Chapter 10
*Lecture Outline
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Chapter 10 Outline
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Properties of Muscle Tissue
Characteristics of Skeletal Muscle Tissue
Contraction of Skeletal Muscle Fibers
Types of Skeletal Muscle Fibers
Skeletal Muscle Fiber Organization
Exercise and Skeletal Muscle
Levers and Joint Biomechanics
(continued)
Chapter 10 Outline—continued
• Naming of Skeletal Muscles
• Characteristics of Cardiac and Smooth
Muscle
• Aging and the Muscular System
• Development of the Muscular System
Introduction
•
There are three types of muscles in the
body:
1. skeletal
2. cardiac
3. smooth
•
•
Most of this chapter emphasizes skeletal
muscle
There are over 700 skeletal muscles and
together they form the muscular system
Properties of Muscle Tissue
There are four unique characteristics of
muscle tissue:
1. Excitability—outside stimuli can initiate
electrical changes in the muscle fiber
(cell) leading to contraction of that
muscle fiber (cell)
2. Contractility—stimulation of muscle
fiber can lead to contraction or
shortening of the muscle fiber
Properties of Muscle Tissue—
continued
3. Elasticity—a muscle fiber’s ability to
return to its original length when the
tension of contraction is released
4. Extensibility—the ability of a muscle
fiber to be stretched beyond its relaxed
length
Skeletal Muscle Tissue
• A skeletal muscle is considered an organ
because it contains and is constructed of
all four tissue types: epithelium,
connective, muscle, and nervous tissues.
• Muscle fibers are striated (possessing
stripes) when observed under a
microscope.
Functions of Skeletal
Muscle Tissue
1.
2.
3.
4.
5.
Body movement
Maintenance of posture
Temperature regulation
Storage and movement of materials
Support
Gross Anatomy of Skeletal Muscle
Figure 10.1
Skeletal Muscle Composition
• Each muscle is comprised of muscle
fibers.
• Muscle fibers are organized into bundles
called fascicles.
• Muscle fibers contain myofibrils.
• Myofibrils are composed of myofilaments.
• Myofilaments are mainly composed of
actin and myosin.
Order of Skeletal Muscle
Structural Organization
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•
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Muscle
Fascicles
Muscle fiber
Myofibrils
Myofilaments
Actin and myosin
Order of Skeletal Muscle
Structural Organization
Connective Tissue Components
• Each muscle has three layers of
concentric connective tissue that is
comprised mainly of collagen and elastic
fibers.
• This connective tissue provides protection,
sites for blood vessel and nerve
distribution, and a means of attaching the
muscle to the skeleton.
Layers of Connective Tissue
1. Endomysium—the innermost layer that
surrounds and electrically insulates each
muscle fiber
2. Perimysium—surrounds individual
fascicles
3. Epimysium—surrounds the entire muscle
4. Deep and superficial fascia—surround
each muscle and separate muscles from
each other
Muscle Attachments
• At the ends of each muscle, all of the
connective tissue merge to form a tendon,
which attaches the muscle to a bone.
• Tendons usually are cordlike in
appearance, but sometimes they are flat
and are called an aponeurosis.
Muscle Attachments
• Most muscles extend over a joint and have
attachments to both articulating bones of that
joint.
• Upon contraction of the muscle, one of the
articulating bones moves and the other one
does not.
• The point of attachment to the bone that does
not move is called the origin.
• The point of attachment to the bone that does
move is called the insertion.
Muscle
Attach
ments
Figure 10.2
Muscle Fiber Terminology
Skeletal muscle fibers have many of the same
components of a typical cell, but some are
named differently. The following list shows the
typical cell name and the name provided to the
muscle fiber, respectively:
1. Plasma membrane = sarcolemma
2. Cytoplasm = sarcoplasm
3. Smooth ER = sarcoplasmic reticulum
Muscle Fiber Terminology
There are two main structures that are
unique to the muscle fiber:
1. Transverse tubules (T-tubules)—deep
invaginations of the sarcolemma that
extend into the sarcoplasm
2. Terminal cisternae—blind sacs at the
end of the sarcoplasmic reticulum
Microscopic Anatomy
of Skeletal Muscle
Figure 10.3
Embryonic Development
of the Skeletal Muscle Fiber
• Embryonic skeletal muscle cells are called
myoblasts. Each myoblast contains a
single nucleus.
• Skeletal muscle fibers are multinucleated
and arise as a result of fusion of many
embryonic myoblasts.
• The nuclei from the myoblasts are
preserved in the mature skeletal muscle
fiber.
Embryonic Development
of the Skeletal Muscle Fiber
Figure 10.4
Myofibrils
• The sarcoplasm of a muscle fiber contains
100–1000 cylindrical structures that
extend the entire length of the cell.
• These structures are termed myofibrils.
• Myofibrils have the ability to shorten,
resulting in contraction of the muscle and
the production of motion.
Myofilaments
•
•
•
Myofibrils are composed of short bundles
of myofilaments.
Myofilaments do not run the entire length
of the muscle fiber but are organized into
repetitive groupings.
Myofilaments are of two types:
1. Thin filaments—actin and associated
proteins
2. Thick filaments—myosin
Microscopic Anatomy
of Skeletal Muscle
Figure 10.3
Thin Filaments
•
•
•
5–6 nm in diameter
Comprised of two strands (F-actin or
filamentous actin) of bead-shaped (Gactin or globular actin) molecules twisted
around each other
Two regulatory proteins are also part of
the thin filament:
– Tropomyosin
– Troponin
Thin Filaments
Figure 10.5
Thick Filaments
• 11 nm in diameter (twice as thick as thin
filaments)
• Composed of bundled molecules of
myosin
• Myosin molecule has a head and
elongated tail
• The heads form crossbridges with the
thin filaments during contraction
Thick Filaments
Figure 10.5
Comparison of Thick
and Thin Myofilaments
Figure 10.5
Organization of Thin
and Thick Filaments
• Organization of thin and thick filaments causes
the basis of skeletal muscle being striated.
• The dark bands, the A bands, contain the entire
myosin molecule and an overlapping portion of
actin.
• The light bands, the I bands, contain thin
filaments but no thick filaments.
• The I bands also contain the protein titin (see
Table 10.2 for its function).
Muscle Fiber Components
Other Components of the
A Bands and I Bands
Using an electron microscope, other components
can be seen within both A bands and I bands:
1. H zone (H band)—light, central region of the
A band where there are no thin filaments
2. M line—a protein meshwork in the H zone that
keeps the thick filaments aligned
3. Z disc (Z band)—a protein structure in the
middle of the I band that serves as the attachment
site for one end of the thin filaments
Fig08.02
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Skeletal muscle fiber
Sarcoplasmic
reticulum
Myosin (thick) Actin (thin)
filaments
filaments
Myofibril
Sarcomere
Z line
(a)
I band
(b)
H zone
Z line
M line
A band
I band
A band
34
Bands and Zones Within a Myofibril
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Connectin
filaments
Z disc
I band
(b)
A band
Myofibrils
Z disc
M line
Z disc
H zone
Sarcomere
(a)
Figure 10.6
Titin
filament
Thin
filament
I band
Thick
filament
M line
Thick
filament
H zone
Thin
filament
A band
Organization of a Sarcomere
• The sarcomere is the functional
contractile unit in a skeletal muscle fiber
• Defined by the area between two adjacent
Z discs
• Myofibrils contain multiple and repeating
sarcomeres
• Each sarcomere shortens as the muscle
fiber contracts
Structure of a Sarcomere
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Connectin
filaments
Z disc
I band
(b)
A band
Myofibrils
Z disc
M line
Z disc
H zone
Sarcomere
(a)
Figure 10.6
Titin
filament
Thin
filament
I band
Thick
filament
M line
Thick
filament
H zone
Thin
filament
A band
Structure of a Sarcomere
Figure 10.6
Components of a Sarcomere
Mechanisms of Skeletal
Muscle Contraction
• Muscle fibers shorten by the interaction
between thin and thick filaments within
each sarcomere.
• The mechanism for contraction is
explained by the sliding filament theory.
Sliding Filament Theory
During contraction, the thick and thin filaments interact
and slide past each other. This causes the following
changes within each sarcomere:
•
width of A band remains constant, but H zone
disappears
•
Z discs in each sarcomere move closer together
•
sarcomere narrows in length
•
I bands narrow
•
length of the thick and thin filaments never changes
whether the muscle is contracted or relaxed
Sliding Filament Model
of Contraction
Figure 10.7
Neuromuscular Junctions
• Muscle contraction begins when a motor
neuron impulse stimulates an impulse in a
muscle fiber.
• The neuromuscular junction is the
region where the motor neuron comes into
close proximity to the muscle fiber.
Neuromuscular Junction
Figure 10.8
Components of the
Neuromuscular Junction
1.
2.
3.
4.
5.
6.
Synaptic knob—expanded end of the neuron
Synaptic vesicles—membrane-bound sacs filled with
acetylcholine (ACh)
Motor end plate—region of sarcolemma across from
the synaptic knob that has folds and indentations to
increase the surface area in that region
Synaptic cleft—narrow space separating the synaptic
knob from the motor end plate
ACh receptors—in the motor end plate that bind to
ACh
Acetylcholinesterase (AChE)—an enzyme in the
synaptic cleft that rapidly breaks down ACh
Neuromuscular Junction
Figure 10.8
Muscle Contraction:
A Summary
1. A nerve impulse causes ACh to be
released into the synaptic cleft.
2. ACh binds to receptors in the motor end
plate initiating a muscle impulse along
the sarcolemma and T-tubule
membranes.
3. Calcium is released from T-tubules into
the sarcoplasm.
Muscle Contraction: A
Summary—continued
4. Calcium ions bind to troponin, causing
tropomyosin to uncover active binding
sites.
5. Myosin heads then bind to actin and form
crossbridges.
6. In the presence of ATP, myosin cycles
through attachment, pivot, detach, and
return events. ATP is also necessary for
relaxation of the muscle fiber.
Muscle Contraction
Figure 10.9
Motor Units
• A motor unit consists of a single motor neuron
and the muscle fibers it controls.
• A motor unit controls only a few muscle fibers in
an entire muscle.
• Larger muscles have more motor units than do
smaller muscles.
• Each muscle fiber obeys the all-or-none
principle—a muscle fiber contracts completely
or not at all.
• When a motor unit is stimulated, all muscle
fibers under its control will contract.
Motor Unit
Figure 10.10
Two Types of Muscle
Contraction
Figure 10.11
Types of Skeletal Muscle Fibers
Skeletal muscles are comprised of a mixture
of three different type of muscle fibers. The
ratio of these three fiber types within a
muscle will determine the speed of the
muscle’s contraction and the sustainability of
the contraction.
1. Slow (Type I, slow oxidative)
2. Intermediate (Type IIa, fast aerobic)
3. Fast (Type IIb, fast anaerobic)
Structural and Functional
Characteristics of Skeletal Muscle
Fiber Types
Microscopic View of Fiber Types
in Skeletal Muscle
Figure 10.12
Distribution of the Three
Muscle Fiber Types
• Usually, skeletal muscles are comprised of a
combination of all three muscle fiber types, but a
single motor unit controls only muscle fibers
from one of the three types.
• Slow fibers dominate muscles such as back and
calf muscles, which contract almost
continuously.
• There are no slow muscle fibers in muscles that
require swift but brief contractions, such as eye
and hand muscles.
Skeletal Muscle Fiber
Organization
Muscle fibers are organized into fascicles within a
muscle but there are four different patterns of
fascicle arrangements:
1. circular
2. parallel
3. convergent
4. pennate
–
–
–
unipennate
bipennate
multipennate
Fascicle Arrangements
Exercise and Skeletal Muscle
• Muscle atrophy—a wasting of tissue that
results in reduction of muscle size, tone, and
power. This can be caused by a lack of
stimulation (exercise) to the muscle.
• Muscle hypertrophy—an increase in muscle
fiber size (not an increase in number of muscle
fibers). Hypertrophy results from repetitive
stimulation of muscle fibers. Mitochondria
increase in number, therefore the amount of
ATP increases. Both myofibrils and
myofilaments increase in number, all resulting in
the muscle increasing in size.
Levers and Biomechanics
• A lever is an elongated, rigid object that
rotates around a fixed point called a
fulcrum.
• Rotation occurs when an effort applied to
one point of the lever exceeds a
resistance located at some other point of
the lever.
• There are three classes of levers found in
the human body.
Three Classes of Levers
Figure 10.13
Actions of Skeletal Muscles
1. Agonist (prime mover)—produces a specific
movement when it contracts. For instance, the
biceps brachii is an agonist that causes flexion
of the elbow joint.
2. Antagonist—is a muscle whose action
opposes that of an agonist. The triceps brachii
would be an antagonist to the biceps brachii
3. Synergist—is a muscle that assists the
agonist or prime mover.
Naming of Skeletal Muscles
Muscle names can be confusing, but their names
incorporate the following qualities of the muscle:
1. Muscle action
2. Body region
3. Muscle attachments
4. Orientation of muscle fibers
5. Muscle shape and size
6. Muscle heads/tendons of origin
Naming of Skeletal Muscles
Figure 10.14
Characteristics of Cardiac
and Smooth Muscle
• The three types of muscle in the human
body are skeletal, cardiac, and smooth
muscle.
• There are similarities and differences
among the three types of muscles.
Cardiac Muscle Fibers
Cardiac muscle fibers are found almost exclusively within
the heart wall. They have the following qualities:
1. striated
2. one or two nuclei
3. form Y-shaped branches
4. join other adjacent cells to form junctions termed
intercalated discs comprised of gap junctions
5. autorhythmic (able to generate a muscle impulse
without nervous stimulation)
6. under involuntary control
Cardiac Muscle Fibers
Figure 10.15
Smooth Muscle Fibers
1. Found in the walls of viscera and blood
vessels
2. Short fusiform cells (widest in the middle
and tapered at each end)
3. One centrally located nucleus
4. No striations
5. Thin filaments attached to dense bodies
6. Under involuntary control
Smooth Muscle Fibers
Figure 10.16
General Comparison
of Muscle Tissue Types
Development of Skeletal Muscle
Figure 10.17