Page 80 - Headlines Histology2024_Neat

small amount of rER are largely confined to the perinuclear cytoplasm. The
sER is poorly developed consisting of narrow tubules with no terminal
cistenae. There are no T tubules.
• The cytoplasm is filled with parallel thin (actin) and thick (myosin)
filaments. The filaments do not have the arrangement seen in the
sarcomeres.
• Intermediate filaments (desmin, vimentin and synemin) are also located
within the cytoplasm where they are attached to electron-dense structures
known as dense bodies that represent the counterpart of Z lines.
• Nexus-like junctions that facilitate the spread of excitation throughout
visceral muscle attach the cells. Desmosomes are also found where they
bind adjacent cells and provide anchorage points for actin and myosin.
Functions
• Contraction of the smooth muscle is an inherent property however, it can be
modulated be autonomic nervous system.
• The smooth muscle maintains prolonged partial contraction (tonus) in the
wall of arterioles that is necessary to keep normal blood pressure in the
blood capillaries.
• In the small intestine, the smooth muscle cell undergoes continuous
rhythmic constrictions passing along the tract propelling the luminal
contents distally.

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