Muscular System

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First found May 22, 2018

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Muscular System
Muscle Contraction
Movement requires muscle
• Three types: skeletal,
smooth, cardiac
• Skeletal will be our
focus
• Long fibrous tissue
• Muscle fibers are
enclosed in layers of
connective tissue
From Largest to smallest
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Muscle
Bundle of fibers called a fascicle
Muscle fiber (one cell)
Bundle of myofibrils
Filaments arranged in sarcomeres
Actin and myosin are the proteins of the
myofilament
Terms
• Cytoplasm is called
sarcoplasm
• Inside the muscle fiber
(muscle cell) are
myofibrils
• They contain 2
proteins: actin and
myosin
A sarcomere
• The space from one Z
line to the next Z line
• Striations (stripes) are
caused by the proteins
of the myofilament
• Sarcomere is the
contracting unit of the
muscle fiber
Z lines
Contraction
• Contractions means
getting smaller
• The myofibril can
contract because actin
and myosin move
• This movement is
described in the
sliding filament theory
Sliding Filament Theory
• Head of myosin
attaches to the actin
• This can happen only
if calcium is present
• Myosin head pulls the
actin filament in
• Makes the sarcomere
shorter
Neuromuscular Junction
Connection
between a
motor neuron
and a muscle
Neuromuscular Junction
• A nerve fibers comes
from the brain or
spinal cord to the
muscle.
• The nerve and the
muscle do not actually
touch
• The gap between them
is called the synaptic
cleft
Neuromuscular Junction
• At the end of the
neuron, many tiny
vesicles are present
• These vesicles store
chemicals called
neurotransmitters
• The neurotransmitter
will go across the gap
(synaptic cleft)
Neuromuscular Junction
• The muscle fiber on
the other side of the
gap is stimulated by
the neurotransmitter
• The muscle fiber
contracts
• The neurotransmitter
is called acetylcholine
After contraction, relaxation
• Acetylcholinesterase
(an enzyme) destroys
the remaining
acetylcholine
• Calcium ions are taken
away
• Without these actions,
the muscle would stay
contracted
Related Conditions
• Nerve gas works by
inhibiting
acetylcholinesterase
• Breathing muscles
cannot relax
• Botulism prevents the
release of
acetylcholine, so
muscles cannot
contract
Related Conditions
• Rigor mortis
• Ca++ pumps run out
of ATP
• Ca++ cannot be
removed
• continuous contraction
• eventually tissues
break down
Contraction Facts
• Threshold stimulus must
be reached to cause a
contraction
• Enough acetylcholine
must reach the receptors
• All or none response
• Either the fiber (and its
motor unit) contracts or it
doesn’t
• A motor neuron comes
from the brain or
spinal cord and
connects to a group of
muscle fibers, called a
motor unit. When a
motor neuron
transmits an impulse,
all the fibers in the
motor unit contract
• (If threshold was
reached)
Contraction
Facts
Contraction
Facts
• A motor unit exhibits
an all or none response
• How, then, can some
muscle contractions be
more forceful than
others?
• Determined by the
number of motor units
stimulated
Contraction Facts
• Where does the energy
come from to power
muscle contraction?
• ATP (adenosine triphosphate)
• If extra energy is
available, it is stored in
creatine phosphate
• Creatine phosphate is
converted to ATP when
needed.
Origin and Insertion
• One end of a skeletal
muscle is attached to
an immovable end,
like an anchor. This is
the ORIGIN.
• The other end is
attached to a movable
part, called the
INSERTION.
Biceps Brachii
Two origins
Insertion
Contraction Facts
• Muscle Twitch
• cycle of contraction
and relaxation
• Contraction only
lasts a fraction of a
second
Contraction Facts
• Tetany is sustained
contraction
• Lacks even partial
relaxation
• Tetanus bacteria can
cause this
• Lockjaw
Contraction Facts
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•
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•
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Muscle cramps
ATP depletion
dehydration
ion imbalance
massage or stretching
increase circulation
Which are You?
• A sprinter or an endurance performer?
• Why do some people excel at one, but not
the other?
• Read the article and find out!
Use It or Lose It!
• Muscle inactivity will lead to weakness and
wasting
• Aerobic exercise will result in stronger,
more flexible muscles with greater
resistance to fatigue.
• Resistance (isometric) exercise will result in
increased size of muscles.
Which type should you do?
• Resistance: body
building; enlarges
individual muscle
cells.
• Aerobic: endurance,
increases strength in
other systems as well.
• YOU NEED BOTH!
Contraction Facts
• Muscle fatigue
• lack of carbohydrate
source (glucose)
• lack of ATP to restore
membrane potential
• lactic acid drops pH
which interferes with
protein function
Oxygen Debt
Body cannot supply
muscles with enough
oxygen during strenuous
exercise
Muscles must switch to
anaerobic respiration
This produces lactic acid,
which the liver will destroy
later
Oxygen debt is the amount
of oxygen liver cells need
to convert the lactic acid
into glucose
Happens later,
while you are
resting or
sleeping
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