Lecture 7.2: Disorders of Muscle Flashcards
Myopathy
A primary disease of muscle
Dystrophy
Degeneration of tissue due to disease (genetic)
Atrophy
Wasting due to underuse
Sarcopenia
Wasting as a result of ageing
Hypertrophy
Increase in the size of an organ due to an increase in volume of its constituent
cells
Hyperplasia
An enlargement of an organ or tissue caused by an increase in the amount of organic tissue that results from cell proliferation
Myosatellite Cells/ Satellite Cells
Aka muscle stem cells
Small multipotent cells with very little cytoplasm found in mature muscle
Skeletal Muscle Repair
Cells cannot divide, but can regenerate by mitotic activity of satellite cells, so that hyperplasia follows muscle injury
Satellite cells can also fuse with existing muscle cells to increase mass (skeletal muscle hypertrophy)
(Adult) Cardiac Muscle Repair
Is incapable of regeneration
Following damage, fibroblasts invade, divide, and lay down scar tissue
Smooth Muscle Repair
Retain their mitotic activity and can form new smooth muscle cells
This ability is particularly evident in the pregnant uterus where the muscle wall
becomes thicker by hypertrophy (swelling) and by hyperplasia (mitosis) of individual cells
Remodelling of Skeletal Muscles
Contractile proteins are replaced every two week
If destruction exceeds replacement then atrophy occurs
If replacement exceeds destruction then hypertrophy occurs, accompanied
by metabolic changes and an increase in blood flow
Effect of Exercise on (Remodelling of ) Skeletal Muscles
Exercise also induces an increase in the number of mitochondria in skeletal muscle
Induces the release of myokines to exert systemic effects
Adjustment of Muscle Length
Frequent stretching leads to the addition of sarcomeres and an increase in power
Inactivity leads to shortening
Disuse Atrophy
Seen in bed rest, limb immobilisation and sedentary behaviour
Affects extensor muscles more than flexor muscles
Loss of contractile proteins leads to reduced fibre diameter and a loss of power
Sarcopenia
Affects 5-10% of >65 year olds
Heat generated during muscle contraction is vital in maintaining body temperature
Risk of hypothermia increases with age
Sarcopenia can be effectively counteracted by resistance training
When does skeletal muscle mass begin to decrease?
Skeletal muscle mass starts to decline from 30 years of age, with a 50% loss of by the age of 80
What is atrophy accompanied by?
Atrophy is accompanied by an increase in connective tissue (including fat)
Denervation Atrophy
Lower motor neuronlesions (i.e. damage occurring between the spinal cord and muscle) are associated with weakness, loss of tone (flaccidity) and muscle atrophy
Neural Regeneration
If cell bodies remain intact, severed axons in the peripheral nervous system can undergo repair
This is supported by proliferating Schwann cells
Once neuromuscular junctions are re-established, muscle function is restored
Ectopic Pacemaker
An excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the heart
Myasthenia gravis: What is it?
An autoimmune disease, associated with the destruction of the end-plate ACh receptors
Body creates Abs against post synaptic nicotinic receptors, this causes destruction as well as blockage. Means ACh cannot stimulate receptors and generate AP, leading to muscle weakness
This is accompanied by loss of junctional folds at the end-plate, and the widening of the synaptic cleft
Myasthenia gravis: Symptoms (4)
Facial weakness, drooping eyelids (ptosis) and double vision
Difficulty speaking, swallowing and breathing (in severe cases)
Fatigability and sudden falling due to reduced ACh signalling (limb weakness)
Severity of disease influenced by general state of health and emotion (e.g. tiredness and stress).
Myasthenia gravis: Management and Treatment
Avoiding anything that triggers the symptoms (tiredness/stress/medications)
Acetylcholinesterase (AChE) inhibitors, such as neostigmine and
physostigmine, increase ACh levels in the synaptic cleft
Surgery to remove the thymus gland
Botulism
Condition affecting neuromuscular transmission
Botulinum toxin (e.g. BoNT-A)
Released by the bacterium Clostridium botulinum blocks ACh release, leading to paralysis, e.g. of respiratory muscles