The document describes the sliding filament theory of muscle contraction. It explains that muscle shortening occurs when the actin filament slides over the myosin filament, reducing the distance between Z-lines in the sarcomere. It further describes the roles of calcium ions, tropomyosin, troponin, actin, myosin and ATP in the cross-bridge cycling that enables the sliding filament movement and generates force. It also mentions the all-or-none law, where a muscle fiber will contract fully or not at all in response to an impulse.

1. How Muscles Contract
Sliding Filament Theory
Lloyd Dean

2. Recap: Let’s do it again!
Team “Oxy”
Team “FOG”
Team “Bolt”
Walk around the
12 press ups
Every 10 seconds
perform an
explosive activity
room until told
otherwise
1:1
3:1
I shall pick the music!
10:1

3. SUMMARY OF SKELETAL MUSCLE FIBER TYPES
Slow oxidative fibers
Myoglobin content
Mitochondrial Density
Filament organization
Type of respiration
Speed of contraction
Duration of contraction
Resistance to fatigue
Twitch
Function
Fast oxidativeglycolytic fibers
Fast glycolytic fibers

4. SUMMARY OF SKELETAL MUSCLE FIBER TYPES
Slow oxidative fibers
Fast oxidativeglycolytic 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 Activities such as sprinting or
e.g., strength training or throwing walking uch as sprinting or
a javelin
walking

5. Aims
By 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

6. Look at the start
Look at the end
Sliding Filament Theory

7. Structure of Skeletal Muscle
Epimysium
Surrounds entire muscle
Merges into tendon that is composed of
tough collagen
Perimysium
Surrounds bundles of muscle fibers
Endomysium
Surrounds individual muscle fibers
Lets make our own!

8. Structure of Skeletal Muscle:
Microstructure
Sarcolemma
Muscle cell membrane
Myofibrils
Threadlike strands within
muscle fibers
Actin (thin filament)
 Troponin
 Tropomyosin
Myosin (thick filament)
“Sarco” means
flesh
“Lemma” means
husk (Outer layer)
Further divisions of
Myofibrils “Myo” is muscle
Z-line
A-band
I-band
Sarcoplasm
Sarcoplasmic reticulum
 Storage sites for calcium
 Surrounds myofibrils
Transverse tubules

12. Muscular Contraction
The 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………..

13. 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 background
Actin 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……..

14. A bit of inspiration!

15. 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....

16. Chapters
1.
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
with the delivery of a
chapter
Know what’s going
through
We will make an iMovie!

17. A Milky Message
Nerve 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)

18. Two Forces Join
Calcium ions join with
troponin
Causes tropomyosin to be
removed from actin
Actin and myosin join
together

19. A Tiresome Pull
Actin and myosin are now
joined
Myosin pulls actin inwards
slightly
ATP enables quick
detachment of actin and
myosin in preparation for
power stroke

20. Powering Through
ATP 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

21. A Milky Removal
Once impulse stops....
Calcium Ions are sent back
to sarcoplasmic reticulum
Tropomyosin rejoins actin
Sarcomere and Z disc
distance increase
Muscle is relaxed

22. Look at the start
Look at the end
Sliding Filament Theory

23. All or None Law
Fiber contracts
completely or not at all