5.2 What are Muscles?
Muscle is one of four main tissue types in the human body (Nervous, Connective, and Epithelial, to name the other three). They are a culmination of hundreds, thousands, or even hundreds of thousands of muscle cells (aka muscle fibres) that contract and relax to allow us to digest food, breathe, speak, blink, pump blood throughout our body, and produce movement.
Types of Muscle Tissue
Typically, when we think about muscle, we think of skeletal muscle, such as our quadriceps or biceps; however, muscle tissue also exists as cardiac and smooth muscle. Let’s explore their differences by clicking on each icon below.
Text Description
Cardiac Muscle:
- Found exclusively in the heart
- Responsible for contracting to eject blood from the heart and begin circulation
- Involuntary (regulated by the autonomic nervous system)
- Striated (striped and aligned microscopic appearance)
Skeletal Muscle:
- A muscle that attaches to a bone
- The most prevalent type of muscle in the human body (makes up 30-40% of body weight)
- Voluntary (i.e., you have conscious control of skeletal muscle contraction)
- Striated (striped and aligned microscopic appearance)
Smooth Muscle:
- Surrounds the body’s internal organs (i.e., blood vessels, digestive tract)
- Contracts slowly for longer durations
- Involuntary (i.e., you have no conscious control of smooth muscle contraction)
Voluntary vs Involuntary Contractions
While sitting there reading this chapter, you can differentiate voluntary vs involuntary contractions by asking yourself: “Can I purposefully contract the muscle?”. Try contracting your blood vessels or small intestine; you can’t; therefore, they are involuntary. Try contracting your heart muscles; you can’t, therefore, they are also involuntary. Now try contracting your biceps brachii or your hip flexor group; you can, therefore, they are voluntary.
Of the three main types of muscle previously mentioned, skeletal muscle is responsible for generating the force required to produce voluntary human movement. You will learn more about skeletal muscle anatomy in Chapter 11.
“10.2 Skeletal Muscle” from Anatomy & Physiology by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU & OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.
