Skeletal Muscles- What Is It, Function, Location, Anatomy

Skeletal Muscles: What Is It, Function, Location, Anatomy

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:45 PM IST

Skeletal muscle is a type of tissue found in the body that can be used to perform movements. Its unique properties include excitability, contractility, extensibility, and elasticity. The structure of skeletal muscle is highly organized and is made up of several layers of connective tissue surrounding bundles of muscle fibers, which allows for an effective build-up of force. At the microscopic level, the ultrastructure of skeletal muscle reveals repeating units known as sarcomeres that are functional units of contraction. There are different types of skeletal muscle, which include slow-twitch and fast-twitch fibers suited to endurance or rapid movement. This is a topic from Locomotion and Movement Chapter of Biology.

This Story also Contains

Definition of Skeletal Muscles
Structure of Skeletal Muscles
Function of Skeletal Muscles
Types of Skeletal Muscle Fibers

Definition of Skeletal Muscles

Skeletal muscles are striated, voluntary tissues of muscles attached to bones by tendons and responsible for initiating or controlling body movements. These muscles have long, cylindrical fibres and striations due to actin and myosin filaments realizing activities right from locomotion to the maintenance of posture or heat production.

Apart from the skeletal, there are other major divisions of muscles cardiac muscle, which is involuntary and found in the heart and smooth muscle, which is involuntary, located within the walls of internal organs. All three types of muscles combine to perform very vital functions necessary for the overall operations of the body.

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Structure of Skeletal Muscles

The structure of the skeletal muscles is defined as:

Microscopic Anatomy of Skeletal Muscles

The anatomical structure of skeletal muscles includes:

Muscle Fiber (Cell)

Each fibre of the external, striated skeletal muscle is, in reality, a rather long, cylindrical cell having several nuclei at its periphery. Such fibres are truly multi-nucleated and are covered by a plasma membrane known as sarcolemma. The latter forms a wrapper for the cytoplasm called the sarcoplasm.

Myofibrils, Myofilaments

These muscle fibres are covered under myofibrils, which in turn are composed of filaments called myofilaments. Myofilaments consist of actin and myosin, which interact to bring about muscle contraction. The pattern of these filaments inside the muscle gives it a striated appearance.

Sarcomere (Functional Unit)

It is the functional unit of muscle contraction.It is technically the segment between two Z adjacent discs. Where overlapping in actin and myosin filaments occurs, which contracts and relaxes by extending and shortening to make a muscle move.

Connective Tissue Components

The components of the connective tissue are:

Endomysium: This is the thin connective tissue surrounding every individual fibre. These also provide structural support and include capillaries and nerves collecting and supplying the muscle fibres respectively.
Perimysium: This is the connective tissue sheath enclosing bundles of muscle fibres the fascicles. It also gives some mechanical support, and it includes larger blood vessels and nerves than the endomysium does.
Epimysium refers to the external connective tissue to the whole muscle. It is continuous with the tendon, and thus forms a protective sheath for the muscle as such and renders some structural integrity.

Blood Supply and Innervation

The blood supply to the skeletal muscles is very rich, with an extensive network of capillaries furnishing the oxygen and nutrient requirements for proper muscle functioning.
Muscle fibres are also innervated by nerves, especially motor neurons, that aid in the voluntary control and coordination of each muscle contraction.

Function of Skeletal Muscles

The skeletal muscle performs the following functions:

Role in Movement

Skeletal muscles of the body originate and control most of their voluntary movements.
This is achieved through the simple act of muscle contraction, thus causing the bone to be pulled, which acts as leverage leading to movement around the joints.
These can be simple actions like walking or picking up something too highly intricate from the playing of musical instruments to sports.

Posture and Support

The other major functions of the skeletal muscles, in conjunction with the provision for movement, include posture and support.
These muscles have a continuous action in counteracting the force of gravity in holding up the body in an upright position and balance.

Heat Production

Skeletal muscle contractions produce heat through metabolic by-products of muscle contractions and play a role in the maintenance of core body temperature.
When exercising or exposed to low temperatures, thermogenesis increases the metabolic rate to maintain the inner temperature through enhanced production of heat as a result of muscle contractions.

Protection of Internal Organs

The skeletal muscles also protect the internal organs through protective mechanisms and additional structural support.
The abdominal wall and thoracic cavity muscles safeguard vital organs like the intestines, heart, and lungs from shock and other forms of physical trauma.
This protective function assumes paramount importance in the preservation of the integrity and safety of these internal systems.

Types of Skeletal Muscle Fibers

The different types of skeletal muscle fibres are:

Red Muscles

The red muscle fibres, otherwise known as Type I or slow-twitch fibres, are rich in myoglobin, generally giving them a red colour.
They have a high density of mitochondria and capillaries.
Thus, having a high amount of mitochondria inside the cell, they can efficiently produce energy in the form of aerobic metabolism.
For that reason, the fibres are made for endurance as well as prolonged activities, such as running a long distance or simply maintaining posture by continued contraction without developing fatigue.

White Muscles

White muscle fibres contain few myoglobins and a few mitochondria, hence their pale colour.
They depend more on anaerobic metabolism for the production of energy, so they can produce rapid and powerful contractions.
Hence, they would do better under brief, intense activities like sprinting or weightlifting.
They are capable of applying great forces but tire more quickly than red muscles.

Smooth Muscle

Involuntary Control: Smooth muscle functions under involuntary control, meaning it is worked without any conscious effort. The autonomic nervous system and various hormones control it.
Location: Smooth muscle resides in the walls of hollow constructions that make up the digestive tract, blood vessels, bladder, and airway passages. It regulates the movement of substances through these systems.
Cell Structure: Smooth muscle cells are spindle-shaped and contain one central nucleus. There are no striations in smooth muscles like there are in skeletal muscles, so it appears smooth under the microscope.
Function: The smooth muscles perform involuntary movements for example, the peristalsis in the intestines, contraction, and dilatation of blood vessels, and regulating the flow of air in the passage of the respiratory tract. The muscle contractions are slower and longer compared to the skeletal muscle.

Cardiac Muscle

Location: Found only in the heart, cardiac muscle forms the bulk of the heart's wall and is responsible for pumping blood throughout the body.
Structure: Composed of short, granular, and slightly branched cells each having a single central nucleus. Junctions between cells are called intercalated disks, containing gap junctions and desmosomes that enable synchronised contraction.
Striations: Like the skeletal muscles, cardiac muscle is striated due to the regular arrangement of actin and myosin filaments.
Contraction: It is involuntary and undergoes rhythmic, continuous contraction independent of any conscious control it is medicated by the self-conducting cells or pacemaker cells of the heart—the sinoatrial node—and the autonomic nervous system.
Function: The heart chambers contraction are rhythmic and they pump blood out into the lungs and the rest of the body. They, therefore, maintain circulation and blood pressure.

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Frequently Asked Questions (FAQs)

1. What are skeletal muscles and their functions?

Skeletal muscles are striated, involuntary muscles inelastically attached to bones. Skeletal muscles mediate movement, maintenance of posture, generation of heat, and protection of internal organs.

2. How do skeletal muscles contract?

The contraction of a muscle originates from myosin filaments that pull on actin filaments, causing them to slide towards the centre of the sarcomere, effectively shortening the muscle. It necessitates ATP and an initiating signal from the nervous system.

3. What are the differences between slow-twitch and fast-twitch muscle fibres?

Slow-twitch fibres are endurance-oriented; therefore, high in myoglobin, and thus resistant to fatigue; fast-twitch fibre types are stranded or fast with low myoglobin and quick to fatigue.

4. What are common disorders of skeletal muscles?

Skeletal muscle disorders include dystrophies of muscle—Duchenne muscular dystrophy, for example—myasthenia gravis, and strains or tears of muscles.

5. How can exercise and nutrition impact skeletal muscle health?

Exercise strengthens and increases the durability of muscle, while a well-balanced diet supplies its restoration and development with the appropriate kinds and amounts of proteins and other nutrients.

6. What are skeletal muscles and how do they differ from other muscle types?

Skeletal muscles are voluntary muscles attached to bones that enable movement. They differ from cardiac and smooth muscles in that they are under conscious control, have a striated appearance, and are typically attached to bones via tendons.

7. How do skeletal muscles generate heat?

Skeletal muscles generate heat as a byproduct of their metabolic activities. During contraction, only about 25% of the energy from ATP is used for mechanical work, while the rest is released as heat. This heat production is crucial for maintaining body temperature.

8. What is the difference between isotonic and isometric contractions?

In isotonic contractions, the muscle changes length while maintaining constant tension. This occurs when lifting or lowering a weight. Isometric contractions involve the muscle generating force without changing length, such as when pushing against an immovable object or holding a static position.

9. What is the role of connective tissue in skeletal muscle structure and function?

Connective tissue in skeletal muscles includes the endomysium (surrounding individual fibers), perimysium (surrounding bundles of fibers), and epimysium (surrounding the entire muscle). These tissues provide structural support, allow force transmission, and contain blood vessels and nerves that supply the muscle.

10. What is motor unit recruitment and how does it affect muscle force production?

Motor unit recruitment refers to the activation of motor units (a motor neuron and the muscle fibers it innervates) to produce muscle force. As more force is needed, more motor units are recruited. This allows for fine control of force production, from gentle movements to maximum exertion.

11. How do skeletal muscles generate force to move bones?

Skeletal muscles generate force through a process called muscle contraction. This involves the sliding of myosin and actin filaments past each other, shortening the muscle fibers. This contraction pulls on tendons, which in turn move the bones they're attached to.

12. What is the role of sarcomeres in skeletal muscle function?

Sarcomeres are the basic functional units of skeletal muscles. They contain the protein filaments actin and myosin, which slide past each other during muscle contraction. The organization of sarcomeres gives skeletal muscles their striated appearance and enables them to generate force.

13. How does the nervous system control skeletal muscle movement?

The nervous system controls skeletal muscles through motor neurons. These neurons transmit electrical signals from the brain or spinal cord to the muscle fibers, causing them to contract. This allows for voluntary control of movement.

14. What is the sliding filament theory of muscle contraction?

The sliding filament theory explains how muscles contract. It states that thin actin filaments slide past thick myosin filaments, shortening the muscle fiber. This sliding is powered by the interaction between myosin heads and binding sites on the actin filaments, fueled by ATP.

15. How do skeletal muscles work in antagonistic pairs?

Skeletal muscles often work in antagonistic pairs, where one muscle contracts while the other relaxes. For example, when you bend your elbow, the biceps contracts while the triceps relaxes. When you straighten your arm, the opposite occurs. This allows for controlled, precise movements.

16. What is the structure of a skeletal muscle fiber?

A skeletal muscle fiber is a long, cylindrical cell containing multiple nuclei. It's composed of myofibrils, which are bundles of protein filaments (mainly actin and myosin). The fiber is surrounded by a cell membrane called the sarcolemma and contains mitochondria, sarcoplasmic reticulum, and other organelles.

17. What is the role of the neuromuscular junction in skeletal muscle function?

The neuromuscular junction is the synapse between a motor neuron and a muscle fiber. It's where the nerve impulse is transmitted to the muscle, triggering contraction. This transmission involves the release of acetylcholine from the neuron, which binds to receptors on the muscle fiber membrane.

18. How does ATP contribute to muscle contraction?

ATP (adenosine triphosphate) is the energy currency of cells. In muscle contraction, ATP powers the movement of myosin heads, allowing them to "walk" along actin filaments. It also enables the detachment of myosin from actin and helps pump calcium ions back into the sarcoplasmic reticulum after contraction.

19. What is the role of calcium in skeletal muscle contraction?

Calcium ions are crucial for initiating muscle contraction. When a nerve impulse reaches a muscle fiber, it triggers the release of calcium from the sarcoplasmic reticulum. These calcium ions bind to troponin, causing a conformational change that exposes binding sites on actin for myosin heads to attach.

20. How do skeletal muscles adapt to exercise?

Skeletal muscles adapt to exercise through various mechanisms. These include increased muscle fiber size (hypertrophy), enhanced mitochondrial density, improved blood supply, and changes in fiber type composition. These adaptations lead to increased strength, endurance, and overall muscle performance.

21. What is the difference between fast-twitch and slow-twitch muscle fibers?

Fast-twitch fibers contract quickly and powerfully but fatigue rapidly. They're used for short bursts of intense activity. Slow-twitch fibers contract more slowly, have greater endurance, and are used for sustained activities like maintaining posture.

22. How do skeletal muscles maintain posture?

Skeletal muscles maintain posture through sustained, low-level contractions. This involves the continuous activation of some muscle fibers while others rest, allowing for long-term support without fatigue. This process is largely controlled by the cerebellum and involves feedback from proprioceptors.

23. How does the size principle apply to skeletal muscle recruitment?

The size principle states that motor units are recruited in order of size, from smallest to largest, as more force is required. Smaller motor units, which control fewer muscle fibers, are activated first for precise, low-force movements. Larger units are recruited for more forceful contractions.

24. What is muscle tone and why is it important?

Muscle tone refers to the constant, slight tension in skeletal muscles, even when at rest. It's important for maintaining posture, supporting joints, and allowing quick responses to stimuli. Muscle tone is maintained by continuous, alternating contractions of motor units within the muscle.

25. How do skeletal muscles repair themselves after injury?

Skeletal muscles can repair themselves through a process involving satellite cells. These cells, located between the muscle fiber and its surrounding basement membrane, activate in response to injury. They proliferate, differentiate into new muscle fibers, and fuse with existing fibers to repair damage.

26. What is the role of myoglobin in skeletal muscles?

Myoglobin is an oxygen-binding protein found in skeletal muscles. It stores oxygen within the muscle fibers and facilitates its transport to the mitochondria. This allows muscles to maintain function during periods of high oxygen demand or when blood supply is temporarily reduced.

27. How do skeletal muscles contribute to thermoregulation?

Skeletal muscles play a crucial role in thermoregulation. They generate heat through their metabolic activities and contractions. In cold conditions, involuntary muscle contractions (shivering) can significantly increase heat production. Muscles also help regulate temperature by altering blood flow to the skin.

28. What is the function of the sarcoplasmic reticulum in skeletal muscles?

The sarcoplasmic reticulum is a specialized type of endoplasmic reticulum in muscle fibers. Its main function is to store and release calcium ions. During muscle contraction, it releases calcium into the sarcoplasm, and during relaxation, it actively pumps calcium back into storage.

29. How do skeletal muscles obtain and use energy during exercise?

Skeletal muscles use different energy systems depending on exercise intensity and duration. For short, intense activities, they rely on stored ATP and creatine phosphate. For longer durations, they use glycolysis (breaking down glucose) and oxidative phosphorylation (using oxygen to produce ATP from various fuels).

30. How does skeletal muscle fiber type influence athletic performance?

The proportion of fast-twitch to slow-twitch fibers in an individual's muscles can influence their athletic performance. Athletes with a higher proportion of fast-twitch fibers may excel in activities requiring short bursts of power, while those with more slow-twitch fibers may perform better in endurance events.

31. How do skeletal muscles contribute to joint stability?

Skeletal muscles contribute to joint stability through active tension and by working synergistically with ligaments and joint capsules. They provide dynamic support to joints during movement and help maintain proper alignment. This is crucial for preventing injuries and ensuring efficient movement.

32. What is the role of fascia in skeletal muscle function?

Fascia is a type of connective tissue that surrounds and separates muscles. It plays several roles in muscle function, including:

33. How do skeletal muscles contribute to blood flow regulation?

Skeletal muscles act as a "second heart" by assisting blood flow, especially in the veins. When muscles contract, they compress nearby veins, pushing blood back toward the heart. This action, combined with venous valves, helps prevent blood pooling in the extremities and aids overall circulation.

34. What is the difference between concentric and eccentric muscle contractions?

Concentric contractions occur when a muscle shortens as it generates force, such as when lifting a weight. Eccentric contractions involve the muscle lengthening while still producing force, like when lowering a weight or resisting gravity. Eccentric contractions can generate more force but are more likely to cause muscle soreness.

35. How do skeletal muscles contribute to proprioception?

Skeletal muscles contain specialized sensory receptors called muscle spindles and Golgi tendon organs. These provide information about muscle length, tension, and rate of length change to the nervous system. This feedback is crucial for proprioception - the sense of body position and movement in space.

36. What is the role of myosin in skeletal muscle contraction?

Myosin is a motor protein that plays a crucial role in muscle contraction. It forms the thick filaments in sarcomeres and has a globular head that can bind to actin. The myosin head uses energy from ATP to "walk" along the actin filament, generating the force for muscle contraction.

37. How do skeletal muscles maintain their resting length?

Skeletal muscles maintain their resting length through a combination of passive tension from elastic elements (like titin) and active tension from low-level muscle contractions. This balance is regulated by the nervous system and helps maintain posture and readiness for action.

38. What is the role of creatine phosphate in skeletal muscle energy metabolism?

Creatine phosphate serves as a rapid, short-term energy reserve in skeletal muscles. It can quickly regenerate ATP by transferring its phosphate group to ADP. This system is crucial for high-intensity, short-duration activities and helps maintain ATP levels during the initial seconds of exercise.

39. How do skeletal muscles contribute to blood glucose regulation?

Skeletal muscles play a significant role in blood glucose regulation. They are a major site of glucose uptake and storage (as glycogen) in the body. During exercise, muscles can use glucose for energy without requiring insulin, helping to lower blood glucose levels.

40. What is the sliding filament theory and how does it explain muscle contraction?

The sliding filament theory explains muscle contraction at the molecular level. It states that thin actin filaments slide past thick myosin filaments, shortening the sarcomere. This sliding is powered by the myosin heads attaching to and "walking" along the actin filaments, using energy from ATP hydrolysis.

41. How do skeletal muscles adapt to disuse or immobilization?

When skeletal muscles are not used or are immobilized, they undergo atrophy (shrinkage). This involves a decrease in muscle fiber size, reduction in protein content, and shifts in fiber type composition. These changes can lead to decreased strength and endurance, highlighting the importance of regular muscle use.

42. What is the role of titin in skeletal muscle function?

Titin is a large protein that acts like a molecular spring in skeletal muscle fibers. It connects the Z-line to the M-line in sarcomeres, providing elasticity and maintaining structural integrity. Titin helps muscles return to their resting length after stretching and contributes to passive tension in the muscle.

43. How do skeletal muscles contribute to lymph flow?

Skeletal muscle contractions assist lymph flow by compressing lymph vessels. This action, similar to their effect on blood vessels, helps push lymph fluid through the lymphatic system. This is important for maintaining fluid balance and supporting immune function throughout the body.

44. What is the difference between a twitch and tetanus in skeletal muscle contraction?

A twitch is a brief contraction in response to a single nerve impulse. Tetanus is a sustained contraction resulting from rapid, repeated nerve impulses that prevent the muscle from fully relaxing between stimuli. Tetanus produces stronger, more prolonged contractions than individual twitches.

45. How do skeletal muscles contribute to bone health?

Skeletal muscles contribute to bone health through the mechanical stress they place on bones during contraction. This stress stimulates bone formation and helps maintain bone density. Regular muscle activity, especially weight-bearing exercise, is crucial for preventing conditions like osteoporosis.

46. What is the role of satellite cells in skeletal muscle?

Satellite cells are muscle stem cells located between the sarcolemma and basement membrane of muscle fibers. They play a crucial role in muscle growth, repair, and regeneration. When activated by injury or exercise, they can proliferate and differentiate into new muscle fibers or fuse with existing ones.

47. How do skeletal muscles store and use glycogen?

Skeletal muscles store glycogen as a readily available energy source. During exercise, especially high-intensity activities, this glycogen is broken down to glucose and used for ATP production. The amount of stored glycogen can significantly affect endurance and performance in prolonged activities.

48. What is the role of troponin and tropomyosin in skeletal muscle contraction?

Troponin and tropomyosin are regulatory proteins associated with actin filaments. At rest, tropomyosin blocks myosin binding sites on actin. When calcium binds to troponin, it causes a conformational change that moves tropomyosin, exposing the binding sites and allowing muscle contraction to occur.

49. How do skeletal muscles contribute to venous return?

Skeletal muscles aid venous return through the "muscle pump" mechanism. When muscles contract, they compress nearby veins, pushing blood towards the heart. This action, combined with the one-way valves in veins, helps overcome the effects of gravity and improves overall circulation, especially in the limbs.

50. What is the difference between aerobic and anaerobic metabolism in skeletal muscles?

Aerobic metabolism uses oxygen to produce ATP and can sustain activity for long periods but at lower intensities. Anaerobic metabolism produces ATP without oxygen, allowing for high-intensity activities but for shorter durations. Skeletal muscles can switch between these systems based on exercise intensity and duration.

51. How do skeletal muscles contribute to overall metabolic rate?

Skeletal muscles significantly contribute to the body's overall metabolic rate. Even at rest, they consume energy for maintenance. During activity, their energy consumption increases dramatically. Having more muscle mass generally leads to a higher basal metabolic rate, influencing overall energy expenditure and body composition.

52. What is the role of mitochondria in skeletal muscle function?

Mitochondria are the powerhouses of skeletal muscle cells. They produce ATP through oxidative phosphorylation, which is crucial for sustained muscle activity. The number and efficiency of mitochondria in muscle fibers can greatly influence endurance capacity and overall muscle performance.

53. How do skeletal muscles adapt to resistance training?

In response to resistance training, skeletal muscles adapt through several mechanisms:

54. What is the role of lactic acid in skeletal muscle function and fatigue?

Lactic acid is produced during intense exercise when oxygen supply is insufficient for aerobic metabolism. Contrary to popular belief, it's not the direct cause of muscle fatigue. Instead, it's a byproduct of anaerobic glycolysis and can be used as a fuel source. The associated hydrogen ions, however, contribute to muscle fatigue by affecting pH and enzyme function.

55. How do skeletal muscles contribute to thermoregulation during exercise?

During exercise, skeletal muscles generate significant heat as a byproduct of their increased metabolic activity. This heat is distributed throughout the body via