Smooth muscle and enteric nervous system Flashcards
What are the two types of muscle in the GIT
Smooth involuntary
Skeletal voluntary
Where is the smooth muscle located?
Most regions
Where is the skeletal muscle located?
Pharynx, top third of oesophagus, external anal sphincter
What are the functions of GIT?
Digestion
Absorption
Secretion
Motility
What is motility in the GIT supported by?
Intestinal smooth muscle
What are the two types of smooth muscle?
Phasic
Tonic
What is phasic smooth muscle?
rapid contraction and relaxation
Where is phasic smooth muscle located?
body of oesophagus, stomach antrum, small and large intestines
What is tonic smooth muscle?
sustained contraction
Where is tonic smooth muscle located?
Sphincters (lower oseophageal, ileocaecal, internal anal) , orad (upper stomach)
What is the basic rate of smooth muscle determined by?
Pacemaker activity- an intrinsic property of the interstital cells of CAJAL/ICC.
What happens when ICC is depolarised?
ICC is electrically coupled to the smooth muscle cells through gap junctions. This allows the spread of slow waves
Stimulation of electrical activity by…
Mechanical- stretch
Pharmacological- ACh, parasympathetics
Inhibition of electrical activity by…
Noradrenaline
Sympathetics
What does stimulation of electrical activity lead to?
oscillating potential increases above the threshold membrane potential. Depolarisation occurs
What does inhibition of electrical activity lead to?
hyperpolarisation. High depolarisation to reach threshold potential
What is the role of threshold for electrical contraction?
Whenever this threshold is breathed, contractile activity occurs. If the threshold is breathed at a greater level, there is greater contractile activity
Why is there lag between electrical activity and contractile activity?
It takes some time between depolarisation and contraction
Where does the Ca2+ come from?
membrane depolarisation lead to the opening of Voltage Operated Calcium Channel (VOCC)
Where does the Ca2+ come from?
membrane depolarisation lead to the opening of Voltage Operated Calcium Channel (VOCC)
PLC pathway- muscarinic ACh receptor
What happens in smooth muscle contraction?
Ca2+ binds to calmodulin
This activates myosin light chain kinase MLCK
MLCK phosporylates myosin to myosin phosphate
Allows binding to actin
How does smooth muscle relaxation occur?
Myosin light chain phosphatase MLCP dephosphorylates myosin phosphate
Phosphorylation of MLCK prevents binding of calmodulin
How is the phosphorylation of MLCK regulated?
PKA pathway i.e. VIP/B adrenergic induces adenyl cyclase induces cAMP induces PKA phosphorylation of MLCK
Innervation of the GIT
Intrinsic- enteric
Extrinsic- autonomic- parasympathetic and sympathetic
What neurones does the intrinsic innervation contain?
Motor: activatory, inhibitory
Sensory
Interneurones
Activation of the myenteric plexus leads to…
increased tonic contraction
increased intensity of rhythmic contraction
increased rate of contraction which increases velocity of conduction
Activation of submucosal plexus leads to…
increased secretory activity
modulated intestinal absorption
