Smooth Muscle
Smooth muscle
Smooth muscles are elongated with tapered ends. Smooth muscle does contain filaments of actin and myosin that extend the length of the cell. Myosin and actin are not organized like skeletal and cardiac muscle. Actin and myosin are more random, which is why they lack striations and appear smooth under the microscope. Sarcoplasmic reticulum is not as well developed as in smooth muscle.
Two Types of Smooth Muscle
1. Multiunit smooth muscle fibers are separate and are not organized into sheets. Multiunit smooth muscle are found in the iris of the eye and walls of blood vessels. Typically it contracts only in response to neuron stimulation or by certain hormones. Multiunit smooth muscle allows for greater control of contraction.
Would you want precise and greater control of contraction for maintaining blood pressure? ____.
Would you want precise and greater control of contraction for controlling the amount of light that reaches the retina? ___________________________________________________________
What would happen if light was poorly controlled to the retina? _________________________
2. Visceral smooth muscle is composed of sheets in close contact with one another. Smooth muscle is found in the walls of hollow organs, such as in the intestines, bladder, stomach, and uterus. Fibers of visceral smooth muscle can stimulate each other producing contraction of adjacent fibers. This allows smooth muscle sheet to work together. Rhythmicity is a pattern of repeated contractions due to self excitation of fibers.
Peristalsis is the wavelike contraction performed by visceral smooth muscle. It combines two features of multiunit smooth muscle, rhythmic contractions and transmission of impulses from cell to cell. Peristalsis helps force intestinal contents down the digestive system.
Smooth muscle contraction is similar to skeletal muscle in that it does include actin and myosin. Membrane impulses causes release of calcium ions into the cell and it uses ATP for contraction.
Differences of Smooth Muscle Contraction.
1. Neurotransmitters. Smooth muscle responds to acetylcholine and norepinephrine. These neurotransmitter produce contraction in some smooth muscle while causing inhibition and in other smooth muscle fibers. Hormones can also alter the degree of response to specific neurotransmitters.
2. Smooth muscle is slower to contract and relax than skeletal muscle. However it can maintain a forceful contraction for a longer period of time with the same amount of ATP.
3. Smooth muscle can change length without changing tautness. For example the stomach can stretch as it is being filled, and continue to maintain the same pressure inside the organ.