Muscle

Muscle

Muscle is a connective tissue, whose primary purpose is to contract. Muscle contraction is used to move parts of the body, as well as to move substances within the body,

There are three general types of muscle. The first two are "striated", they contain sarcomeres; the third type is "smooth":

cardiac muscles - these are formed found within the heart
skeletal muscles - these are attached to the skeleton and used to facilitate movement
smooth muscles - these are found within the intestines and blood vessels.

Table of contents

1 Contraction and relaxation
2 Muscular composition
3 Exercise
4 Motor system

Contraction and relaxation

The three types of muscles have significant differences, but all use the movement of actin, against myosin, to produce contraction and relaxation. Contraction is stimulated by electrical impulses transmitted by the nerves, and by the motor nerves and motoneurons in particlular. Muscles and muscular activity account for a lot of the body's energy consumption.

Muscle is composed of muscle cells (sometimes known as "muscle fibers"). Within the cells are myofibrils; myofibrils contain sarcomere, which is composed of actin and myosin. Muscle cells are grouped together into bundles of fascicle; the bundles are then grouped together to form muscle.

Exercise

Exercise is often recommended as a means of improving motor skills. Excerise does not increase the number of muscle cells, but it can improve aerobic capacity, muscle mass, and strength.

Motor system

Vertebrates move muscles in response to voluntary and autonomic signals from the brain. Deep muscles, superficial muscles, muscles of the face and internal muscles all correspond with unique regions in the brain. Muscles react to reflexive nerve stimuli that do not always send signals all the way to the brain, but most muscle activity is the result of complex interactions between various areas of the brain.

Nerves that control muscles in mammals correspond with neuron groups along the primary motor area of the brain's cerebral cortex. Commands are routed to basal ganglia and to the cerebellum before being relayed to connections in the pons and medulla for transmission to synapses at the muscles. Along the way, feedback loops such as that of the extrapyramidal system contribute signals to influence muscle tone and response.

Deeper muscles such as those involved in posture often are inervated from origins in the brain stem.

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