Lesson 1: Functions of the Muscular System
By the end of this lesson, students will be able to:
- Describe the three types of muscle tissue and their primary functions.
- Explain how the muscular and skeletal systems work together to produce movement.
- Identify and describe major body movements.
- Explain how muscle structure relates to muscle function.
Jump to Multilingual Approach Lesson Slides with translation
Introduction
The muscular system is responsible for movement throughout the body. Muscle tissue also contributes to posture, stabilization, and the movement of substances within internal organs. Because muscles can only contract, they must work together in coordinated groups to produce a wide range of movements.
Muscle Contraction and Antagonistic Pairs
Muscles generate force by contracting. During contraction, a muscle shortens and thickens. Muscles cannot actively push or lengthen; they can only pull on the structures to which they are attached (Figure 1).
Because muscles can only pull, most body movements require muscles to work in antagonistic pairs. In an antagonistic pair, one muscle contracts while the opposing muscle relaxes, allowing movement in opposite directions. This arrangement enables bidirectional movement at joints.
Types of Muscle Tissue
There are three major types of muscle tissue in the human body (Figure 2):
Skeletal Muscle
Skeletal muscle is attached to bones and is responsible for voluntary body movements. It is the primary focus of this module because it produces skeletal movement and contributes to posture and stability.
Cardiac Muscle
Cardiac muscle is found only in the heart. Specialized structural features allow cardiac muscle cells to contract together as a functional unit, producing the coordinated contractions required to pump blood.
Smooth Muscle
Smooth muscle is found in the walls of hollow organs and tubes, such as the digestive tract, blood vessels, and urinary bladder. Its contractions move substances through these structures and help regulate their diameter.
Figure 2. Comparison of skeletal, cardiac, and smooth muscle tissues.
Skeletal Muscle Attachments: Origin and Insertion
Skeletal muscle movement is described in relation to two attachment points:
- Origin: The relatively stationary attachment of a muscle.
- Insertion: The attachment that moves during contraction.
When a skeletal muscle contracts, the insertion is pulled toward the origin (Figure 3).
Figure 3. Skeletal muscle attachments showing origin and insertion.
Major Body Movements
Abduction and Adduction
Abduction is the movement of a limb away from the body’s midline. Adduction is movement of a limb toward the body’s midline (Figure 4).
Figure 4. Abduction and adduction of the upper limb.
Flexion and Extension
Flexion decreases the angle between two body parts at a joint. For example, bending the knee or bringing the chin toward the chest decreases the angle at the joint (Figure 5).
Extension increases the angle between body parts, such as straightening the knee or returning the head to an upright position.
Figure 5. Examples of flexion and extension at the knee and neck.
Pronation and Supination
Pronation rotates the forearm so that the palms face posteriorly (or downward when standing in the anatomical position).
Supination rotates the forearm so that the palms face anteriorly (or upward when standing in the anatomical position). The term “supination” is often remembered by imagining holding a bowl of soup in the hands (Figure 6).
Figure 6. Pronation and supination of the forearm.
Structure and Function of Muscle Tissue
As with all body systems, structure and function are closely related in muscle tissue.
Skeletal Muscle
The arrangement of skeletal muscle fibers and their connection to the nervous system allow for voluntary control. Skeletal muscles are responsible for conscious movements such as walking, speaking, writing, and many aspects of sphincter control.
Cardiac Muscle
Cardiac muscle is involuntary and contracts automatically. Specialized connections between cells allow the heart to function as a coordinated pumping organ.
Smooth Muscle
Smooth muscle is also involuntary. It controls movements within internal organs, including the movement of food through the digestive tract, the regulation of blood vessel diameter, and other reflexive functions.
The structural characteristics of each muscle type enable it to perform its specific role within the body.
Summary
The muscular system comprises three types of muscle tissue: skeletal, cardiac, and smooth. Skeletal muscle, along with the skeletal system, produces voluntary movement and operates through antagonistic muscle pairs. Muscle actions are described using anatomical movement terms such as abduction, adduction, flexion, extension, pronation, and supination. The structure of each muscle type is closely related to its function, allowing muscles to perform specialized roles throughout the body.
Multilingual Approach Lesson Slides with translations
Use the interactive below to access the multilingual lesson slides.
Lesson Video
Watch this lesson video to hear an A&P instructor walk you through the lesson.
Follow the link to the recording.
Practice Questions
Use these practice questions to assess your knowledge before you move on to the next section.
Try this crossword puzzle for more practice!
