Choudhury - Regulation of GI Function: Nerves and Smooth Muscle

Question 1

Calcium influx in smooth muscles invokes…

Answer 1

A chemical change in the THICK FILAMENT that cause contraction(s)

Question 2

The structure found in smooth muscle that is analogous to the sarcoplasmic reticulum in skeletal muscle?

Answer 2

Varicosities: axon swelling at each contact point; contain neurotransmitters

These are not found in skeletal muscles

Question 3

Multi-unit muscle?

Answer 3

“one cell, one neuron”

“gives you very fine control…iris of the eye and hair of the skin, some blood vessels and the vas deferens”

Question 4

Single-unit smooth muscle?

Answer 4

SLOW WAVE, prolonged

Contracts as a single unit, one nerve for multiple muscle cells

Found in: uterus, GI tract

Question 5

Difference from skel. m. in electrical activity?

Answer 5

Smooth m. can produce slow-wave, graded action potentials

Question 6

Pacemaker cells of the GI tract are called?

Answer 6

Interstitial cells of Cajal

“ICC in some books”

Question 7

Slow-wave explained…

Answer 7

Slow wave potentials:

ØMembrane undergoes self-

induced hyperpolarization

and depolarization swings

ØA burst of action potentials

occurs if a depolarization

swing brings the membrane to threshold

Question 8

What is the role of Ca2+ in the Excitation-Contraction Coupling of Smooth Muscle?

Answer 8

In sm. m., Ca2+ turns on the cross-bridge by inducing a change in the myosin (thick filament) by phosphorylation

(skeletal m. induces a change in actin (thin))

Question 9

Latch state of smooth mm. significance?

Answer 9

Maintenance of smooth muscle tone without fatigue

• Decreased rate of detachment lowers rate of cycling and ATP expenditure
• Mimics rigor state at low ATP levels in skeletal m

Question 10

“Remember three things for the smooth muscle…”

Answer 10

“… hormone activated receptors (hormonal), electrical couplers (neuronal), and pacemaker potentials (the ICC)” all motivate the contraction of smooth muscle

Ca2+ in smooth muscles will have longer degradation as well

Question 11

What does parasympathetic activity cause?

Answer 11

promotes digestive and absorptive processes; increases motility and secretions

Question 12

Increased sympathetic activity:

Answer 12

promotes decreased motility and secretions; increased sphincter constriction

Question 13

Where do we find the Myenteric Plexus (Auerbach’s plexus)?

Answer 13

Between the outer longitudinal and inner circular muscle layers of the muscularis externa throughout the GI tract

Question 14

Where do we find the Submucosal Plexus (Meissner’s plexus)?

Answer 14

In the submucosa of the small and large intestines

Question 15

STUDY

Answer 15

SUMMARY