2. There are 3 types of muscle, that vary slightly in structure and properties:
skeletal (voluntary), smooth (involuntary) and cardiac.
3. End view of a muscle fibre
muscle fibres are âfullâ of
long parallel protein
structures
- the myofibrils
4. The cell membrane (sarcolemma) of the muscle fibre links with the
sarcoplasmic reticulum, which extends throughout the muscle fibre
5. Muscle tissue is not
made up of
individual âcellsâ, but
giant muscle fibres
As embryonic muscle
tissue differentiates,
individual cells fuse
together, creating
multinucleate
structures, the muscle
fibres
6. Within a muscle fibre
are many long,
banded structures, the
myofibrils.
These myofibrils
extend the whole
length of a muscle
fibre.
Myofibrils have a
regular repeating
pattern. Each repeating
âunitâ is called a
sarcomere
7. A sarcomere is composed of 2 overlapping types of fibrous proteins,
actin and myosin
11. The arrival of an impulse releases Calcium ions
allowing myosin/ actin cross links to form
actin
myosin
12. An action
potential is
transmitted to
the muscle
fibreâs
sarcolemma and
spreads
throughout the
muscle fibre
along its
sarcoplasmic
reticulum
13. A muscle contraction is
caused by the interlocking
actin and myosin fibres
sliding over one another,
shortening the muscle.
The arrival of a nerve
impulse, and its spread
throughout the muscle
fibre causes this âslidingâ
contraction
14. Myosin molecules have a head
and âtailâ, and occur in
âbundlesâ or filaments
Actin molecules are globular
and occur in chains
In a resting muscle, any reaction between actin & myosin is prevented by
tropomyosin, which blocks actinâs binding site
15. when a nerve impulse stimulates a muscle
to contract....
The action potential spreads throughout the muscle
fibre, along its sarcoplasmic reticulum
Releasing Calcium ions into the cytoplasm
Calcium ions allow myosin âheadsâ to form cross
links with actin
The myosin molecule pulls the actin molecule âbackâ,
shortening the overall length of the fibre
ATP provides the energy to release the myosin head
and change its angle, ready to bind again
16. So long as the actin binding sites are âopenâ, myosin will
continue to bind, contract and move the actin fibres along.
This process requires energy as ATP
17. 1. Stages in muscle contraction
The muscle fibre is at rest;
Myosin is prevented from forming cross links with
actin
18. 2. Stages in muscle contraction
When Calcium ions
are present, actin sites
are âunblockedâ
19. 3. Stages in muscle contraction
Cross- bridges
can form
20. 4. Stages in muscle contraction
The myosin head pulls the actin âbackâ
21. Summary
âą Energy provided by ATP is needed for any contraction to occur
âą a muscle is always âreadyâ to contract, but this is prevented (or âinhibitedâ) by
a lack of Ca2+
ions
âą Ca2+
must be present to unblock actinâs binding sites.
âą AFTER a contraction, Ca2+
is pumped back into the sarcoplasmic reticulum
âą So, in the absence of Ca2+
, the muscle relaxes