Anatomy of skeletal muscle
ppt #1 Unit 4 Muscles
Muscular System
Chapter 11
Muscle Intro
• Functions of muscles
•
•
•
•
Movement: respiration, circulation, defecation
Stability: resists gravity and provides tension to tendons
Communication
Heat Production: muscle provides 85% of body heat
Types of Muscle
●Skeletal – striated & voluntary
●Smooth – involuntary
●Cardiac - heart
The word “striated”
means striped.
Skeletal muscle
appears striped
under a microscope.
Connective Tissue
• Perimysium: A thick connective layer that surrounds each fascicle.
• Epimysium/Deep Fasciae: a layer that surrounds each muscle
• Superficial fascia: the layer of connective tissue between the muscle
and skin, can be fatty
EPIMYSIUM = outermost layer, surrounds entire
muscle.
PERIMYSIUM = separates and surrounds fascicles
(bundles of muscle fibers)
ENDOMYSIUM =
surrounds each
individual muscle
fiber
This model of the muscles
uses straws to represent
fibers.
Green = endomysium
Muscles and Muscle Fiber Structure
Muscles are composed of many FIBERS that
are arranged in bundles
called FASCICLES
Individual muscles are separated by FASCIA,
which also forms tendons
Muscle Layers
Muscle Fiber
Endomysium
Perimysium
Epimysium
Epimysium
Perimysium
Endomysium
How are muscle cells created?
• In embryonic development, STEM CELLS called Myoblasts fuse to produce each
muscle fiber.
• Each muscle fiber= 1 muscle cell with many
myofibrils
• Each muscle fiber= many flattened or sausage
nuclei pushed against
•
the plasma membrane
• Fiber (cell) plasma membrane= Sarcolemma
• Fiber (cell) cytoploasm = Sarcoplasm
•
shaped
Nucleus
Sarcolemma
Mitochondrion
Sarcoplasm
Myofibril
• Muscle Fiber (cell) plasma membrane= Sarcolemma
• Muscle Fiber (cell) cytoploasm = Sarcoplasm
•
• The Sarcoplasm contains many long protein bundles=
•
myofibrils
• The Sarcoplasm also contains lots of Glycogen (stored carb)
which provides energy and red pigment Myoglobin
• Which stores Oxygen.
• Other organelles are packed into the spaces between the
myofibrils like:
• Sarcoplastic Reticulum: has channels to release FLOOD of Ca+
Forms a network around each myofibril
• T Tubules= Transverse tubules which signal the SR to release
Ca+
Mitochondria: Produces ATP from O2 and glucose (cellular
respiration)
Structure of Myofibrils
• Myofibrils are the long protein cords that fill most of the muscle
cell
• Each Myofibril is a bundle of parallel protein microfilaments
called:
Myofilaments
• 3 kinds of Myofilaments:
1. Thick Filaments: hundreds of protein called : MYOSIN
•
looks like golf clubs
2. Thin Filaments: 2 intertwined strands of protein ACTIN
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•
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Fibrous Actin with “globs” of Globular Actin
F-Actin
G-Actin
each G-Actin has a site that binds to the head of myosin
Myosin and Actin are Contractile Proteins
Thin Filaments continued
• Thin Filaments also have 40-60 protein bundles of
• Tropomyosin
• When muscle is relaxed, the tropomyosin blocks the actins and prevents myosin from
binding.
• Thin filaments also have Troponin: a Ca+ binding protein
• Tropomyosin and Troponin are Regulatory proteins
3. Elastic Filaments: made of huge springy proteins called
Titan, this helps stabilize the thick filaments
overstretching.
• Accessory Proteins include Dystrophin
and helps prevent
Myofibrils are made of
ACTIN = thin filaments
MYOSIN = thick filaments
Myofilaments ACTIN (thin) and MYOSIN (thick)
-- form dark and light bands
 A band = dArk • thick (myosin)
 I band = lIght • thIn (actin)
Filament organization
Actin and Myosin are in all cells and control
motility they are
Contractile proteins (act to shorten muscle
fibers)
Actin and Myosin are organized in a precise
array which then is seen as striations in the
muscle.
Striated muscle has DARK A bands
alternating with light I bands
A bands= thick filaments lying side by side
- very dark where thick and thin
overlap
H bands= lighter region with no overlap of
thick and thin…just thick
I Bands = is region with only thin filaments
and is anchored to Z disc by
elastic
filaments
Z disc = Protein disc to which thin and
elastic filaments are anchored
Sarcomere= segment of myofibril from one
disc to the next Z disc
Z
A muscle shortens because
individual sarcomeres
shorten and pull the z discs
closer to each other.
As discs are pulled closer
they pull on the
sarcolemma to achieve
shortening of the cell.
It is important to remember the hierarchy
fasicles
myofibrils
myofilaments
actin
myosin