10 Muscular System
Learning Objectives
- Identify the anatomy of the muscular system
- Describe the main functions of the muscular system
Muscular System Word Parts
Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Muscular System.
Introduction to the Muscular System
When most people think of muscles, they think of the muscles that are visible just under the skin, particularly of the limbs. These are skeletal muscles, so-named because most of them move the skeleton. But there are two additional types of muscles: the smooth muscle and the cardiac muscle. The body has over 600 muscles which contribute significantly to the body’s weight.
Watch Muscles, Part 2 – Organismal Level: Crash Course Anatomy & Physiology #22 (11 minutes)
Muscular System Medical Terms
Anatomy (Structures) of the Muscular System
Muscle is one of the four primary tissue types of the body, and it is made up of specialized cells called fibers. The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle (see Figure 10.1). All three muscle tissues have some properties in common; they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from polarized to depolarized) and send an electrical wave called an action potential along the entire length of the membrane. Fascia is fibrous connective tissue that encloses muscles.
Three Types of Muscle Tissues
- Smooth – mainly associated with the walls of the internal organs. Also known as visceral muscles and are responsible for involuntary muscle movement – such as breathing, etc.
- Cardiac – heart muscle or myocardium. Its appearance is similar to a skeletal muscle and is responsible for the pumping of blood. It gives the heart beat.
- Skeletal – closely associated with the skeletal system. Also known as striated muscles and are responsible for voluntary muscle movement – such as swallowing, etc.
Smooth Muscle
Smooth muscle, so named because the cells do not have striations, is present in the walls of hollow organs like the urinary bladder, uterus, stomach, intestines, and in the walls of passageways, such as the arteries and veins of the circulatory system, and the tracts of the respiratory, urinary, and reproductive systems. Smooth muscle is also present in the eyes, where it functions to change the size of the iris and alter the shape of the lens; and in the skin where it causes hair to stand erect in response to cold temperature or fear.
Cardiac Muscle
Cardiac muscle tissue is only found in the heart. Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Similar to skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle (see Figure 10.1). Cardiac muscle fibers cells also are extensively branched and are connected to one another at their ends by intercalated discs. An intercalated disc allows the cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump.
Skeletal Muscle
Skeletal muscles act not only to produce movement but also to stop movement, such as resisting gravity to maintain posture. Small, constant adjustments of the skeletal muscles are needed to hold a body upright or balanced in any position. Muscles also prevent excess movement of the bones and joints, maintaining skeletal stability and preventing skeletal structure damage or deformation.
Skeletal muscles are located throughout the body at the openings of internal tracts to control the movement of various substances. These muscles allow functions, such as swallowing, urination, and defecation, to be under voluntary control. Skeletal muscles also protect internal organs (particularly abdominal and pelvic organs) by acting as an external barrier or shield to external trauma and by supporting the weight of the organs.
Skeletal muscles contribute to the maintenance of homeostasis in the body by generating heat. This heat is very noticeable during exercise, when sustained muscle movement causes body temperature to rise, and in cases of extreme cold, when shivering produces random skeletal muscle contractions to generate heat.
Concept Check
- Compare and contrast the 3 types of muscles tissues.
- Where in the body do you find each of the muscle types?
Physiology (Function) of the Muscular System
The main function of the muscular system is to assist with movement. Muscles work as antagonistic pairs. As one muscle contracts, the other muscle relaxes. This contraction pulls on the bones and assists with movement. Contraction is the shortening of the muscle fibers while relaxation lengthens the fibers. This sequence of relaxation and contraction is influenced by the nervous system.
Muscles also work to keep the posture of the body. This is done through muscle contraction where the trunk is kept straight either when sitting or standing.
Watch the video: Joint Movements (6 minutes)
| Action | Meaning |
|---|---|
| flexion | Decreasing the angle between two bones; bending a limb. |
| extension | Increasing the angle between two bones; straightening out a limb. |
| abduction | Movement away from the midline of the body |
| adduction | Movement toward the midline of the body |
| rotation | Circular movement around an axis (central point). Internal rotation is toward the center of the body and external rotation is away from the center of the body. |
| dorsiflexion | Decreasing the angle of the ankle join so that the foot moves upward, toward the knee or ceiling. This is the opposite movement of stepping on the gas pedal when driving a car. |
| plantar flexion | Motion that moves the foot downward toward the ground as when pointing the toes or stepping on the gas pedal. Plant/o means sole of the foot. |
| supination | As applied to the hand and forearm, where the elbow is bent, the act of turning the palm up. As applied to the foot, it is outward roll of the foot/ankle during normal motion. |
| pronation | As applied to the hand and forearm, where the elbow is bent, the act of turning the palm down. As applied to the foot, it is inward roll of the foot/ankle during normal motion. |
Naming of Muscles
There are many nomenclatures for naming muscles. Some of these include:
- divisions – biceps, triceps, quadriceps
- size – maximus (largest), minimus (smallest)
- shape – deltoid (triangular), trapezious (trapezoid)
- action – flexor (to flex), adductor (towards midline of body)
Muscular System Medical Abbreviations
Diagnostic Procedures
Electromyography (EMG) is a procedure that assesses the function of nerve cells that control muscles. Electrodes, either attached to the skin or inserted into the muscle, allow for the recording of electrical impulses. EMG can identify functional problems with the peripheral nerves, muscles, or with the signals between the nerves and the muscles. This is just one test in a series of tests that assist in the diagnosis of neuromuscular disorders (Mayo Clinic Staff, 2019). To learn more, please visit the Mayo Clinic’s Electromyography webpage.
Magnetic Resonance Imaging (MRI) (Figure 10.4) is a test that uses radio frequency waves and a magnetic field to produce clear images that aid in the diagnosis of a wide range of conditions (National Institute of Biomedical Imaging and Bioengineering, n.d.). Leung (2017) notes that there has been increased clinical use in using MRI for the treatment and monitoring of muscular disorders due to the high-quality MRI images that distinguish skeletal muscles from fat (para. 4). To learn more, please visit the National Institute of Biomedical Imaging and Bioengineering MRI webpage.
Range of Motion Testing is a diagnostic procedure used to determine the amount of movement around a specific joint.
Medical Terminology in Context
Medical Specialties Related to Muscular System
Orthopedic Surgeon
Orthopedic Surgeons are medical doctors who complete specialized training in the prevention, diagnosis, treatment and surgery of disorders and diseases related to the musculoskeletal systems (American Academy of Orthopaedic Surgeons, 2021). For more details please visit the American Academy of Orthopaedic Surgeons’s page on Orthopaedic Surgeons.
Neurologist
Neurologists are medical doctors who complete an additional specialized training in the prevention, diagnosis, and treatment of disorders and conditions related to the brain, spinal cord, nerves and muscles (American Academy of Neurology, 2021). For more details visit the American Academy of Neurology’s webpage.
Kinesiologist
Kinesiologists are regulated health-care professionals with a degree in kinesiology or related discipline. Kinesiologists work in a variety of settings that assist people with pain management, injury prevention, and health promotion through biomechanics (American Kinesiology Association, 2021). To explore career options for kinesiologists, visit the American Kinesiology Association’s Career Center webpage. To learn more about kinesiologists and careers in this field, visit the Zippia Kinesiologist Overview webpage.
Occupational Therapist
Occupational therapist helps people across the lifespan to do the things they want and need to do through the therapeutic use of daily activities (occupations). Occupational therapy practitioners enable people of all ages to live life to its fullest by helping them promote health, and prevent—or live better with—injury, illness, or disability. To learn more please visit the American Occupational Therapy Association webpage.
Certified Occupational Therapist Assistant
Certified occupational therapist assistants and aides help patients develop, recover, improve, as well as maintain the skills needed for daily living and working. To learn more please visit the Occupational Outlook Handbook: Occupational Therapy Assistants and Aides.
Physical Therapist
Physical therapists help people to maximize their quality of life. They work with people of all ages and abilities, and in a variety of settings. They help people rehabilitate from devastating injuries, manage chronic conditions, avoid surgery and prescription drugs, and create healthy habits. To learn more please visit: American Physical Therapy Association
Physical Therapist Assistant
Assist physical therapists in providing physical therapy treatments and procedures. May, in accordance with state laws, assist in the development of treatment plans, carry out routine functions, document the progress of treatment, and modify specific treatments in accordance with patient status and within the scope of treatment plans established by a physical therapist. Generally requires formal training. To learn more please visit: Physical Therapist Assistants
References
American Academy of Neurology. (2021). What is a neurologist? https://www.aan.com/tools-and-resources/medical-students/careers-in-neurology/what-is-a-neurologist/
American Academy of Orthopaedic Surgeons. (2021). Orthopaedic Surgeons: Restoring mobility and keeping our nation in motion. https://www.aaos.org/about/what-is-an-orthopaedic-surgeon/
American Kinesiology Association. (2021). Career Center. https://www.americankinesiology.org/SubPages/Pages/Careers%20In%20Kinesiology#rn
American Occupational Therapy Association. (2021). What is Occupational Therapy. https://www.aota.org/conference-events/otmonth/what-is-ot.aspx
American Physical Therapy Association. (2021). Careers in Physical Therapy. https://www.apta.org/your-career/careers-in-physical-therapy
Mayo Clinic Staff. (2019, May 21). Electromyography (EMG). Mayo Clinic Patient Care and Information. https://www.mayoclinic.org/tests-procedures/emg/about/pac-20393913
National Institute of Biomedical Imaging and Bioengineering. (n.d.) Magnetic Resonance Imaging (MRI). National Institutes of Health. https://www.nibib.nih.gov/science-education/science-topics/magnetic-resonance-imaging-mri
Occupational Therapy Assistants and Aides. (Sept 2021). Occupational Outlook Handbook. https://www.bls.gov/ooh/healthcare/occupational-therapy-assistants-and-aides.htm
U.S. Bureau of Labor Statistics. (2021). Occupational Therapists. https://www.bls.gov/ooh/healthcare/physical-therapists.htm#tab-1
U.S. Bureau of Labor Statistics. (2021). Physical Therapist Assistants. https://www.bls.gov/oes/current/oes312021.htm#nat
Test Yourself
Use these practice activities to review the concepts in this chapter. If you prefer, there is a printable version of these activities.
Identify meanings of key word components of the muscular system.
Apply the rules of medical language to pronounce, break into word parts, and define the following terms.
Practice pronouncing and defining these commonly abbreviated muscular terms.
Use terms related to the muscular system:
Place the given medical terms in context to complete the scenarios below.
Test your knowledge by answering the questions below.
Chapter Attributions
This chapter was adapted by Karen Hobbs from “Muscular System” by Stacey Grimm; Coleen Allee; Elaine Strachota; Laurie Zielinski; Traci Gotz; Micheal Randolph; and Heidi Belitz. Licensed under a CC BY 4.0 license.
Media Attributions
Muscles, Part 2 – Organismal Level: Crash Course Anatomy & Physiology #22 by CrashCourse is licensed under the Standard YouTube license.
Joint Movements by Dr Matt & Dr Mike is licensed under the Standard YouTube license.
Joints: Crash Course Anatomy & Physiology #20 by CrashCourse is licensed under the Standard YouTube license.
Also known as striated muscles. Skeletal muscles are responsible for voluntary muscle movement.
The heart muscle, also known as the myocardium. Its appearance is similar to skeletal muscle. It pumps blood and gives the heart beat.
Also known as visceral muscles. Smooth muscle is mainly associated with the walls of internal organs. Smooth muscles are responsible for involuntary muscle movement.
biological process that results in stable equilibrium
in opposition to each other
in opposition to each other
