Skeletal 2 Flashcards
Time course for activation of contraction:
Draw the graphs for neuron membrane potential in mV, Muscle fibre membrane potential in mV and development of tension during one muscle twitch
Lecture Slide
Sequence:
1. NMJ
2. EC coupling
3. Muscle twitch
Modulation of contraction Summation & tetanus:
Draw a diagram showing muscle twitches
Lecture slide:
summation:
second stimulus causes release of more Ca2+
Modulation of contraction β-adrenergic activation:
General process and what do
Adrenaline/β-agonists do…
Adrenaline and B agonist bind to B2 adrenoceptor on muscle membrane. This activates Camp causing activation of PKA. PKA acts ont he phosphorylation on the DHPR and RYR1 receptors.
- increased force by increasing SR Ca2+ release (phosphorylation of RyR1).
- Speed up relaxation (phosphorylation of PLB, increased SR Ca2+ load).
3.Slow muscle fibres may show opposite effects
Types of contraction
Isometeric
isotonic (concentric, eccentric)
What is isometeric contraction
A contraction in which no external shortening takes place. So still producing force, but just enough to keep balance.
force of weight = force developed by muscles
What is isotonic contraction
Contraction in which movement takes place. So producing more force than the weight of the object.
So, there is mismatch between tension (force) generated by the contracting muscle and the (constant) load on the muscle.
Two types of isotonic contraction
Concentric: muscle shortening
Eccentric: Muscle is lengthening
What is isotonic concentric contraction
- diagram showing movement, relationship of force of muscles and weight, def and example
Concentric contraction: muscle length decreases against an opposing load.
Force of weight LESS THAN force developed by muscle(s)
Examples include: lifting a weight, cycling, rowing or swimming, where active muscles are shortening.
Isotonic (Eccentric) Contraction:
- diagram showing movement, relationship of force of muscles and weight, def and example
Eccentric contraction: muscle length increases as it resists a load.
Force of weight GREATER than force developed by muscle(s)
Examples include: climbing down mountains, running down hill, downward motion of “push-ups”.
What is assosciated with eccentric contractions
Muscle injury, and delayed onset muscle soreness (DOMS) are associated with eccentric contractions. Leading to muscle damage and therefore cytokine release = more muscle growth.
As muscles are activated while it is lengthening
what form of movement is strengthening exercises
eccentric
what is Delayed Onset Muscle Soreness
Not all sarcomeres lengthen evenly during eccentric contractions. Once a sarcomere ‘gives way’ it will be massively stretched as a
result of the descending limb of the force-length relationship.
Sarcomeres stretched beyond their optimal length develop less
force. The “weakest” sarcomeres in series will always lengthen first,
giving rise to the “popping sarcomere” theory.
DOMS a combination of muscle & connective tissue microtrauma,
followed by inflammatory processes and oedema.
why was lactic acid theory for muscle soreness rejected
Lactic acid theory rejected, as concentric contractions (which also produce lactic acid) do not cause DOMS.
Lactic acid returns to normal levels within one hour of exercise, and therefore cannot cause the pain that occurs much later.
Force length relationship - define and relation to muscle
The relationship between muscle length and the force generated during isometric contraction.
The maximal active isometric force a muscle can exert depends on its length
the amount of overlap between the actin and myosin contractile filaments determines the maximum isometric force a sarcomere can produce
essentially, the longer the muscle the more force potential
what does the force look like on a graph at passive force, stimulus and zero force.
lecture slide
Draw the Active Force Length Relationship graph
lecture slide
- the more length, the more tension until it reaches the optimal resting length then there is a loss of tension.