GIT: Electrical Activity of GIT smooth Muscles

Question 1

Define slow waves (basal Electrical Rhythim)

Answer 1

slow. fluctuating changes in resting membrane potential, thus non-true action potentials, causong rhythmic depolarization & repolarization around -65mv to -45mv

Question 2

BER/ slow waves occur in smooth muscles of GIT except

Answer 2

• Eosophagus
• proximal part of stomach

Question 3

Frequency of BER/slow is determined by

Answer 3

site of segment:
* Stomach =4/min
* duodenum=12/min
* distal ileum=8/min
* cecum=2/min
* sigmoid colon=6/min

Question 4

Cells initiating BER

Answer 4

Interstitial cells of Cajal

Question 5

Importance of BER/slow waves

Answer 5

• Doesn’t cause muscle contractions
• but allow smooth muscles to generate spike potentials, getting potential close to firing level

Question 6

Site of interstitial cells of Cajal

Answer 6

• Stomach & small intestine: outer surface of circular muscle layer near Myenteric plexus
• Colon: at submucosal border of circular muscle

Question 7

in spike potentials, depolarization is caused by

Answer 7

Ca2+ influx

Question 8

in spike potentials, repolarization is caused by

Answer 8

K+ efflux

Question 9

Importance of spike potentials

Answer 9

they cause contraction due to entry of Ca2+

Question 10

effect of sympathetic & parasympathetic innervation on Spike potentials

Answer 10

• Parasympathetic: Acetylecholine —-> increases number of spike potentials & muscle contractions
• Sympathetic: Epinephrine —-> decrease number of spike potentials

Question 11

Enumerate plexuses of Enteric Nervous system (intrinsic)

Answer 11

• Myenteric plexus (auerbach)
• Submucosal (meissner’s)

Question 12

Site of myenteric plexus

Answer 12

Outer longitudinal & inner circular muscle layers

Question 13

Myenteric plexus is responsible for control of

Answer 13

Motility & movement

Question 14

Site of Submucosal plexus

Answer 14

Middle circular muscle layer & mucosa

Question 15

Submucosal plexus is responsible for control of

Answer 15

• Endocrine secretions
• mucosal blood flow

Question 16

Preganglionic parasympathetic fibers of GIT externsic innervation

Answer 16

• Vagus N
• Pelvic N

end by synapsing with Cholenergic neurones of ENS (intrinsic)

Question 17

Postganglionic parasympathetic fibers of GIT externsic innervation

Answer 17

(Originating from ENS)
* Cholinergic neurones
* peptidergic neurones (secreting VIP & Substance P)

Question 18

Mention importance of vagus nerve in GIT innervation other than parasympathetic supply

Answer 18

Carries sensory information from mechanoreceptors & chemoreceptors of GIT

Question 19

Preganglionic & pistganglionic sympathetic fibers of extrinsic innervation of GIT

Answer 19

Preganglionic: synapse in ganglia outside GIT

Postganglionic:
* secrete norepinephrine on neurones of ENS (intrinsic)
* Or directly on smooth muscles, glands & blood vessels