Transcript SlidingFilamentModel2

Sliding Filament Model
of Muscle Contraction
HOOK
• Muscle is only biological
cell/tissue that can cause
rapid, large-scale
movement
• Role of filamentous
proteins understood as
great and early
breakthrough in
cell/molecular biology—
lots of protein available,
(like Hemoglobin)
I normally cover neurons and
muscle together as part of unit on
movement—see website
Larry M. Frolich, Ph.D.
April 15, 2010
Sliding Filament Model
of Muscle Contraction
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OUTLINE
Motor Unit
Muscle Cell Architecture
and Function
Sliding Filamentous
Proteins
Muscle Force Properties
Muscle Cells and Neurons
• are unique to animals
• have “excitable”
membranes that transmit
action potentials
• allow for rapid large-scale
movements
• Motor Unit is one motor
neuron plus the muscle
cells that it stimulates (or
synapses with)--the
minimal construct that
allows for movement in
our body
Muscle cells
• Muscle fibers are cells—visible to naked eye as fibers in
meat, chicken, fish
• Sarcolemma is muscle cell membrane—”excitable” so has
action potentials just like neurons
• Because cell is large, T-tubules carry action potential—
ionic depolarization—into internal parts of cell
• Sarcoplasmic reticulum releases calcium which triggers
actin-myosin protein filaments to contract
Sequence of events Motor Neuron to Muscle contraction at cellular level
(from the Brain Top to Bottom) [link]
Muscle cell or muscle “fiber” is composed of myofibrils which
contain sarcomeres or contractile “units”
MyoSarco(= muscle)
Molecular Basis of Muscle
Function
• Actin-Myosin
“sliding filament”
model
• Explains
– Muscle movement
or shortening
– Muscle force
generation or
“contraction”
• Actin and myosin
filamentous proteins
are packed parallel
in sarcomeres
How does the actin-myosin complex (sarcomere)
shorten and contract the muscle?
•
Actin = thin filament
“lattice-work”
• Myosin = thick filament
“core”
• Ca release triggers the
formation of molecular
cross-bridges from myosin
to actin
• Cross-bridges “row” or
“reach” for more adjacent
binding site on actin.
And the result is
muscle movement
Details, details,
details…
• Tropomyosin and troponin
create binding site on actin
filament
• Presence of Ca++ exposes
binding site
• “Cocked” cross-bridge on
myosin (uses ATP) then
attaches to binding site and
pulls or “rows” actin filament
• Cross-bridge linkage is
broken and re-cocks to link
with next binding site
Details Video
Sliding Filament Model explains
• Why muscle has peak force
at certain length: (ideal
actin-myosin overlap for
cross-bridge formation)—
BUCKET DEMO
• More muscle cells means
more muscle force: (more
cross-bridge formation)—
EMG, Isolated muscle online
lab
• Concentric/isometric/eccent
ric contraction: Crossbridges continue to form
and “reach” even if opposing
force is greater