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
Overview
 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
http://www.edukshun.info/wpcontent/uploads/2008/04/big-muscles.jpg
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.
Microscopically
 Nonstriated (no
lines)
 Striated (lines
running through)
micro.magnet.fsu.edu/
http://phelafel.technion.ac.il/~tamarh/website/images/different-kinds-of-muscles-2.jpg
Categorizing muscles
Categorizing muscles
Controllability
Involuntary (no control)
Voluntary (control)
Categorizing muscles
Location
 Cardiac: Involuntary, only found in
heart
 Smooth: Involuntary, lines digestive
organs
 Skeletal: voluntary muscles found
attached to bones
Functions of the
Muscular System
 Movement of body
parts—by pulling on
bones. Bones act as
levers, joints as the
fulcrum.
 Guard entrances and
exits
 Posture
 Stabilizing joints
 Create heat
Physiology of muscle
 Contraction is achieved by the
simultaneous shortening of all
the sarcomeres within a cell.
 Three stages:
 Neural stimulation
 Contraction
 Relaxation.
Neural Stimulation
 Takes place at the
neuromuscular
junction.
 The nerve cell
releases a
neurotransmitter
neurotransmitter—a
chemical used for cell
to cell communication.
http://www.freewebs.com/soaring_sphincter_travel_agency/ner
ve%20impulse2.bmp
Neural Stimulation
 Muscles respond to
the neurotransmitter
acetylcholine (Ach).
 Ach binds to receptors
on the sarcolemma.
 The binding of Ach
affects the transport
of ions across the
sarcolemma
www.cells.de/.../Neuromuscular-junction.jpg
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 cell.
 Sodium/potassium pumps maintain these unequal ion
concentrations.
upload.wikimedia.org/wikipedia/commons/thumb/...
Neural Stimulation
 This imbalance produces an unstable
condition. When stimulated by Ach the
membrane loses its ability to maintain the
imbalance.
 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
www.cvphysiology.com
 When calcium
(released by the
sarcoplasmic
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
actin.
Myosin crossbridges at work…
http://www.patrickcarlberg.dk/images/thinfilament.jpg
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).
Stimulus
Squinting
Sensory
Nerves
Motor
Nerves
Regulator
Receptor
Effectors
Light reduced
Video links
 http://www.hippocampus.org/Biology
search for Biology for AP/Skeletal Muscle
contraction
 Crash course—Muscles
http://www.youtube.com/watch?v=jqy0i1KXU
O4
 Bozeman Science—Muscles
http://www.youtube.com/watch?v=mejCXr7p3
7U&list=PLCC2DB523BA8BCB53&index=17
Animations
 http://www.wisc-
online.com/objects/ViewObject.aspx?ID=AP2
904
 http://highered.mcgrawhill.com/sites/0072437316/student_view0/cha
pter42/animations.html#
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
ATP
 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.
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
together.
Body Movements
 Flexor—decreases
the angle of the
joint by bringing the
bones closer
together
 Extensor—extends
a joint by increasing
the angle between
the bones
Body Movements
 Rotator—
movement around
an axis (partway
around)
 Tensor—important
posture/positioning
muscles that make
a body part more
rigid or tense.
Body Movements
 Abduction—
moving away
from the
midline
 Adduction—
moving toward
the midline
 Depressor—
produce a
downward
movement
 Levatator—provide
an upward
movement
 Sphincter—
decreases the size
of an opening
www.cescg.org
www.mda.org
Body Movements
Special Movements
 Pronator—
motion of palm
downward
 Supinator—
palm moves
upward
Special Movements
 Inversion—turning
the sole of your
foot medially
 Eversion—turning
the sole of your
foot laterally
Special Movements
 Dorsiflexion—
pointing your
toes up toward
your shin
 Plantar
Flexion—
pointing your
toes
downward
Muscular System
Pathologies
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
loose.
Strain
 Most common muscle
ailment
 An injury due to
overworking the
muscle’s force on the
joints.
 Injury to the tendon
or muscle tissue
http://www.nlm.nih.gov
http://www.fairview.org
Sprain
 A sprain is an injury
to a ligament. (A
ligament is a thick,
tough, fibrous tissue
that connects bones
together.)
 Ligaments prevent
abnormal movements.
When too much force
is applied to a
ligament they can be
stretched or torn.
www.eorthopod.com
Contusion
 Bruising of
the muscle
www.bruisepatch.com
Muscle Spasms
 Involuntary,
abnormal
contractions of a
muscle or muscle
group
 Caused by a wide
range of medical
conditions
www.cure-back-pain.org
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
cramping
www.answers.com
Paralysis
 Complete failure of a muscle function
 Rigid paralysis—excessive muscle
stiffness
 Flaccid paralysis—complete lack of muscle
contraction
 Many causes…including spinal injury and
poisoning

Eg: Tetanus--Caused by soil bacteria
that produces poisons that cause rigid
paralysis
Dermatomyositis
 Inflammation of
the muscle and
overlying skin.
 Cause: unknown,
but it can be
treated with drugs
(to reduce
inflammation) and
sun avoidance
www.nytimes.com
Muscular dystrophies
 Group of conditions
that involve
progressive weakness
in the voluntary
muscles.
 Usually due to the
inability of the
nervous system to
stimulate muscle
action
 Eventually results in
muscle atrophy and
wasting.
esciencenews.com
Tetany
 Calcium
imbalance
disease that
causes
extended
periods of
spasms in the
arm and leg
muscles.
 Do NOT confuse
this with the
bacterial disease
tetanus!
Cachexia
 Type of muscle loss associated with
diseases such as AIDS and cancer.
www.aids-images.ch
Also found
in starvation
and a common
consequence
of anorexia
and bulimia
Cachexia
 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
repair.
 Insulin-like
growth factor-1: known
to lessen with maturity
 Cytokines cause muscle atrophy and
are known to increase with age