Victor Forge
The human body is made up of more than 600 muscles, which help us do everything from moving our bodies to breathing and staying alive. There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. Skeletal muscle is the most common type of muscle in the body and is the only type that contracts voluntarily, under the influence of the central nervous system. Cardiac and smooth muscle are involuntary muscles controlled by the autonomic nervous system. The development of muscles has been crucial for the evolutionary success of vertebrates, with the evolution of paired fins and limbs and their associated musculature allowing vertebrates to gain increased locomotor agility, populate the land, and acquire fine motor skills.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Muscle tissue types in vertebrates | Skeletal, cardiac, and smooth muscle |
| Muscle tissue types in invertebrates | Transversely striated, obliquely striated, and smooth muscle |
| Most common muscle type in the human body | Skeletal muscle |
| Muscle composition | Elastic tissue, muscle fibres, and fibrils |
| Muscle functions | Movement, breathing, circulation, and digestion |
| Types of muscle movement | Voluntary and involuntary |
| Muscle development | Myogenesis during embryonic development |
| Muscle structure | Connective tissue layer of fascia surrounding each fibre and individual muscle |
| Muscle shape | Elongated, multinucleate muscle cells |
| Muscle growth | Stimulated by exercise |
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What You'll Learn
Skeletal muscle development
During embryogenesis, the development of skeletal muscle in the limbs and trunk of the vertebrate embryo occurs through the segmentation of the paraxial mesoderm, which produces somites. This process progresses from head to tail, with the dorsolateral regions of the somites differentiating into dermomyotomes, the origin of both dermatomes and myotomes. The latter develops into axial and limb muscles. One of the intriguing aspects of muscle differentiation is the question of how vertebrate skeletal muscle cells become multinucleated, with two main hypotheses being proposed.
The development of skeletal muscle is closely tied to muscle connective tissue (MCT). MCT plays a critical role in regulating normal muscle development and ensuring proper integration with other components of the musculoskeletal system, such as tendons, bones, nerves, and vasculature. Defects in MCT-muscle interactions during development can lead to various birth defects, highlighting the importance of understanding their complex interplay.
In addition to embryonic and foetal development, muscle stem cells also play a crucial role in post-natal growth and regeneration. These stem cells, known as satellite cells, remain quiescent until activated by exercise, injury, or disease. By studying muscle stem cells, scientists gain insights into muscle construction and a better understanding of muscle-related diseases and regeneration processes.
Overall, skeletal muscle development is a dynamic and carefully regulated process that involves the interaction of various biological systems. By studying this process, researchers can enhance our understanding of muscle function, disease, and repair, ultimately contributing to improved health outcomes and treatments for muscle-related conditions.
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Muscle connective tissue
The human body has over 600 muscles, which help us do everything from moving our bodies to breathing and staying alive. Skeletal muscle is the most common type of muscle in the body, making up between 30% and 50% of our total body mass.
Skeletal muscle consists of numerous muscle cells called muscle fibres. These muscle fibres are surrounded by three layers of connective tissues, which form a muscle. The innermost layer is called the endomysium, which surrounds each muscle fibre. The middle layer is the perimysium, which surrounds a group of muscle fibres, forming a fascicle. The outermost layer is the epimysium, which encircles all the fascicles to form a complete muscle.
Tendons are cord-like extensions of these three linings, connecting the muscle to a bone or to other muscles. An aponeurosis is a flat, broad extension of the three muscle linings and serves the same function as a tendon. Fascia is a term for a layer or sheet of connective tissue. The deep fascia surrounds the epimysium and encloses or lines other nearby structures such as blood vessels, nerves, and the body wall.
Connective tissue is one of the basic tissue types of the body. It connects, supports, and helps bind other tissues. It can be broken down into two primary categories: connective tissue proper and specialised connective tissue. Connective tissue proper is further subdivided into loose and dense connective tissues. Dense connective tissue, such as ligaments and tendons, is composed mainly of densely packed collagen fibres. Collagen runs in a parallel course in loose connective tissue and then joins to form a larger bundle.
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Muscle evolution
The human muscle system evolved to increase the chances of survival. Muscles, along with ligaments and tendons, are present throughout the body, aiding in many functions. The evolution of muscles in humans is linked to the transition from living in trees to living on the ground. This transition also led to changes in diet, energy expenditure, and social interactions.
The evolution of the human muscle system is closely tied to the development of bipedalism, which influenced the arrangement and function of muscles. As humans began to walk on two feet, the human thigh bone developed an inward slope down to the knee, allowing the gluteal abductors to adapt to the stress and build the necessary muscle for balance. The muscles near the ankle also played a crucial role in providing the push needed for walking and running. The shift to bipedalism resulted in the loss of the ability to grab objects with four appendages, but it freed up the hands for tasks such as holding weapons, throwing spears, and performing other complex tasks.
The evolution of the head in vertebrates, including humans, was accompanied by the development of cranial muscles essential for eye movement, feeding, vocalization, and facial expressions. The evolution of paired fins and limbs in vertebrates led to increased locomotor agility, the ability to populate the land, and the acquisition of fine motor skills. The diaphragm, unique to mammals, evolved to increase respiratory capacity and separate the thoracic and abdominal cavities.
In addition to these evolutionary changes, humans have also developed taller over time, which has resulted in the lengthening of back muscles at the base of the tailbone and hips, leading to increased weight. The muscles in the human body can be categorized into three types: skeletal (striated), cardiac, and smooth muscle. Skeletal muscles are voluntary muscles that an individual can control, while cardiac and smooth muscles are involuntary and are controlled by the autonomic nervous system. Skeletal muscles make up between 30% and 50% of an individual's total body mass and are responsible for various functions, including breathing, eating, and moving bones.
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Muscle fibres
Skeletal muscle fibres are classified into two types: type 1 and type 2. Type 1 fibres use oxygen to generate energy for movement and have a high density of mitochondria, which makes them dark. Type 2 fibres are further divided into subtypes 2A and 2B. Type 2A fibres can also use oxygen to generate energy but contain fewer mitochondria, making them light. Type 2B fibres do not use oxygen to generate energy but instead store energy for short bursts of movement. They contain very few mitochondria and appear white.
The number of slow and fast-twitch fibres in the body varies between individuals and is determined by genetics. Slow-twitch fibres are more common in people who excel at endurance sports, while fast-twitch fibres are more common in sprinters. Both types of fibres can be influenced by training. For example, sprint training can improve the power generated by slow-twitch fibres, and endurance training can increase the endurance level of fast-twitch fibres. However, training cannot make slow-twitch fibres as powerful as fast-twitch fibres, nor can it make fast-twitch fibres as fatigue-resistant as slow-twitch fibres.
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Muscle groups
The human body has more than 600 muscles, which account for about 30-50% of a person's body weight. These muscles help the body to move, breathe, and perform other vital functions. There are three main types of muscles: skeletal, cardiac, and smooth muscle.
Skeletal Muscle
Skeletal muscles are the most common type of muscle in the body and make up 30-40% of total body mass. They are attached to bones by tendons and are under voluntary control, meaning that their movement can be consciously controlled. Examples of skeletal muscles include shoulder, hamstring, and abdominal muscles.
Cardiac Muscle
Cardiac muscle is a special type of muscle tissue found only in the heart. It is an involuntary muscle, meaning that its movement is automatic and not under conscious control. The heart beats thousands of times a day, helping to pump blood around the body and keep the person alive.
Smooth Muscle
Smooth muscle tissue lines some of the body's organs and is also under involuntary control. It helps with functions such as digestion and waste removal.
When exercising, it is common to group muscles together by their location (e.g. chest, leg, or back muscles) or by the type of movement they perform (e.g. abductors, flexors, or extensors). There are two main types of exercises targeting muscle groups: compound exercises, which work several muscle groups at once, and isolation exercises, which target a specific muscle within a muscle group.
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Frequently asked questions
There are more than 600 muscles in the human body.
There are three types of muscles: skeletal, cardiac, and smooth muscle.
Skeletal muscles are the most common type of muscle in the body, making up between 30% and 40% of our total body mass. They are attached to the bones of the skeletal system and are responsible for movements like locomotion and maintaining posture.
Cardiac muscles are found only in the walls of the heart and are controlled by the autonomic nervous system. They contract to squeeze out blood and then relax to allow the heart to fill with blood again.
Smooth muscles are found within the walls of organs and structures such as the esophagus, stomach, intestines, and blood vessels. They contract and relax involuntarily, without conscious intervention.
