Lecture 32- Muscle plasticity: fibre types Flashcards Preview

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Flashcards in Lecture 32- Muscle plasticity: fibre types Deck (27):

What changes can we make to muscles?

larger, smaller
stronger, weaker
faster, slower
more resistant to fatigue
repair better after injury


there are ___ myHC species indentified in mammalian muscles fibres (could be more)



limb muscles myHCs include

types 1, IIa, IIx, IId and IIb


even very slow muscles (e.g soleus), contain a portion of ___ muscle fibres

fast - and this can be changed


Is fibre composition fixed or malleable?

malleable - we can change it under certain circumstances


which elements other than myHC can be altered/

Sr density, capillary density, mitochondria, fibre diameter, contractile and regulatory proteins, fibre composition

every element of muscle can be altered


My HC isoforms differ in their functional properties. They are influenced by...

hormone levels, exercise, injury and ageing

MyHC inferred from functonal histochemical, electrophoretic and immunohistochemical analysis


What are Myosin light chains thought to influence?

speed of shortening and also stabilishing the myosin head during cross-bridge cycling

There are heaps of possible combinations of mHC and Light chains in human myosin molecules - think beyond just fast and slow


top endurance athletes typically have what amount of type I fibres in their leg muscles?

greater than 80%


clenbuterol will do what to fibre composition in rats?

slow fibre to fast fibre (type II)

plus hypertrophy


Cross-reinnervation experiments gave clues as to ....

muscle fibre plasticity - muscles properties can change if the nerve input is reversed.


true or False

The type of stimuli that is sent to muscle, dictates how quickly the muscle is contracted and whether its resistant to fatigue



low freq stimulation =

high freq stimulation =

low freq stimulation = slow-twitch characteristics

high freq stimulation = fast-twitch characteristics

the total number of impulses determines the fatiguabillity of the fibres


What is the S.A.I.D (specific adaptation to imposed demand) principles

every structural element of msucle can be altered if given the proper stimulus

fibre type distribution, MyHC composition, fibre diameter, capillary density etc...

biochemical adaptations e.g mitochondrial ezymes

generally there are two adaptive responses of skeletal muscle that can be considered:
- increased or decreased use


What are the skeletal muscle adaptions in increased use?

chronic electrical stimulation

chronic stretch

compensatory hypertrophy

intermittent electrical stimulations



What are examples of potential inactivity causing disuse muscle atrophy?

himdlimb unweighting


limb (plaster) casting

prolonged bed rest

space flight (weightlessness)




In limb casting there is rapid changes in the size of the muscle, 40% of fire less in the 6 weeks.

are the changes the same with bedrest?

similar but not as makred as with plaster casting

the length at which the muscle is held is important


True or false

immobilization in the shortening position decreases muscle loss

False it accentuates muscle loss

immobilization in a lengthening position leads to better mass and function preservation - stretch is an important stimuli


What are the positives of studying muscle plasticity through electrical stimulation?

''clean'' way of investigating muscle adaptation

repeatable, quantifiable amount of ''exercise''

provides insights into other forms of muscle adaptation such as physical activity

has clinical application e.g cardiac assist

most extensively studied


How does electical stimulation result in muscle plasticity?

activates the ''fast'' muscle with ''slow'' muscle like freq.

fast muscle changes its metabolic and then its contractile properties to compltely transform into a slow muscle

these changes result from a transfomation of fast fibres into slow fibres

NOT from a loss of fast fibres with replacement of slow fibres through regeneration


What are the major changes after chronic stimulation?

increased capillary density

proliferation of mitochondria - increased oxidative status

decrase in SR and Ca2+ ATP ase

expression of different myosin and troponin isoforms

these changes all occur with different time courses


With exercise we're not stimulating the muscle continuously so the time course of changes with electicla stimulation takes ___



true of false

studies have shown changes in fatiguabililty but rarely alteration in myosin isoform expression cnverting type II fibres to type I


stimulation in some patients with SC injury have shown some evidence of a transformation of fast to slow myosins and increases in oxidative enzymes


Within the first few hours of transformation, the SR begins to ____

within 2-12 days, incraeses in
- ___________ ____________
- ___________ ____________

these changes reflect an increased metabolic activity of the muscle

Within the first few hours of transformation, the SR begins to swell

within 2-12 days, incraeses in
- mitochondrial number, oxidative enzyme activity
- capillary blood flow, o2 consumption

these changes reflect an increased metabolic activity of the muscle


The sequence of adaptive events is:

Ca2+ handling (SR is overwhelmed) ---> enzyme activities --> myosin heavy chains


True or false

Muscle metabolic enzymes, capillaries, SR and T-system are much harder to change than contractile proteins


much easier to change


With the change from fast twitch to slow twitch the atrophy should be viewed in what context?

a deliberate response of the muscle fibre to chronic stimulation - perhaps to decrease diffusion distances from the muscle fibre to the interstitial spaces which contain the capillaries

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