Physiology of Muscles
The Sliding Filament Theory
The Neuromuscular System
Linkage between the _______________system and the
_______________ system (nerve impulses from the brain or
spinal cord).
Motor Unit
• Motor Unit =
• Motor Units range from small (eye
movements) to large (quadriceps of
leg).
Muscle Twitch
• A single nervous impulse and the
resulting contraction.
• Nerves transmit impulses in
“waves” that ensure smooth
movements.
Neuromuscular Joint
•
•
•
•
Junction point between the nervous and muscular systems.
A chemical neurotransmitter is released (Ach - acetylcholine)
Detected by receptors on surface of muscle fibre.
Results in muscle contraction
The “All-or-None” Principle
• When a motor unit is stimulated to contract, it
will do so to it’s fullest potential (maximum)
• Whether a motor unit consists of 10 muscle
fibres or 800, either
_____________________________________
_____________________________________
Outside Anatomy of Skeletal Muscle
• Skeletal muscle makes up a substantial portion of human body
weight
• The _________________ (outer connective tissue) binds
groups of muscle fibres called __________________ together
which are then bound by the larger/stronger
______________
• The ___________________ envelopes the entire muscle, it
changes its properties as it becomes one with the tendon
• Remember the ______________________ of the long bone?
– This is where the tendon of the muscle attaches to the
bone
– Muscle is attached to bone at two locations:
• Origin=
• Insertion=
Perimysium
Epimysium
Endomysium
Inside Anatomy of Skeletal Muscle
• The endomysium (sheath of connective tissue) surrounds
each individual muscle fibre
• Beneath the endomysium is the sarcolemma a plasma
membrane containing the muscle cell’s cytoplasm
(sarcoplasm)
– The endomysium is surrounded by a rich blood supply and, therefore,
a good system for O2 and CO2 removal
– Nerves also supply the muscle
• Thread like structures, myofibrils, run the length of the
muscle
– Within the myofibril are thin (Actin) and thick (Myosin) filaments
– Actin and Myosin are contained within Sarcomeres (compartments)
Myofibril
Myosin – thick filaments
Actin – thin filaments, contains the proteins:
– Troponin –
– Tropomyosin –
Together, actin and myosin, have a swivel-locking mechanism
– This is the “Sliding Filament Theory”
Myofibril
Sliding Filament Theory
• Myosin head will not attach to actin unless
____________ is released by the sarcoplasmic
reticulum (SR)
• _______ (acetylcholine) initiates this
• _______________ swivels, allowing the binding
sites on ___________ filament
(_____________) to be exposed
• During contraction, protein filaments interact at
molecular level causing them to slide across each
other (the sarcomere shortens)
REST
• the cross-bridges extend toward _____________
• The _____________and ______________ are now in a
coupled position.
• The level of _______________ concentration is low
Sliding Filament Theory
STIMULATION:
• myosin ___________________ form a type of bond
with selected sites on the actin filament
• Acto-myosin formation takes place
• There is an immediate increase of intracellular
_______
• This is brought about by the arrival of the action
potential at the transverse tubules, which causes Ca2+
to be released by the SR
• The inhibitory action of _______________ that
prevents actin-mysoin interaction is released when
Ca2+ ions bind rapidly with troponin in the actin
filament.
• Now the muscle is “turned on”
Sliding Filament Theory
CONTRACTION
• Cross-bridges _________________________
• The muscle shortens and the __________ slides over
the _______________
• Tension develops
• The _________ is broken down to ______ plus
_____plus energy
• Contraction will continue as long as
___________ions remain at a level that inhibits the
troponin-tropomyosin system
Sliding Filament Theory
RELAXATION
• nerve stimulus to the muscle is removed,
_________ions move back into the SR
• The retrieval of __________from the troponintropomyosin proteins “____________” the active sites
on the actin filaments
• This deactivation accomplishes two things:
– It prevents any mechanical link between the myosin crossbridges and the actin filaments
– It reduces the activity of myosin ATPase so there is no more
splitting. Muscle now returns to resting state.
THE ROLE OF
ADENOSINE TRI-PHOSPHATE (ATP)
• ATP is a chemical compound stored in muscles,
which contains three phosphates attached by highenergy bonds to adenosine.
• When the myosin heads on the myosin filaments
attach themselves to binding sites on the actin, ATP
is broken down and the energy released causes the
myosin to pull on the actin.
• As the work of the muscle increases, more and more
ATP is used up.
• ATP  ___________________________
For more help on the sliding filament
theory
• http://www.blackwellpublishing.com/matthe
ws/myosin.html