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For other uses of "muscle", see muscle (disambiguation).

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A top-down view of skeletal muscle
Muscle is a kind of soft tissue of animals. Muscle cells contain protein filaments that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and cause motion. They are primarily responsible for maintenance of and changes in posture, locomotion of the organism itself, as well as movement of internal organs, such as the contraction of the heart and movement of food through the digestive system via peristalsis.
Muscle tissues are derived from the mesodermal layer of embryonic germ cells. They are classified as skeletal, cardiac, or smooth muscles. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh.
Muscles are predominantly powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads.
The term muscle is derived from the Latin musculus meaning "little mouse" perhaps because of the shape of certain muscles or because contracting muscles look like mice moving under the skin.[1][2]
Contents [hide]
1 Anatomy
1.1 Types of tissue
1.2 Histogenesis
1.3 Microanatomy
1.4 Gross anatomy
1.5 Muscular system
2 Physiology
2.1 Function
2.2 Energy consumption
2.3 Nervous control
2.3.1 Efferent leg
2.3.2 Afferent leg
2.4 Efficiency
3 Strength
3.1 Physiological strength
3.2 The "strongest" human muscle
4 Health
4.1 Exercise
4.2 Hypertrophy
4.3 Atrophy
4.4 Disease
5 Evolution
6 See also
7 References
8 External links
Anatomy

The anatomy of muscles includes both gross anatomy, comprising all the muscles of an organism, and, on the other hand, microanatomy, which comprises the structures of a single muscle.
Types of tissue
Main article: Muscle tissue

Types of muscle (shown at different magnifications)
Muscle tissue is a soft tissue, and is one of the four fundamental types of tissue present in animals. There are three types of muscle tissue recognized in vertebrates:
Skeletal muscle or "voluntary muscle" is anchored by tendons (or by aponeuroses at a few places) to bone and is used to effect skeletal movement such as locomotion and in maintaining posture. Though this postural control is generally maintained as an unconscious reflex, the muscles responsible react to conscious control like non-postural muscles. An average adult male is made up of 42% of skeletal muscle and an average adult female is made up of 36% (as a percentage of body mass).[3]
Smooth muscle or "involuntary muscle" is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and the arrector pili in the skin (in which it controls erection of body hair). Unlike skeletal muscle, smooth muscle is not under conscious control.
Cardiac muscle is also an "involuntary muscle" but is more akin in structure to skeletal muscle, and is found only in the heart.
Cardiac and skeletal muscles are "striated" in that they contain sarcomeres and are packed into highly regular arrangements of bundles; smooth muscle has neither. While skeletal muscles are arranged in regular, parallel