Sliding Filament Theory

Lloyd Dean

How Muscles Contract

Recap: Let’s do it again!

Team “Oxy” Team “FOG”

Walk around the room until told otherwise

1:1

12 press ups

3:1

I shall pick the music!

Every 10 seconds perform an explosive activity

10:1

Team “Bolt”

SUMMARY OF SKELETAL MUSCLE FIBER TYPES

Slow oxidative fibers Fast oxidative-glycolytic fibers

Fast glycolytic fibers

Myoglobin content

Mitochondrial Density

Filament organization

Type of respiration

Speed of contraction

Duration of contraction

Resistance to fatigue

Twitch

Function

SUMMARY OF SKELETAL MUSCLE FIBER TYPES

Slow oxidative fibers Fast oxidative-glycolytic fibers

Fast glycolytic fibers

Myoglobin content High High Low

Mitochondrial Density Highest Moderate Lowest

Filament organization Striated Striated Striated

Type of respiration Aerobic Aerobic and anaerobic Glycolysis

Speed of contraction Slow Fast Fast and strong

Duration of contraction Long Brief Short

Resistance to fatigue High Moderate Low

Twitch Slow twitch Fast twitch Fast twitch

Function Endurance activities e.g., running a marathon

Short periods of intense activity e.g., strength training or throwing a javelin

Activities such as sprinting or walking uch as sprinting or walking

AimsBy the end of the lesson you should be able

to:

Describe the sliding filament theory

Explain the microstructure of muscle

State the all or nothing law

Look at the start

Look at the end

Sliding Filament Theory

Structure of Skeletal Muscle

EpimysiumSurrounds entire muscle Merges into tendon that is composed of tough collagen

PerimysiumSurrounds bundles of muscle fibers

EndomysiumSurrounds individual muscle fibers

Lets make our own!

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

“Sarco” means flesh“Lemma” means husk (Outer layer)

“Myo” is muscle

Muscular ContractionThe sliding filament model

(Hugh Huxley, 1954)

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……..

A bit of inspiration!

Cast (Check out by clicking this link) Nervous Impulse – The brain “Polices” the body. It sends a

“Message” and “S.O.S” to muscle which helps it to contract!

Acetylcholine – A “Help!”ing horming

Calcium – Calcium “Ion”. A bit like a “Lion in Zion”

Tropomyosin – Doesn’t want Actin and Myosin to become attached. Scary!

Troponin – Actin and Myosin “Lean on” “Glee”fully to help remove tropomyosin

Actin and Myosin – “Montague & Capulets” protein filament families

ATP – An energetic friend

Now to the chapters of our story....

Chapters1. A Milky Message

2. Two Forces Join

3. A Tiresome Pull

4. Powering Through

5. A Milky Removal

We need to build this story together!

You will be involved You will be involved with the delivery of with the delivery of a chapter a chapter

Know what’s going Know what’s going throughthrough

We will make an i-We will make an i-Movie!Movie!

A Milky MessageNerve Impulse sent to

neuromuscular junction (Place where the brain and muscle communicate)

Hormone (Acetylcholine) diffuses

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

Look at the start

Look at the end

Sliding Filament Theory

All or None Law

Fiber contracts completely or

not at all