Muscular System | Diagram, Types and Functions

The muscular system is composed of muscle fibers that enable the body to move, maintain posture, and circulate blood. It consists of three different types of muscles: the skeletal muscles, cardiac muscles, and visceral muscles. The essential function of the muscular system is to support involuntary and voluntary movement and to maintain stability and posture in all living organisms. In this article, we will discuss the muscular system, its types, functions, and disorders that can affect its functioning.

What is the Muscular System?

Definition of Muscular System: The muscular system is an organ system made up of muscle fibres that allow the body to move, maintain posture, and circulate blood. 

The muscular system is a complex of tissues comprising highly elongated and contractile cells called myocytes. The myocytes together form the muscle fibers that serve as the units of locomotion and movement in the body. Muscle fibers are highly contractile and can contract up to one-third of their total length. This allows them to bring out the contraction of muscles. The muscular system forms around 40- 50% of the body mass and primarily contains three types of muscles that are differentiated in structure, function, and shape. These are

• Skeletal muscles: These are striated in appearance. They have multinucleated myocytes that are cylindrical.
• Smooth muscles: These are non-striated in appearance. These have a singular nucleus in each myocyte and are spindle-shaped.
• Cardiac muscles: These are branched muscle fibers that are striated.

The primary function of the muscular system is contraction. By contracting and relaxing, they allow a wide range of movement of the different parts of the body and its organs. This maintains all physiological functions essential for living, like breathing, digestion, etc.

Diagram of the Muscular System

The diagram of Muscular System is shown below:

Types of Muscle

Muscles can be categorized into three types based on structure and function. These categories are skeletal muscles, smooth or visceral muscles, and cardiac muscles. The structure and function of these muscle types are as follows.

Skeletal Muscles

Skeletal muscles are also known as striated or voluntary muscles. They form a significant part of the musculoskeletal system and are responsible for the locomotion and movement of body parts. These muscles are cylindrical and are characterized by the presence of multiple nuclei and striations. Striations are caused by a repeating unit in the muscle fiber called the sarcomere. Sarcomeres have alternating thick filaments of myosin that give a dark band (red) and a thin filament of actin that gives a light band (white). This alternating dark and light band gives rise to the striated appearance of skeletal muscles.

Skeletal muscles are attached to the bones by tendons. These muscles are under conscious control and are responsible for voluntary movements such as walking, running, and lifting. They are vital in providing structural support and maintaining posture. These muscles are also responsive to neural signals in response to external stimuli.

Smooth Muscles

Smooth muscles are also called non-striated, visceral, or involuntary muscles. These muscles do not have any striations in their fibers and are spindle-shaped, with only one nucleus per myocyte. Smooth muscles are found in the walls of internal organs, such as the stomach, intestines, and blood vessels. Smooth muscles are involuntary and operate without conscious control. They perform tasks regulated only by internal nervous signaling and not external stimuli. They have essential roles in digestion, like swallowing, blood vessel constriction, and other internal organ movements.

Cardiac Muscles

Cardiac muscles are found only in the heart. They can be identified by the branched appearance of their fibers, striated and uninucleated fibers. These muscles are unique as they possess striations like skeletal muscles but work involuntarily like smooth muscles. They maintain the rhythmic pumping of blood throughout the circulatory system.

Functions of the Muscular System

The muscular system contributes to almost all physiological activities. The most essential functions of the muscular system are:

• Movement: The muscular system enables movement as skeletal muscles contract and relax under conscious control to produce multiple movements. These movements range from fine motor skills like writing to powerful contractions involved in weightlifting.
• Maintaining Posture and Stability: All body muscles work together to maintain posture and stability. They support the skeleton, prevent the body from collapsing under weight, and help move the bones to different positions for everyday activities like sitting, walking, running, or eating.
• Temperature Regulation: As muscles work, they generate heat, especially during exercise or exposure to cold environments. Muscles produce extra heat to keep the body warm by shivering or burning fat.
• Protecting Internal Organs: Smooth muscles within the walls of organs serve as a layer of insulation for the internal organs, protecting them from damage and shock. These muscles also work involuntarily to achieve functions like digestion, excretion, respiration, etc.
• Maintain Heartbeat and Blood Flow: Cardiac muscles work involuntarily to pump blood to all regions of the blood, which is necessary for survival.

Diseases of the Muscular System

The muscular system is susceptible to injury and diseases like any other body organ system. The common diseases of the muscular system are:

• Muscle Strains and Sprains: Overuse or improper use of muscles can lead to strains or sprains. Common injuries, like stretching or tearing muscle fibers or ligaments, cause pain and limited motion.
• Tendonitis: A strain in the tendons that attach muscles to the bone can also cause pain and discomfort.

Conclusion – Muscular System

The muscular system is an organ system that is responsible for movement, posture, and circulation. It is made up of three types of muscle: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones and are responsible for voluntary movement. Smooth muscles are found in the walls of organs and blood vessels and are responsible for involuntary movement. Cardiac muscle is found in the heart and is responsible for pumping blood. The muscular system is controlled by the nervous system and allows us to move, maintain our posture, and circulate blood. Without the muscular system, we would not be able to survive.

FAQs on Muscular System

What are the 4 Main Functions of the Muscular System?

The main functions of the muscular system are coordinating movement and locomotion along with breathing, digestion, heart beating, posture regulation, and protection of internal organs.

What are the Three Muscle Types?

The three types of muscles in humans are skeletal muscles (visceral muscles), smooth muscles, and cardiac muscles.

How do Muscles Work?

The muscular system works by contracting and relaxing voluntarily upon stimulus or involuntarily by nervous signals to cause movement by moving the body in the desired direction.

Is Cardiac Muscle Striated?

Yes, cardiac muscles are involuntary muscles like smooth muscles, but they possess striations like skeletal muscles.

What is the Difference Between Striated and Non-Striated Muscle?

Striated muscled possesses dark bands or striations and are voluntary in action, while non-striated muscles do not have any striations and are involuntary.