Dr. B Ch 09_lecture_presentation

© 2012 Pearson Education, Inc.
9
The Muscular System:
Skeletal Muscle Tissue
and Organization
PowerPoint® Lecture Presentations prepared by
Steven Bassett
Southeast Community College
Lincoln, Nebraska

Introduction
There are three types of muscle tissue:
 Skeletal muscle—Skeletal muscle tissue moves the body by pulling on
bones of the skeleton.
 Skeletal muscle fibers arise from embryonic cells called myoblasts.
 Work voluntarily.
 Striated microscopic pattern.
 Cardiac muscle—Cardiac muscle tissue pushes blood through the arteries
and veins of the circulatory system.
 Work involuntarily.
 Striated microscopic pattern.
 Intercalated discs.
 Branchd fibers.
 Smooth muscle—Smooth muscle tissues push fluids and solids along the
digestive tract and hollow organs and perform varied functions in other
systems.
 Work involuntarily.
 Smooth microscopic pattern.

Introduction
Muscle tissues share four basic properties:
 Excitability: the ability to respond to stimulation
 Skeletal muscles normally respond to stimulation by the
nervous system.
 Cardiac and smooth muscles respond to the nervous system
and circulating hormones.
 Contractility: the ability to shorten actively and exert
a pull or tension that can be harnessed by connective
tissues
 Extensibility: the ability to continue to contract over a
range of resting lengths
 Elasticity: the ability of a muscle to rebound toward
its original length after a contraction

Functions of Skeletal Muscles
Skeletal muscles are contractile organs directly or
indirectly attached to bones of the skeleton.
They work voluntarily.
 Skeletal muscles perform the following functions:
 Produce skeletal movement
 Maintain posture and body position
 Support soft tissues and stabilize the joints.
 Regulate entering and exiting of material
 Maintain body temperature

Skeletal muscle surrounding
• From inside out:
• Sarcolema
• Plasma membrane of muscle fiber.
• Endomysium
• Connective tissue surrounding the muscle fiber.
• Perimysium
• Connective tissue surrounding the fascicle. Fascicle is a
bundle of muscle fibers.
• Epimysium
• Connective tissue surrounding the muscle.
• Deep fascia
• Connective tissue surrounding the skeletal muscles together.

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

Figure 9.1 Structural Organization of Skeletal Muscle
Epimysium
Muscle fascicle
Endomysium
Perimysium
Nerve
Muscle fibers
Blood vessels
SKELETAL MUSCLE
(organ)
MUSCLE FASCICLE
(bundle of cells)
Perimysium
Muscle fiber
Endomysium
Epimysium
Blood vessels
and nerves
Endomysium
Perimysium
Tendon
MUSCLE FIBER
(cell)
Mitochondria
Sarcolemma
Myofibril
Axon
Sarcoplasm
Capillary
Endomysium
Myosatellite
cell
Nucleus

Anatomy of skeletal muscle
fiber
• Sarcolemma
• The plasma membrane of the muscle fiber.
• Sarcoplasmic reticulum
• the ER that stores calcium ions.
• Terminal cisterna
• an expanded part of ER next to T tube.
• T tube
• an extension of sarcolema into the muscle fiber.
• Triad
• The combination of one T tube and two flaked Terminal Cisterna.

Figure 9.3ab The Formation and Structure of a Skeletal Muscle Fiber
Muscle fibers develop
through the fusion of
mesodermal cells
called myoblasts.
Development of a
skeletal muscle fiber
External appearance
and histological view
Myoblasts
Myosatellite cell
Nuclei
Immature
muscle fiber

Figure 9.3b–d The Formation and Structure of a Skeletal Muscle Fiber
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.
Myofibril
Sarcolemma
Sarcoplasm
Nuclei
MUSCLE FIBER
Mitochondria
Sarcolemma
Myofibril
Thin filament
Thick filament
Triad Sarcoplasmic T tubules
reticulum
Terminal cisterna
Sarcolemma
Sarcoplasm
Myofibrils

Figure 9.4b Sarcomere Structure
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
I band A band
H band Z line Titin
Zone of overlap M line Thin
filament
Thick
filament
Sarcomere
H band Z line
I band
Z line Zone of overlap M line
Sarcomere
TEM ´ 64,000
A band

Anatomy of Skeletal Muscles
• Levels of 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

Skeletal muscle
 Sarcomere Organization
 Thick and thin filaments within a myofibril are organized in the
sarcomeres.
 All of the myofibrils are arranged parallel to the long axis of the
cell, with their sarcomeres lying side by side.
 A band: the dark area of sarcomere that contains thick filaments.
 I band: the light area between A bands.
 H band: the light area within the A band.
 M line: the dark line within the H band.
 Z line: the area of a myofibril, where actin filaments attach to one
another.

Skeletal muscle
 Thin and Thick Filaments
 Each thin filament consists of a twisted strand of
several interacting proteins 5–6 nm in diameter and 1
μm in length.
 Troponin holds the tropomyosin strand in place.
 Thick filaments are 10–12 nm in diameter and 1.6 μm
in length, making them much larger than thin
filaments.

Figure 9.5 Levels of Functional Organization in a Skeletal Muscle Fiber
SKELETAL MUSCLE
MUSCLE FASCICLE
MUSCLE FIBER
MYOFIBRIL
SARCOMERE
Surrounded by:
Epimysium
Contains:
Muscle
fascicles
Surrounded by:
Perimysium
Contains:
Muscle fibers
Surrounded by:
Endomysium
Contains:
Myofibrils
Surrounded by:
Sarcoplasmic
reticulum
Consists of:
Sarcomeres
(Z line to Z line)
Contains:
Thick filaments
Thin filaments
I band A band
Z line M line
H band
Titin Z line

Figure 9.6ab Thin and Thick Filaments
The attachment
of thin filaments
to the Z line
Active
site
The detailed structure of a thin filament showing
the organization of G actin, troponin, and
tropomyosin
Myofibril
Sarcomere
H band
Z line M line
Actinin Z line Titin
Troponin Nebulin Tropomyosin
G actin
molecules
F actin
strand

Figure 9.6cd Thin and Thick Filaments
Myofibril
Sarcomere
Z line M line
H band
A single myosin molecule detailing the structure and
movement of the myosin head after cross-bridge
binding occurs
The structure of
thick filaments
Titin
M line
Myosin tail
Myosin
head
Hinge

Muscle Contraction
 Contracting muscle fibers exert a pull, or
tension, and shorten in length.
 Sarcoplasmic reticulum stores calcium
ions.
 Caused by interactions between thick
and thin filaments in each sarcomere
 Triggered by presence of calcium ions
 Contraction itself requires the presence
of ATP.

Muscle Contraction
The Sliding Filament Theory
 Explains the following changes that occur
between thick and thin filaments during
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.

Figure 9.7 Changes in the Appearance of a Sarcomere during Contraction of a Skeletal Muscle Fiber
A relaxed sarcomere showing location
of the A band, Z lines, and I band
I band A band
Z line H band Z line
During a contraction, the A band stays the same
width, but the Z lines move closer together and
the I band gets smaller. When the ends of a
myofibril are free to move, the sarcomeres
shorten simultaneously and the ends of the
myofibril are pulled toward its center.

Muscle Contraction
 The Start of a Contraction
 Triggered by calcium ions in the sarcoplasm
 Electrical events at the sarcolemmal surface
 Trigger the release of calcium ions from the terminal
cisternae
 The calcium ions diffuse into the zone of overlap and
bind to troponin.
 Troponin changes shape, alters the position of the
tropomyosin strand, and exposes the active sites on
the actin molecules.

Figure 9.10a The Neuromuscular Synapse
A diagrammatic view of a
neuromuscular synapse
Motor
neuron
Axon
Muscle fiber
Path of action
potential
Neuromuscular
synapse
Motor
end plate
Myofibril

Figure 9.10ab The Neuromuscular Synapse
Path of action
potential
A diagrammatic view of a
Motor
neuron
Axon
Muscle fiber
Neuromuscular
synapse
Motor
end plate
Myofibril
One portion of a
Glial cell
Synaptic terminal
Sarcolemma
Mitochondrion
Myofibril

Figure 9.10bc The Neuromuscular Synapse
One portion of a
Arriving action
potential
Synaptic cleft
Sarcolemma of
motor end plate
Glial cell
Synaptic terminal
Sarcolemma
Mitochondrion
Myofibril
Detailed view of a terminal,
synaptic cleft, and motor end
plate. See also Figure 9.2.
Synaptic
vesicles
ACh
ACh
receptor
Junctional
fold
AChE site
molecules

Skeletal muscle
 The End of a Contraction
 When electrical stimulation ends:
 The SR will recapture the Ca2+ ions.
 The troponin–tropomyosin complex will cover the
active sites.
 And, the contraction will end.

Figure 9.11 The Events in Muscle Contraction
STEPS IN INITIATING MUSCLE CONTRACTION STEPS IN MUSCLE RELAXATION
ACh released, binding
to receptors
Sarcoplasmic
reticulum
releases Ca2+
Active-site
exposure,
cross-bridge
formation
T tubule Sarcolemma
Action
potential
reaches
T tubule
Ca2+
Actin
Myosin
Motor
end
plate
Synaptic
terminal
Contraction
begins
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
• A motor unit is all muscle fibers controlled
by a single motor neurone.
• At the end of each motor neuron there are
synaptic vesicles containing
neurotransmitters. The neurotransmitter
involved in the process of contraction is
Acetylcholine.
• The enzyme in the synaptic cleft that
destroys Ach and shuts down the
contraction is Acetylcholineesterase (AchE)

Figure 9.12 The Arrangement of Motor Units in a Skeletal Muscle
KEY
Motor unit 1
Motor unit 2
Motor unit 3
SPINAL CORD
Muscle fibers
Axons
of motor
neurons
Motor
nerve

Muscle Tone
 Some of the motor units of muscles are always
contracting, producing a resting tension in a
skeletal muscle that is called muscle tone.
 Resting muscle tone stabilizes the position of
bones and joints.

Muscle Hypertrophy and Atrophy
 Exercise causes increases in
 Number of mitochondria
 Concentration of glycolytic enzymes
 Glycogen reserves
 Myofibrils
 Each myofibril contains a larger number of thick and thin
filaments.
 The net effect is an enlargement, or hypertrophy, of
the stimulated muscle.
 Disuse of a muscle results in the opposite,
called atrophy.

Types of Skeletal Muscle Fibers
 The features of fast fibers, or white fibers,
are:
 Large in diameter—due to many densely
packed myofibrils
 Large glycogen reserves
 Relatively few mitochondria
 Their mitochondria are unable to meet the demand.
 Fatigue easily
 Can contract in 0.01 seconds or less following
stimulation

Figure 9.13a Types of Skeletal Muscle Fibers
LM ´ 170
LM ´ 170
Note the difference in the size of
slow muscle fibers (above) and
fast muscle fibers (below).
Slow fibers
Smaller diameter,
darker color due to
myoglobin; fatigue
resistant
Fast fibers
Larger diameter,
paler color;
easily fatigued

 Slow fibers, or red fibers, features are
 Only about half the diameter of fast fibers
 Take three times as long to contract after
stimulation
 Contain abundant mitochondria
 Use aerobic metabolism
 Have a more extensive network of capillaries
than do muscles dominated by fast muscle
fibers.
 Red color because they contain the red pigment
myoglobin

Intermediate fibers have properties
intermediate between those of fast fibers and
slow fibers.
 Intermediate fibers contract faster than slow
fibers but slower than fast fibers.
 Intermediate fibers are similar to fast fibers
except
 They have more mitochondria.
 They have a slightly increased capillary supply.
 They have a greater resistance to fatigue.

Figure 9.14ab Skeletal Muscle Fiber Organization
Parallel muscle
(Biceps brachii muscle)
Parallel muscle with
tendinous bands
(Rectus abdominis
muscle)
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Fascicle
Cross section
Body
(belly)

Figure 9.14e Skeletal Muscle Fiber Organization
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Extended
tendon
Unipennate muscle
(Extensor digitorum muscle)

Figure 9.14g Skeletal Muscle Fiber Organization
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Tendons
Cross section
Multipennate muscle
(Deltoid muscle)

Figure 9.14h Skeletal Muscle Fiber Organization
(h)
(d)
(g)
(a)
(b)
(e)
(c)
(f)
Contracted
Relaxed
Circular muscle
(Orbicularis oris muscle)

Muscle Terminology
 Origin: the end of the muscle that remains
stationary
 Insertion: the end of the muscle that moves
 Commonly the origin is proximal to the insertion.
 Muscle Actions
 There are two methods of describing actions.
 The first references the bone region affected.
 For example, the biceps brachii muscle is said to perform
“flexion of the forearm.”
 The second method specifies the joint involved.
 For example, the action of the biceps brachii muscle is
described as “flexion of the elbow.”

Muscle Terminology
 Muscles can be grouped according to their
primary actions into three types:
 Prime movers (agonists): are muscles chiefly
responsible for producing a particular movement
 Synergists: assist the prime mover in performing that
action
 Antagonists: are muscles whose actions oppose that
of the agonist
 If the agonist produces flexion, the antagonist will produce
extension.
• Fixators
• Agonist and antagonist muscles contracting at the same time to
stabilize a joint

Organization of Skeletal Muscle Fibers
• Most muscle names provide clues to their
identification or location
 Size of the muscle
 Magnus: large
 Brevis: short
 Specific body regions
 Brachialis
 Shape of the muscle
 Trapezius
 Orientation of muscle fibers
 Rectus, transverse, oblique
 Specific or unusual features
 Biceps (two origins)
 Identification of origin and insertion
 Sternocleidomastoid
 Primary functions
 Flexor carpi radialis
 References to actions
 Buccinators

Table 9.2 Muscle Terminology

Levers and Pulleys: A Systems Design for
Movement
First-class levers
 Second-class levers
 Characteristics of second-class levers are:
 The force is magnified.
 The resistance moves more slowly and covers a shorter distance.
 Third-class levers
 The characteristics of the third-class lever are:
 Speed and distance traveled are increased.
 The force produced must be great.

Figure 9.15a The Three Classes of Levers
R F
Resistance
Fulcrum
Applied
force
Movement completed
R
F
AF
AF
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.

Figure 9.15b The Three Classes of Levers
R
Movement completed
AF
F
F
F
AF
In a second-class lever, the resistance lies between the applied force and
the fulcrum. This arrangement magnifies force at the expense of distance
and speed; the direction of movement remains unchanged.

Figure 9.15c The Three Classes of Levers
In a third-class lever, the force is applied between the resistance
and the fulcrum. This arrangement increases speed and distance
moved but requires a larger applied force.
Movement completed
R
F
AF
AF
R
F

Aging and the Muscular System
Skeletal muscle fibers become smaller in
diameter.
 Skeletal muscles become smaller in
diameter and less elastic.
 Tolerance for exercise decreases.
 The ability to recover from muscular injuries
decreases.

Dr. B Ch 09_lecture_presentation

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