Smooth Muscle Flashcards
What shape are smooth muscle cells? How many nuclei
Spindle
1
Do smooth muscles use the sliding filament theory?
Yes, however no sarcomeres!
Describe the structure of the myosin and actin molecules
One myosin molecule in the centre of actin molecules
Actin attached to dense plate on cell membrane, and dense bodies within the cell
Is actin associated with tropomyosin or troponin?
tropomyosin
Why is smooth muscle contractions slower than skeletal muscle?
Slower formation of cross bridges
Slower hydrolysis of ATP by myosin
Why doesn’t smooth muscle always need an external stimulus e.g. chemical or electrical? Give an example of this
It is myogenic - unstable membrane and stretch causes the cell to stimulate itself
Uterus
Most cells are not directly innervated by nerve fibres. Which nervous system controls smooth muscle?
autonomic
How do individual nerve fibres manage to stimulate many smooth muscle cells, even though they are not directly innervate?
Diffusion and spread of excitation
Via gap junctions
Does smooth muscle fatigue easily?
No, 30% less energy than skeletal muscle
Hence can have tonic contractions
What are the 2 types of skeletal muscle contractions?
Phasic - alter between contracting and relaxing
Tonic - continuous slow contraction
What is the myometrium? What happens to the number of gap junctions at the end of pregnancy and whY?
Smooth muscle in the uterus
Increases for synchronised contractions
Describe the process of how smooth muscle contracts
Rise in cystolic calcium
Calcium bins to calmodulin which activates myosin light chain kinase (MLCK)
MLCK phopsohrylates which enhances contraction
MLCK dephosphorylates and decreases myosin ATPase activity
Decrease in cystoscope calcium
