Smooth Muscle Pacemakers

Question 1

What is the difference between a smooth muscle slow wave and pacemaker potential?

Answer 1

Slow wave + Pacemaker potentials are types of myogenic action potentials.

Slow wave: (aka Basic Electrical Rhythm) wave-like fluctuations im membrane potential that cyclically bring the membrane potential closer or further away from threshold. S.musc. connected by gap junctions (low resist). Cyclical Na+ in/out. Reaching threshold depends on starting point.

Pacemaker Potentials: (pacesetter cells) Always reach threshold and create regular rhythms of contraction. These cells dont contract. Only few in syncytium. AP flows through gap junctions. Intensity of contraction depends on number of APs when pacemake reaches threshold.

Question 2

What factors influence smooth muscle motility in the small intestine?

Answer 2

Parasymp. Increases motility.

Symp Decreases motility

Intensity of contraction depends on the number/frequency of APs.

Amount of intracellular Ca2+ determines strength

Question 3

Describe the migrating myo-electric complex (MMC) in humans.

Answer 3

In fasted individual, s.intestine motility follows different pattern. Bursts of intest electrical and contractile activity separated by periods of quiescence. Propogte from duod -> terminal illeum. (every 75-90mins)

• Phase 1: Quiescent phase: slow waves: few APs: few contractions
• Phase 2: Irregular Aps & contractions. raadual increase in intensity + freq.
• Phase 3: Intense electrical/contractual activity that lasts for 3-6 mins
• Phase 4: Rapid decline in activity which eventually blends into phase 1.

Motilin is responsible hormone.

Question 4

What is the function of the MMC?

Answer 4

“sweeps bowel clean” = the “housekeeper” of the digestive system.

Inhibits the migration of colonic bacteria into the terminal illeum.