What are Striated Muscles and Their Functions?

Striated muscle, also known as skeletal muscle, is a type of muscle tissue characterized by its striped or striated appearance and it plays an important role in the movement of the human body. Striated muscles are composed of long, cylindrical cells known as muscle fibers.

These muscles are characterized by their striped or striated appearance under a microscope that shows the organized arrangement. This article helps in understanding the biology of striated muscles which is essential to know how our bodies move, maintain posture, and perform various physical activities.

What is Striated Muscle?

Striated muscles, also known as skeletal muscles, play a crucial role in the movement and functioning of the human body. The term “striated” refers to the alternating dark and light bands observed in the microscopic structure of these muscles. These muscles are attached to bones by tendons and are responsible for voluntary movements in the body. Striated muscles are characterized by a striped or striated appearance under a microscope, which is a result of the arrangement of compressible units within the muscle fibers.

How do Striated Muscles work?

Striated muscles work through a coordinated process of contraction and relaxation, enabling voluntary movements in the body and composed of long, cylindrical cells called muscle fibers, these muscles are organized into bundles known as fascicles. Within muscle fibers, actin and myosin filaments create sarcomeres, the basic units of contraction. When a nerve impulse stimulates the muscle, calcium ions are released, allowing myosin heads to form cross-bridges with actin filaments.

This initiates a power stroke resulting in muscle contraction. The neuromuscular junction, where nerves communicate with muscle fibers, plays a crucial role in initiating this process. Muscle relaxation occurs when calcium ions are transported back preventing further cross-bridge formation.

Diagram of the Striated Muscle

The diagram of the striated muscle is as follows:

Structure of Striated Muscles

The structure of striated muscles is highly organized, consisting of several levels that contribute to their function. Striated muscles are characterized by alternating dark and light bands, giving them a striped or striated appearance. Striated muscles are made up of long, cylindrical cells called muscle fibers and these fibers contain multiple nuclei. The structural components of striated muscles:

Muscle Fiber

Striated muscles are made up of long, cylindrical cells called muscle fibers and these fibers contain multiple nuclei.

• Cellular Level: The basic structural unit of striated muscles is the muscle fiber, also known as a muscle cell. These are long, multinucleated cells with a cylindrical shape.
• Plasma Membrane (Sarcolemma): The muscle fiber is surrounded by a plasma membrane called the sarcolemma, which encloses the cytoplasm of the muscle cell.

Myofibrils

Within the muscle fiber, there are numerous thread-like structures called myofibrils, which run parallel to the length of the fiber.

• Subcellular Level: Muscle fibers contain numerous myofibrils, which are long, cylindrical structures that run parallel to the length of the muscle fiber.
• Contractile Units: Myofibrils are composed of repeating units called sarcomeres, which are contractile units of striated muscles.

Filaments

It refers to the protein structures actin and myosin, within sarcomeres that enable muscle contraction.

• Thin Filaments: Composed primarily of the protein actin, along with regulatory proteins like tropomyosin and troponin.
• Thick Filaments: Composed mainly of the protein myosin. Thick filaments are located in the central region of the sarcomere.

I-Bands and A-Bands

The I-band contains only thin filaments shortens during muscle contraction, while the A-band maintains constant length during contraction to ensure proper muscle function.

• I-Bands: Light bands within the sarcomere, consisting of thin filaments only. They extend from the Z-line towards the center of the sarcomere.
• A-Bands: Dark bands within the sarcomere, consisting of both thick and overlapping thin filaments.

H-Zone

The H zone in striated muscle is a region within the sarcomere and it shortens during muscle contraction. The central region of the A-band where only thick filaments are present, without overlapping thin filaments.

M-Line and Central Structure

The M-line in striated muscle is a structural protein line and helps in the regulation of muscle contraction. Located at the center of the sarcomere, the M-line supports the thick filaments and contributes to sarcomere stability.

Sarcoplasmic Reticulum (SR)

Sarcoplasmic Reticulum (SR) is a specialized endoplasmic reticulum that stores and releases calcium ions, essential for muscle contraction.

• Specialized Endoplasmic Reticulum: The sarcoplasmic reticulum is a specialized endoplasmic reticulum within muscle cells.
• Calcium Storage: The SR stores and releases calcium ions, which play a crucial role in muscle contraction.

Transverse Tubules (T-Tubules)

Transverse Tubules in striated muscles are tiny tube-like structures that help transmit electrical signals.

• Tunnel-Like Structures: Invaginations of the sarcolemma that extend into the muscle fiber.
• Conduction of Electrical Signals: T-tubules help transmit the action potential deep into the muscle fiber, ensuring muscle contraction.

Types of Striated Muscles

Striated muscles also known as skeletal muscles, can be classified into two main types based on their contraction patterns and control:

Skeletal Muscle (Voluntary Muscle)

Skeletal muscles, also known as voluntary or striated muscles, are attached to bones by tendons and are under conscious control. They are responsible for body movements, such as walking, running, and lifting weights. Skeletal muscle is multinucleated and has a highly organized structure with distinct striations.

Cardiac Muscle (Involuntary Muscle)

Cardiac muscle is found in the heart. It is also striated, like skeletal muscle, but differs in structure and function. Cardiac muscle is involuntary, meaning it contracts without conscious control, and it is responsible for the beating of the heart.

Dysfunction of Striated Muscles

Dysfunction of striated muscles can result from various conditions and significantly impact the body’s ability to perform voluntary movements. One common issue is muscle atrophy, where there is a loss of muscle mass and strength, often caused by factors such as lack of physical activity and aging. Conversely, muscle hypertrophy involves an abnormal increase in muscle size, commonly associated with intense resistance training or underlying health conditions. Injuries, such as muscle strains or sprains, can result from overexertion or traumatic events, causing pain, swelling, and limited mobility. The treatment of striated muscle dysfunction depends on the underlying cause and may involve physical therapy and medications.

Functions of Striated Muscles

Striated muscles perform several crucial functions in the human body. These muscles are under conscious control, allowing individuals to perform voluntary movements. Here are some key functions of striated muscles:

• Voluntary Movement: Striated muscles are responsible for voluntary movements of the body. They enable actions such as walking, running, jumping, lifting, and reaching. The precise control of striated muscles allows for coordinated motion.
• Postural Support: Striated muscles play a vital role in maintaining posture and body position. They work continuously to support the skeletal structure against the force of gravity, contributing to stability while sitting or moving.
• Heat Generation: Striated muscles generate heat through their contractions. This activity contributes to the body’s ability to regulate temperature. In response to cold, muscles may undergo contractions (shivering) to generate additional heat.
• Metabolism and Energy: The contraction of striated muscles requires energy, leading to increased metabolic activity. Engaging in physical activities involving skeletal muscles contributes to caloric expenditure, supporting a healthy metabolism.
• Joint Stability: Striated muscles crossing joints provide support and stability to the skeletal system. They facilitate joint movements and contribute to the overall coordination of the musculoskeletal system.

Conclusion – Striated Muscles

Understanding the biology of striated muscles is essential to know the complex process involved in human movement. Striated muscles are characterized by alternating dark and light bands, giving them a striped or striated appearance when viewed under a microscope which is a result of the arrangement of contractile units within the muscle fibers.

This structural organization allows for precise and coordinated movements essential for various functions, including voluntary movement and the rhythmic pumping of the heart and it highlights their essential role in daily activities, physical performance, and overall well-being. Regular physical activity, proper nutrition, and adequate rest contribute to the proper functioning and health of these muscles.

FAQs – Striated Muscles

What do Striations in Striated Muscles Represent?

Striations in striated muscles represent the organized arrangement of sarcomeres, the basic contractile units. The striated pattern reflects the ordered and repeatable structure essential for voluntary movement.

Why are Striated Muscles called Skeletal Muscles?

Striated muscles are called skeletal muscles because they are primarily attached to the skeleton by tendons. These muscles help in voluntary movements and are under conscious control, allowing for actions such as walking, running, and lifting.

Why are Striated Muscles Multinucleated?

Striated muscles are multinucleated due to the fusion of multiple myoblasts during development. The striated multinucleated muscle ensures efficient control over cellular functions.

What is the Main Function of Striated Muscles?

The main function of striated muscles, or skeletal muscles help in voluntary movement and provide conscious control over body actions such as walking, running, and lifting.

Is Striated Muscle Voluntary or Involuntary?

Striated muscles, also known as skeletal muscles, are voluntary muscles. They are under conscious control, allowing individuals to regulate body movements such as walking, talking, and other physical activities.

What is the Difference Between Striated and Non Striated Muscles?

Striated muscles, also known as striped muscles, have cross striations and are attached to bones or tendons. Non-striated muscles, also known as unstriped muscles, have no cross striations and are located in the lining of inner organs.

Why is Cardiac Muscle Not Multinucleated?

Cardiac muscle are not multinucleated as the myoblasts that form the cells of the cardiac muscle do not fuse.