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.
Solutions Answers for Critical Thinking Questions 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. In comparison to skeletal muscles, the action potential in these cells is rather slower, but they can last for about fifty times more.
Sodium channels are responsible for this characteristic of smooth muscles; in contrast to skeletal muscle, smooth muscle has a slower opening of sodium channels s low repolarization. Question: What initiates an action potential on a muscle cell? Answer: When more amount of sodium ions moves across the plasma membrane as compared to the potassium ions, an electrochemical gradient develops. This gradient leads to depolarization of the membrane, which then initiates an action potential.
Smooth muscles can be looked after if we will focus a little on our diet and lifestyle. We can easily take care by doing the following tips and bits:. Got a question about smooth muscles? Join our Forum: Smooth muscle vs dense regular connective tissue. Our community might be able to help!
Try to answer the quiz below and see what you have learned so far about smooth muscles. Muscle cells are specialized to generate force and movement.
Learn about the different types of muscle tissues in this tutorial and the molecular mechanisms of contraction Read More.
The circulatory system is key to the transport of vital biomolecules and nutrients throughout the body. Learn about the different components and functions of the human circulatory system dealt with in detail in this tutorial. The lymphatic system is also elucidated elaborately here The gastrointestinal system breaks down particles of ingested food into molecular forms by enzymes through digestion and then transferred to the internal environment by absorption.
Find out more about these processes carried out by the gastrointestinal system through this tutorial The kidneys are responsible for the regulation of water and inorganic ions.
Read this tutorial to learn about the different parts of the kidneys and its role in homeostasis A sensory system is a part of the nervous system consisting of sensory receptors that receive stimuli from the internal and external environment, neural pathways that conduct this information to the brain and parts of the brain that processes this information.
Know the different sensory systems of the human body as elaborated by this tutorial Humans are capable of only one mode of reproduction, i. Haploid sex cells gametes are produced so that at fertilization a diploid zygote forms. This tutorial is an in-depth study guide regarding male and female reproductive physiology Nervous System.
Cell Biology. Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum. Table of Contents. Biology Definition: Question: What is smooth muscle? Answer: Smooth muscle is an involuntary, non-striated type of vertebrate muscle capable of slow rhythmic involuntary contractions. Smooth muscle, also called an involuntary muscle , displays no cross stripes when examined under a microscope.
It is made up of spindle-shaped narrow cells with a single centrally-located nucleus. Smooth muscles contract involuntarily and slowly. A great part of internal organs and the majority of the area of the digestive tract is lined with smooth muscles. The muscular system includes all the muscles of the animal body.
There are three types of muscles : skeletal muscles , smooth muscles, and cardiac muscles. Both the skeletal muscles and the cardiac muscles have striations when viewed under the microscope. In contrast, the smooth muscle lacks striations. This is because of the uniform distribution of myosin filaments in the smooth muscle cell. Apart from the lack of striations, the smooth muscle differs from the other two by the cell shape.
The smooth muscle cells are typically spindle-shaped and the nuclei are centrally located. They are also capable of contracting to a much smaller fraction of their resting length. They are responsible for the rhythmic involuntary movements of these organs. Dephosphorylation of myosin light chains terminates smooth muscle contraction.
Unlike skeletal muscle smooth muscle is phosphorylated during its activation. This creates a potential difficulty in that simply reducing calcium levels won't produce muscle relaxation. Myosin light chain phosphatase MLCP is, instead is responsible for dephosphorylation of the myosin light chains ultimately leading to smooth muscle relaxation.
Smooth muscle consists of two types single-unit and multi-unit. Single-unit smooth muscle consists of multiple cells connected through connexins that can be stimulated in a synchronous pattern from only one synaptic input. Connexins allow for cell-to-cell communication between groups of single-unit smooth muscle cells.
This inter-cellular communication allows ions and molecules to diffuse between cells giving rise to calcium waves. This unique property of single-unit smooth muscle allows for synchronous contraction to occur. This allows for multi-unit smooth muscle to have much finer control. Multi-unit smooth muscle is found in the airways of the lungs, large arteries, and ciliary muscles of the eye. Due to autonomic control regulatory effects of smooth muscle, every surgery will be impacted by its overall function.
Monitoring a patient's vital signs during surgery is paramount to a successful procedure and the stressors of surgery can have a vast impact on the autonomic nervous system which is responsible for regulating smooth muscle contraction. Surgery can even be targeted at modifying the function of smooth muscle as in the case of a vagotomy.
Overstimulation of the vagus nerve has been speculated to be a possible cause for peptic ulcer disease, vagotomy is a classical surgical procedure that aims at treating this disorder by removing the vagus nerve at the level of the stomach and thus removing stimulation. However, this procedure has fallen out of favor recently due to advancements in medical therapy for peptic ulcer disease but may still show some benefit in certain patients.
Proper management requires an in-depth knowledge of how alpha and beta blockades will affect smooth muscle and the downstream effects of those changes on bodily functions.
Smooth muscle is an integral part of the human body, its function is required for life and can be found in almost every organ system. In the cardiovascular system, smooth muscle is used in vessels to maintain blood pressure and flow, in the lungs it opens and closes airways, in the gastrointestinal system it plays a role in motility and nutrition collection, and yet it still serves a purpose in almost every other organ system as well. The wide distribution of smooth muscle throughout the body and its many unique properties make it imperative for medical professionals to have an in-depth understanding of its anatomy, physiology, function, and disease applications.
From a functional aspect, smooth muscle physiology is responsible for maintaining and preserving every vital sign. Regardless of whether a patient presents with acute emergent disease or a chronic disease, it is likely that smooth muscle has played some role in its development.
In an acute setting, many life-saving therapies directly target smooth muscle. In these settings, a firm foundation and understanding of smooth muscle will help health professionals save lives. An even broader understanding of smooth muscle will help clinicians to increase the quality of life of their patients. As part of the biopsychosocial model, it is also important to take into consideration the psycho-social factors that may be overlooked with the diseases of smooth muscle, for example, a patient diagnosed with neurogenic bladder disease may become socially isolated to avoid the embarrassment associated with their disease state.
When approaching smooth muscle dysfunction, it is important for healthcare providers to appreciate the many facets of how the disease will impact their patients. As with all aspects of medicine, a continuing amount of research will likely change our future understanding of smooth muscle and its overall effects on disease.
Current research into smooth muscle has shown promise in future implications such as restoring endothelial tissue which in the future could lead to new ways to encourage revascularization. Even small changes in understanding like this could have an astronomical impact on the treatment and mortality of cardiovascular disease in the future.
Smooth muscle anatomy, physiology, and function remain a broad and relatively elusive topic despite the amount of funding and research efforts put into understanding it. As more time and effort is put into understanding smooth muscle our ability to treat the pathophysiology that comes with its dysfunction will broaden. It is important the clinicians continue to learn and study the impact that smooth muscle can have. As discussed, future methods may involve stimulating the regrowth of tissue with smooth muscle modulating factors.
It is not inappropriate to think that many advances in the future of medical management will focus on impacting smooth muscle in some way or another. Respiratory care. Expert opinion on pharmacotherapy. GISSI effects of lisinopril and transdermal glyceryl trinitrate singly and together on 6-week mortality and ventricular function after acute myocardial infarction. Gruppo Italiano per lo Studio della Sopravvivenza nell'infarto Miocardico. Lancet London, England. Sinha S,Iyer D,Granata A, Embryonic origins of human vascular smooth muscle cells: implications for in vitro modeling and clinical application.
Cellular and molecular life sciences : CMLS. Stem cells translational medicine. Khalil RA,. Journal of applied physiology Bethesda, Md. The Journal of physiology.
Lazebnik LB,Lychkova AE, Interaction between different parts of the autonomic nervous system in the regulation of smooth muscles in the femoral artery and trachea.
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