Muscle is a soft tissue found in most animals. They are primarly responsible for maintaining and changing posture,locomotion as well as movement of internal organs. They are derived from the mesodermal layer of embryonic germ cells in a process known as myogenesis. Based on locomotion three types of muscles are identified.

2.  Muscle is a soft tissue found in most animals.
 They are primarly responsible for maintaining
and changing posture,locomotion as well as
movement of internal organs.
 They are derived from the mesodermal layer
of embryonic germ cells in a process known
as myogenesis.
 Based on locomotion three types of muscles
are identified. They are

3. 1.Striated muscle
2.Non-striated muscle
3.Cardiac muscle

4.  Striated muscle
 Striated muscles are closely associated with
skeletal components. So it is called skeletal
muscle.
 They are voluntary in nature.
 Non-striated muscle
 Non-striated muscles are located in the inner
walls of hollow visceral organs of body like
alimentary canal,reproductive tract etc.
 They do not exhibit any striation and are smooth
in appearance. So they are called smooth
muscles.
 Cardiac muscle
 Cardiac muscles are the muscles of heart. They
are striated and involuntary in nature.

6. Ultra structure of skeletal muscle
 Each muscle cell is called muscle fibre. Each
muscle fibre is surrounded by endomysium.
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Endomysium
Muscle fibre
2.A group of muscle fibres bundled to gether by
collagen to form fasciculi or fascicle.
3.Each fascicle is surrounded by perimysium.

8. All the fascicle collectively form the the muscle
belly. Each muscle belly is surrounded by a
connective layer called epimysium.

10.  The plasma membrane of the muscle fibre is
called sarcolemma and the cytoplasm is called
sarcoplasm. The sarcoplasm contains numerous
protein filaments are called myofibrils.
 Each myofibril contains thin filament actin and
thick filament myosin.
 Myofibril is surrounded by network of tubules and
channels called sarcoplasmic reticulum. The
calcium stored in this area.

12. Actin
 Actin is a fibrous protein. It is an insoluble protein.
 It exists in two forms,namely G-actin and F-actin
 G-actin is the globular actin. It is spherical in
shape.
 F –actin is the filamentous actin. It is in the form of
a double helix.

13.  In the resting muscles,the actin remains in the
form of G-actin. During muscle contraction, the G-
actin becomes F-actin.
 During muscle contraction,actin combines with
myosin to form actomyosin.
 actin +myosin--------actomyosin
Myosin
Myosin is a fibrous protein. It is an insoluble
protein.
It is in the form of golf stick.
It consists of rode like-head,neck and tail regions.
The head is also called cross bridge as it attaches
with the actin during muscle contraction.

14. Diagram showing myosin filament.
ATP = Adenosine triphosphate.

15. Tropomyosin and Troponin
 Tropomyosin and troponin are the two main
proteins that regulate actin and myosin
interactiions.
 Tropomyosin is a long strand that twisted around
F-actin filament and prevents muscle contraction.
 Troponin is distributed in regular intervals on the
surface of tropomyosin.

17. SARCOMERE
 A sarcomere is the basic unit of skeletal muscle
tissue.
 It is made up of central dark band and two half
light bands.
 The two half light bands are firmly attached to the
Z line.
 The region of the dark band represents H zone.

18.  The light band contains actin and it is called I
band or Isotropic band.
 The dark band contains myosin and it is called A
band or Anisotropic band.
 The actin is a thin filament and myosin is a thick
filament.

19. MECHANISM OF MUSCLE
CONTRACTION
 The mechanism of muscle contraction is best
explained by sliding filament theory.
 This theory was proposed by Huxley and Hanson
in 1957.
 It states that the contraction of muscle fibre takes
place by the sliding of the thin filament over the
thick filaments.
 Mechanism
1.An action potential is originating in the central
nervous system(CNS) and reach as to the alpha
motor neuron.
2.The junction between alpha motor neuron and
sarcolemma of the muscle fibre is called
neuromuscular junction or motor end plate.

20. 3.The neural signal reaching this junction and
releases a chemical called acetyl choline. It leads
to the depolarisation of motor end plate.
4.It spreads through the muscle fibre and releases
calcium ions from sarcoplasmic reticulum.
5.The calcium binds with troponin on actin filament.
It allows the movement of tropomyosin.
6.Utilising the energy from ATP hydrolysis, the head
of myosin bind active sites on actin and form a
cross bridge and causes muscle contraction.
7.The ATP molecule split again and myosin head is
reactivated for the next cycle to begin.

21. Diagram showing power stroke by myosin head.
Stage 1: Myosin head binds with actin; Stage 2:
Tilting of myosin head (power stroke) drags the
actin filament.

22. THANK YOU…….