This document discusses the structure and function of skeletal muscle. It describes the classification of muscles, the structure of muscle fibers including myofibrils and sarcomeres, and the molecular components actin and myosin that enable contraction. It explains that calcium triggers the interaction of actin and myosin heads, leading to muscle shortening. Energy for contraction comes initially from ATP and phosphocreatine, then from glycogen and oxidative metabolism. The document also distinguishes between isotonic contraction, where muscle length changes, and isometric contraction, where tension but not length changes.

1. SARCOMERE,
SARCOTUBULAR SYSTEM
DR.NILESH KATE.
M.D.
ASSOCIATE PROFESSOR,
DEPARTMENT OF PHYSIOLOGY,
ESIC MEDICAL COLLEGE &
HOSPITAL,
GULBARGA.

2. OBJECTIVES.
 Introduction
 Classification of Muscles
 Structure of Skeletal Muscle
 Myofibrils
 Sarcomere
 Molecular level of Myosin and Actin
 Action of Actin, Myosin and Calcium in contraction
 Walk – Along –Theory
 Energy source of Muscle contraction
 Iso metric and Iso Tonic contraction

3. Introduction
 We are born with about 300 to 350 bones but
some of the bones fuse together as we grow
and by the time we reach young adulthood we
have on an average about 206 bones.
 There are about 650 muscles in the body, and
they are divided into three different types,
skeletal, visceral and cardiac.

4. Introduction
 About 40% of your body weight is accounted for by
muscles.
 largest --The gluteus maximus muscle, located in the
buttocks.
 Longest– Sartorius.
 Smallest – stapedius.
 Strongest – Masseter in the jaw.
 Shortest– styloglossus. Tensor tympani (skeletal)
 Contrary to what people assume, muscles do not
push, but can only pull.

5. Muscle Classification

6. Functional anatomy & organization.
Structural organization
•Endomysiym.
•Fasciculi – Perimysium.
•Muscle belly –
Epimysium.
•Tendons.

7. Structural organization

8. Structure of muscle fibre.
Long cylindrical.
Sarcolemma.
Sarcoplasm.
Cell organelle.
Sarcoplasmic
reticulum.
Myofibrils.
Sarcotubular
system.

9. Myofibrils
 Diameter- 1-2 μm
 Length – 1-4 cm.
 Made up of
Myofilaments.
 Thick – Myosin.(1500)
 Thin – Actin.(3000)

10. Myofilaments
 Arrangement of
Myofilaments under
light microscope.
 Alternate light & dark
bands.

11. Striations of muscle fibres.
 Due to difference in the refractive index.
 ‘A’ Band – Dark band
 Anisometropic to polarized light.
 Length --- 1.5 μm
 ‘H’ zone – centre of A band
 H means Henson or “Hell” – light.

12. Striations of muscle fibres.
 “M” Line – centre of H zone.
 Pronounced during muscle contraction.
 I Band - Light band.
 Isotropic to polarized light. “Z” Line – Dark
 Z Wischenscheibe – German- Between disc.

13. Sarcomere
 A portion of myofibril
that lies between two
successive Z discs is
called sarcomere.
 Sarcomere =
 ½ I band + A band +
½ I band.
 The structural &
functional unit of
muscle fiber.

14. Myofilaments.
 Contractile apparatus.
 Contractile proteins.
 Myosin
 Actin
 Regulatory proteins.
 Troponin
 Tropomyosin.
 Anchoring proteins.
 α Actinin
 Titin.
 Nebulin
 Dystrophin

15. Thick filaments.
 Twice the diameter.
 Each thick filament
surrounded by 6 thin
flaments.
 Myosin .
 Mol.wt – 4,80,000.
 6 polypeptide chains
 4 – light
 2 – heavy.

16. Myosin .
 Globular head.
 Myosin II
 The tails of myosin molecules
bundles to form the body of
myosin filament with heads
hangs to the side.
 The part of head hangs from
body form the arm
 Thus the protruding arms and
heads -- cross- bridges
 Participate is actual muscle
contraction.

17. Thin filaments.
 Head end – extend into
A band
 Tail end – anchored to
the Z line.
 Contractile protein
 Actin
 Regulatory proteins
 Tropomyosin
 Troponin.

18. Actin
 300-400 molecules/ thin
filaments.
 Long double helix of 2
chains of globular units.
 Globular molecules-G
Actin.
 Chain formed – F Actin.

19. Tropomyosin
 40-60 molecules/ thin
filaments.
 Long filaments.
 Lie in groove between
2 actin filaments.
 Covers binding sites
on actin.
 Thus regulatory
proteins.

20. Troponin
 Small globular units.
 3 subunits.
 Troponin ‘I’ – Affinity for
Actin.
 Troponin ‘T’ – Affinity
for Tropomyosin.
 Troponin ‘C’- Affinity for
Calcium

21. Anchoring proteins.
 α Actinin – cross link the Actin
filaments in the area of Z line.
 Titin. – Interconnect Z line.
 Nebulin.– connect α actinin with
troponin- tropomyosin complex.
 Dystrophin-glycoprotein
complex.– provide structural
support & strength.

22. Sarcotubular system.
 Sarcotubular system –
with sarcoplasmic
reticulum
 Imp role in internal
conduction of
depolarization within
the muscle fibre.
 Formed by
 Transverse tubular
system (T)
 Longitudinal
sarcoplasmic reticulum.

23. Transverse tubular system (T)
 Invagination of
sarcollema into muscle
fibre at junction of A & I
bands.
 Rapid transmission.
 Its membranes contains
voltage gated Ca
channels
Dihydropyridine
receptors.
 Activate longitudinal SR.

24. Longitudinal sarcoplasmic
reticulum.
 Sarcoplasmic tubules of
sarcoplasmic reticulum.
 Run in long axis of muscle
fibres.
 Do not open to exterior.
 Terminal cisterns.
 Triad- T tubule + 2
terminal cisterns.
 Ryanodine receptors.

25. Energy source for Muscle Contraction
 The energy source -- ATP
 Large amount of ATP are
cleaved during contraction
process. When greater the
work is done more ATP is
cleaved. This is called Fenn
effect.
 ATP – 1 to 2 seconds
 Phosphocreatine – 5 to 8
seconds
 Glycogen – 1 minute
 Oxidative metabolism – for
many hours.

26. Isotonic Contraction
 Isotonic contraction:
In this muscle contract
with change in length
of muscle fibre but no
change in tension.
Eg., Walking, Running,
Lifting a load

27. Isometric contraction:
In this type the muscle contract
with change in tension but
no change in length of the
muscle fibre.
Eg.,
 Muscle which helps in
maintaining posture
against gravity.
 Contraction of the arm
muscles when trying to
push a wall.

28. Summary
 Introduction
 Classification of Muscles
 Structure of Skeletal Muscle
 Myofibrils
 Sarcomere
 Molecular level of Myosin and Actin
 Action of Actin, Myosin and Calcium in contraction
 Energy source of Muscle contraction
 Iso metric and Iso Tonic contraction

29. Thank you.