Flashcards in Alterations in Skeletal Muscle Function Deck (84):
What are the functions of skeletal muscle?
How can skeletal muscle function be modified?
- Remodelling of muscles
- Alterations of neuromuscular transmission
- Muscular dystrophies
- Other myopathies
What can happen to the contractile proteins actin and myosin?
They can increase and decrease in nuber
When does the remodelling of muscles occur?
How long does it take to replace a contractile protein?
What happens if destruction > replacement?
What happens if replacement > destruction?
Why does skeletal muscle change with exercise?
What happens to skeletal muscle with exercise?
- Sarcoplasmic reticulum swells
- Increased volume of mitochondria
- Increased Z band width
- Increased ATPase
- Increased density of T tubule systems
- Increased in no. of contractile protein
Does exercise cause hyperplasia?
Give an example of a high intensity activity?
Weight lifting, e.g. 70-90% intensity, short duration, modest frequency
What is the effect of high intensity activity?
Stimulates contractile protein synthesis, fatter muscle fibres and larger muscles, which increases muscle mass and stength
What can high intensity activity lead to?
Give an example of an endurance exercise
Jogging e.g. low intensity, for a longer duration, 5 times a week
What is the advantage of endurance exercise over high intensity exercise?
It increases endurance, but without hypertrophy
What does endurance exercise stimulate?
Synthesis of mitochondrial proteins and vascular changes
What is the result of the stimulation of mitochondrial proteins and vascular changes in endurance exercise?
Allows for greater oxygen utilisation
What does endurance exercise result in a shift to?
Oxidative metabolism of lipids
What can lead to disuse atrophy?
- Bed rest
- Limb immobilisation
- Sendentry behaviour
What happens in disuse atrophy?
Loss of protein leading to reduced fibre diameter, leading to loss of power
At what age does muscle atrophy occur?
How much muscle mass has been lost my the age of 80?
What is the loss of muscle mass with ageing called?
What can muscle atrophy with age lead to?
Problems with temperature regulation
How can muscle atrophy with age lead to hypothermia?
Not enough muscle mass to generate heat themselves
What is denervation atrophy known as?
Neurogenic muscular atrophy
What are the signs of lower motor neurone legions?
How quickly does reinnervation need to occur for recovery from denervation atrophy?
Within 3 months
What happens in a muscle with spinal muscular atrophy?
The atrophic fibres are small, angulated and brightly eosinophilic, with an apparent increase in number of nuclei
What causes an increase in muscle length?
What happens when muscles lengthen?
What changes of neurology occur in adjustment of muscle length?
- Stretch response
- Stretch reflex
What changes to viscoelastic properties occur in adjustment of muscle length?
Change in connective tissue alignment
What reduces the length of muscle?
What are the steps in neuromuscular transmission?
- Opening of presynaptic voltage-dependant calcium channels, causing ACh release
- ACh binds to nicotinic receptor
- Binding of ACh to its receptor opens the sodium channel
- Sodium entry depolarises muscle
Where are nicotinic receptors located?
On folded end-plate regions
What does the depolarisation of muscle following neuromuscular transmission cause?
Release of calcium ions from SR, therefore muscle contraction
How is ACh terminated in neuromuscular transmission?
What happens at high motor neurone firing rates?
ACh release decreases by 25%
What needs to be true of ACh receptors?
They must be occupied
Give an example of a neuromuscular junction disorder?
What causes Myasthenia Gravis?
Autoimmune destruction of the end patch ACh receptors (IgA antibodies to AChRs)
What is the result of the autoimmune destruction in Myasthenia Gravis?
What are the symptoms of Myasthenia Gravis?
- Sudden falling
- Double vision
- Effected by general state of health, e.g. fatigue and emotion
What causes the fatiguability and sudden falling in Myasthenia Gravis?
Sudden ACh release
What is ptosis?
Drooping upper eyelids
How to the symptoms of Myasthenia Gravis change over time?
What is the treatment for Myasthenia Gravis?
- Acetylcholinesterase inhibitors
- Immune suppressants
What does plasmapheresis do?
Remove harmful antibodies from patients serum
Give 2 toxins that inhibit neuronal Na + channel
What toxin inhibits Ca 2+ channel?
What toxin inhibits K + channel?
Give 2 toxins that inhibit ACh release?
Give 2 toxins that inhibit acetylcholinesterase
Give 3 toxins that inhibit the muscle Na + channel
Give 2 toxins that stimulate AChR channel?
Give 2 toxins that inhibit the AChR channel?
What are the two main causes of muscular dystrophies?
Give 8 types of muscular dystrophy
- Duchenne type
- Becker type
- Limb gurdle
- Congenital Mersonin Deficiency
Where does Duchenne and Becker type muscular dystrophy affect?
- Upper legs
- Upper arms
What causes Duchenne type muscular dystrophy?
Complete absence of dystrophin
What causes Becker type muscular dystrophy?
Altered truncated dystrophin
Where does Emery-Dreifus muscular dystrophy affect?
Where does limb gurdle muscular dystrophy affect?
- Upper arms
- Upper legs
What causes limb gurdle muscular dystrophy?
Deficiency of sarcoglycans
Where does facioscapulohumeral muscular dystrophy affect?
Where does distal muscular dystrophy affect?
Where does occulopharyngeal muscular dystrophy affect?
What causes Congenital Mersonin Deficiency?
50% deficiency of merosin
What are the consequences of protein abnormality?
- Muscle fibres tear themselves apart on contraction
- Enzyme creatine (phospho)kinase liberated into serum
- Calcium enters cell causing cell death
- Pseudohypertrophy (swelling), before fat and connective tissue replace muscle fibres
When does Duchenne muscular dystrophy first become apparent?
What is the sign of Duchenne muscular dystrophy?
What is Gower’s sign?
Pushing on knees to give power
What is meant by contractures?
Imbalance between agonist and antagonistic muscles
How is Duchenne muscular dystrophy treated?
What is being done to help with Duchenne muscular dystrophies?
Genetic research, e.g. into gene therapy, stem cells etc
What can skeletal muscle disorders be caused by?
What is the root of denervation disorders?
What are myopathies?
Primary muscle diseases
Give 5 types of myopathies
- Electrolyte imbalances
Give 3 examples of inflammatory myopathies
Give an example of a myopathy caused by an electrolyte imbalance?
What can the result of thyrotoxicosis be?
Increased basal metabolic rate and protein catabolism