Sliding theory

8/13/2019 Sliding theory

1/18

Muscle Cross Section

Bundles of fibres /

fibers Fasciculi

connective tissue

Perimysium. Each Fasciculicontains

10 to 100 muscle

fibres


2/18

Sliding Theory of Contraction


3/18

Muscle Fibers

Muscle fibers can rangefrom 10 to 80micrometers indiameter and may beup to 35cm long.

A large strong muscle,such as thoses formingyour Quadriceps wouldhave a large number offibers within eachbundle.

A smaller muscle usedfor precisionmovement, such asthose in the hand wouldcontain far fewer fibresper Fasciculi.


4/18

Sarcolemmafibres cell membrane

Sarcoplasmcells cytoplasm

Myofibrils: cylindrical organelles

Sarcoplasmic Reticulum: network of tubules,through which nerve impulses travel,Calcium storage,


5/18

Myofibrils

Each muscle fiber contains hundreds to

thousands of Myofibrils.

These are bundles of Actin and Myosin

proteins which run the length of the muscle

fiber and are important in muscle contraction.

Each Myofibril can be broken down into

functional repeating segments called

Sarcomeres.


6/18

Sliding Theory

At a very basic level each muscle fibre is made

up of smaller fibres called myofibrils.

These contain even smaller structures called

actin and myosin filaments.

These filaments slide in and outbetween each

other to form a muscle contraction, hence

called the sliding filament theory.


7/18

Structures Invoved

Myofibril:A cylindrical organelle running the length of themuscle fibre, containing Actin and Myosin filaments.

Sarcomere: The functional unit of the Myofibril, dividedinto I, A and H bands.

Actin: A thin, contractile protein filament, containing'active' or 'binding' sites.

Myosin: A thick, contractile protein filament, withprotusions known as Myosin Heads.

Tropomyosin:An actin-binding protein which regulates

muscle contraction. Troponin:A complex of three proteins, attached to

Tropomyosin.


8/18

Sarcomere

Part of myofibril

This is the smallest unit of skeletal muscle that

can contract.

Sarcomeres repeat themselves over and over

along the length of the myofibril.


9/18


10/18

The process of a muscle contracting can be

divided into 5 sections:


11/18

Step 1

1. A nervous impulse arrives at theneuromuscular junction, which causes arelease of a chemical called Acetylcholine.

The presence of Acetylcholine causes thedepolarisation of the motor end plate whichtravels throughout the muscle by thetransverse tubules, causing Calcium (Ca+) tobe released from the sarcoplasmic reticulum.


12/18

2. In the presence of high concentrations of Ca+,

the Ca+ binds to Troponin, changing its shape

and so moving Tropomyosin from the active

site of the Actin. The Myosin filaments can

now attach to the Actin, forming a cross-

bridge.


13/18

3 The breakdown of ATP releases energy which

enables the Myosin to pull the Actin

filaments inwards and so shortening the

muscle.

This occurs along the entire length of every

myofibril in the muscle cell.


14/18

4 The Myosin detaches from the Actin and thecross-bridge is broken when an ATP moleculebinds to the Myosin head.

When the ATP is then broken down the Myosinhead can again attach to an Actin binding sitefurther along the Actin filament and repeat the'power stroke'.

This repeated pulling of the Actin over themyosin is often known as the ratchetmechanism.


15/18

5 This process of muscular contraction can last

for as long as there is adequate ATP and Ca+

stores.

Once the impulse stops the Ca+ is pumped

back to the Sarcoplasmic Reticulum and the

Actin returns to its resting position causing

the muscle to lengthen and relax.


16/18

Stretched Muscle

the I - bands and the H -zone is elongated dueto reduced overlappingof the myosin and actin

filaments.

There would bereduced musclestrength because fewcross bridges can formbetween actin andmyosin.


17/18

Partially Contracted Muscle

more overlapping of the

myosin and actin with

lots of potential for

cross bridges to form. The I - bands and H -

zone are shortened.


18/18

Fully Contracted Muscle

Because the thin actin

filaments have

overlapped there is a

reduced potential forcross bridges to form

again.

Therefore there will be

low force productionfrom the muscle.

Sliding theory

Documents

Transcript of Sliding theory