19. Macroscopic events of muscle contraction Flashcards Preview

2nd Midterm Essay 17-32 > 19. Macroscopic events of muscle contraction > Flashcards

Flashcards in 19. Macroscopic events of muscle contraction Deck (8)
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1
Q

Elements:

A
  • Amongst contractile components of the muscle (CC/sarcomere), muscle contains serial elastic components (SEC) and parallel elastic components (PEC), too.
  • During stimulation, first the SEC elements will reach equilibrium with load because the contraction of CC (no movement yet, only tension).
    • This is followed by constant tension.
2
Q

Twitch:

A
  • To an appropriate stimulus muscle answers with a contraction: a muscle twitch occurs.
  • Muscle twitch = a single contraction-relaxation cycle
  • An AP is not directly followed by a calcium transient:
    • The observable latency is partly derived from the latency of measuring instruments, or it’s a realbiological latency.
  • The sum of the two latencies is called virtual latency.
3
Q

Isometric contraction:

A
  • Only tension is changed but not the length of the muscle
  • Occurs when muscle tries to lift such heavy load which it is not able to move
4
Q

Isotonic contraction:

A
  • Muscle shortens with constant tension
  • Regular physiological behaviour
5
Q

Auxotonic contraction:

A
  • In natural conditions, muscle shortens and in the same time, tension is also increasing in it.
  • Example: when a muscle works against a spring.
6
Q

Preload:

A
  • After stimulation contractile machinery will first stretch SEC elements (isometric period), and when tension reaches equilibrium with the load, contraction becomes isotonic, twitch is continued with shortening of the muscle.
  • Most of the contraction in association with locomotion are like that.
7
Q

Afterload:

A
  • If we block the free movement of the muscle with a frame, then no more shortening is possible from a certain level, but muscle is still able to increase tension.
  • At the beginning it is isotonic, then an isometric period follows.
8
Q

Summation

A

addition of skeletal muscle contraction forms caused by different reasons

  • All-or-none: A single fiber under constant metabolic conditions contracts according to the “all-or-none” law = to an adequate stimulus, response is maximal, to smaller stimulus there is no response.
  • Quantal summation: If the increase of tension is caused by the participation of more and more fibers (addition of elementary units). If the demand is higher, a more frequent AP recruits more and more fibers.
  • Contraction summation: Repetitive stimuli may cause increasing contraction, for the previous calcium transient may not be completed when a new stimulus elicits additional calcium release. Thus, the amplitude of contraction is increased.
  • Staircase effect (treppe): New stimuli applied shortly after the end of a twitch may elicit new contractions with gradually increasing amplitudes: it is caused by IC calcium, which has no time to be removed in between stimuli (warming up).
  • Tetanus: If we apply stimuli with increasing frequency we enhance possible summation modes: finally muscle reaches maximal contraction state – a tetanus is formed.