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.
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
9.
10.
11.
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……..
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