a sarcomere is nothing but unit of contraction in muscle. this slide show explains in detail about contraction in myology

1. SARCOMERE- A
CONTRACTILE UNIT
RADHIKA CHINTAMANI
ASST. PROFESSOR
OMT

2. CONTENTS
Definition
Mechanism of contraction
Types of muscle contraction: concentric, isotonic and
isokinetic.

3. Sarcomere
The portion of the myofibril that is located between two Z
disks is called the sarcomere.

4. The portion of the sarcomere that extends over both the
length of the thick filaments and a small portion of the
thin filaments is called the anisotropic or A band.
Areas that include only actin filaments are called
isotropic or I bands.

5. The terms anisotropic and isotropic refer to the behavior
of these portions of the fibers when light shines on them.
The central portion of the thick filament (A band area) in
which there is no overlap with the thin filaments is called
the H zone. H zone consists of wide middle portion of
thick filament known as M band.

6. Mechanism of contraction
A. Rest stage: the active site is
inactive and actin attachment site
remains closed
B. Calcium channels are opened up
leading to ATP influx thus
activating the inactive site of
myosin and the calcium helps in
bondage of myosin to actin.
C. Once the bond of actin myosin that
is cross bridge formation is formed
due to the swiveling mechanism,
the myosin shifts its attachment to
another site of actin: this leads to
contraction.

7. D. Recharging: once the ATP is
consumed and there is fatigue or
relaxation seen, the bond breaks.
E. Relaxation: The rest stage is re-
attained , thus stating the closure of
the actin site and inactive state
attainment of the myosin site

8. Types of contraction
Isotonic:
 Concentric
 Eccentric

9. Isometric
Isokinetic: An isokinetic muscle contraction is one in
which a muscle shortens as it contracts with constant
speed of movement