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The human body is an intricate machine with over 600 muscles, each playing a crucial role in our daily lives. From pumping blood to lifting heavy objects, muscles are the powerhouses that enable our every movement. But what exactly are these muscles made of? This is an important question to understand the mechanics of our bodies and the incredible processes that occur within us. Let's delve into the fascinating world of muscles and explore their composition, functions, and various types.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | More than 600 |
| Muscle composition | Thousands of small fibres woven together |
| Muscle fibres | Elastic |
| Muscle tissue | Skeletal, cardiac, and smooth |
| Muscle cell nuclei | Single, double, triple, or quadruple |
| Skeletal muscle tissue | Striated, multinucleate, voluntary |
| Muscle contraction | Stimulated by electrical impulses or internal pacemaker cells |
| Muscle movement | Contraction or relaxation |
| Muscle function | Provide movement, heat generation, and support to the body |
| Muscle fuel | Glucose, calcium, magnesium, potassium, and sodium |
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Skeletal muscle
The primary function of skeletal muscle is contraction, which is stimulated by electrical impulses transmitted by the motor nerves. Skeletal muscles are voluntary muscles, meaning that their contractions are controlled consciously. Skeletal muscles vary considerably in size, shape, and arrangement of fibres. They range from extremely tiny strands such as the stapedium muscle of the middle ear to large masses such as the muscles of the thigh.
The skeletal muscle is considered an organ of the muscular system. Each skeletal muscle may be made up of hundreds or even thousands of muscle fibres bundled together and wrapped in a connective tissue covering. The connective tissue framework is usually formed from the somatic lateral plate mesoderm. Tendons are cords of tough connective tissue that attach skeletal muscles to bones.
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Cardiac muscle
Muscle is a soft tissue, and there are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. The cardiac muscle is a specialised type of tissue that exists only in the heart.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The mechanism behind each coordinated contraction involves the cardiac muscle and electrical impulses. These contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
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Smooth muscle
The primary function of smooth muscle is contraction, which occurs involuntarily. Smooth muscle consists of two types: single-unit and multi-unit. Single-unit smooth muscle comprises multiple cells connected through connexins, allowing synchronous contraction with just one synaptic input. Multi-unit smooth muscle, on the other hand, provides finer control as each cell receives its own synaptic input. Smooth muscle contractions are stimulated by internal pacemaker cells, which then propagate contractions to neighbouring muscle cells.
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Muscle fibres
Skeletal muscle fibres are further classified into two types: type 1 and type 2. Type 1 fibres use oxygen to generate energy for movement and have a higher density of mitochondria, giving them a darker appearance. Type 2 fibres are further divided into subtypes: type 2A and type 2B. Type 2A fibres can use oxygen to generate energy but contain fewer mitochondria, and type 2B fibres do not use oxygen and instead store energy for short bursts of movement. Type 2B fibres appear white due to their low mitochondria content.
The speed of contraction in muscle fibres depends on the rate at which myosin's ATPase hydrolyzes ATP to produce cross-bridge action. Fast fibres hydrolyze ATP twice as rapidly as slow fibres, resulting in quicker cross-bridge cycling. The number of slow and fast-twitch fibres in the body varies between individuals and is determined by genetics. However, training can influence the type of fibres present, with endurance training increasing the endurance level of fast-twitch fibres and sprint training improving the power generated by slow-twitch fibres.
Cardiac muscle fibres, found only in the heart, have their own rhythm and are interconnected. They contract due to impulses generated by pacemaker cells, which spread in a wavelike pattern, facilitating the heart's beating. Smooth muscle fibres, on the other hand, are involuntary and do not have a striated appearance like skeletal and cardiac muscles. They are shorter and have an oblong shape.
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Muscle contractions
Muscles are made up of thousands of small fibres woven together. These fibres are elastic and are bundled tightly together. Each bundle is wrapped in a thin, transparent membrane called a perimysium. An individual muscle fibre is made up of blocks of proteins called myofibrils, which contain a specialised protein (myoglobin) and molecules to provide the oxygen and energy required for muscle contraction.
There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. The primary function of muscle tissue is contraction. The three types of muscle tissue use the movement of actin against myosin to create contraction. Skeletal muscle tissue is striated and consists of elongated, multinucleate muscle cells called muscle fibres. It is responsible for the movement of the body. Skeletal muscles work with bones to give the body power and strength.
Cardiac muscle cells, also called cardiomyocytes or myocardiocytes, predominantly contain only one nucleus, although populations with two to four nuclei do exist. The myocardium is the muscle tissue of the heart and forms a thick middle layer between the outer epicardium layer and the inner endocardium layer. Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems. Cardiac muscle contractions are stimulated by internal pacemaker cells, which regularly contract and propagate contractions to other muscle cells they are in contact with.
Smooth muscle is non-striated. Smooth and cardiac muscle contract involuntarily, without conscious intervention. These muscle types may be activated through the interaction of the central nervous system or by innervation from the peripheral plexus or endocrine (hormonal) activation. Skeletal muscle only contracts voluntarily, under the influence of the central nervous system.
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Frequently asked questions
Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle.
Skeletal muscle tissue is striated and consists of elongated, multinucleate muscle cells called muscle fibres. Skeletal muscles are formed from the fusion of many smaller cells during fetal development, resulting in long, straight muscle fibres that contain many nuclei.
Cardiac muscle cells, also called cardiomyocytes or myocardiocytes, predominantly contain only one nucleus, although populations with two to four nuclei do exist. The myocardium is the muscle tissue of the heart and forms a thick middle layer between the outer epicardium layer and the inner endocardium layer.
Smooth muscle tissue lines some of the body's organs, but most organs are also made of other types of tissue. Smooth muscle contracts involuntarily, without conscious intervention.
