Block IV: Smooth muscle Flashcards
How is the cell shape in smooth muscle?
Spindle shaped cells and single nuclei per cell; nuclei centrally located
is the smooth muscle striated?
no (no sarcomeres)
diameter of fibers in smooth muscle?
Small diameter fibers (cells) = 2 -3 nuclear diameters across
smooth muscle is electrically coupled by?
gap junctions; not much innervation
identify
Microgaph of smooth muscle in both longitudinal and cross-section adjacent layers
What structures are found in the smooth muscle that contain alpha actinin (cross-link for actin thin filaments in Z-band of skeletal and cardiac muscle?
Membrane attachment plaques & cytoplasmic dense bodies; which can serves as an
attachment point for actin thin filaments located within the cytoplasm of the smooth
muscle and also the intermediate filament cytoskeleton of the smooth muscle.
identify
Smooth muscle LS
identify
smooth muscle CX
identify
EM of smooth muscle cut in crosssection. The arrows point to cytoplasmic dense
bodies and membrane attachment plaques
How are thick and thin filaments of smooth muscle?
Thick & thin filaments are present, but not in form of ordered sarcomeres. The thick
filament has a different structure than in skeletal or cardiac muscle
– Side polar structure
Explain the composition of the smooth muscle contraction
An array of intermediate filaments is bound to the cytoplasmic dense bodies & holds them in place in cell
Actin filaments of opposite polarity are bound to 2 sides of cytoplasmic dense bodies as in z-band in skeletal
Myosin thick filaments interact with actin from 2 different cytoplasmic dense bodies by a sliding filament mechanism giving contraction
How is the sarcoplasmic reticulum is smooth msucle?
much less developed than in skeletal or cardiac. Typically consists just of small sacs of SR or tubules of SR
How are t-tubules in smooth muscle?
T-tubules are absent
Why arent t-tubules necessary?
Because of the small diameter of the smooth muscle cells, it is not necessary to have an elaborate system such t-tubules and terminal cisternae for the release of calcium all through out the smooth muscle cell at the same time.
identify
smooth muscle longitudinally sectioned
What does calcium regulation of contraction for smooth muscle consists of?
Regulation of contraction involves binding Ca+2 -Calmodulin to myosin light chain kinase and phosphorylation of myosin light chain, not tropomyosin-troponin complex
What are some factors that can cause contraction or relaxation of smooth muscle?
This contraction in smooth muscle can be evoked by a variety of factors including: 1)
mechanical stimuli such as stretching of vascular smooth cell; (2) electrical
depolarizations of the cell by neurotransmitters or gap junctions; and (3) binding of
hormones and chemical factors such as vasopressin and angiotensin II to receptors
on the membrane of the smooth muscle. In addition, other signaling molecules such
as nitric oxide by binding to receptors on the smooth muscle may cause relaxation of
the smooth muscle. In most cases these factors all act through 2nd messengers
Can mature skeeltal msucle divide?
No
How does growth of skeletal muscle happen?
Growth of skeletal muscle is primarily by hypertrophy, the cells get larger in volume.
How can regeneration of skeletal muscle happen?
Some regeneration or repair can take place, but this is by way of small relatively
undifferentiated fibers or cells called satellite cells which sit inside the basal
lamina of the muscle fiber
Can cardiac muscle be regenerated?
Cardiac muscle normally can not divide or regenerate, although limited division
has been observed. Areas of damage are replaced with CT, and thus lose
functional ability to contract
Can smooth muscle regenerate?
Smooth muscle cells retain their ability to divide and regenerate. They also can undergo hypertrophy and increase in size in areas such as the myometrium of the uterus under pregnancy
