L26 - Smooth Muscle Flashcards
What are examples of tubular and hollow organs? (10)
- Airways
- Aorta
- Arteries and veins
- Bladder
- Eye
- Intestine
- Prostate
- Skin (hair follicles, nipples)
- Uterus
- vagina
How does vasodilation occur?
Relaxation of vascular smooth muscle
- increases the blood supply to tissue
How does vasoconstriction occur?
Contraction of vascular smooth muscle
- decreasing the blood supply to tissues
What are examples of visceral organs?
- intestine
- stomach
What is the smooth muscle like in the intestine?
- longitudinal layer of smooth muscle outside
- circular layer of smooth muscle inside
What are the layers of smooth muscle in the stomach?
- inner oblique
- circular layer
- longitudinal
What is the purpose of the inner oblique layer in the stomach?
Churning and mechanical digestion
What is the purpose of the circular layer in the stomach?
Forms pyloric sphincter
- regulates flow of stomach contents into duodenum
What is the purpose of the longitudinal layer of the stomach?
Moves food towards the pylorus
What are possible functions of the trachea and bronchia’s smooth muscle? (3)
- peristalsis, assists exhalation and mucus propulsion
- distribution of airflow during ventilation
- stabalises the airway wall, enhances effectiveness of cough/ejection of foreign material
What are single unit smooth muscles like? (3)
- fibres aggregated into sheets/bundles
- connected by gap/nexus junctions
- contracts as a syncytium
What are examples of single unit smooth muscle? (5)
- intestine
- stomach
- bladder
- uterus
- small diameter blood vessels
What are multi-unit smooth muscles like? (3)
- few/no gap junctions (no electrical coupling)
- fine grain control
- activateed by neural/hormonal signals
What are examples of multi-unit smooth muscle? (3)
- large arteries
- large airways in lungs
- pilomotor muscles (hair follicle)
What are properties of smooth muscle? (7)
- involuntary
- smooth appearance
- no sarcomeres (dense bodies)
- Ca2+ binding to calmodulin (not troponin)
- slow myosin ATPase (compared to skeletal muscle)
- less extensive SR (compared to skeletal muscle)
- no T-tubules
What are smooth muscle cells like? (5)
- single nucleus
- spindle shaped (2-10mcm diam, 50-400mcm long)
- interconnect to form sheet of smooth muscle
- no sarcomeres
- no troponin
How are smooth muscle cells dense bodies? (4)
- analogous to Z-discs of striated muscle sarcomeres
- rich in a-actinin
- attached to sarcolemme by intermediate filaments
- anchor actin filament = exert force
What is the mechanism of smooth muslce contractions? (2)
- intiated by Ca2+ regulated phosphorylation of myosin (not Ca2+ activated troponin)
- Calmodulin binds to Ca2+ = starts contraction
What are the 2 sources of Ca2+? (2)
- internal calcium stores
- external influx through calcium ion channels
What is calmodulin?
The calcium binding protein in smooth muscle
What are the steps in the smooth muscle cross bridge cycling? (3)
- resting muscle
- activation of contraction
- terminating cross bridge
What happens during resting muscle in the smooth muscle cross bridge cycling?
Dephosphorylated myosin head group held close to myosin filament
What happens during activation of contraction in the smooth muscle cross bridge cycling? (4)
- muscle stimulated Ca2+ inc
- Ca2+ binds to calmodulin
- Ca2+-Calmodulin complex binds to myosin light chain kinase (MLCK)
- Active MLCK uses ATP to add Pi to MLC in myosin head group
= drives cross bridge away from thick filament, binds to actin
What type of cross bridge cycling happens in smooth muscle?
ATP dependent
