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Muscle fibers & tissue
Where chemical energy is used to produce force &
movement
Types of muscle
Identified based on structure, result of
contraction, & control.
• Skeletal – attached to bone & responsible
for supporting & moving the skeleton,
neurons cause movement & is voluntary
• Smooth – surround organs & tubes,
contraction changes diameter or propels
fluids, controlled by ANS, hormones & other
chemical messengers
• Cardiac- heart, contractions propel blood,
regulated by ANS
•
Muscle
Bundle of muscle fibers bundled together by
connective tissue.
 Most fibers do not extend the entire length of
a muscle
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Striated (skeletal) muscle
Under a microscope looks like a series of light
and dark bands going across the muscle. Looks
like it has different bands.
 Results from thin & thick filaments of the
myofibrils
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http://www.scienceclarified.com/images/uesc_07_img0385.jpg
Muscle fiber
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Single skeletal muscle cell
Can be as long as 20 cm
nvo.com
Myofibrils
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Occupies most of
the cytoplasm
Long “filaments” that
stretch the length of
a muscle fiber (cell)
Bundled together
Sarcomere is a single
unit inside the
myofibril, they are
lined up end to end
repeating along the
length of the
myofibril.
Sarcomere
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Made of alternating thick & thin filaments
Thick filament made of myosin
Thin filament made of actin
During contraction these filaments work to
shorten the length of the sarcomere by “sliding”
along one another.
bodyplusmind.co.uk
Damage to fibers
If destroyed cannot be replaced by other
muscle fibers, but by undifferentiated cells
near the muscle fibers. These do not have
the capacity to rebuild severe damage.
 Most of restoration of strength comes
from increasing the size of remaining
fibers.
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Calcium
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Calcium in the cytoplasm is important for
muscle contraction
The electrical stimulation provided to the
muscle increases the concentration of Ca in
the cytoplasm
Increased levels of Ca make muscle
contraction possible.
Relaxation begins as Ca is pumped out of
the cytoplasm
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/
Neuromuscular junction
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Area of muscle fiber under the axon terminal.
ACh released into this junction
ACh acts to open Ca channels to allow Ca into the cytoplasm.
Can be re-stimulated before contraction ends, results in tetany
(sustained muscle contraction) http://fig.cox.miami.edu/~cmallery/150/neuro/neuromuscular-sml.jpg
Rigor Mortis
The stiffening of skeletal muscles after
death
 Complete by 12 hours post mortem
 Filaments are stuck in position & cannot
slide
 Rigor mortis starts to disappear about 48
hours after death
 Disappears due to decomposition of
muscle tissue

tendons

Connect muscles to bones
http://www.medical-look.com/systems_images/Skeletal_Muscle_Fibers.gif
Moving bones
Analogy people pulling on a rope
 Each fiber is analogous to a person
 Rope is analogous to the connective
tissue & tendon
 http://www.argosymedical.com/flash/armfl
ex/landing.html
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Smooth muscle
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Single nucleus
Able to divide to produce more cells
Under a microscope does not have bands
Innervated by autonomic nervous system
Still uses actin, myosin and Ca for contractions.
Fibers have a smaller diameter than skeletal fibers
Has the ability to stretch a great deal w/o
affecting function (bladder)
class.kmu.edu.tw
Smooth Muscle Contraction
Actin & myosin are not organized
Can have 2X as much actin as myosin
Ca acts on a different molecule that results in contraction
Not as much ATP is required to, contraction is slower, but
does not fatigue.
 Can maintain contraction for long period of time.
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cytochemistry.net
Smooth muscle innervation
Axon forms many branches and access
many areas along the same muscle fiber
 Some neurotransmitters excite others
relax
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http://www.mfi.ku.dk/PPaulev/chapter2/images/n2-11.jpg
Gap junctions
Contraction may be stimulated by the
contraction/excitation of surrounding fibers
 Channels between fibers allow flow of ions
which conducts the impulse to the next cell
 Examples: Intestines, blood vessels, uterus
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Cardiac muscle
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http://webanatomy.net/histology/cardiac/cardiac_muscle.jpg
Combines
properties of
skeletal and
smooth muscle
Cells are striated,
short, and have
branching
Has specialized
cells responsible
for conducting
starting the heart
beat and quickly
spreading the
contraction
throughout the
heart muscle
Cardiac innervation
Receives signals from the sympathetic and
parasympathetic system
 Sympathetic releases norepinephrine
(responsible for racing heart)
 Parasympathetic releases ACh which
inhibits contractions
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Refractory period
Period when a muscle cannot be excited
 Extremely long in cardiac muscle
 Cardiac muscle cannot experience tetany
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Potassium
Potassium also plays a role in muscle
contraction
 Differences exist in the amount of K let
back into the cell during contraction
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