Sliding Filament Theory

Lloyd Dean

How Muscles Contract

Structure of Skeletal Muscle

EpimysiumSurrounds entire muscle

PerimysiumSurrounds bundles of muscle fibers

EndomysiumSurrounds individual muscle fibers

Structure of Skeletal Muscle:MicrostructureSarcolemma

Muscle cell membrane

MyofibrilsThreadlike strands

within muscle fibersActin (thin filament)

TroponinTropomyosin

Myosin (thick filament)

Further divisions ofMyofibrils

Z-lineA-bandI-band

SarcoplasmSarcoplasmic

reticulumStorage sites for

calciumSurrounds myofibrils

Transverse tubules

Muscular ContractionThe sliding filament model

Muscle shortening occurs due to the movement of the actin filament over the myosin filament

Reduction in the distance between Z-lines of the Sarcomere

Lets see a preview before the play………..

Sliding Filament Theory:A Love Story

Winner of 2 Golden Globes and 3 Oscar’s.Directed by Lloyd Dean and his award winning

students

The backgroundActin and Myosin are in deeply in love and wish to

live a happy life together and stay in full muscle contraction.

The nasty Tropomyosin has other idea’s…….

Let’s see the cast……..

Cast Actin – The thin protein that needs some HELP to join with

Myosin

Myosin - The thick protein

Acetylcholine – A helping hormone

Troponin – Will assist in removing the horrid tropomyosin from actin

Tropomyosin – Doesn’t want actin and myosin to become attached

ATP – Energetic friend

Calcium – Will it win it’s battle against tropomyosin?

Nervous Impulse - Messenger

Now to the chapters of this story.........

Chapters1. A Milky Message

2. Two Forces Join

3. A Tiresome Pull

4. Powering Through

5. A Milky Removal

A Milky Message Nerve Impulse (Action Potential)

sent via motor unit to neuromuscular junction (Place where the brain and muscle communicate)

Hormone (Acetylcholine) diffuses from Axon terminals in neuron

Sodium Ions diffuse into spaces left by Ach which cause action potential to run through the muscle fibre

This causes calcium ions to be released in the sarcoplasmic reticulum (Surrounds myofibrils)

Two Forces JoinCalcium ions join

with troponin

Causes tropomyosin to be removed from actin

Actin and myosin join together

A Tiresome PullActin and myosin

are now joined

Myosin pulls actin inwards slightly

ATP enables quick detachment of actin and myosin in preparation for power stroke

Powering ThroughATP is broken down

This enables Myosin to powerfully pull actin inwards

Sarcomere and distance between Z discs shortens

This process continues at a high rate and as long as there are calcium ions present

A Milky RemovalOnce impulse stops....

Calcium Ions are sent back to sarcoplasmic reticulum

Tropomyosin rejoins actin

Sarcomere and Z disc distance increase

Muscle is relaxed

All or None Law

Fiber contracts completely or

not at all