Smooth muscle
- Found in hollow organs and tubes such as airway and blood vessels.
- Has single nucleus per cell.
- Spindle shaped cells.
- Has no sarcomeres like skeletal muscles.
3 types of filaments
1. Thick filament
- Bundles of Myosin
- More heads available for binding (no gap)
- Arranged so it sends filaments in opposite directions rather than in the middle.
2. Thin filaments
- Actin
- Tropomyosin
- No troponin
3. Intermediate filaments
- For structural stability
The filaments are arranged in a cris-cross pattern across the cell and held together and
stabilised by ‘dense bodies’ which replaces Z lines as smooth muscles don’t have
sarcomeres.
When the cell contracts, the thin filaments pass in opposite directions along thick filaments.
In smooth muscle, there is a myosin light chain which wraps around the neck of myosin. This
plays a crucial role because myosin head will only bind to actin when the myosin light chain
is phosphorylated.
1. Release of Ca2+ causes it to bind with a signalling molecule called calmodulin.
2. Calmodulin activates an enzyme called myosin light chain kinase.
3. Myosin light chain kinase adds a phosphate group therefore phosphorylates the
myosin light chain so the cross-bridge cycle can take place.
- Found in hollow organs and tubes such as airway and blood vessels.
- Has single nucleus per cell.
- Spindle shaped cells.
- Has no sarcomeres like skeletal muscles.
3 types of filaments
1. Thick filament
- Bundles of Myosin
- More heads available for binding (no gap)
- Arranged so it sends filaments in opposite directions rather than in the middle.
2. Thin filaments
- Actin
- Tropomyosin
- No troponin
3. Intermediate filaments
- For structural stability
The filaments are arranged in a cris-cross pattern across the cell and held together and
stabilised by ‘dense bodies’ which replaces Z lines as smooth muscles don’t have
sarcomeres.
When the cell contracts, the thin filaments pass in opposite directions along thick filaments.
In smooth muscle, there is a myosin light chain which wraps around the neck of myosin. This
plays a crucial role because myosin head will only bind to actin when the myosin light chain
is phosphorylated.
1. Release of Ca2+ causes it to bind with a signalling molecule called calmodulin.
2. Calmodulin activates an enzyme called myosin light chain kinase.
3. Myosin light chain kinase adds a phosphate group therefore phosphorylates the
myosin light chain so the cross-bridge cycle can take place.
