1.8

Question 1

characteristics of the smooth muscle cell

Answer 1

uninucleated
small cells
lack striations
no T tubules
found in walls of hollow organs

Question 2

2 types of smooth muscle cells

Answer 2

single unit

multi unit

Question 3

characteristics of single unit SMC

Answer 3

Gap Junctions btw the cells
allows easy electrical conduction
more common

Question 4

characteristics of Multi unit SMC

Answer 4

Each muscle fiber acts as a seperate motor unit

Question 5

where can we find multi unit SMC?

Answer 5

iris and ciliary muscles of the lens

Question 6

what are the three possible sources of increased intracellular [Ca++]?

Answer 6

1. VGCaCh (brings Ca++ from the extracellular)
2. LGCaCh (brings Ca++ from the extracellular)
3. IP3-gated Ca++ Ch (from the SR) very similar to RYR

**we also have Ca++ induce Ca++ release

Question 7

What are IP3-gated Ca++ Ch? location?

Answer 7

they are present on the Sarcoplasmic Reticulum

remember Gq? so the IP3 generated from its action is the ligand for this R (PLC!!)

Question 8

Describe the SMC contraction pathway

Answer 8

Ca++ binds Calmodulin -> activation of MLCK (Myosin Light Chain Kinase) -> MLCK phosphorylates Myosin Light Chain -> increased ATPase activity -> cross-bridge cycling

Question 9

characteristic of SMC contraction

Answer 9

• long lasting Ca++ signal in the cell
• contraction requires less ATP
• slow actin myosin cycle in the cell
• actin myosin cross bridges