Answer:
Movement
Movements of the body are brought about by the harmonious contraction and relaxation of selected muscles. Contraction occurs when nerve impulses are transmitted across neuromuscular junctions to the membrane covering each muscle fibre. Most muscles are not continuously contracting but are kept in a state ready to contract. The slightest movement or even the intention to move results in widespread activity of the muscles of the trunk and limbs.
Movements may be intrinsic to the body itself and carried out by muscles of the trunk and body cavity. Examples are those involved in breathing, swallowing, laughing, sneezing, urinating, and defecating. Such movements are largely carried out by smooth muscles of the viscera (alimentary canal and bladder, for example); they are innervated by efferent sympathetic and parasympathetic nerves. Other movements relate the body to the environment, either for moving or for signaling to other individuals. These are carried out by the skeletal muscles of the trunk and limbs. Skeletal muscles are attached to bones and produce movement at the joints. They are innervated by efferent motor nerves and sometimes by efferent sympathetic and parasympathetic nerves.
Every movement of the body has to be correct for force, speed, and position. These aspects of movement are continuously reported to the central nervous system by receptors sensitive to position, posture, equilibrium, and internal conditions of the body. These receptors are called proprioceptors, and those proprioceptors that keep a continuous report on the position of limbs are the muscle spindles and tendon organs.
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