Smooth Muscle and Motility Flashcards
What are the types of muscle in the GIT and what is the distinction between the 2
- Smooth - Involuntary
- Skeletal - Voluntary
Where in the GIT are smooth and skeletal muscle found
- Smooth muscle - most regions
- Skeletal muscle - Pharynx, top third of oesophagus, external and sphincter
What are the 2 types of smooth muscle and what is the major distinction between the 2
- Phasic - Rapidly contracts
- Tonic - Allows for sustained contraction
Where in the GIT is phasic smooth muscle found
- Body of oesophagus
- Stomach of antrum
- Small and large intestines
Where in the GIT is tonic smooth muscle found
- Lower oesophageal sphincter
- Ileocecal valve
- Internal anal sphincter
- Upper stomach (orad)
PACE MAKEING??
What causes the contraction of smooth muscle
- An increase in the oscillating membrane potential of the ICC above the threshold
What stimulates depolarisation of smooth muscle cells in muscle contraction
- Stretch
- ACh
- Parasympathetic innervation
What causes the relaxation of smooth muscle in the GIT
- The movement of the oscillating membrane potential away from the threshold value.
What stimulates hyperpolarisation of smooth muscle cells in smooth muscle relaxation
- Noradrenaline
- Sympathetic innervation
What intrinsically innervates the gastrointestinal tract
- Enteric nervous system
What extrinsically innervates the gastrointestinal tract
- Autonomic nervous system
What are the 2 divisions of the enteric nervous system
- Submucosal plexus
- Myenteric plexus
Where is the submucosal plexus found
- Between submucosa and circular muscle
Where is the myenteric plexus found
- Between longitudinal and circular muscle
What divisions of the autonomic nervous innervate smooth muscle contraction and smooth muscle relaxation
- Parasympathetic - contraction
- Sympathetic - relaxation
What are the effects of activating the myenteric plexus
- Increase in tonic contraction
- Increase in intensity/rate of phasic contractions
- Increase in velocity of conduction
What are the effects of activating the submucosal plexus
- Increase in secretory activity
- Modulation of intestinal absorption
What are the 3 main levels of organisation in the enteric nervous system
- Receptors
- Sensory neurones
- Motor neurones
What are the 2 types of receptors in the enteric nervous system
- Mechanoreceptors
- Chemoreceptors
What are the 2 types of motor neurones in the enteric nervous system
- Inhibitory
- Excitatory
What are the effects of stimulating the sympathetic and parasympathetic nervous system in extrinsic innervation
- Sympathetic - Motility is inhibited (due to hyperpolarisation)
- Parasympathetic - Motility is increased (due to depolarisation)
What is the supply of parasympathetic innervation to the digestive organs
- Vagus nerve (oesophagus to transverse colon)
- Pelvic nerves (descending colon to rectum)
What causes an excitatory reflex in the gut wall
- Stimulation of sensory neurones that activate an excitatory motor neurone
