Transcript Muscles - AP Bio Take 5

Muscles
(View Video)
Part I : Anatomy of Muscle
SEE HANDOUT
See
handout
FASCIA
tendon
MUSCLE - INTERNAL STRUCTURE
Below fascia:
• thick connective tissue called
epimysium.
• surrounds the muscle but does
not extend into the tendon
• may look like a white sheath.
Below epimysium :
Layer of connective tissue called
the perimysium.
Divides the muscle into bundles
called "fascicles“
This makes the muscle look as if
it is divided into small
compartments.
The perimysium is thinner than
the epimysium.
• Within each compartment /
fascicle, there are groups of
muscle fibers (muscle cells).
Each muscle fiber is
surrounded by another layer of
connective tissue called
endomysium.
• All of the connective tissue
layers (fascia, epimysium,
perimysium and
endomysium)
1. allow the muscle fibers to move
independently.
2. provide a passageway for
nerves and blood vessels into
and out of the muscle.
Muscle Cells = Muscle Fibers
Facts
Cell Shape: thin and cylinder shaped. The
end of each fiber is attached to the C.T.
associated with the muscle.
Cell membrane : sarcolemma.
Invaginations (called T-tubules or
transverse tubules) are present. They
remain open to the outer surface and also
penetrate deeply into the interior of the
muscle fiber.
Function: plays a role in muscle
contraction
Cytoplasm : small amount, called
sarcoplasm.
Other organelles:
many small oval nuclei
(multinucleated)
 many mitochondria
thread-like structures called
myofibrils.
The myofibrils run parallel to each
other. They are the portions of
the muscle that actually contract.
Surrounding each myofibril, there
is a network of canals that form
the sarcoplasmic reticulum. It is
similar to the E.R. in other cells.
Now, color muscles
diagrams for study and
work on review sheet!
Role of Sarcoplasmic Reticulum
• The sarcoplasmic
reticulum forms a "sleeve"
around each myofibril.
• It stores the Ca++ needed
for muscle contraction.
• It releases the Ca++ when
the muscle is stimulated.
When the stimulation
stops, the Ca++ return to
these storage areas.
Sliding Filament Theory
See
movie
link
Myofibrils are
made of two
protein filaments:
Actin and myosin
• Each myofibril contains
two types of protein
filaments. They are
myosin filaments and
actin filaments.
• The myosin filaments
are thicker than the
actin filaments
Myosin
filaments
• Each myosin filament
is composed of many
rod-shaped proteins
that are wound
together into a spiral.
The ends are "clubshaped" or "paddleshaped“ called
myosin heads.
• The myosin heads
occur in clusters
•
Actin Filaments
• The thin actin
filaments are actually
more complex than the
myosin filaments.
• Each actin filament is
composed of three
types protein.
• They are: actin,
tropomyosin and
troponin.
All three play a
special role in
muscle
contraction!
1. actin = present in the
largest amount.
It forms two long strands
of globular protein which
are twisted together.
2. tropomyosin = This protein
is long, double-stranded
and twisted. It is not
globular, therefore it is
much thinner than actin
and is twisted around the
actin.
3. troponin = This is a globular
protein. It is attached in
clusters to the
tropomyosin.
Section of
myofibril
SKELETAL MUSCLE
STRIATIONS coordinate with
actin/myosin
Muscle tissue has a definite
pattern of "stripes" (striations) on
the myofibrils.
“Z” lines are a series of dark
stripes at intervals.
The region between two Z lines is
called a sarcomere.
The sarcomere
is the actual
contractile unit
of the muscle
fiber.
There are many
sarcomeres per
myofibril.
• Moving inward from each Z line,
light colored area called I band.
This area only contains actin
filaments.
• Continuing inward, there is a dark
area. It is called the A band. In
the center of the A band, there is a
lighter, central stripe called the H
zone. The H zone contains only
myosin filaments. The rest of the
A band is where the actin and
myosin filaments overlap.
• When the muscle contracts, the
H zone disappears and the I
band becomes narrower until
the muscle relaxes again.
Part II: Physiology of Muscle
Sliding Filament Theory
See
movie
link
See movie link
Neuromuscular junction
See
Video
ONE
See handout on Union of
Nerve and muscle
See Two
handouts:
1. Picture
2. Physiology of
muscle
contraction
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