QuestionSBA
QuestionChoice
Smooth muscle cells are fusiform cells, typically 200-300um long. In contrast, skeletal muscle cells can be much longer, spanning the entire distance of muscles. For example, skeletal muscle cells in the sartorius (the longest muscle in the body, spanning from the ASIS to Pes anserinus) can reach up to 600mm in length.
10001179
d
The cells can reach up to 600mm in length
QuestionChoice
Although smooth muscle cells do allow calcium entry from the extracellular space, cardiac muscle also allows this through dihydropyridine receptors. The difference is that the sources of calcium entry into the cytoplasm are much more varied in smooth muscle, and are under both neurotransmitter and hormonal control for the tight regulation of contraction in different situations.
10001178
c
Allow calcium entry from the extracellular space
QuestionChoice
Smooth muscle is the only type of muscle that does not contain sarcomeres. In cardiac and skeletal muscle, there are: linear Z-discs at either end of each sarcolemma to which actin connects; I bands in which there is actin and titin to anchor myosin but no myosin itself; A bands where actin and myosin overlap; and central M bands in which there is myosin but no actin. These structures can be seen on transmission electron microscopy.
10001177
b
Contain sarcomeres
QuestionChoice
Smooth muscle cells are typically stimulated to relax by nitric oxide. This occurs because nitric oxide activates soluble guanylate cyclases, generating cGMP which activates PKG. Amongst other functions, PKG lays down inhibitory phosphorylation marks on MLCK, reducing the phosphorylation of myosin, and subsequently reducing contraction.

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10001180
e
Contraction stimulated by nitric oxide
QuestionChoice
Smooth muscles are called smooth due to the lack of striations visible on microscopy. This is because actin and myosin are arranged around dense bodies in the cytoplasm and are attached to attachment plaques in the plasma membrane rather than in sarcomeres.
10001176
a
Contain dense bodies and attachment plaques
Concept
Chapter
2693
3783
Types of muscle
Topic
154
Musculoskeletal physiology and disease
12782
Which of the following statements only applies to smooth muscle cells?
a