Properties of the Isolated Mammalian
( G. I. Motility Lab )
By : K Boparai
Instructor : S Sundaram
December 09, 2002
If we were to compare smooth muscle with skeletal muscle we notice that they are very different from one another. Firstly, smooth muscles have a slow cycling of myosin cross bridges as compared to skeletal muscle. However, the fraction of time that the cross bridges remain attached to the actin filaments is believed to be greatly increased in smooth muscle. Secondly, Less energy is required to sustain the same tension of contraction in smooth muscle as in skeletal muscle. Thirdly, The maximum force of contraction of smooth muscle is often even greater than that of skeletal muscle. This great force of smooth muscle contraction results from the prolonged period of attachment of the myosin cross-bridges to the actin filaments.
The Gastrointestinal tract has 2 major networks of nerve fibers - Myenteric plexus and the Submucous plexus. The plexuses are interconnected, and they contain motor neurons that innervate the smooth muscle. This is the enteric nervous system. The intestine also receives a dual extrinsic innervation from the autonomic nervous system, with parasympathetic cholinergic activity generally increasing the activity of intestinal smooth muscle and the sympathetic noradrenergic activity generally decreasing it while causing the sphincters to contract.
The GI tract is made up of smooth muscles. The individual smooth muscle fibers are between 200 and 500 micrometers in length and 2 and 10 micrometers in diameter, and they are arranged in bundles of as many as 1000 parallel fibers.
In general, smooth muscle can be divided into Visceral smooth muscle and Multi-unit smooth muscle. Visceral smooth muscle occurs in large bundles. Within each bundle, the muscle fibers are electrically connected with one another through large numbers of gap junctions that ...