Muscle Sensory Receptors

Abstract

The central nervous system (CNS) obtains information on whatever occurs in the muscles (i.e., mechanical and chemical changes) through sensory receptors located within muscles and joints, as well as in the portion of skin deformed by the motion. Several types of sensory receptors lie within skeletal muscles. (1) The very sensitive muscle spindles monitor muscle length and send this information to the CNS via the fastest conducting afferent nerve fibers in the body. (2) Golgi tendon organs are located in the musculo‐tendinous junctions and provide information about muscle force. (3) Free nerve endings with slow‐conducting, thinly myelinated or unmyelinated nerve afferents are sensitive to mechanical, chemical, and nociceptive stimuli. The description of the specific features and peculiarities of each of these receptor types is preceded by a brief overview of receptors in general, particularly about basic processes that take place in the receptive terminal (i.e., the transduction of the stimulus and the encoding of information into neural signals that are self‐regenerating) that can be transferred for long distances without decrement. In addition, a brief description of afferent nerve fibers carrying this information, as well as a description of the relationship between stimulus and sensation, will follow. Then, most of the chapter is devoted to the muscle spindle, which is justified by the anatomical and functional complexity and the relevance of this receptor in several body functions. A few models are presented concerning different aspects of the muscle spindle receptive function, and a brief reference is made to its involvement in the myotatic reflex, motor control, and high‐level body functions.