Definitions regarding Muscle Contraction

1. Definitions Regarding Muscle
Contraction
Dr.Sara Sadiq

2. Muscle
• Contractile unit of the body
• Cellular arrangement shows
banded appearance
• Cell membrane=> sarcolemma
• Cytoplasm=> sarcoplasm
• Types?????

3. Myofibrils
• Individual muscle fiber
• Contain
1500 myosin(thick)
filaments
3000 actin (thin) filaments

4. Structure
• I-band =>Light band containing actin
filament
• A-band =>Dark band containing actin
and myosin filament where they
overlap
• H-zone => light area in center of A-
band. Seen when muscle is stretched
beyond its resting length
• M-line =>dark line in center of H-zone
• Z-disc =>disk of filamentous protein to
which actin filaments are attached.
They attach myofibril together

5. Sarcomere
• Portion of myofibril b/w two z-
disc
• ½ I-band + 1 A-band + ½ I-band
• Structural and functional unit of
muscle fiber
• Contraction => reduces length
• Relaxation => increases length

6. Motor Unit
• All muscle fibers are supplied
by single motor neuron,
collectively called as motor
unit

7. Muscle Twitch
• Contractile response of a skeletal muscle to single
stimulus

8. Isometric Contraction
• Iso => same
• Metric => length
• Length of muscle remain same but tension is
developed in the muscle
• No external work is done
• e.g.
1) contraction of arm muscle when trying to
push a wall
2) maintaining posture against gravity

10. Isotonic Contraction
• Iso => same
• Tonic => tone or tension
• Tension in the muscle remains same
while its length decreases
• External work is done
• E.g.
1) Contraction of muscle while lifting
weight
2) Contraction of leg muscle during
running

12. Summation Of Muscle Contraction
• Adding together of individual
muscle contraction to give
strong muscle contraction

13. Tetanization
• Muscle is stimulated at
higher frequency successive
contractions fuse together
and can not be
distinguished from one an
other
• Critical frequency => lowest
frequency at which
tetanization occurs

14. Asynchronous Summation Of Motor Unit
• In coordinate summation of
motor unit
• Importance => tetanization
does not occur even when
frequency is great enough

15. Muscle Fatigue
Loss of capacity of muscle to respond to stimulus
Causes:
• Prolonged and strong contraction
• Glycogen depletion
• Lactic acid accumulation
• Decrease neuromuscular transmission
• Decrease blood flow

16. Muscle Hypertrophy
• Increase muscle size due to forcefull
muscular activity for a long period of
time

17. Muscle Atrophy
Decrease size of muscle
Causes:
• Muscle not used for prolonged time
• Muscle denervation

18. Rigor Mortis
After death muscle contracts
and become rigid
Cause:
• Loss of ATP---> needed for
separation of cross bridges

19. Muscle Fasciculation
• An abnormal impulse in motor nerve causes
whole motor unit to contract like a wave
over the skin of that motor unit
• Cause:
• Destruction of anterior motor neuron
• E.g. poliomyelitis