T3 L3: Physiology of skeletal muscle Flashcards
How does muscle grow?
By hypertrophy
There is synthesis of myofilaments, addition of sarcomeres, satellite cell activation, angiogenesis, and vascularisation
What is the effect of endurance exercise on muscles?
Increased fibre diameter, blood supply, and mitochondrial content
There will be more oxidative enzymes
Fibres will become slower (transformation from IIx to IIa fibres)
What is the effect of non-endurance exercise?
Conversion of IIa into IIx fibres
There is increase in IIx fibre size due to increased numbers of sarcomeres and myofilaments
Results in much larger muscle
What is the effect of ice on muscles?
It reduces swelling by reducing perfusion
Good after an acute injury like a sprain, or after overuse injury
What is the effect of heat on muscles?
It helps to relax and loosen muscles
Used before activities that irritate chronic injuries like strains because it increases blood flow
What is the mechanism behind Aspirin?
It inhibits COX which reduces the synthesis of prostaglandins and part of the arachidonic acid
What are the side effects of blocking prostaglandins and arachidonic acid?
Gastro-intestinal adverse effects
Eg. stomach bleeding, ulcers
What are the anabolic effects of testesterone?
- Increases protein synthesis
- Decreases catabolism
- Reduces fat (increases BMR and increases differentiation to muscles rather than fat cells)
What is catabolism?
Breaking down of large molecules
What is BMR?
Basal metabolic rate
What are the effects of anabolic steroid abuse?
They’re used to increase muscle size and strength.
Large doses are needed
Male- testicular atrophy, sterility, baldness
Female- breast/uterus atrophy, menstrual changes, facial hair, deepening of voice
What is the effect of bed-rest of muscles?
Weight-bearing muscles atrophy
- Decreased muscle protein synthesis
- Myofibrillar breakdown
- Reduced strength
- Loss of type I fibres
Transition of type I to type IIa
Treated by resuming minor activity early
How does a contracture form?
If the limb is immobilised for a long period of time, the process of growth is reversed so sarcomeres are removed and the muscle shortens
Why do multinucleate cells not divide?
Because mitosis with multiple nuclei is usually impossible
How are muscles regenerated?
Satellite cells are activated which proliferate, differentiate, and fuse onto fibres and contribute to forming multinucleate myofibers
What are the progenitor cells of muscles?
Satellite cells
What is myalgia?
Muscle pain caused by injury, overuse, infections, or autoimmune
What is myopathy?
Muscular weakness due to muscular fibre dysfunction
What is paresis?
Weakness, partial loss, or impaired voluntary movements,
What are fasciculations?
Involuntary large visible neurogenic twitches in single motor units
-Usually occur in lower motor neurone diseases
What are fibrillations?
Small involuntary myogenic spontaneous contractions of individual muscle fibres
Can be identified by electromyography
What is rhabdomyolysis?
Rapid breakdown of skeletal muscle
Causes: trauma, drugs, hyperthermia, ischaemia to skeletal muscle
Symptoms: muscular pain, vomiting, confusion, dark urine
What is the treatment for Rhabdomyolysis?
Intravenous fluid to treat shock and haemodialysis to clear the blood
How is Rhabdomyolysis diagnosed?
Urine will be very dark and will be tested for myoglobin
Hyperkalaemia is tested for because when muscle cells lyse, they release K+
What is myasthenia gravis?
Progressive muscle weakness and fatigability
Caused by a depletion of nicotinic ACh receptors because of autoimmune destruction of the receptors
What are some initial symptoms of myasthenia gravis?
Ptosis and diplopia because those muscles are so weakened
What is the treatment for myasthenia gravis?
-AChE inhibitors
Eg. Pyridostigmine increases ACh activity at the NMJ
Eg. Edrophonium is used for diagnosis because it should temporarily improve symptoms
- Thymectomy reduces 70% of symptoms
- Immunosuppressive drugs
- Plasmapheresis: removal of anti-AChR antibodies from the blood
What is Spinal muscular atrophy (SMA)?
AKA floppy baby syndrome
It’s caused by the death of lower motor neurones in the anterior horn of the spine
Aetiology: autosomal recessive gene
What is meant by fibre type grouping?
Different types of muscle fibres grouped together
What is malignant hyperthermia?
A rare genetic susceptibility to gas anaesthetics causing SERCA to work too hard
Symptoms: increased O2 consumption, CO2, acidosis, tachypnea, muscles overheat, the body overheats, muscles are damaged (rhabdomyolosys), hyperkalaemia, muscles become rigid
What is the treatment for malignant hyperthermia?
Dantrolene sodium will stop the abnormal calcium release by inhibiting the ryanodine receptor
What is Gower’s sign?
A sign of muscular dystrophy where the patient is too weak to stand up so has to use their hands
What is duchenne muscular dustrophy?
An X-linked disease caused by a mutation on the dystrophin protein
