Download Muscular System

Muscular System
Skeletal, Smooth, &
Cardiac
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Our body without
muscles!!! AHHH!!
Muscles
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The term muscle?
“mus” of course is
Latin and means little
mouse.
The connection???
When flexing, muscles
look like little mice
scurrying beneath the
skin…who knew?
About our Muscles
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Almost half the body’s
weight is muscle.
Muscles produce all
movement in our body and
allow for circulation.
Muscles are made of
special tissues that can
contract or shorten when
they receive a signal from
the brain.
About our Muscles
Muscles are attached to bones by
stretchy tissue called tendons.
 When muscles contract, they pull on the
tendons which pull on the bones and
cause our limbs to move.
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About our Muscles
Who can remember…what are the three
types of muscle tissue?
 Skeletal
 Cardiac
 Smooth
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Cardiac Muscle
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Only in heart
Involuntary
Striated (like
skeletal)
Makes up wall of
heart
Pumps 5 liters of
blood per minute
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Fibers branch and
have single nucleus
per cell
 Function: pumping
of the heart
Cardiac Muscle
Smooth
Smoothmuscle
Muscle
Involuntary
 Walls all hollow organs (except heart)
 Regulates blood flow in arteries
 Expels urine from urinary bladder
 Regulates flow of air through lungs
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Smooth Muscle
Skeletal Muscle
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Striated muscle
 Made of muscle
tissue, nervous
tissue, blood, &
connective tissues
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Under voluntary
control
 All of these muscles
attach to skeleton
Skeletal Muscle
Characteristics of Muscles
Tissue!
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Muscle tissue is endowed with some
special functional properties that enable
it to perform its duties
– Excitability (responsiveness)
– Contractility
– Extensibility
– Elasticity
Function of Muscles!
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Of course muscles perform 4 important
functions
– Produce Movement
– Maintain Posture
– Stabilizing Joints
– Generating Heat!
About our Muscles
There are more than 640 muscles and
they hardly ever work alone.
 Muscles can get shorter and pull, but
they can’t push
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About our Muscles
Most muscles are arranged in opposing
teams
 1 team pulls the body part 1 way and
the other team pulls it back again
 (Abduction and adduction)
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Vocabulary
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Abduction- pulls
away
 Adduction- pulls
toward you
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Voluntary- can be
controlled by
thoughts in the brain
 Involuntaryautomatically
controlled by brain
Skeletal Muscle: Nerve
and Blood Supply
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Each muscle is served by one nerve, an
artery, and one or more veins
 Muscles are rich in arteries and veins to carry
fuel and oxygen to the muscles and and veins
to carry waste products and carbon dioxide
away.
 Each skeletal muscle fiber is supplied with a
nerve ending that controls contraction
Skeletal Muscle
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Each muscle is a discrete organ composed of
muscle tissue, blood vessels, nerve fibers,
and connective tissue
 Please familiarize yourself with the Table on
pg 282…The Organizational level of skeletal
muscles.
 The Muscle (organ), Fascile (a portion of the
muscle), Muscle fiber (cell), Myofibril or fibril
(complex organelle), Sacromere (segment of
a myofibril), and myofilament or filament. We
will discuss this in more detail in a few slides.
Skeletal Muscle
Skeletal Muscle
Skeletal Muscle
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In an intact muscle, the individual muscles
fibers are wrapped and held together by
several different connective tissue sheaths.
 Together these connective tissue sheaths
support each cell and reinforce the muscle as
a whole, preventing the bulging muscles from
bursting during exceptionally strong
contractions.
Skeletal Muscle
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The three connective tissue sheaths are:
– Endomysium – fine sheath of connective tissue
composed of reticular fibers surrounding each
muscle fiber
– Perimysium – fibrous connective tissue that
surrounds groups of muscle fibers called fascicles
– Epimysium – an overcoat of dense regular
connective tissue that surrounds the entire muscle
Skeletal Muscle
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surrounds the entire muscle
Skeletal Muscle
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An individual
skeletal muscle is
separated from
adjacent muscles
and held in position
by layers of dense
connective tissue
called fascia.
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This connective
tissue surrounds
each muscle and
may project beyond
the end of its muscle
fibers to form a
cordlike tendon.
Skeletal Muscle
Skeletal Muscle:
Attachments
Most skeletal muscles span joints and
are attached to bone in at least two
places
 When muscles contract the movable
bone, the muscle’s insertion moves
toward the immovable bone, the
muscle’s origin.
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Skeletal Muscle:
Attachments
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Muscles attach:
– Directly – epimysium of the muscle is fused
to the periosteum of a bone
– Indirectly – connective tissue wrappings
extend beyond the muscle as a tendon or
aponeurosis.
– Of the two indirectly is much more common
because of the durability of tendons.
Microscopic Anatomy of a Skeletal
Muscle Fiber
This section can be very confusing…I
am giving you a less detailed version.
 Hope this helps I promise its much
easier to understand. 
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Microscopic Anatomy of a Skeletal
Muscle Fiber
One muscle fiber is an elongated
multnucleate cell that has a banded
appearance.
 The muscle fiber (or cell) is composed
of a Myofibrils (fibril).
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Microscopic Anatomy of a Skeletal
Muscle Fiber
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These Myofibrils occupy most of the volume
of a cell and are composed of a number of
thick and thin filaments.
 The thick filaments are made of a protein
known as myosin and the thin filaments of a
protein called actin.
 This arrangement of bands are called
Sarcomere and it is this sacromere that is the
contractile unit of the muscle cell or fiber
Sarcomeres
Sarcomeres
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Within the muscle
cell are supporting
structures to
generate energy,
the mitochondria
and some fuel
stores.
Sacroplasmic Reticulum
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There is also a network of channels
within the muscle to transmit signals
from the surface throughout the muscle
called the sacroplasmic reticulum. (This
is the Endoplasmic Reticulum of the
muscle cell)
A little more detail
on Myosin Filament
Thick filaments are composed of the
protein myosin
 Each myosin molecule has a rod-like tail
and two globular heads
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– Tails – two interwoven, heavy polypeptide
chains
– Heads – two smaller, light polypeptide
chains called cross bridges
A little more detail
on Myosin Filament
A little more detail
on the Thin Filaments
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Thin filaments are chiefly composed of the
protein actin
 The subunits contain the active sites to which
myosin heads attach during contraction.
 Tropomyosin and troponin found in the thin
filaments are the molecular switches that
control the interaction of actin and myosin
during a muscle contraction.
Ultrastructure of Myofilaments:
Thin Filaments
How do Muscle actually contract?
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When you want to move, electrical impulses
come from the brain, down through the spinal
cord and are transmitted through the motor
nerves to the muscles.
 At the junction between the nerve end and
the muscle (the motor end plate), chemical
signals are released from the nerve endings.
(acetylcholine). This binds to a key on the
surface of the muscle (the receptor)
How do Muscle actually contract?
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The binding of this chemical to the receptor
causes calcium to enter the muscle cell, and
this enable the troponin proteins to move the
myosin up the actin molecule.
 This causes the functional unit, the
sarcomere, to shorten and when several of
these shorten along the length of the fibre,
the muscles as a whole contracts and
shortens.
How do Muscle actually contract?
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To release the bond between actin and
myosin needs energy, to shorten the muscle
further or to cause it to relax.
 When the signal for contraction ends, the
calcium is pumped back into the
sacroplasmic reticulum and the muscle
relaxes.
Contraction of Skeletal
Muscle Fibers
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The operation of most skeletal muscles
involves the use of leverage and lever
systems
 The force exerted by a contracting muscle on
an object is called muscle tension
 The opposing force exerted on the muscle by
the weight of the object to be moved is called
the load.
Contraction of Skeletal
Muscle Fibers
Contraction of muscle fibers (cells) and
muscles (organs) is similar
 The two types of muscle contractions
are:
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– Isometric contraction – increasing muscle
tension (muscle does not shorten during
contraction)
– Isotonic contraction – decreasing muscle
length (muscle shortens during contraction)
Isometric Contractions
Tension increases to the muscle’s
capacity, but the muscle neither
shortens nor lengthens
 Occurs if the load is greater than the
tension the muscle is able to develop
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Isometric Contractions
Isotonic Contractions
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In isotonic contractions, the muscle
changes in length (decreasing the angle
of the joint) and moves the load
Isotonic Contractions
Muscle Twitch
A muscle twitch is the response of a
muscle to a single, brief threshold
stimulus
 There are three phases to a muscle
twitch
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– Latent period
– Period of contraction
– Period of relaxation
Phases of a Muscle Twitch
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Latent period – first few
msec after stimulus; EC
coupling taking place
Period of contraction –
cross bridges form;
muscle shortens
Period of relaxation –
Ca2+ reabsorbed;
muscle tension goes to
zero
Treppe: The Staircase Effect
Staircase – increased contraction in
response to multiple stimuli of the same
strength
 Contractions increase because:
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– There is increasing availability of Ca2+ in
the sarcoplasm
– Muscle enzyme systems become more
efficient because heat is increased as
muscle contracts
Treppe: The Staircase Effect
Muscle Tone
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Muscle tone:
– Is the constant, slightly contracted state of all
muscles, which does not produce active
movements
– Keeps the muscles firm, healthy, and ready to
respond to stimulus
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Spinal reflexes account for muscle tone by:
– Activating one motor unit and then another
– Responding to activation of stretch receptors in
muscles and tendons
Muscle Metabolism: How do
Muscles Get the Energy Needed for
Contraction?
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ATP is the only source used directly for
contractile activity.
 Remember ATP’s produced in the
Mitochondria. They are energy storing
molecules…the energy is released when one
of the phosphate bonds is broken then
forming ADP.
 Muscles can work in one of two
environments…Aerobic and Anaerobic
Exercise.
Energy Sources for Contraction
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ATP supplies
energy for
contractions
 Active muscles
depend on cellular
respiration for
energy
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ATP is necessary for
both muscle
contraction and
relaxation
Aerobic Exercise
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As long as it has enough oxygen, a muscle
cell will form ATP by aerobic reactions.
 This is internal stores of ATP and can be
supplemented by high energy phosphate
compounds called Creatine Phospate (cp).
 This can be for several hours in well
conditioned adults.
Anaerobic Exercise
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If the rate at which energy is demanded is
high…generally when muscle contractile activity
reaches 70% of maximum; then this is supplemented
by contributions from anaerobic metabolism.
The immediate consequences include:
– The production of lactic acid in the muscles which
immediately breaks down to lactate and hydrogen
ions.
– Bulging muscles compress blood vessels.
– Oxygen delivery is impaired
Muscle Metabolism: Anaerobic
Glycolysis
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The lactic acid:
– Diffuses into the bloodstream
– Is picked up and used as fuel by the liver,
kidneys, and heart
– Is converted back into pyruvic acid by the
liver
Muscle Fatigue
Muscle fatigue – the muscle is in a state of
physiological inability to contract
 Muscle fatigue occurs when:
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– ATP production fails to keep pace with ATP use
– There is a relative deficit of ATP, causing
contractures
– Lactic acid accumulates in the muscle
– Ionic imbalances are present
Muscle Fatigue
Intense exercise produces rapid muscle
fatigue (with rapid recovery)
 Na+-K+ pumps cannot restore ionic
balances quickly enough
 Low-intensity exercise produces slowdeveloping fatigue
 SR is damaged and Ca2+ regulation is
disrupted
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Oxygen Debt
Oxygen debt – the extra amount of O2
needed for the above restorative processes
 This is why your muscles ache
 Vigorous exercise causes dramatic changes
in muscle chemistry
 For a muscle to return to a resting state:
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Oxygen reserves must be replenished
Lactic acid must be converted to pyruvic acid
Glycogen stores must be replaced
ATP and CP reserves must be resynthesized
Heat Production During Muscle
Activity
Only 40% of the energy released in
muscle activity is useful as work
 The remaining 60% is given off as heat
 Dangerous heat levels are prevented by
radiation of heat from the skin and
sweating
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Heat Production
Product of cellular respiration
 Muscles act as heat source because
muscle tissue represents such a large
portion of the body
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Effects of Aerobic Exercise
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Aerobic exercise results in an increase
of:
– Muscle capillaries
– Number of mitochondria
– Myoglobin synthesis
Effects of Resistance Exercise
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Resistance exercise (typically
anaerobic) results in:
– Muscle hypertrophy
– Increased mitochondria, myofilaments, and
glycogen stores
Muscle Fatigue
 Fatigue and cramps
Muscle loses its
may occur together
ability to contract
 Cramps occur when
 Causes: decreased
intracellular fluid
blood flow, ion
triggers uncontrolled
imbalances,
stimulation of the
physcological loss of
muscle
desire to exercise
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Muscle Fatigue
Usually due to accumulation of lactic
acid
 Athletes usually produce less lactic acid
than nonathletes b/c of their ability to
supply oxygen and nutrients to muscles
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