The document discusses the mechanism of muscle contraction in skeletal muscles, focusing on structure and physiological processes such as excitation-contraction coupling. It details how muscle twitch, summation, tetanus, and the staircase phenomenon contribute to muscle functionality. Additionally, it highlights the relationship between muscle length, tension, and types of contractions (isometric, isotonic, concentric, eccentric).

1. Ms.Shilpi Damor
Assistant Professor, Deptt. of Zoology
Poddar Group of Institutions,jaipur
MECHANISM OF MUSCLE
CONTRACTION

2. Skeletal Muscle
Actin
A.Muscle Fiber
1. Sarcolemma
2. Sarcoplasm
3. Myofibrils – contractile elements
Myosin
a.Actin Filament
F- actin strands
Tropomyosin
Troponin ( T,I,C)
b.Myosin Filament

9. Structure Of Myofibril

15. Events of muscle contraction

17. Conformation change in troponin causes it to shift and thus
expose myosin binding site

18. Excitation–Contraction
Coupling
Excitation–contraction coupling is the physiological process of
converting an electrical stimulus to a mechanical response. It is the link
(transduction) between the action potential generated in the
sarcolemma and the start of a muscle contraction.

20. NOTE:
• Muscle contractions can be described based on two variables:
length and tension.
• A muscle contraction is described as isometric if the muscle
tension changes but the muscle length remains the same.
• In contrast, a muscle contraction is isotonic if muscle tension
remains the same throughout the contraction.
• If the muscle length shortens, the contraction is concentric; if
the muscle length lengthens, the contraction is eccentric.
• Therefore, neither length nor tension is likely to remain the
same in muscles that contract during loco motor activity.

27. Muscle twitch

28. Muscle twitch
• A single action potential causes a
brief contraction followed by
relaxation
• This response is called a muscle twitch.
• The twitch starts about 2 ms after the
start of depolarization of the membrane,
before repolarization is complete

29. Muscle twitch
• Duration of the twitch varies with the type of muscle
being tested
• Fast muscle fibers, primarily those concerned with
fine, rapid, precise movement, have twitch durations
as short as 7.5 ms
• Slow muscle fibers, principally those involved in
strong, gross, sustained movements have twitch
durations up to 100 ms
• The strength of twitch depends on the number of
motor units activated

30. Summation and tetanus

31. Summation
• If 2 stimuli are delivered in rapid succession the
second twitch will be greater than the first
• This only occurs if repolarization is not
complete
• The tension developed during summation is
considerably greater than that during the single
muscle twitch

32. Tetanus
• With rapidly repeated stimulation, activation
of the contractile mechanism occurs
repeatedly before any relaxation has
occurred
• Individual responses fuse into one
continuous contraction
• Such a response is called a tetanus or
tetanic contraction

33. Tetanus
• It is a complete tetanus when there is no
relaxation between stimuli and an incomplete
tetanus when there are periods of incomplete
relaxation between the summated stimuli
• During a complete tetanus, the tension developed
is about four times that developed by the
individual twitch contractions

34. Staircase phenomenon (treppe)
• When a series of stimuli is delivered to skeletal
muscle, there is
an increase in the tension developed during each
twitch until,
after several contractions, a uniform tension per
contraction is reached
• This phenomenon is known as treppe, or the
"staircase" phenomenon
• This is the basis of “warm up”
• Treppe is believed to be due to increased
availability of Ca2+ for binding to troponin C,
accumulation of heat or effect of pH
• It also occurs in cardiac muscle although
cardiac muscles cannot be tetanised
• It should not be confused with summation of
contractions and tetanus

35. Staircase phenomenon (treppe)