At a clinical level, there are two main things to consider in relation to tone in the muscle:
- Neurogenic component: overactive muscle contraction
- Biomechanical component: stiffening and shortening of the muscle and other soft tissues due to immobility
Illustration: Muscle > Muscle fibre > Sarcomere
Muscles consist of contractile tissue and connective tissue. The working mechanism of contractile tissue is myosin and actin myofilaments which interlock.
Units of the contractile tissue are sarcomeres which lie in series and form myofibrils. Bundles of myofibrils form muscle fibres. These fibres are held together to form fascicles which form the entire muscle.
Connective tissue surrounds and binds each fibre. This is made up of collagen and elastic fibres.
After a stroke there may be:
- A reduction in the number of sarcomeres (atrophy)
- A decrease in overall length of sarcomeres (muscle becomes shorter)
- A relative increase in proportion of connective tissue (muscle becomes stiffer)
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Page last reviewed: 01 May 2020