Muscle in Health and Disease Flashcards
What is the role of muscle?
- 40% body mass
- 80% water
- store for intracellular ions
- important for heat production
What are the properties of skeletal muscle?
- actin and myosin sarcomere bands causing contraction
- individual cells fuse into multinucleated fibres
- linked to motor neurons
- many form a motor unit contracting together
- satellite cells
What are satellite cells?
- repair cells
- take up central location in damaged cells
- as they mature and repair muscle they are pushed peripherally so centre becomes full of contractile proteins
What happens if an axon is damaged?
- in periphery/spinal cord
- muscle fibres of motor unit become inactive
- undergo atrophy = small angulated muscle fibres
- sprouting of neighbouring motor neuron axons synapse with denervated fibres
- motor units enlarge and appear as groups
- if these neurons die = group atrophy
What is infantile hypotonia?
- floppy baby syndrome
- low muscle tone
- myopathic cause = most fibres small and few massive hypertrophic fibres
What are the 2 types of congenital fibre disproportion?
1) large type 1 muscle fibres paler and small type 2 muscle fibres darker
2) small type 1 paler and large type 2 muscle fibres darker
(slow type 1 aerobic metabolism and fast type 2 mixed aerobic and anaerobic)
What is sarcopenia?
- age related
- 0.5-1% muscle mass per year after 50
- no difference for men and women
- if physically inactive more muscle mass loss
What are the general symptoms of muscle disorders?
- pain and weakness
- twitching and cramps
- muscle atrophy and contractures
- family history
- drug use/exposure
- endocrine disorders
How are muscle disorders diagnosed?
- biopsy(gold standard, variation in fibre size, necrosis, infiltrate of inflammatory cells)
- EMG (fibrillation potential and positive waves when muscles at rest = damage, release of calcium from nearby damaged muscles causing neighbouring to contract)
What are the common inflammatory myopathies?
- polymyositis
- dermatomyositis
- both the same and only difference is can get rash with dermatomyositis (purple, streaky)
- autoimmune
- proximal muscle weakness
- associated with microbial infection
- starts at periphery of fascicle
- macrophages infiltrate into muscle
- weakening of large proximal muscles of shoulders/arm/thigh
- elevated creatine kinase
What is the significance of subcutaneous calcifications?
- in muscles and skin
- inflammatory myopathy sign
- anti-nuclear antibody positive -> anti-jo` antibody
What is the treatment for inflammatory myopathy?
- corticosteroids
- high dose of prednisolone per day
- maintain until creatine kinase normal
- also azathioprine and methotrexate
What is the prognosis of inflammatory myopathy?
- death from malignancy, infection, pulmonary involvement
- more likely death if anti-jo 1 positive
What is inclusion body myositis?
- most common muscle disease of elderly
- attacks particular set of muscles
- finger flexors and shoulder abductors
- knee extensors (quads)
- poor prognosis
- mild creatine kinase elevation
- polyneuropathy
- dysphagia as affects oesophagus skeletal muscle at top 1/3
What does a biopsy for inclusion body myositis show?
- empty vacuoles
- cellular material clumps
- filamentous inclusions containing presenelin 1, apolipoprotein E, hyperphosphorylated tau, amyloid like material
