Smooth muscle and enteric nervous system

Question 1

What are the two types of muscle in the GIT

Answer 1

Smooth involuntary

Skeletal voluntary

Question 2

Where is the smooth muscle located?

Answer 2

Most regions

Question 3

Where is the skeletal muscle located?

Answer 3

Pharynx, top third of oesophagus, external anal sphincter

Question 4

What are the functions of GIT?

Answer 4

Digestion
Absorption
Secretion
Motility

Question 5

What is motility in the GIT supported by?

Answer 5

Intestinal smooth muscle

Question 6

What are the two types of smooth muscle?

Answer 6

Phasic

Tonic

Question 7

What is phasic smooth muscle?

Answer 7

rapid contraction and relaxation

Question 8

Where is phasic smooth muscle located?

Answer 8

body of oesophagus, stomach antrum, small and large intestines

Question 9

What is tonic smooth muscle?

Answer 9

sustained contraction

Question 10

Where is tonic smooth muscle located?

Answer 10

Sphincters (lower oseophageal, ileocaecal, internal anal) , orad (upper stomach)

Question 11

What is the basic rate of smooth muscle determined by?

Answer 11

Pacemaker activity- an intrinsic property of the interstital cells of CAJAL/ICC.

Question 12

What happens when ICC is depolarised?

Answer 12

ICC is electrically coupled to the smooth muscle cells through gap junctions. This allows the spread of slow waves

Question 13

Stimulation of electrical activity by…

Answer 13

Mechanical- stretch

Pharmacological- ACh, parasympathetics

Question 14

Inhibition of electrical activity by…

Answer 14

Noradrenaline

Sympathetics

Question 15

What does stimulation of electrical activity lead to?

Answer 15

oscillating potential increases above the threshold membrane potential. Depolarisation occurs

Question 16

What does inhibition of electrical activity lead to?

Answer 16

hyperpolarisation. High depolarisation to reach threshold potential

Question 17

What is the role of threshold for electrical contraction?

Answer 17

Whenever this threshold is breathed, contractile activity occurs. If the threshold is breathed at a greater level, there is greater contractile activity

Question 18

Why is there lag between electrical activity and contractile activity?

Answer 18

It takes some time between depolarisation and contraction

Question 19

Where does the Ca2+ come from?

Answer 19

membrane depolarisation lead to the opening of Voltage Operated Calcium Channel (VOCC)

Question 20

Where does the Ca2+ come from?

Answer 20

membrane depolarisation lead to the opening of Voltage Operated Calcium Channel (VOCC)
PLC pathway- muscarinic ACh receptor

Question 21

What happens in smooth muscle contraction?

Answer 21

Ca2+ binds to calmodulin
This activates myosin light chain kinase MLCK
MLCK phosporylates myosin to myosin phosphate
Allows binding to actin

Question 22

How does smooth muscle relaxation occur?

Answer 22

Myosin light chain phosphatase MLCP dephosphorylates myosin phosphate
Phosphorylation of MLCK prevents binding of calmodulin

Question 23

How is the phosphorylation of MLCK regulated?

Answer 23

PKA pathway
i.e. VIP/B adrenergic induces adenyl cyclase
induces cAMP
induces PKA
phosphorylation of MLCK

Question 24

Innervation of the GIT

Answer 24

Intrinsic- enteric

Extrinsic- autonomic- parasympathetic and sympathetic

Question 25

What neurones does the intrinsic innervation contain?

Answer 25

Motor: activatory, inhibitory
Sensory
Interneurones

Question 26

Activation of the myenteric plexus leads to…

Answer 26

increased tonic contraction
increased intensity of rhythmic contraction
increased rate of contraction which increases velocity of conduction

Question 27

Activation of submucosal plexus leads to…

Answer 27

increased secretory activity

modulated intestinal absorption