon. The patella is, in turn, attached to the
tibial tuberosity by the patellar ligament. The quadriceps
femoris muscles produce extension at the knee by this
two-link system. The quadriceps tendon pulls on the
patella in one direction throughout the movement, but
the direction of force applied to the tibia by the patellar
ligament changes constantly as the movement proceeds.
Aging and the Muscular System
• Changes occur in muscles as we age
• Skeletal muscle fibers become smaller in diameter
• Due to a decrease in the number of myofibrils
• Contain less glycogen reserves
• Contain less myoglobin
• All of the above results in a decrease in strength
and endurance
• Muscles fatigue rapidly
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Aging and the Muscular System
• Changes occur in muscles as we age (continued)
• There is a decrease in myosatellite cells
• There is an increase in fibrous connective tissue
• Due to the process of fibrosis
• The ability to recover from muscular injuries
decreases
© 2015 Pearson Education, Inc.
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