Skeletal Muscle Tissue
Contraction
Chapter 10
Anatomy and Physiology
Mr. Knowles
Liberty Senior High School
A Brief Review of Skeletal
Muscle Tissue
Connective Tissue
• Epimysium
separates the…
Structures
Entire muscle from
other tissue.
• Perimysium divides Bundles of muscle
the muscle into…
fibers- fascicles.
• Endomysium
surrounds the…
Individual skeletal
muscle fibers.
How does a skeletal
muscle cell differ from
most other eukaryotic
cells?
A Comparison
•
•
•
•
•
•
Most Cells
Small; < 100 μm long •
One Nucleus
•
Normal metabolism- •
needs normal enzymes;
one copy of genes.
100’s of mitochondria •
Endoplasmic Reticulum•
No myofibrils
•
Skeletal Muscle
Large; 12 inches long
Multiple Nuclei
High metabolismneeds more enzymes;
more genes.
1,000’s of mitochond.
Sarcoplasmic
Reticulum
Myofibrils
Sarcolemma
Sarcoplasm
Nucleus
Special Terms for Muscle Fibers
• Sarcoplasm- cytoplasm of a muscle
fiber.
• Sarcolemma- unique cell membrane
of a muscle fiber.
• The sarcolemma forms tubes that
travel into sarcoplasm at right anglesTransverse Tubules (T tubules).
• Action Potentials (unequal charges)
travel down these T tubules.
Inside a Muscle Fiber…
• Each T tubule encircles cylindrical
structures- myofibrils.
• Myofibrils- 1-2 μm in diameter and as
long as entire cell. 100’s – 1,000’s of
myofibrils/cell.
• Myofibrils – are bundles of
myofilaments – 2 kinds of protein
filaments called actin (thin filaments)
and myosin (thick filaments).
Inside the muscle fiber…
• Myofibrils can shorten and contract the
muscle fiber.
• Myofibrils are attached to the
sarcolemma on its inner surface.
• Collagen fibers are attached to the
sarcolemma on its outer surface. These
fibers extend into the tendon.
• Myofibrils  pull on sarcolemma 
pulls on tendon  muscle contraction.
Muscle Fiber
Sarcolemma
Tendon
Myofibrils
Collagen
Intracellular
Extracellular
Triad
Terminal
Cisternae
T Tubule
Sarcoplasmic Reticulum
• Pumps Ca+2 out of the sarcoplasm and
stores it.
• The resting cell has very little Ca+2 in the
sarcoplasm. 1000X more Ca+2 in the SR
than in the sarcoplasm.
• The SR is made up of terminal cisternae
that lie on above the junction of thin and
thick filaments in the sarcomeres.
The Organization of the
Myofibril
• Myofilaments are organized into
repeating functional unitsSarcomere- smallest functional unit
of the fiber.
• Sarcomere = myosin + actin + other
stabilizing proteins.
Fig. 10-3.
P. 282
Inside the Sarcomere…
• Have two regions or Bands:
1. A Bands- are dArk bands and have
three parts.
a. M line- a protein that connects
neighboring thick filaments, keeps their
position.
b. H zone- a region with only thick
filaments.
c. Zone of Overlap- thin and thick
filaments overlap.
Inside the Sarcomere…
• Have two Bands:
2. I Bands- are lIght bands; only find
thin filaments.
a. Z lines- mark the boundaries
between the adjacent sarcomeres on the
myofibril; have connectin – a connecting
protein that interconnects thin filaments.
b. Titin- a protein that aligns thick and
thin filaments; resist extreme stretching.
Z Line
A Band
I Band
Z lines
Thin Filaments (Actin)
Contains three proteins:
• F actin- a twisted strand of 300-400
globular (G) actin molecules.
– Each G actin has an active site- a
region where thick filaments can
bind.
• Tropomyosin are strands of protein
that wrap around F actin. They cover
the active site. This prevents actinmyosin interaction.
Thin Filaments (Actin)
• Troponin- three globular subunits (parts).
– One subunit binds to tropomyosin and
locks the two together.
– Another subunit binds to a G actin
molecule, holding troponin and
tropomyosin to the actin.
– The third subunit binds to a Ca+2 ion.
Resting cells have low Ca+2 and so this
subunit is empty in the resting cell.
Thick Filaments (Myosin)
• Made of 500 myosin molecules.
• Each myosin – two subunits twisted
around each other.
• Myosin has a long, attached tail
bound to other myosin molecules in
the thick filament.
Thick Filaments (Myosin)
• The free head projects outward, toward
the nearest thin filament. Head can bind
to the active site on the G actin.
• Between the head and the tail there is a
flexible hinge that lets the head swing
back and forth.
• All myosin molecules are arranged with
their tails pointing toward the M line.
Supporting the Myofibrils
• Desmin- is a complex network of
protein that twists around each Z line
and connects adjacent myofibrils.
• Vertical bands of desmin can be seen
with a light microscope and give the
fiber a banded appearance-striated
muscle.
The
Sliding Filament
Theory
An explanation of how
skeletal muscle cells
contract.