week 3: 10.10 smooth muscle tissue contracts to move substances within internal passageways Flashcards
what does smooth muscle tissue form in almost every organ
sheets, bundles, or sheaths around other tissues
smooth muscles general function
coordinate the movement of substances through internal passageways
role of smooth muscle in the integumentary system
smooth muscles around blood vessels regulate the flow of blood to the superficial dermis, smooth muscles of the arrector pili elevate hairs
cardiovascular system
smooth muscles around blood vessels control blood flow through vital organs and help regulate blood pressure
respiratory system
smooth muscles contract or relax to alter the diameters of the respiratory passageways and change their resistance to airflow
digestive system
extensive layers of smooth muscle in walls of digestive tract play essential role in moving materials along the tract,
smooth muscles in walls of gall bladder contracts to eject bile into digestive tract,
urinary system
smooth muscle tissue in walls of small blood vessels alter rate of filtration in kidneys,
layers of smooth muscle in walls of uterus transport urine to urinary bladder,
contraction of smooth muscle in wall of urinary bladder forces urine out of the body
reproductive system
males: layers of smooth muscle help move sperm along reproductive tract, cause ejection of glandular secretions from accessory glands into the reproductive tract
females: layers of smooth muscle help move oocytes along reproductive tract,
contractions of smooth muscle is walls of uterus expel fetus in delivery
shape and typical dimensions of smooth muscle cells
relatively long and slender
5-10μm diameter
30-200 μm length
spindle shaped
single centrally located nucleus
does smooth muscle fiber have T tubules
no
sarcoplasmic reticulum forms a loose network throughout the sarcoplasm
nonstriated muscle
smooth muscle cells lack myofibrils and sarcomeres
as a result has no striations
thick filament arrangement of smooth muscle
thick filaments scattered throughout the sarcoplasm of a smooth muscle cell
smooth muscle cells have more myosin heads per thick filament
thin filaments arrangments
thin filaments are attached to dense bodies
some of the dense bodies are firmly attached to the sarcolemma
what are dense bodies
structures distributed throughout the sarcoplasm in a network of intermediate filaments composed of desmin (protein)
when sliding occurs between thick and thin filaments, cell shortens, why
dense bodies and intermediate filaments anchor the thin filaments
significance of dense bodies not being arranged in straight line
when contraction occurs, muscle cell twists like corkscrew
how are adjacent smooth muscle cells bound together
at dense bodies
transmitting the contractile forces from cell to cell throughout the tissue
althoug smooth muscle cells are surrounded by connecitce tissue, collagen fibers never
unite to form tendons or aponeuroses as thy do in skeletal muscles
trigger for smooth muscle contraction
appearance of free calcium ions in the cytoplasm
upon stimualtion,
surge of calcium ions enters the cell from the extracellular fluid and SR releases additional calcium ions
net result of events after stimulation
rise in calcium ion conc throughout the cell
calcium ions activity once in the sarcoplasm
interact with calmodulin (calcium-binding protein)
what does calmodulin acitvate
myosin light chain kinase enzyme
enables myosin heads to attach to actin
why are tension development and resting length of smooth muscle not related
thick and thin filaments are sacttered and not organised into sarcomeres
plasticity
ability to function over a wide range of lengths
smooth muscles can contraxt over a range of lengths —- times greater than skeletal muscles
4
example of importance of plasticity
digestive organs e.g the stomach
two categories of smooth muscle cells
multiunit
visceral
how are multiunit smooth muscle cells innervated
in motor units comparable to those of skeletal muscles
but each smooth muscle cell may be connected to more than one motor neuron
what do many visceral smooth muscle cells lack
direct contact with any motor neuron
what does nural activity in multiunit smooth muscle cells produce and what does this resemble
produces AP that travels over sarcolemma
resembles skeletal and cardiac muscle cells
how are visceral smooth muscle cells arranged
sheets or layers
within the layers of the visceral smooth muscle cells, how are adjacent muscle cells connected
gap junctions
result of gap junctions
when one muscle cell contracts, electrical impulse can travel to adjacent smooth muscle cells
contraction spreads in a wave that involves every smooth muscle cell in the layer
smooth muscle cells can also contract or relax in response to
chemicals, hormones, conc of oxygen or CO2, extreme stretching or irritation
electormagnetic coupling
stretching the muscle can produce depolarisation
smooth muscle tone
multiunit and visceral smooth muscle tissue have normal background level of smooth muscle tone
