Download The Muscular System

2/12/2013
Characteristics of Muscles
The Muscular System
The
Muscular
System
Muscle cells are elongated
(muscle cell = muscle fiber)
Contraction of muscles is
due to the movement of
microfilaments
All muscles share some
terminology
Muscles are responsible
for all types of body
movement
Three basic muscle
types are found in the
body
–Skeletal muscle
–Cardiac muscle
–Smooth muscle
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– Prefix myo refers to muscle
– Prefix mys refers to muscle
– Prefix sarco refers to flesh
Cardiac Muscle Characteristics
Smooth Muscle Characteristics
Has no striations
Spindle-shaped
cells
Single nucleus
Involuntary – no
conscious control
Found mainly in
the walls of hollow
organs
Classification of muscle
Has striations
Usually has a
single nucleus
Joined to another
muscle cell at an
intercalated disc
Involuntary
Found only in the
heart
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Voluntary
Involuntary
Skeletal
Cardiac
Smooth
Limbs
Heart
Viscera
Striated
Non-striated
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Note: Control, Location and Structure
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Muscle Control
Function of Skeletal Muscles
Skeletal Muscle
Type of
muscle
Nervous
control
Type of
control
Example
Skeletal
Skeletal
Controlled
by CNS
Voluntary
Lifting a
glass
Cardiac
Regulated
by ANS
Involuntary Heart
beating
Smooth
Controlled
by ANS
Involuntary Peristalsis
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Skeletal Muscle Characteristics
Produce
movement
Maintain posture
Stabilize joints
Generate heat
There are about 650 muscles
in the human body. They
enable us to move, maintain
posture and generate heat. In
this section we will only study
a sample of the major
muscles.
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Skeletal Muscle Characteristics
Most are
attached by
tendons to
bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by
connective tissue
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Connective Tissue Wrappings of
Skeletal Muscle
Endomysium –
around single
muscle fiber
Perimysium –
around a
fascicle
(bundle) of
fibers
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Connective Tissue Wrappings of
Skeletal Muscle
Microscopic Anatomy of
Skeletal Muscle
Skeletal Muscle Attachments
Epimysium blends into a
connective tissue
attachment
Epimysium –
covers the
entire skeletal
muscle
Fascia – on the
outside of the
epimysium
Cells are multinucleate
Nuclei are just beneath the
sarcolemma
– Tendon – cord-like structure
– Aponeuroses – sheet-like
structure
Sites of muscle
attachment
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Microscopic Anatomy of
Skeletal Muscle
– Bones
– Cartilages
– Connective tissue coverings
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Microscopic Anatomy of Skeletal
Muscle
Sarcolemma – specialized plasma
membrane
Sarcoplasmic reticulum – specialized
smooth endoplasmic reticulum
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Microscopic Anatomy of Skeletal
Muscle
Myofibril
Sarcomere
– Bundles of myofilaments
– Myofibrils are aligned to give distinct
bands
– Contractile unit of a muscle fiber
I band =
light band
A band =
dark band
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Microscopic Anatomy of Skeletal
Muscle
Microscopic Anatomy of Skeletal
Muscle
Organization of the sarcomere
Microscopic Anatomy of Skeletal
Muscle
Organization of the sarcomere
– Thick filaments = myosin filaments
Myosin filaments have heads
(extensions, or cross bridges)
Myosin and
actin overlap
somewhat
– Thin filaments = actin filaments
Composed of the protein myosin
Has ATPase enzymes
Composed of the protein actin
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Microscopic Anatomy of Skeletal
Muscle
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Muscle Contraction
To Summarize . . .
At rest, there is a bare zone that
lacks actin filaments
Sarcoplasmic
reticulum
(SR) – for
storage of
calcium
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Skeletal muscle tissue is made of
cells called muscle fibers.
Muscle fibers contain small cylinders
called myofibrils.
Myofibrils are made of sarcomeres
linked end-to-end.
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Properties of Skeletal Muscle
Activity
Nerve Stimulus to Muscles
Nerve Stimulus to Muscles
Skeletal muscles
must be
stimulated by a
nerve to contract
Motor unit
Irritability – ability to
receive and respond to a
stimulus
Contractility – ability to
shorten when an
adequate stimulus is
received
Neuromuscular junctions –
association site of nerve and muscle
– One neuron
– Muscle cells
stimulated by that
neuron
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Transmission of Nerve Impulse to
Muscle
Nerve Stimulus to Muscles
Transmission of Nerve Impulse to
Muscle
Neurotransmitter – chemical
released by nerve upon arrival of
nerve impulse
Synaptic cleft –
gap between nerve
and muscle
– The neurotransmitter for skeletal muscle
is acetylcholine
– Nerve and muscle
do not make
contact
– Area between
nerve and muscle
is filled with
interstitial fluid
Neurotransmitter attaches to
receptors on the sarcolemma
Sarcolemma becomes permeable to
sodium (Na+)
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Sodium rushing into the cell
generates an action potential
Once started, muscle contraction
cannot be stopped
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The Steps in Muscle Contraction
The Steps in Muscle Contraction
When a muscle is relaxed, myosin
and actin filaments are not attached.
1. Myosin attaches to a binding site on
an actin filament. Calcium is
required to make a binding site
available for myosin.
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The Steps in Muscle Contraction
2. The myosin head rotates and causes
the actin filament to slide along the
myosin filament. The sliding causes
the filaments to overlap more, and
the sarcomere becomes shorter.
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The Sliding Filament Theory
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The Steps in Muscle Contraction
The Steps in Muscle Contraction
During contraction, myosin attaches
to binding sites on actin, forming
cross-bridges. Using ATP, the crossbridges pull the actin toward the
center of the sarcomere.
3. After the myosin head has rotated as far
as it can, it must let go of the actin fiber.
ATP is required for myosin to detach from
actin. The myosin head snaps back into
its original position, using the energy in
the ATP. The ATP becomes ADP and
releases a phosphate ion.
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The Steps in Muscle Contraction
The Steps in Muscle Contraction
To summarize . . .
4. Calcium exposes a new actin
binding site and myosin reattaches
to actin. Steps 1 through 3 happen
again.
The cross-bridges break, myosin
binds to another site, and the cycle
begins again until the muscle fiber is
contracted.
Myosin filaments bind to
actin filaments, actin
filaments move inward,
and sarcomeres shorten to
cause muscle contraction.
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Contraction of a Skeletal Muscle
Muscle fiber contraction is “all or none”
Within a skeletal muscle, not all fibers
may be stimulated during the same
interval
Different combinations of muscle fiber
contractions may give differing responses
Graded responses – different degrees of
skeletal muscle shortening
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Types of Graded Responses
Types of Graded Responses
Twitch
Tetanus (summing of contractions)
– Single, brief contraction
– Not a normal muscle function
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– One contraction is immediately followed
by another
– The muscle does
not completely
return to a
resting state
– The effects
are added
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Types of Graded Responses
Muscle Response to Strong Stimuli
Types of Graded Responses
Unfused (incomplete) tetanus
Fused (complete) tetanus
– Some relaxation occurs between
contractions
– The results are summed
Muscle force depends upon the
number of fibers stimulated
More fibers contracting results in
greater muscle tension
Muscles can continue to contract
unless they run out of energy
– No evidence of relaxation before the
following contractions
– The result is a sustained muscle
contraction
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Energy for Muscle Contraction
Initially, muscles used stored ATP for
energy
– Bonds of ATP are broken to release
energy
– Only 4-6 seconds worth of ATP is stored
by muscles
After this initial time, other pathways
must be utilized to produce ATP
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Energy for Muscle Contraction
Energy for Muscle Contraction
Direct phosphorylation
Aerobic Respiration
– Muscle cells contain
creatine phosphate (CP)
– Series of metabolic
pathways that occur in
the mitochondria
– Glucose is broken down
to carbon dioxide and
water, releasing energy
– This is a slower reaction
that requires continuous
oxygen
CP is a high-energy
molecule
– After ATP is depleted, ADP
is left
– CP transfers energy to
ADP, to regenerate ATP
– CP supplies are exhausted
in about 20 seconds
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Energy for Muscle Contraction
Energy for Muscle Contraction
Begin October 18, 2010
Anaerobic
glycolysis
(continued)
Anaerobic glycolysis
– Reaction that breaks
down glucose without
oxygen
– Glucose is broken down
to pyruvic acid to produce
some ATP
– Pyruvic acid is converted
to lactic acid
– This reaction is
not as efficient,
but is fast
Huge amounts of
glucose are
needed
Lactic acid
produces muscle
fatigue
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The Muscular System
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Five Golden Rules of Gross
Muscle Activity
Muscles and Body Movements
1. all muscles cross at least one joint
2. bulk of muscles lies proximal to the
joint crossed
3. all muscles have at least 2
attachments: origin & insertion
4. muscles only pull/never push
5. during contraction the muscle
insertion moves toward the origin
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Movement is
attained due to a
muscle moving an
attached bone
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The Muscular System
Muscles and Body Movements
Muscles are attached
to at least two points
Types of Muscle Contractions
Isotonic contractions
– Myofilaments are able to slide past each
other during contractions
– The muscle shortens
– Origin – attachment to
an immoveable bone
– Insertion –
attachment to a
movable bone
Isometric contractions
– Tension in the muscles increases
– The muscle is unable to shorten
Myofilaments “skidding their wheels”
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Muscle Tone
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Effects of Exercise on Muscle
Muscle Tone
Some fibers are contracted even in a
relaxed muscle
Different fibers contract at different
times to provide muscle tone
The process of
stimulating various
fibers is under
involuntary control
Aerobics result in stronger muscles
due to increase blood supply
Muscle fibers increase mitochondria
and oxygen storage
Muscle becomes more fatigue
resistant
Heart enlarges to pump
more blood to body
Does not increase skeletal
muscle size
When muscles are not worked they
atrophy (waste away) and become
flaccid.
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Effects of Exercise on Muscle
Results of increased
muscle use from
resistance training
Individual muscle
cells make more
contractile filaments
& connective tissue
increases
– Increase in muscle size
– Increase in muscle
strength
Muscle Fatigue and Oxygen Debt
Begin October 19, 2010
When a muscle is fatigued, it is
unable to contract
The common reason for muscle
fatigue is oxygen debt
– Oxygen must be “repaid” to tissue to
remove oxygen debt
– Oxygen is required to get rid of
accumulated lactic acid
Increasing acidity (from lactic acid)
and lack of ATP causes the muscle to
contract less
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The Muscular System
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Types of Ordinary Body
Movements
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Flexion & Extension
Flexion
Extension
Rotation
Abduction
Circumduction
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Abduction & Adduction
Flexion & Extension
Rotation
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Special Movements
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Dorsiflexion & Plantar Flexion
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Inversion & Eversion
Dorsiflexion
Plantar flexion
Inversion
Eversion
Supination
Pronation
Opposition
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Pronation & Supination
Opposition
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Diseases and Disorders of the
Muscular System
Myalgia: Muscle pain due to strain, tearing
of muscle fibers. It also is a symptom of an
immune response along with a fever.
Myositis: Inflammation of muscle tissue due
to injury or disease.
Charley Horse (fibromyositis): Inflammation
of muscle tissue and the tendons associated
with that muscle due to injury (tear or
severe bruising- contusion)
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Cramps: Painful, involuntary muscle spasms
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Muscular Dystrophy
Cerebral Palsy
Congenital muscle-destroying disease
affect specific muscle groups
Muscle fibers degenerate & atrophy
due to an absence of dystrophin, a
protein that helps keep muscle cells
intact
Duchenne’s M.D.
Most common &
serious—
Poliomyelitis
This disorder is characterized
by paralysis and or
weakened muscles due to
loss of muscle tone. It can
be caused due to lack of
oxygen to the region of the
motor region of the
cerebrum of the brain which
controls conscious control of
muscles. This is often
attributed to complication
during birth.
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Poliomyelitis: Polio is
due to a viral infection
which affects the
motor neurons that
control skeletal
muscles. It often
leads to paralysis and
can result in death by
paralysis of the
diaphragm. Due to
vaccine developed by
Jonas Salk, the virus
has been virtually
eliminated in the US.
However, it still poses
a threat in developing
countries.
– Mostly in males (diagnosed between2-6 yrs)
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Aging
Myasthenia gravis
Rare adult disease caused by
antibodies to acetylcholine
receptors at the neuromuscular
junction which prevents the
muscle contraction from
occurring
Drooping upper eyelids,
difficulty swallowing & talking,
muscle weakness & fatigue
Death occurs when respiratory
muscles cease to function
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Connective Tissue
increases
Amount of Muscle tissue
decreases
Muscles become
stringier(sinewy)
Body weight declines due
to loss of muscle mass
By age 80, muscle strength
usually decrease by 50%
without weight training
exercises
– Survival is rare beyond early 30’s
– X-linked recessive
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Types of Muscles
Prime mover – muscle with the major
responsibility for a certain movement
Antagonist – muscle that opposes or
reverses a prime mover
Synergist – muscle that aids a prime
mover in a movement and helps prevent
rotation
Fixator – stabilizes the origin of a prime
mover
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Naming of Skeletal Muscles
Naming of Skeletal Muscles
Direction of muscle fibers
Naming of Skeletal Muscles
Location of the muscle
– Example: rectus (straight)
Location of the muscle’s origin and
insertion
– Example: many muscles are named for
bones (e.g., temporalis)
Relative size of the muscle
– Example: sterno (on the sternum)
Number of origins
– Example: maximus (largest)
Shape of the muscle
– Example: triceps (three heads)
– Example: deltoid (triangular)
Action of the muscle
– Example: flexor and extensor (flexes or
extends a bone)
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Head and Neck Muscles
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Trunk Muscles
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Deep Trunk and Arm Muscles
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Muscles of
the Pelvis,
Hip, and
Thigh
Superficial
Muscles:
Anterior
Muscles of
the Lower
Leg
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Superficial
Muscles:
Posterior
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