- Explanation of skeletal muscle contraction, how they work, and how they look during contraction and relaxation. - The anatomy of skeletal muscle has been explained well ... - The mechanism of muscles has also been clarified sequentially ... Thank you ...

1. SKELETAL MUSCLES
PRESENTED BY :-
Yash ruhela
1st year from B-pharmacy
TO :- NIDHI TYAGI MAM
SRM INSTITUTE OF PHARMACY

2. SKELETAL MUSCLES
● These are related to skeletal system so they also known as skeletal
muscles.
● Transverse lines are found at regular intervals, they also called striped
or striated muscle.
● Their contractions are controlled by will power of animals so they are
called voluntary muscle.

4. ANATOMY OF SKELETAL
MUSCLE
● Skeletal muscle tissue is surrounded by connective tissue.
● It is separated from skin by subcutaneous layer [ superfacial facia ], which is composed of
connective tissue and adipose tissue.
● Under the superfacial facia lies the deep facia.
● Below the deep facia, these are three layers of connective tissue which strengthen muscles.
Epimysium: - it is outer most layer.
it surrounds the entire muscle.
Perimysium: - it is middle layer.
it surrounds the group of muscle fiber called fascicles.
Endomysium: - it is the deepest layer.
it surrounds each muscle fiber separately.

6. ● Skeletal muscles are composed of many individual cells known
as muscle fiber.
● Group of muscle fibers called fascicule.
● Many fascicules combined to form a muscle.
● Muscle fibers attached to a tough cord of connective tissue
called Tendon and tendon further attached with a bone.

8. ANATOMY OF SKELETAL
MUSCLE FIBER (SMF)
● It is cylindrical or tubular in shape, long and unbranched in size.
● Diameter of mature SMF ranges from 10 to 100 um.
● Length of mature SMF is about 10 cm and sometimes it should up to 30 cm.
● Outer membrane of muscle fiber is called sarcoplasm.
● Each muscle fiber contains multinucleated sarcoplasm.
● Sarcoplasm is a plasma membrane of muscle cell and sarcoplasm is cytoplasm of a muscle fibers.
● At high magnification, the sarcoplasm appears stuffed with little thread. These small structures
are the myofibrils, the contractile organelles of skeletal muscle.
● Myofibrils are about 2um in diameter and extend the entire length of a muscle fiber.
● Myofibrils are arranged in parallel row and forms the dark and light line.
● These dark and light lines are made up of actin and myosin protein. Both proteins are filamentous
protein.
● Actin filaments are thin while myosin is thick.

10. Actin = thin filaments.
Myosin = thick filaments.

11. COMPONENTS OF SARCOMERE
● I band- it is light line or band which is made up of only actin filaments.
- These bands are mono refractive in polarized light so it is called Isotropic
band.
● A band- it is dark and middle part of sarcomere .
-It contains entire thick filament and those parts of thin filament that overlap
with thick filament.
● H zone- a narrow region of ‘ a- band ‘ that has only thick filament but no thin filament.
● M line- a region in the centre of ‘ h- zone ‘ that contains protein which holds the thick
fialments together at the Centre of sarcomere.
● Z line- in the centre of each ‘ i- band ‘ is an elastic fiber called ‘ z- line ‘ which bisects it.
-The thin filament are firmly attached to z- line.
● Z discs- narrow regions that separate on sarcomere from the next.
-Z-discs are made up of “actinin” protein.

13. ● The portion of myofibril between two successive z - line is
considered as functional unit of contraction called
sarcomere.
● Sarcomere = 1 A - band + 2 half I - band.
● Length of sarcomere = 2.5um ( I- band = 1um and myosin
= 1.5um).
● 1 myosin filament is surrounded by 6 actin filament.
● 1 actin filament is surrounded by 3 myosin filament.

15. MECHANISM OF MUSCLE
CONTRACTION
● It is the best explained by the sliding filament theory.
● According to this theory, contraction of muscle fibers takes place by the sliding of thin
filament over the thick filament.
● Muscle contraction is initiated by by a singnal sent by CNS via a motor neuron.
● A junction between muscle neuron and sarcolemma of muscle fiber is called neuromuscular
junction or motor - end plate.
● At this juntion, neural signal releases a neurotransmitter ( acetylcholine ) which generates
an action potential in the sarcolemma and it cause release of ca+2 ions in the sarcoplasm.
● Increase in ca+2 ions level leads to binding of ca+2 with a subunit of troponin on actin
filament and remove the masking of active site for myosin attachment.

16. ● Myosin heads become enrgized by using the energy from ATP and it attaches to binding
site of actin filament to form a cross bridge.
● This pulls the attached actin filament toward the centre of A - band.
● Z - line attached to actins are pulled inwards causing shortening of sarcomere i.e;
contraction.
● The myosin releasing the ADP and P1 goes back to its relaxed state. A new ATP binds and
the crossbridge is broken.
● The ATP is again hydrolysis by myosin hesd and the process continues till the ca+2 ions
are pumped back to sarcoplasmic cisternae resulting in masking of actin filament.
● This causes the return of Z - line back to their original position i.e; relaxation.

20. NEUROMUSCULAR JUNCTION
● Neuromuscular junction also called myoneural junction.
● It is the site of chemical communication between a nerve fibre and a muscle cell.
● A nerve fiber divides into many terminal branches; each terminal ends on a region of muscle fibre called the
END PLATE.
● Embedded in the end plate are thousands of receptors, which are long protein molecules that form channels
through the membrane.
● Upon stimulation by a nerve impulse, the terminal releases the chemical neurotransmitter acetylcholine from
synaptic vesicles.
● Acetylcholine then binds to the receptors, the channel open, and sodium ions flow into the end plate.
● This initiates yhe end plate potential, the electrical event that leads to contraction of the muscle fibre.

21. NEURO
MUSCULAR
JUNCTION