1. MUSCLES

2. There are three basic types of muscle:-
Found only in
heart tissue
Found in
voluntary muscle
tissue e.g. biceps
Found in
involuntary
muscle tissue
e.g. stomach,
artery walls

3. skeletal muscle
Also called voluntary muscle as it is
under conscious control
also called striated muscle because of its striped appearance.

5. structure of skeletal muscle
made up of hundreds of specialised cells called muscle fibres, which are several cms long
the surface membrane of each muscle fibre is called the sarcolemma
the cytoplasm is called the sarcoplasm and contains many nuclei and mitochondria

7. sarcolemma
sarcoplasm
myofibril
nuclei

8. myofilaments actin myosin muscle fibre myofibril myofilament myofibril
made of
myofilament
made of
myofibril

9. Within each muscle fibre are many parallel myofibrils
Each myofibril consists of overlapping thick and thin myofilaments
Thick myofilaments are made of the large protein myosin, a fibrous protein from which globular heads project
Thin myofilaments are composed of the smaller protein actin

10. The filaments are arranged in a very specific order, forming distinct striations/stripes along the muscle fibre
The stripes are caused by the thick and thin filaments and areas of overlap

12. M

14. the sarcomere
The thicker myosin filaments create the darker striations called the A-band
Within the A-band is a slightly lighter band, called the H-zone
At the centre of the H-zone is the M-line
The thinner actin filaments create a light band called the I-band
At the centre of the I-band is the Z-line
The distance between adjacent Z-lines is called a sarcomere

15. A band H zone I band Z Line
Width of myosin filament, contains H band and dark region either side where myosin and actin filaments overlap
H zone
region within the A band containing only myosin filaments
I band
lighter region with only actin
Z Line
occurs at the centre of the I band and marks the end of the one sarcomere and the beginning of the next

17. Muscle contraction
When a muscle contracts the actin filaments are pulled over the mysoin filaments (towards the M line) by myosin heads.
This causes the following changes:
The Z lines become closer together, so the sarcomere shortens
The I bands become shorter
The H zone becomes narrower
However the A band (length of myosin) does not change in length

18. H zone
Myosin heads

19. H zone
Myosin heads

21. how an action potential
causes a muscle
to contract
The synapse between the axon of a motor neurone and a muscle is called the neuromuscular junction

22. striated muscle fibres are stimulated by motor neurones
innervated by a
motor neurone
Motor end plate

23. Motor end plate

24. motor end plate in section
myelin sheath
synaptic
cleft
vesicle
axon terminal
presynaptic
membrane
mitochondria
postsynaptic
membrane
sarcolemma
sarcoplasm
sarcoplasmic
reticulum
Myofibril contains repeating
dark and light bands, responsible
for the striped appearance
A band
Dark band
I band
Light band

25. An action potential arriving at the neuromuscular junction causes the release of neurotransmitter that crosses the synaptic cleft
This causes the depolarisation of the sarcolemma (post-synaptic membrane of the muscle fibre)
resulting in an action potential which propagates along the entire length of the sarcolemma as an impulse

26. sarcoplasmic reticulum
sarcolemma AP AP
Ca2+ AP
myofibril
T tubule
sarcoplasmic reticulum

27. The sarcolemma is indented forming T tubules deep
into the cell and surrounding the myofibrils.
These tubules lie close to the sarcoplasmic
reticulum.

28. The T-tubules and sarcoplasmic reticulum carry the impulse through the muscle fibre
and causes the sarcoplasmic reticulum to release calcium ions into the sarcoplasm
Ca2+ cause ancillary proteins, covering binding sites on the actin filaments to be displaced, so the binding sites are uncovered.
The globular myosin heads on the myosin filaments attach to the actin forming acto-myosin cross-bridges

30. The myosin heads rotate back pulling the thin actin filaments over the thick myosin filaments
Energy from ATP is needed to detach the heads
The detached heads regain their original position, and attach to another actin binding site further along the filament
The cycle of attachment, rotation, detachment is repeated in a ratchet type mechanism
The process continues as long as APs are propagated through the muscle fibre
As the thin filaments are pulled over the thick filaments the sarcomeres and myofibrils shorten

31. QUESTION
Froggy p348 Q 7

32. REVIEW

33. the structure and function
Give an account of
the structure and function
of skeletal muscle