Skeletal muscles constitute one of the three types of muscles found in our body. They form an integral part of the body structure since they are responsible for making all the body parts move to cater to the demands. In simple words, the skeletal muscle structure controls the skeletal functions of motion. Tendons are what attach all the skeletal muscles to the bones of the body.

As the only voluntary muscle in the body, skeletal muscle mass forms 40% of the body weight. In the subsequent sections, we shall discuss all the roles, working, structure, types, as well as characteristics of skeletal muscle in detail.

The Three Types of Muscle

There are three basic types of muscles in our body. Let us examine them to get a clearer view of the skeletal muscle.

All the muscles have a discrete structure to facilitate their respective distinct roles. The succeeding table gives an overview of all three types of muscles.

Three Types of Muscle Tissue

Property	Skeletal Muscles	Cardiac Muscles	Smooth Muscle
Type of Muscle Tissue	Voluntary, i.e., they work under our control	Involuntary, i.e., they are not under our direct control	Involuntary, i.e., they are not under our direct control
Location	Attached to the bones by tendons	Heart	The lining of the internal organs
Function	Voluntary movement of the body. Maintain the body temperature.	Pumping of blood	Regulation of blood flow Movement of materials within the body.
Striation	Striated muscle	Striated muscle	Non-striated muscle
Structure	Bundle of muscle fibers called fascicule. Cylindrical in shape. Sarcolemma, a plasma membrane.	Cylindrical Branched Single nucleated	Spindle-shape like that of a rugby ball. Single nucleus

All these three types of muscle tissues work in coordination to facilitate overall body functioning.

What are Skeletal Muscles?

A Skeletal muscle is a voluntary muscle that is attached to the bones through connective tissues called tendons. As a part of the central nervous system, each skeletal muscle tissue is under our control and mainly facilitates body actions.

They are striated and made from flexible muscle fibers to allow agility in movement. They constitute a crucial part of the musculoskeletal system that consists of tendons, ligaments, soft tissues, bones, and muscles. The system is vital as it supports the weight of the body and maintains its structure.

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Characteristics of Skeletal Muscles

Every skeletal muscle tissue has the following characteristics-

Stretchable: The muscles can expand or stretch to a great degree.
Contractility: The muscles are flexible enough to contract.
Excitable: The skeletal muscle tissue is highly responsive to stimuli to facilitate reflex actions.
Elastic: The muscles can stretch to a significant extent and return to their pristine state.

Types of Muscle Tissue in The Skeletal Muscles

There are two fundamental types of skeletal muscles, namely red muscles and white muscles. Each has its distinct function to fulfill. Let us see the characteristics of skeletal muscles:

Red Muscles: Red muscles are red due to the presence of myoglobin, a red pigment that is vital for oxygen supply. They have the following features:

The diameter is small.
More mitochondria, relatively.
Copious amount of blood capillaries.
They can contract for a long time, but slowly.

White Muscles: White muscles are white as they contain negligible myoglobin. They have the following characteristics:

Larger diameter
Lesser Mitochondria
They contract faster but cannot contract long without causing fatigue and pain.

How Does a Skeletal Muscle Function?

Skeletal muscles are responsible for body locomotion primarily. However, they serve a few other important functions:-

One vital skeletal muscle function is the protection of all vital internal organs of the body from injuries or damages. They additionally give structural support to tender internal organs.
The muscles provide a frame to the body and maintain the posture. They also provide a balance to the body.
They also help in controlling the release of bowels and urine.
Lastly, they facilitate the regulation of body temperature by producing heat through movement. For instance, shivering is a response to cold, which facilitates heat

Fun Facts

A few fascinating facts about skeletal muscles, one of the three types of muscle, are:-

There are 600 skeletal muscles in the body.
Gluteus Maximus, the biggest muscle in the body, is the primary facilitator of upward movement on staircases. It is present in the buttocks.
The skeletal muscle mass is 36% more in males as compared to females.

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FAQs on Skeletal Muscle: Structure, Functions, and Types

1. What are skeletal muscles and where are they located in the human body?

Skeletal muscles are a type of muscle tissue that is attached to the bones of the skeleton, primarily by tendons. They are responsible for executing all voluntary movements of the body. These muscles are found throughout the body, with common examples including the biceps and triceps in the arms, the quadriceps in the legs, and the muscles of the abdominal wall.

2. What are the primary functions of the skeletal muscle system?

The primary functions of the skeletal muscle system are crucial for overall body operation and include:

Movement and Locomotion: Contracting to pull on bones, which produces body movements like walking, running, and lifting.
Posture Maintenance: Continuously making small adjustments to hold the body in stationary positions, such as sitting or standing, by counteracting gravity.
Heat Generation: Producing heat as a by-product of metabolic activities (thermogenesis), which is essential for maintaining a stable body temperature.
Protection and Support: Shielding internal organs from external trauma and supporting the weight of visceral organs.

3. Why are skeletal muscles also known as striated and voluntary muscles?

Skeletal muscles are known by these names for two distinct reasons based on their structure and control mechanism. They are called striated muscles because under a microscope, they display a pattern of alternating light (I-bands) and dark (A-bands) stripes. This appearance results from the precise, repeating arrangement of actin and myosin filaments. They are called voluntary muscles because their contraction is consciously controlled by the somatic nervous system, allowing an individual to decide when and how to move a particular body part.

4. How is a skeletal muscle organised, from the whole muscle down to the myofibril?

A skeletal muscle has a highly organised hierarchical structure. The entire muscle is wrapped in a dense connective tissue sheath called the epimysium. Inside, the muscle is segmented into bundles of muscle fibres called fascicles, with each fascicle being wrapped by the perimysium. Within a fascicle, each individual muscle fibre (a single muscle cell) is enclosed by a delicate connective tissue layer called the endomysium. Finally, each muscle fibre contains numerous rod-like contractile elements called myofibrils, which run parallel to the cell's length.

5. What is a sarcomere, and why is it considered the functional unit of muscle contraction?

A sarcomere is the specific segment of a myofibril located between two successive Z-discs. It is considered the fundamental functional unit of a skeletal muscle because it is the smallest portion of the muscle capable of contraction. The coordinated shortening of millions of sarcomeres along the myofibril leads to the shortening of the entire muscle fibre. This process is what generates force and movement. Its structure contains the complete machinery of contractile proteins (actin and myosin) and regulatory proteins needed for this process to occur.

6. What are the roles of the contractile proteins, actin and myosin, in skeletal muscle?

Actin and myosin are the primary contractile proteins in skeletal muscle whose interaction generates force:

Myosin forms the thick filaments. Each myosin molecule has a 'head' that can bind to actin and uses energy from ATP to pivot. This pivoting action, known as the power stroke, is the force-generating step.
Actin forms the thin filaments. It contains specific binding sites for the myosin heads. When the muscle is stimulated, these sites become exposed, allowing myosin to attach and initiate the contraction cycle.

7. How does the sliding filament theory explain the mechanism of muscle contraction?

The sliding filament theory explains that muscle contraction is not caused by the filaments shortening, but rather by them sliding past one another. The mechanism is as follows: when a muscle fibre is stimulated, the myosin heads on the thick filaments attach to the binding sites on the actin filaments, forming cross-bridges. The myosin heads then pivot, pulling the actin filaments towards the centre of the sarcomere (the M-line). This action shortens the I-band and the H-zone, bringing the Z-discs closer together and resulting in the overall contraction of the muscle fibre. The process is fuelled by ATP.

8. How do skeletal, smooth, and cardiac muscles differ in terms of their structure, function, and control?

Skeletal, smooth, and cardiac muscles are the three types of muscle tissue in the body, each with significant differences:

Structure: Both skeletal and cardiac muscles are striated (striped), whereas smooth muscle is non-striated. Cardiac muscle cells are branched and interconnected by unique junctions called intercalated discs, unlike the long, unbranched cylindrical fibres of skeletal muscle.
Location: Skeletal muscles are attached to the skeleton. Smooth muscles are located in the walls of hollow internal organs like the intestines, stomach, and blood vessels. Cardiac muscle is found exclusively in the walls of the heart.
Control: Skeletal muscle is voluntary, meaning its contraction is under conscious control. In contrast, both smooth and cardiac muscles are involuntary; their contractions are automatically regulated by the autonomic nervous system and hormones.