Factors influencing contractile activity of smooth muscle

6 Factors influencing contractile activity of smooth muscle 

Many factors influence the contractile activity of smooth muscle. The strength of contraction of multiunit smooth muscle may be enhanced by stimulation of a greater number of cells, or contractile units. This mechanism is directly comparable to motor-unit recruitment employed by skeletal muscle. As the number of contracting muscle cells increases, so does the strength of contraction. However, this mechanism is of no value in single-unit smooth muscle. Due to the presence of gap junctions, all of the muscle cells in the tissue are activated at once. 

Other factors that influence contractile activity include  

The autonomic nervous system (ANS) modifies contractile activity of both types of smooth muscle. As discussed in Chapter 9, the ANS innervates the smooth muscle layer in a very diffuse manner, so neurotransmitter is released over a wide area of muscle. Typically, the effects of sympathetic and parasympathetic stimulation in a given tissue oppose each other one system enhances contractile activity while the other inhibits it. The specific effects (excitatory or inhibitory) that the two divisions of the ANS have on a given smooth muscle depend upon its location. 

Many hormones and other blood-borne substances (including drugs) also alter contractile activity of smooth muscle. Some of the more important substances include epinephrine norepinephrine angiotensin II vasopressin oxytocin and histamine. Locally produced substances that may alter contraction in the tissue in which they are synthesized include nitric oxide prostaglandins leukotrienes carbon dioxide and hydrogen ion. 

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