Muscle is a soft tissue, one of the animal tissues that makes up the three different types of muscle. Muscle tissue gives skeletal muscles the ability to contract. Muscle is formed during embryonic development, in a process known as myogenesis. Muscle tissue contains special contractile proteins called actin and myosin which contract and relax to cause movement. Among many other muscle proteins present are two regulatory proteins, troponin and tropomyosin.

The body contains three types of muscle tissue: (a) skeletal muscle, (b) smooth muscle, and (c) cardiac muscle. (Same magnification)
A schematic diagram of the different types of muscle cells (same order as above).
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Anatomical terminology

Muscle tissue varies with function and location in the body. In vertebrates the three types are: skeletal or striated; smooth muscle (non-striated) muscle; and cardiac muscle.[1] Skeletal muscle tissue consists of elongated muscle cells called muscle fibers, and is responsible for movements of the body. Other tissues in skeletal muscle include tendons and perimysium.[citation needed] Smooth and cardiac muscle contract involuntarily, without conscious intervention. These muscle types may be activated both through the interaction of the central nervous system as well as by receiving innervation from peripheral plexus or endocrine (hormonal) activation. Striated or skeletal muscle only contracts voluntarily, upon the influence of the central nervous system. Reflexes are a form of non-conscious activation of skeletal muscles, but nonetheless arise through activation of the central nervous system, albeit not engaging cortical structures until after the contraction has occurred.[citation needed]

The different muscle types vary in their response to neurotransmitters and hormones such as acetylcholine, noradrenaline, adrenaline, and nitric oxide depending on muscle type and the exact location of the muscle.[citation needed]

Sub-categorization of muscle tissue is also possible, depending on among other things the content of myoglobin, mitochondria, and myosin ATPase etc.[citation needed]

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