How does smooth muscle divide

The two types have different locations in the body and have different characteristics. Single-unit muscle has its muscle fibers joined by gap junctions so that the muscle contracts as a single unit. This type of smooth muscle is found in the walls of all visceral organs except the heart which has cardiac muscle in its walls , and so it is commonly called visceral muscle.

Because the muscle fibers are not constrained by the organization and stretchability limits of sarcomeres, visceral smooth muscle has a stress-relaxation response. This means that as the muscle of a hollow organ is stretched when it fills, the mechanical stress of the stretching will trigger contraction, but this is immediately followed by relaxation so that the organ does not empty its contents prematurely.

This is important for hollow organs, such as the stomach or urinary bladder, which continuously expand as they fill. In general, visceral smooth muscle produces slow, steady contractions that allow substances, such as food in the digestive tract, to move through the body. Multiunit smooth muscle cells rarely possess gap junctions, and thus are not electrically coupled.

As a result, contraction does not spread from one cell to the next, but is instead confined to the cell that was originally stimulated. Stimuli for multiunit smooth muscles come from autonomic nerves or hormones but not from stretching. This type of tissue is found around large blood vessels, in the respiratory airways, and in the eyes. Similar to skeletal and cardiac muscle cells, smooth muscle can undergo hypertrophy to increase in size. Unlike other muscle, smooth muscle can also divide to produce more cells, a process called hyperplasia.

This can most evidently be observed in the uterus at puberty, which responds to increased estrogen levels by producing more uterine smooth muscle fibers, and greatly increases the size of the myometrium. Smooth muscle is found throughout the body around various organs and tracts. Smooth muscle cells have a single nucleus, and are spindle-shaped. Smooth muscle cells can undergo hyperplasia, mitotically dividing to produce new cells.

Smooth muscle can be stimulated by pacesetter cells, by the autonomic nervous system, by hormones, spontaneously, or by stretching. The fibers in some smooth muscle have latch-bridges, cross-bridges that cycle slowly without the need for ATP; these muscles can maintain low-level contractions for long periods.

Single-unit smooth muscle tissue contains gap junctions to synchronize membrane depolarization and contractions so that the muscle contracts as a single unit. Single-unit smooth muscle in the walls of the viscera, called visceral muscle, has a stress-relaxation response that permits muscle to stretch, contract, and relax as the organ expands.

Multiunit smooth muscle cells do not possess gap junctions, and contraction does not spread from one cell to the next. Why can smooth muscles contract over a wider range of resting lengths than skeletal and cardiac muscle? Smooth muscles can contract over a wider range of resting lengths because the actin and myosin filaments in smooth muscle are not as rigidly organized as those in skeletal and cardiac muscle. Since it is not under conscious control, smooth muscle is involuntary muscle.

Smooth muscle fibers are elongated spindle-shaped cells with a single nucleus. In general, they are much shorter than skeletal muscle cells. The nucleus is located centrally and the sarcoplasm is filled with fibrils. The thick myosin and thin actin filaments are scattered throughout the sarcoplasm and are attached to adhesion densities on the cell membrane and focal densities within the cytoplasm.

Since the contractile proteins of these cells are not arranged into myofibrils like those of skeletal and cardiac muscle, they appear smooth rather than striated. Smooth muscle fibers are bound together in irregular branching fasciculi that vary in arrangement from organ to organ. These fasciculi are the functional contractile units. There is also a network of supporting collagenous tissues between the fibers and the fasciculi.

Cardiac muscle shares important characteristics with both skeletal and smooth muscle. Functionally, cardiac muscle produces strong contractions like skeletal muscle. However, it has inherent mechanisms to initiate continuous contraction like smooth muscle. The rate and force of contraction is not subject to voluntary control, but is influenced by the autonomic nervous system and hormones.

Histologically, cardiac muscle appears striated like the skeletal muscle due to arrangement of contractile proteins. It also has several unique structural characteristics:.

Collagenous tissues are found surrounding individual cardiac muscle fibers. There is abundance vascularization within this supporting tissue, which is required to meet the high metabolic demands of cardiac muscle.

The cardiac muscle fibers are joined end to end by specialized junctional regions called the intercalated discs. The intercalated discs provide anchorage for myofibrils and allow rapid spread of contractile stimuli between cells. Such rapid spread of contraction allows the cardiac muscles to act as a functional syncytium.

The intercalated discs contain three types of membrane-to-membrane contact:. In addition to the contractile cells, there is a specialized system made up of modified muscle cells whose function is to generate the stimulus for heartbeat and conduct the impulse to various parts of the myocardium.

This system consists of sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibers. How are fibers connected? Location and number of nuclei How are fibers connected? Morphology Location of muscle Answer:. Slides Please select whether to view the slides in study mode or quiz mode. In study mode, the images will contain labels and a description.

In quiz mode, labels and description will be hidden. Study Mode. With this dye, the A-bands are stained dark and the I-bands light. Since both cardiac muscle fibers and skeletal muscle fibers are striated, how would you differentiate between them in a histological slide? This is a section of the tongue. Begin by identifying groups of fasciculi cut in transverse section. Unlike other muscle, smooth muscle will also divide quite readily to produce more cells, a process called hyperplasia.

This can most evidently be observed in the uterus at puberty, which responds to increased estrogen levels by producing more uterine smooth muscle fibers. Smooth muscle is found throughout the body around various organs and tracts. Smooth muscle cells have a single nucleus, and are spindle-shaped. Smooth muscle cells can undergo hyperplasia, mitotically dividing to produce new cells. Smooth muscle can be stimulated by pacesetter cells, by the autonomic nervous system, by hormones, spontaneously, or by stretching.

The fibers in some smooth muscle have latch-bridges, cross-bridges that cycle slowly without the need for ATP; these muscles can maintain low-level contractions for long periods.

Single-unit smooth muscle tissue contains gap junctions to synchronize membrane depolarization and contractions so that the muscle contracts as a single unit. Single-unit smooth muscle in the walls of the viscera, called visceral muscle, has a stress-relaxation response that permits muscle to stretch, contract, and relax as the organ expands.

Multiunit smooth muscle cells do not possess gap junctions, and contraction does not spread from one cell to the next. Why can smooth muscles contract over a wider range of resting lengths than skeletal and cardiac muscle? Skip to content Learning Objectives Understand the structure and function of smooth muscle tissue By the end of this section, you will be able to: Understand the difference between single-unit and multi-unit smooth muscle Describe the microanatomy of a smooth muscle cell Explain the process of smooth muscle contraction Explain how smooth muscle differs from skeletal muscle.

Figure Sections Summary Smooth muscle is found throughout the body around various organs and tracts. Review Questions. Critical Thinking Questions 1. Describe the differences between single-unit smooth muscle and multiunit smooth muscle. Glossary calmodulin regulatory protein that facilitates contraction in smooth muscles dense body sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments hyperplasia process in which one cell splits to produce new cells latch-bridges subset of a cross-bridge in which actin and myosin remain locked together pacesetter cell cell that triggers action potentials in smooth muscle stress-relaxation response relaxation of smooth muscle tissue after being stretched varicosity enlargement of neurons that release neurotransmitters into synaptic clefts visceral muscle smooth muscle found in the walls of visceral organs.