Physiology of Muscles

The Sliding Filament Theory

The Neuromuscular System

Motor UnitMotor Unit• Motor Unit =

• Motor Units range from small (eye movements) to large (quadriceps of leg).

Muscle TwitchMuscle Twitch • A single nervous impulse and the

resulting contraction.• Nerves transmit impulses in

“waves” that ensure smooth movements.

Linkage between the _______________system and the _______________ system (nerve impulses from the brain or spinal cord).

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=

EpimysiuEpimysiumm

PerimysiuPerimysiumm

EndomysiEndomysiumum

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 TheorySTIMULATION: • 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 CaCa2+2+ to be released by the SR

• The inhibitory action of _______________ that prevents actin-mysoin interaction is released when CaCa2+2+ 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 TheoryRELAXATION• nerve stimulus to the muscle is removed,

__________________ions move back into the SR• The retrieval of ____________________from the troponin-

tropomyosin proteins “____________” the active sites on the actin filaments

• This deactivation accomplishes two things:– It prevents any mechanical link between the myosin cross-

bridges 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 high-energy 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/matthews/myosin.html