10. Characteristics of smooth muscle Flashcards
General: what are the 2 major parts of the smooth muscle
single-unit smooth muscle
o Multi-unit smooth muscle
General: Single-unit is found
Single unit smooth muscle is found in the walls of the body’s hollow and tubular organs
General: single-unit: what does it do
Sustained contraction of the smooth muscle in
walls transfers pressure to the content or the organ, while alternating contractions and relaxations lead to mixing of the content.
o Can also create waves of contraction = peristaltic movements
General: Multi-unit: found in
Multi-unit smooth muscle is primarily located in the eyes and skin
General: multi-unit: responsible for:
Adjusting the diameter of the pupils according to the intensity of light
▪ Altering the curvature of the lens in the eye
▪ Changing the angle of hairs relative to skin
surface
Structure: what does it contain
Contain both actin and myosin filaments, but they are not organized in sarcomers.
Structure: actin filament
the actin filaments are attached to dense protein lattices, which are analogous to the Z-discs in skeletal muscle fibers.
Structure:myosin filaments where are they
Myosin filaments are located between the actin filaments.
Structure: myofilament bundles end
The ends on the myofilaments bundles
are attached to dense protein plates in the cell membrane.
Structure: intermediate filaments what do they do
These filaments do not participate in the
contraction, but are a part of the cytoskeleton
that determined the shape of the cell.
Contraction of smooth muscles: step 1
Stimulation of the cells result in increased calcium
concentration in the cytosol, due both to calcium influx through ion channels in the cell membrane, and to calcium release from the sarcoplasmic reticulum.
Contraction of smooth muscles: step 2
Calcium binds to calmodulin
Contraction of smooth muscles: step 3
Calcium-calmodulin complex activates myosin kinase.
Contraction of smooth muscles: step 4
The activated myosin kinase transfers a phosphate group from ATP to the myosin heads.
Contraction of smooth muscles: step 5
Phosphorylated myosin heads hydrolyze ATP and bind to actin.
Contraction of smooth muscle: step 6
Cross-bridges are formed and broken as long as the myosin heads are phosphorylated, causing the cell to contract.
Contraction of smooth muscle: step 7
When stimulation of the cell ceases, calcium pumps in the cell membrane and in the membrane of the sarcoplasmic reticulum will remove more calcium from the cytosol than flows in.
Contraction of smooth muscle: step 8
The calcium concentration in the cytosol falls and calcium dissociates from calmodulin, and the activation of myosin kinase ceases.
Contraction of smooth muscle: step 9
Myosin phosphatase dephosphorylates the myosin heads, which then lose their ATPase activity and the ability to bind to actin.
Signals for smooth muscle contraction/relaxation: Relaxation of smooth muscle cells =
Relaxation of smooth muscle cells = vasodilation
Signals for smooth muscle contraction/relaxation:Extension (stretching) of certain smooth muscle cells results in contraction
Bayliss effect
