Muscular System

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Transcript Muscular System

Muscular System
Read Ch 6
Review Questions begin on page 198
S/A #2, 7, 10, 12, 18, 20, 21
At the Clinic #2, 5, 6
 Over ½ of body’s
mass is muscle—
90% of that is
skeletal muscle
 These contractile
cells have high
energy needs, so
it’s common to see
an ample blood
supply associated
with muscles
Overview con’t:
 Blood provides glucose and oxygen while
removing metabolic waste products
 Muscles (and nervous tissue) consume
almost 70% of the food energy taken into
your body daily
 Muscle is as intensive a consumer of
calcium as is the skeletal system—much
of the Ca stored in bones is made
available for the muscles’ needs.
 Nonstriated (no
 Striated (lines
running through)
Categorizing muscles
Categorizing muscles
Involuntary (no control)
Voluntary (control)
Categorizing muscles
 Cardiac: Involuntary, only found in
 Smooth: Involuntary, lines digestive
 Skeletal: voluntary muscles found
attached to bones
Cardiac Muscle
 Involuntary, striated muscle
 Have two nuclei per cell
 These branched cells communicate with
one another with intercalated disks
 Cardiac cells have a natural contraction
cycle called the intrinsic beat
 Intercalated disks help synchronize the
intrinsic beat so all cardiac muscles act in
Smooth muscle
 Non-striated,
involuntary muscle
 Location: found in the
lining of blood vessels,
digestive organs, urinary
system and parts of the
respiratory system
Smooth muscle
 These cells produce weak involuntary
contractions that can last for long periods
of time
 Assist with dilation and constriction of the
bv and respiratory system
 In the digestive tract, they produce
pulsating contractions called peristalsis
(moves food and wastes though system)
Skeletal muscle—our focus
 Voluntary, striated
 Provides movement of
the bones and joints
 Skeletal muscle is
composed of many
individual cells that
have fused together
into a long fiber.
(have many nuclei in
each one)
Muscle cell structure
 Sarcomere—the contractile unit of a
muscle cell (there are thousands of
these in one cell)
 Myofibril—long chains of
sarcomeres. Each muscle fiber is
made up of many bundled myofibrils
running parallel to one another for
the length of the cell
Video of sarcomere shortening
Muscle cell structure
 Sarcolemma—the membrane of the muscle
 Bands of proteins called myofilaments
 Thick (myosin)
 Thin (actin, tropomyosin and troponin)
Myofilament arrangement
 Thick (myosin) and thin (actin,
troponin, tropomyosin) arrange to
form an overlapping pattern w/in a
 Thin
myofilaments are attached to
the Z-line
 In between these thin myofilaments
are the thick myosin filaments which
appear to be floating within the cell.
Myofilament arrangement
 Surrounding each
sarcomere is an
organelle called
the sarcoplasmic
reticulum (a
system of tubes
transporting Ca
needed for
Functions of the
Muscular System
 Movement of body
parts—by pulling on
bones. Bones act as
levers, joints as the
 Guard entrances and
 Posture
 Stabilizing joints
 Create heat
Muscle cell Function
 Contraction is achieved by the
simultaneous shortening of all
the sarcomeres within a cell.
 Three stages: Neural
stimulation, contraction,
Neural Stimulation
 Takes place at the
 The nerve cell
releases a
chemical used for cell
to cell communication.
Neural Stimulation
 Muscles respond to
the neurotransmitter
acetylcholine (Ach).
 Ach binds to
receptors on the
 The binding of Ach
affects the transport
of ions across the
Neural Stimulation
 In a resting muscle, the concentration of sodium ions is
normally higher in the fluid outside the muscle cell while
the concentration of potassium ions is higher inside the
 Sodium/potassium pumps maintain these unequal ion
Neural Stimulation
 This imbalance produces an unstable
condition. When stimulated by Ach the
membrane loses its ability to maintain the
 Once the membrane is stimulated, it
opens the ion channels permitting the free
flow of sodium into the muscle cell and
potassium out of the cell.
 In turn, calcium stored in the
sarcoplasmic reticulum is released to
begin the contraction phase
Muscle Contraction
 When calcium
(released by the
reticulum) binds to
the troponin,
contraction begins.
 Troponin sits on
tropomyosin on the
same region where
actin binds to myosin.
Muscle Contraction
 Ca bumps troponin off the binding site,
permitting myosin to attach to actin.
 Troponin also transmits info that activates
ATP synthesis around the myosin. The
ATP provides energy for the myosin head
to swivel and pull the myosin toward the
Muscle Relaxation
 Relaxation occurs when there are no
more neural stimulations exciting the
sarcolemma. The sodium and potassium
ion levels are completely recovered
 The sarcoplasmic reticulum has retrieved
most of the Ca, causing the release of the
myosin heads from the actin.
 There is no mechanism for the muscle
cell to lengthen (so we’ll discuss how that
happens later in the lecture).
 Nerve impulse arrives at muscle cell
 Ca+2 released from SR into sarcoplasm
 Ca+2 combines with troponin molecules in the
thick filaments of myofibrils (Myosin)
Troponin without Ca+2 doesn’t interact like this
 Myosin interacts with Actin and pulls toward
 Contraction of muscle
Video of contraction occurring…
Animation of entire process…
Other factors found in muscle fibers
ensuring adequate muscle contractions:
 Creatine Phosphate: stores energy in muscle
cells. It collects this energy from ATP and is
capable of storing it for long periods of time.
 Glycogen (stored form of glucose) can supply
glucose when muscles cells need it to produce
 Myoglobin is a chemical that stores oxygen for
certain muscle cells. This O2 permits muscle
cells to provide large amounts of ATP during
continuous or heavy work.
Muscle Attachment Fibers
 Tendons—
connect muscle
to bone
 Aponeuroses—
connect muscles
to muscles
Musculature terms
 Origin—
fixed end
end of
 Insertion—
end (distal
end of
Skeletal Muscle Action
 Muscle cells either contract or don’t…so
we get graded effects based on
contraction of more individual fibers at
the same time.
 Strength is achieved by stimulating more
individual fibers to fire
 Endurance is achieved by producing
contraction and relaxation groups working
Skeletal Muscle Action
 Antagonistic effects occur
when one muscle opposes
or resists the action of
another muscle.—if
nothing else, your muscles
are acting against the
antagonistic force of
 The antagonistic actions
are essential for pulling
the relaxed muscle cells
back to their original
Skeletal Muscle Action
 Synergistic effects
occur when muscles
work together to
produce a common end
result…the muscles of
the forearm work
synergistically with the
muscles of the fingers
to produce a fist.
5 golden rules of
skeletal muscle
 All muscles cross at least one joint
 Typically the bulk of the muscle lies
proximal to the joint crossed
 All muscles have at least two
attachments, the origin and the insertion
 Muscles can only pull; they never push
 During contraction, the muscle insertion
moves toward the origin
Body Movements
 Flexor—decreases
the angle of the
joint by bringing the
bones closer
 Extensor—extends
a joint by increasing
the angle between
the bones
Body Movements
 Rotator—
movement around
an axis (partway
 Tensor—important
muscles that make
a body part more
rigid or tense.
Body Movements
 Abduction—
moving away
from the
 Adduction—
moving toward
the midline
 Depressor—produce a
downward movement
 Levatator—provide an
upward movement
 Spincter—decreases
the size of an opening
Body Movements
Body Movements
 Pronator—motion
of palm downward
 Supinator—palm
moves upward
Special Movements
turning the sole of
your foot medially
the sole of your
foot laterally
Special Movements
 Dorsiflexion—
pointing your
toes up toward
your shin
 Plantar
pointing your
toes downward
Muscular System
Rigor Mortis
 Calcium leakage out of the
sarcoplasmic reticulum into the
sarcomere. Common after death.
Eventually, the muscle cells
structures start to decay, causing
the muscles to become soft and
 Most common muscle
 An injury due to
overworking the
muscle’s force on the
 Injury to the tendon
or muscle tissue
 A sprain is an injury
to a ligament. (A
ligament is a thick,
tough, fibrous tissue
that connects bones
 Ligaments prevent
abnormal movements.
When too much force
is applied to a
ligament they can be
stretched or torn.
 Bruising of
the muscle
Muscle Spasms
 Involuntary,
contractions of a
muscle or muscle
 Caused by a wide
range of medical
Muscle Cramp
 Painful contraction of
a muscle
 Extreme muscle
exertion is the most
common cause of
cramps, although
certain poisons and
bacterial infections
can also cause muscle
 Complete failure of a muscle function
Rigid paralysis—excessive muscle stiffness
Flaccid paralysis—complete lack of muscle
 Many causes…including spinal injury and
Eg: Tetanus--Caused by soil bacteria that
produces poisons that cause rigid paralysis
 Inflammation of
the muscle and
overlying skin.
 Cause: unknown,
but it can be
treated with drugs
(to reduce
inflammation) and
sun avoidance
Muscular dystrophies
 Group of conditions
that involve
progressive weakness
in the voluntary
 Usually due to the
inability of the
nervous system to
stimulate muscle
 Eventually results in
muscle atrophy and
 Calcium
disease that
periods of
spasms in the
arm and leg
 Do NOT confuse
this with the
bacterial disease
 Type of muscle loss associated with
diseases such as AIDS and cancer.
Also found
in starvation
and a common
of anorexia
and bulimia
 A slower form is a normal consequence of
aging b/c the body reduces its ability to
rebuild muscle structure as you age.
Brought about by sedentary lifestyles—
resulting from other age related illnesses
Neural stimulation also is lessened as you
age; important for muscle upkeep
Nutritional issues with muscle loss
 Protein turnover: muscles need lots of
protein to maintain their integrity
Malnutrition and undernutrition as we age
greatly affects protein turnover.
Can be caused by poor diets or income levels
Lack of appetite as we age is another
contributing factor
As we age, our digestive system can’t absorb
some of the impt amino acids needed for
muscle cell growth/maintenance.
Muscle atrophy—other causes
 Decline in sex hormones and other
chemical messages needed for
muscle cell growth, maintenance and
 Insulin-like
growth factor-1: known
to lessen with maturity
 Cytokines cause muscle atrophy and
are known to increase with age