New Chapt 17-Smooth muscle(1)

New Chapt 17-Smooth muscle(1) - Chapter 17 Smooth Muscle We...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
193 Chapter 17 Smooth Muscle We now need to very briefly consider smooth muscle. Although we will see that the basic contractile mechanisms are the same in that they involve the interaction of actin and myosin, smooth muscle differs from skeletal muscle in several important respects. First, smooth muscle fibers are much smaller than skeletal muscle fibers. Each smooth muscle fiber is a single cell having a single nucleus. The cells are spindle-shaped, about 2-20m in diameter, and 10-100 times as long as they are wide (Fig. 1). Fig. 1. Three major classes of vertebrate muscle, showing the morphology (left) and relationships between electrical and mechanical activity (right panel). A: skeletal muscle fibers have a striated appearance. They are cylindrical and multinucleated. These fibers have brief action potentials and brief contractions. B: Cardiac muscle cells are also striated but are not innervated by a motor neuron. Fibers are joined end-to-end by gap junctions that allow electrical current to flow from one cell to the next. Both the action potentials and contractions of these cells are prolonged. C: Smooth muscle fibers are small and spindle shaped, each with a single nucleus. They are joined laterally by gap junctions into electrically coupled groups. The innervation is diffuse. The transmitter is released into spaces from varicosities (swellings) along an autonomic nerve and diffuse to many fibers. While the action potentials are brief, the resultant contractions are slow and long lasting. Secondly, smooth muscle fibers are electrically coupled to each other through gap junctions. Bundles of smooth muscle fibers coupled in this manner actually form functional units (Fig. 1). Thirdly, smooth muscle fibers lack striations (hence the name, smooth muscle)--the characteristic organization of actin and myosin filaments into sarcomeres present in skeletal and cardiac muscle is absent. Actin and myosin filaments are still present in smooth muscle fibers,
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
194 but there are no Z lines and the contractile proteins are not organized as sarcomeres. Rather the actin filaments are anchored to dense bodies, which are functionally similar to Z lines of skeletal
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 4

New Chapt 17-Smooth muscle(1) - Chapter 17 Smooth Muscle We...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online