Download Muscles - Part 1

Chapter 6
THE MUSCULAR SYSTEM
Three Types of Muscle Tissue
1. Skeletal
2. Cardiac
3. Smooth
Similarities of Muscle
1. All muscle cells are elongated and are
therefore called muscle fibers.
2. Muscle has the ability to shorten, or contract.
3. All muscle cells contain one of the following
prefixes: myo-, mys-, or sarco-
Skeletal Muscle Fibers
 Skeletal Muscle
Fibers – Are
packaged into
organs called skeletal
muscles that attach
to the body’s
skeleton.
 Cover our bony
“underpinnings” and
help form the
smoother contours of
the body.
Skeletal Muscle Fibers:
Characteristics




Cigar-shaped
Multinucleate cells
Largest of the muscle fiber types
Known as striated muscle because
its fibers appear to be striped.
 Only muscle type subject to
conscious control (voluntary
control).
 Can also be activated by reflexes
(without our “willed command”)
 Can contract rapidly and with great
force, but tires easily and must rest
after short periods of activity.
Skeletal Muscle
Fibers: Anatomy
 Skeletal muscle fibers are soft
and surprisingly fragile. Yet
skeletal muscles can exert
tremendous power - how so?
 The reason they are not ripped
apart as they exert force is that
thousands of their fibers are
bundled together by CT, which
provides strength and support
to the muscle as a whole.
Skeletal Muscle Fibers:
Anatomy
 Endomysium – A
delicate CT sheath that
encloses each muscle
fiber.
 Perimysium – A coarse
fibrous membrane that
are wrapped around
several sheathed muscle
fibers.
 Fascicle – A bundle of
muscle fibers.
Skeletal Muscle Fibers:
Anatomy
 Epimysium – An even
tougher “overcoat” of
CT that bounds
together many
fascicles; Covers the
entire muscle.
 The epimysia blend into
the strong, cordlike
tendons , which attach
muscles indirectly to
bones, cartilages, or CT
coverings of each other.
Functions of Tendons
1. Anchor Muscles
 Tendons attach muscles to
bones.
2. Provide Durability
 Tendons are mostly tough
collagenic fibers, so they can
cross rough bony projections.
3. Conserve Space
 Because of their relatively
small size, more tendons than
fleshy muscles can pass over a
joint.
 http://www.davidlnelson.md/T
endon_Surgery.htm
Shape of Skeletal Muscles
 Many people think of muscles as having an
enlarged “belly” that tapers down to a tendon at
each end.
 However, muscles vary considerably in the way their
fibers are arranged.
 Many are spindle-shaped as just described above.
 Other fibers are arranged in a fan shape or a circle.
Smooth Muscle
Characteristics
 No striations.
 Involuntary (cannot consciously
control it).
 Found mainly in the walls of
hollow visceral organs such as
the stomach, urinary bladder,
and respiratory passages.
 Propels substances along a
definite tract, or pathway,
within the body.
Smooth Muscle Cells
 Spindle-shaped.
 Have a single nucleus.
 Arranged in sheets or layers.
 Most often, there are two
such layers, one running
circularly and the other
longitudinally.
 As the two layers alternately
contract and relax, they
change the size and shape of the organ.
 Contraction is slow and sustained.
 Examples: Movement of food through the digestive
tract and emptying the bowels and bladder.
Cardiac Muscle
 Found only in the heart.
 The heart serves as a pump,
propelling blood into the blood
vessels and to all the tissues of
the body.
 Is striated.
 Involuntary.
 Cardiac muscle fibers are
branching cells joined by
special junctions called
intercalated discs.
Cardiac Muscle Fiber
Anatomy
 The cardiac fibers are
cushioned by small amounts
of soft CT and arranged in
spiral or figure 8-shaped
bundles.
 When the heart contracts, its
internal chambers become
smaller, forcing the blood
into the large arteries leaving
the heart.
Cardiac Muscle
Contraction
 The structural features and
arrangement allows the heart
activity to be closely
coordinated.
 Cardiac muscle contracts at a
fairly steady rate set by the
heart’s “in-house” pacemaker.
 Can also be stimulated by the
nervous system to shift it into
“high gear” for short periods, as
when you race to catch the bus.
Muscle Functions
1.
2.
3.
4.
Produces Movement
Maintains Posture
Stabilizes Joints
Generates Heat
Muscle Functions: Produce
Movement
 Just about all movements of the human
body are a result of muscle contraction.
 Mobility of the body, which includes all




locomotion and manipulation.
Enable us to respond quickly to changes in the external
environment.
Allow us to express our emotions silently (smiles and
frowns).
Smooth and cardiac muscles work
together to circulate blood and maintain
blood pressure.
Smooth muscle forces fluids such as
bile and urine through internal body
channels.
Muscle Functions: Maintaining
Posture
 The skeletal muscles function continuously to
maintain body posture.
 Making one tiny adjustment after another.
 So that we can maintain an erect or seated
posture despite the never-ending downward pull
of gravity.
Muscle Functions: Stabilizing
Joints
 As the skeletal muscles pull on bones to cause
movements, they also stabilize the joints of
the skeleton.
 Muscle tendons are extremely important in
reinforcing and
stabilizing joints
that have poorly
fitting articulating
surfaces.
 For example:
The shoulder joint
Muscle Functions: Generating
Heat
 Generation of body heat is a by-product of
muscle activity.
 As ATP is used to power muscle contraction,
nearly ¾ of its energy escapes as heat.
 Skeletal muscle is
most responsible for
generating heat.
 This heat is vital in
maintaining normal
body temperature.
Muscular System
 The term muscular system
applies specifically to skeletal
muscle.
 Therefore, we will be
concentrating on this muscle
type only in this
unit.