NM 9 - Smooth and heart muscles

Question 1

6 Characterises in of multiunit smooth muscles

Answer 1

• Neurogenic controlled by nerves
• rich innervation
• well developed NMJ
• no spontaneous activity
• no ECC
• no action potentials

Question 2

6 Characterises of visceral smooth muscle

Answer 2

Myogenic controlled by local factors - stretch hormones
sparse innervation
poorly developed NMJ
some pacemaker cells
Gap junctions
Action potentials

Question 3

What regulates cross bridge formation in smooth muscle

Answer 3

Cross bridge formation is not regulated by the troponin tropmysoin complex but instead by the regulatory protein calmodulin

Question 4

EC Coupling In smooth muscle

Answer 4

; Ca++ binds to calmodulin
* Ca++/calmodulinactivatesmyosinlightchainkinase which activates myosin allowing crossbridge formation
* Phosphorylatedcross-bridgescycleuntiltheyare dephosphorylated by myosin phosphatase.
* MyosinATPaseactivityisslowandmuscle contraction is slow and sustained

Question 5

EC Coupling in heart muscle

Answer 5

The dihydropyridine receptor allows Ca++ from the T system into the cell where it activates the ryanodine receptor to release Ca++ from the S.R.
* Eventsduringcrossbridgecyclingaresimilartoskeletal muscle
* Ca++ exits the cell mainly by a Na/Ca exchanger