Skeletal 2 Flashcards

1
Q

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

A

Lecture Slide

Sequence:
1. NMJ
2. EC coupling
3. Muscle twitch

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2
Q

Modulation of contraction Summation & tetanus:
Draw a diagram showing muscle twitches

A

Lecture slide:

summation:
second stimulus causes release of more Ca2+

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3
Q

Modulation of contraction β-adrenergic activation:

General process and what do
Adrenaline/β-agonists do…

A

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.

  1. increased force by increasing SR Ca2+ release (phosphorylation of RyR1).
  2. Speed up relaxation (phosphorylation of PLB, increased SR Ca2+ load).

3.Slow muscle fibres may show opposite effects

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4
Q

Types of contraction

A

Isometeric
isotonic (concentric, eccentric)

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5
Q

What is isometeric contraction

A

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

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6
Q

What is isotonic contraction

A

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.

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7
Q

Two types of isotonic contraction

A

Concentric: muscle shortening
Eccentric: Muscle is lengthening

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8
Q

What is isotonic concentric contraction
- diagram showing movement, relationship of force of muscles and weight, def and example

A

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.

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9
Q

Isotonic (Eccentric) Contraction:

  • diagram showing movement, relationship of force of muscles and weight, def and example
A

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”.

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10
Q

What is assosciated with eccentric contractions

A

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

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11
Q

what form of movement is strengthening exercises

A

eccentric

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12
Q

what is Delayed Onset Muscle Soreness

A

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.

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13
Q

why was lactic acid theory for muscle soreness rejected

A

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.

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14
Q

Force length relationship - define and relation to muscle

A

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

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15
Q

what does the force look like on a graph at passive force, stimulus and zero force.

A

lecture slide

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16
Q

Draw the Active Force Length Relationship graph

A

lecture slide

  • the more length, the more tension until it reaches the optimal resting length then there is a loss of tension.
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17
Q

define:
Preload
afterload
Total load

A

Preload is the load experienced by the muscle in a relaxed state, (muscle length)

Afterload is the load a muscle works against during contraction.

Total load is the sum of the preload plus the afterload.

18
Q

The Force Velocity Relationship:
what is it
- what is Vmax

A

When muscle is allowed to shorten against a constant force (isotonic contraction), both the velocity and the extent of shortening are inversely related to the force on the muscle.

The force-velocity relationship describes the fact that the force-generating capacity of the muscle also depends on the contraction velocity and on whether it is an eccentric or concentric contraction

Vmax, the maximum velocity of shortening, reflects the maximum rate of cross-bridge
turnover.

19
Q

Force Velocity Relationship:
- What happens if load opposing contraction is INCREASING the velocity of shortening should…

  • What happens if the load on the muscle is constant the speed of shortening should be …
  • What happens if the load weight is increasing on the muscle what type contraction…
  • when is maximum force developed
A

the velocity of shortening should DECREASE

the speed of shortening should be constant – Isotonic contraction

eccentric contraction

Maximum force, is developed when there is no shortening (isometric contraction). The velocity of shortening is maximal when no force is developed.

20
Q

Equation for force, work and power

A

Force = mass (kg) x acceleration due to gravity (9.807 m s-2) Unit: Newton (N)

Work = force x distance Unit: Joule (J)

Power = work/time Unit: Watt (W)
= force x velocity.
= force x distance/time

21
Q

what limits maximum sprinting

A

The force-velocity relationship is the most important contractile property of muscle that limits maximum sprinting speed

22
Q

Isometric contraction: produces what/doesnt produce what

A

No Movement = No
Work & No Power.

but you are developing force

23
Q

Energetics of Muscle Contraction:
how fast can ATP be made and used by muscle

A

In order to sustain contractile activity skeletal muscle metabolism must produce molecules of ATP as rapidly as they break down.

24
Q

What sources of ATP in muscle

A
  1. Creatine phosphate releases stored energy to convert ADP to ATP when converting to creatine
  2. Aerobic metabolism provides most ATP needed for contraction
  3. At peak activity, anaerobic glycolysis needed to generate ATP
25
Q

3 different energy sources

  • draw graph
A

ATP-CP: Immediate energy supply

Glycolysis:
Short term energy supply system

Aerobic:
Long term energy supply system

26
Q

Skeletal muscle fibres can be classified depending on..

A

fibre type.

27
Q

Differences in contractile proteins between fibre types:

How many isoforms for each fibre type

A

o Actin: 2 isoforms
o Tropomyosin: 2 isoforms
o Myosin heavy chain: at least 7 isoforms

28
Q

Classification of fibres and what makes them different to eachother

A

Classification:
1. Type I (slow, oxidative),
2. Type II B (fast, glycolytic) and
3. Type II A (fast, oxidative)

Differences among muscle fibre types are due to differences in their proteins. In skeletal muscle there are two different isoforms of both actin and tropomyosin, and at least seven different isoforms of the myosin heavy chain

29
Q

Causes of muscle weakness

A
  • Muscle fatigue
  • Muscular dystrophy. * Sarcopenia
30
Q

Muscle fatigue defination and cause

A

Defined as a failure to maintain the required, or expected, power output, leading to reduced muscle performance.

Cause not clearly established:
Many potential sites between brain and the contractile protein interactions

31
Q

Muscle fatigue:
Types and description

A

Central fatigue
* Decreased activation from CNS.
* Decreased number of motor units recruited.

Peripheral fatigue
Affecting the cellular mechanisms that control force.
- Smaller Ca2+ transient
- Reduced Ca2+ sensitivity of the myofilaments
- Slower crossbridge cycling

32
Q

Causes of central and peripheral fatigue

A

– accumulation of metabolites
– depletion of muscle energy supplies (eg. glycogen).

33
Q

Metabolite accumulation theory of fatigue

A

Lecture slide

34
Q

Duchenne’s Muscular Dystrophy (DMD) Clinical features

A
  • Muscles normal at birth but rapid muscle degeneration and Increasing skeletal muscle weakness & degeneration

– wheel chair by ~ age 10
– respiratory failure ~ age 20 -> problems with skeletal muscles affect eating , breathing , chewing

  • Cardiac involvement (dilated cardiomyopathy)
  • Caused by mutation in the dystrophin gene which causes loss of dystrophin
  • DMD has an X-linked recessive inheritance and is passed on by the mother, who is a carrier.
35
Q

What is early stage of DMD characterised by and effect on enzymes

A

Early stage of DMD is characterised by increased cell membrane permeability:

  • soluble enzymes such as creatine kinase leak out.
  • ions such as Ca2+ enter.
36
Q

Draw the diagram of aging related loss of muscle function

and example of this

A

Lecture slide

Sarcopenia “poverty of flesh”
* A primary consequence of aging.
* Muscle mass/body mass ratio decreased.
* Significant loss of muscle strength

37
Q

Describe sarcopenia
-is it reversable
-what happens to fibres
- changes to type 1/2 fibres
-changes to capillary:fibre ratio

A

Intrinsic age-related changes in muscles and in muscle fibers that are immutable and irreversible.

  • Denervation of fast fatigable fibers and motor units, and motor unit remodeling.
  • An increase in the % of Type I fibres (SO), with no change in mean fibre XSA for Type I or Type II fibres.
  • A decrease in the capillary:fibre ratio
38
Q

The power developed by a muscle depends on ..

A

The power developed by a muscle depends on the rate of muscle shortening

No shortening = no developed power = no work done.

39
Q

Mechanical power output

A

The rate at which work is done by a muscle, its mechanical power output, depends on the
force that the muscle can develop, the rate at which it can shorten, and the rapidity with which it can be turned on at the beginning of a contraction and turned off at its end.

40
Q

myosin isoforms have different ATPase activities and so what isoforms are best for long runs vs sprints

A

Type II B (fast glycolytic) fibres have high rates of ATP turnover. High energy phosphate
stores are extensive, and ATP is reconstituted via relatively inefficient, but rapid, anaerobic
glycolytic metabolism. Suitable for short sprints and middle distance running.

Type I (slow oxidative) fibres have lower rate of ATP turnover. Plentiful mitochondria and myoglobin. ATP is reconstituted via relatively efficient, but slow, oxidative metabolism. Suitable for sustained long distance running.