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9: Muscular System

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    This chapter describes the structure and functions of the muscular system. It compares and contrasts the three major types of muscle tissue and explains in detail how muscles contract according to the sliding filament theory. The chapter also relates physical exercise to fitness and health and describes several musculoskeletal and neuromuscular disorders.

    • 9.1: Case Study- Muscles and Movement
      Forty-three-year-old Nasir has a rare condition called cervical dystonia, which is also called spasmodic torticollis. In this condition, the muscles in the neck contract involuntarily, often causing the person’s head to twist to one side. Fortunately for Nasir and other cervical dystonia sufferers, there is a treatment that can significantly reduce symptoms in many people—and it might surprise you!
    • 9.2: Introduction to the Muscular System
      The largest percentage of muscles in the muscular system consists of skeletal muscles, which are attached to bones and enable voluntary body movements. There are almost 650 skeletal muscles in the human body, many of them shown in the figure below. Besides skeletal muscles, the muscular system also includes cardiac muscle - which makes up the walls of the heart - and smooth muscles, which control movement in other internal organs and structures.
    • 9.3: Types of Muscle Tissue
      Muscle tissue is a soft tissue that makes up most of the tissues in the muscles of the human muscular system. Other tissues in muscles are connective tissues, such as tendons that attach skeletal muscles to bones and sheaths of connective tissues that cover or line muscle tissues. Only muscle tissue per se, however, has cells with the ability to contract.
    • 9.4: Muscle Contraction
      A muscle contraction is an increase in the tension or a decrease in the length of a muscle. Muscle tension is the force exerted by the muscle on a bone or other object. A muscle contraction is isometric if muscle tension changes, but muscle length remains the same. An example of isometric muscle contraction is holding a book in the same position. A muscle contraction is isotonic if muscle length changes, but muscle tension remains the same.
    • 9.5: Physical Exercise
      Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. We generally think of physical exercise as activities that are undertaken for the main purpose of improving physical fitness and health. However, physical activities that are undertaken for other purposes may also count as physical exercise. Scrubbing a floor, raking a lawn, or playing active games with young children or a dog are all activities that can have health benefits.
    • 9.6: Disorders of the Muscular System
      Musculoskeletal disorders are injuries that occur in muscles or associated tissues (such as tendons) because of biomechanical stresses. They may be caused by sudden exertion, over-exertion, repetitive motions, or long periods maintaining awkward positions. Musculoskeletal disorders are often work- or sports-related, and generally just one or a few muscles are affected. They can often be treated successfully, and full recovery can be very likely.
    • 9.7: Case Study Conclusion- Needing to Relax and Chapter Summary
      As you learned in the beginning of this chapter, botulinum toxin—one form of which is sold under the brand name Botox - does much more than smooth out wrinkles. It can be used to treat a number of disorders involving excessive muscle contraction, including cervical dystonia. You also learned that cervical dystonia, which Nasir suffers from, causes abnormal, involuntary muscle contractions of the neck. This results in jerky movements of the head and neck.

    This page titled 9: Muscular System is shared under a CK-12 license and was authored, remixed, and/or curated by Suzanne Wakim & Mandeep Grewal via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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