Muscle Tissue
Chapter 10
Overview of Muscle Tissue

There are three types of muscle tissue
– Skeletal muscle
– Cardiac muscle
– Smooth muscle

These muscle tissues differ in the
structure of their cells, their body
location, their function, and the means by
which they are activated to contract
Overview of Muscle Tissue



All skeletal and smooth muscle cells are
elongated and are referred to as muscle
fibers
Muscle contraction depends on two types
of myofilaments, actin and myosin
All prefixes of myo or mys and sarco
reference muscle
Skeletal Muscle Tissue



Skeletal muscle tissue appears as distinct skeletal
muscle that attach to the skeletal system
Skeletal muscle has obvious striations
It is a voluntary muscle under conscious control
Cardiac Muscle Tissue




Cardiac muscle occur only in the heart
The muscle is striated but involuntary
Cardiac fibers are short, fat, branched and
interconnected
Cardiac muscle cells are interlocked by
intercalated discs and function as a single unit
Smooth Muscle Tissue



It is found in the walls of hollow organs such as
the stomach, urinary bladder, and intestines
It has no striations
It is not subject to voluntary control
Differences in Contractions




Skeletal muscle can contract rapidly but
tire easily and must be rested
Skeletal muscle contractions vary in force
depending on use
Cardiac muscle contracts at a steady rate
but can accelerate to cope with demand
Smooth muscle contracts in steady,
sustained contractions and continues on
tirelessly
Muscle Functions

Muscle performs four important
functions in the body:
–
–
–
–
Producing movement
Maintaining posture
Stabilizing joints
Generating heat
Producing Movement




Movement results from skeletal muscle
contraction
Skeletal muscle are responsible for all
locomotion and manipulation
Allows you to interact or react with your
external environment
It controls eye movement, facial
expression (skeletal); circulation
(cardiac), and moves gas, liquids, and
solids through organs (smooth)
Maintaining Posture


Skeletal muscles are utilized constantly to
maintain sitting, standing, and moving
postures
Postural muscle develop to compensate
for the never ending pull of gravity
– Our developmental milestones as an infant
are our initial victories over gravity

Curves of the spinal column are shaped
by the interplay of skeletal muscle and
gravity
Stabilizing Joints



Skeletal muscle provide the dynamic
stability of joints
Many joints are poorly reinforced by
ligaments and connective tissue
Many joints have noncomplementary
surface which do not contribute to
stability
Generating Heat




Muscles generate heat as they contract
The heat generated is vitally important to
maintain normal body temperature
Skeletal muscle generates most of the
heat because it represents 40% of body
mass
Excess heat must released to maintain
body temperature
Functional Characteristics

Excitability or irritability
– It has the ability to respond to a stimulus

Contractility
– It has the ability to shorten forcibly

Extensibility
– Muscle fibers can be stretched

Elasticity
– Resume its normal length after being
shortened
Skeletal Muscle
Anatomy of a Skeletal Muscle


Each skeletal
muscle is a
discrete organ
with thousands
of fibers
Muscle fibers
predominate the
tissue but it also
contains, blood
vessels, nerve
fibers, and
connective tissue
Connective Tissue Wrappings



Each muscle fiber
is wrapped by fine
sheath of areolar
connnective called
endomysium
Several fibers are
gathered side by
side into bundles
called fascicles
Each fascicle is
bound by collagen
a fiber layer called
the perimysium
Connective Tissue Wrappings



Fascicles are
bound by a dense
fibrous connective
tissue layer called
the epimysium
The epimysium
surrounds the
entire muscle
External to the
epimysium is the
deep fascia that
binds muscles into
functional groups
Connective Tissue Wrappings



All the connective tissue
layers are continuous
with one another as well
as with the tendons that
join muscles to bone
When muscle fibers
contract they pull these
connective tissue sheaths
which in turn transmit
the force to the bone to
be moved
Connective tissues
supports each cell
Nerve and Blood Supply




Normal activity of skeletal muscle is totally
dependent on its nerve and blood supply
Each skeletal muscle fiber is controlled by a
nerve ending (neuromuscular junction)
Contracting muscle fibers use huge amounts
of energy which requires a continuous
supply of oxygen and nutrients
In general, each muscle is served by an
artery and one or more veins
Attachments


Most muscles span joints and have at least
two attachments an origin and an insertion
Origin
– Attachment of a muscle that remains relatively
fixed during muscular contraction
– Generally a more proximal or axial location

Insertion
– Attachment of a muscle that moves during
muscular contraction
– Generally a more distal or appendicular
attachment
Attachments



Direct attachments
have the epimysium
attaching directly to
the periosteum of the
bone or
perichondrium of a
cartilage
Indirect attachments
have the epimysium
attaching to a tendon
or an aponeurosis
Temporalis has both
muscle attachments
Contraction of Skeletal Muscle




The principles of contraction of a muscle
cell can be generalized to the entire muscle
The force exerted is called tension, the
resistance to the force is called the load
A contracting muscle does not always
shorten (isometric or isotonic)
Skeletal muscle can contract with varying
force for different periods of time which
enhances its efficiency
The Motor Unit



Each muscle is served by at least one
motor nerve which contains hundreds of
motor neuron axons
As a nerve enters a muscle it branches
into a number of axonal terminals, each
of which forms a neuromuscular junction
with a single nerve fiber
A motor neuron and all the muscle fibers
it supplies is called a motor unit
The Motor Unit


When a motor
neuron transmits
an electrical
impulse, all the
muscle fibers that it
innervates respond
by contracting
The average
number of muscle
fibers per unit is
150, but it ranges
from 4 to several
hundred
The Motor Unit


Muscles that exert
very fine control
have small motor
units (eyes, fingers)
Large muscles of
locomotion and
weight bearing
have large motor
units and as a
consequence have
less precise control
The Motor Unit



The muscle fibers
in a unit are not
clustered together
but rather are
spread throughout
the entire muscle
Stimulation of a
single unit causes a
weak contraction of
the entire muscle
This allows control
of the intensity of
the contraction
Skeletal Muscle Fiber



Skeletal muscle fibers
are long and cylindrical
These cells are huge
Diameter of 10-100 m
up to 10 times average
cell size
Length is phenomenal
for a cell - from several
centimeters to dozens of
centimeters in long
muscles
Skeletal Muscle Fiber



These cells actually
form by the fusion of
hundreds of embryonic
cells
Because of its
development skeletal
muscle fiber contains
many nuclei
Nuclei lie at the cell
periphery, just deep to
the sarcolemma
Myofibrils and Sarcomeres



Under the microscope
stripes called striations
are visible in skeletal
muscle fibers
These striations result
from the internal
structure of long rods
called myofibrils within
the sarcoplasm
Note that fibrils are to
be distinguished from
fibers and filaments
Myofibrils and Sarcomeres


Myofibrils are
unbranched cylinders
that are present in large
numbers making up
80% of the sarcoplasm
Myofibrils can be
conceptualized as
specialized contractile
cellular organelles
unique to muscle fibers
Myofibrils and Sarcomeres

Different myofibrils in
a fiber are separated
and surrounded by
narrow regions of
sarcoplasm that contain
rows of mitrochondria
and glycosomes that
supply energy for
muscle contraction
Myofibrils and Sarcomeres

Distinguishing
individual myofibrils is
histologically difficult
because the striations of
adjacent myofibrils line
up almost perfectly
Myofibrils and Sarcomeres



A myofibril is a long
row of repeating
segments called
sarcomeres
The sarcomere is the
basic unit of
contraction in skeletal
muscle
The boundaries at each
end of the sarcomere
are called z discs
Myofibrils and Sarcomeres

Attached to each Z disc
and extending toward
the center of the
sarcomere are many
fine myofilaments
called thin (actin)
filaments, which consist
primarily of the protein
actin, although they
contain other proteins
as well
Myofibrils and Sarcomeres

In the center of each
sarcomere and
overlapping the inner
ends of the thin
filaments is a
cylindrical bundle of
thick (myosin)
filaments
Myofibrils and Sarcomeres


Myosin filaments are
mostly myosin and
some ATPase enzymes
that split ATP to release
energy required for
muscle contraction
Both ends of a thick
filament are studded
with knobs called
myosin head or cross
bridges
Types of Skeletal Muscle Fiber



Not all skeletal muscle fibers are alike as
they vary on the type of contractions they
produce
Muscle fiber can be divided by the
strength, speed, and endurance of the
contraction to which they contribute
Specifically the fibers are referred to as
red slow twitch, white fast twitch and
intermediate fast-twitch fibers
Types of Skeletal Muscle Fiber



Red slow twitch are relatively thin fibers
They are named for the abundant
myoglobin (oxygen binding pigment) in
their sarcoplasm
Red fibers obtain their energy from
aerobic (oxygen requiring) reactions and
thus have relatively large numbers of
mitrochondria (the site of aerobic
metabolism) and a rich blood supply
from an extensive network of capillaries
Types of Skeletal Muscle Fiber




Red slow twitch fibers contract slowly,
are resistant to fatigue as long as oxygen
is present
Deliver prolonged contractions
Used in many of the postural muscles of
the axial skeleton
Because their fibers are thin, slow twitch
fibers do not generate much power
Types of Skeletal Muscle Fiber



White fast twitch fibers are pale because
they contain little myoglobin
The fibers are about twice the diameter
of red slow twitch fibers, they contain
more myofibrils and generate more
power
The fibers depend on anaerobic pathways
(no oxygen used) to make ATP
Types of Skeletal Muscle Fiber




They contain few mitrochondria or
capillaries but have many glycosomes
containing glycogen as a fuel source
White fast twitch fibers contract rapidly
and tire quickly
This fiber type is common in the muscle
of the upper limbs
Used to lift heavy objects for brief
periods
Types of Skeletal Muscle Fiber



Intermediate fast twitch are sized
between the other two fiber types
Like white fibers they contract quickly;
like slow twitch they are oxygen
dependent and have a high myoglobin
content and a rich supply of capillaries
Because they are intermediate fibers they
depend largely on aerobic metabolism,
and are less fatigue resistant
Types of Skeletal Muscle Fiber



They are more powerful than red fibers,
but not as strong as white
This type of fiber is abundant in the
muscles of the lower limbs
Used to move the body for long periods of
time in activities like walking and jogging
Types of Skeletal Muscle Fiber




Because muscles contain a mixture of the
three fiber types, each muscle can perform
different tasks at different times
For example the Gastrocnemius muscle can
be used for sprinting, walking and as a
postural muscle
Although everyone’s muscles contain
mixtures of the three fiber types, some
people have relatively more of one type
These differences are genetically controlled
Next Section


Turn to “Smooth Muscle” on page 255 of
your text
You are not responsible for the section on
sliding filament theory
Smooth Muscles


Smooth muscle
lacks the courser
connective tissue
seen in skeletal
muscle
Small amounts of
endomysium is
found between
smooth muscle
fibers
Smooth Muscles


Smooth muscles are
organized into
sheets of closely
apposed fibers
These sheets occur
in the walls of all
but the smallest
blood vessels and in
the walls of hollow
organs of the
respiratory, urinary
digestive and
reproductive tracts
Smooth Muscles



In most cases two
sheets of muscles
are present with
their fibers aligned
at right angle to
each other
These forms the
longitudinal (long
axis) and circular
(encircling) layer
These two layers
squeeze the contents
of the organ
End of Chapter
Chapter 9