About the book
The proprioception, or sense of proprioception, is a quality of the somatosensibility that can be defined as the perception of body and limb position with respect to the space, or of each segment of the body with respect to the body itself. Thus, it is the sense of positioning and movement. Proprioception plays a key role in the interactions with environment since it helps the planning and performance of movements.
The sense of proprioception includes various aspects or submodalities such as position sense, motion sense (kinaesthesia; including the duration, direction, amplitude, speed, acceleration and timing of movements), force tension sense, and change in velocity sense.
Proprioception is mediated by proprioceptors, a specialized subset of about 10-15% of mechanosensory neurons localized in dorsal root ganglia that convey information about the stretch and tension of muscles, tendons, joints and perhaps the skin. So, the neurological basis of proprioception originates from proprioceptors with contact specialized sensory organs in muscles (muscle spindles), tendons (Golgi tendon organs), joints (different morphotypes of sensory corpuscles including Ruffini’s corpuscles and Pacinian corpuscles) and the skin (cutaneous mechanoreceptors). Thereafter, the information originated in the proprioceptors forming complex nerve pathways reach the central nervous system at the level of the spinal cord, the cerebellum and the cerebral cortex for processing. Hence, proprioception can be regarded as a continuous loop of feedforward and feedback inputs between sensory receptors throughout the body and the nervous system.
In limb and axial muscles, the proprioception originates in the muscle spindles. Nevertheless, the cephalic muscles, with the exception of the extraocular muscles and those innervated by the mandibular branch of the trigeminal nerve, lack muscle spindles. But the facial or pharyngeal proprioception plays key roles in the regulation and coordination of facial musculature and diverse reflexes. At the basis of these functional characteristics are the multiple communications between cranial nerves. Substituting muscle spindles by other kinds of proprioceptors might be at the basis.
On the other hand, since the stimuli for proprioceptors are mechanical (stretch, tension, and so) proprioception can be regarded as a modality of mechanosensitivity. During the last decade progress has been made to understanding the molecular basis of mechanosensitivity. However, identity of mechanotransducers is poorly know. The mechanogated ion channels acid-sensing ion channel 2 (ASIC2), transient receptor potential vanilloid 4 (TRPV4) and PIEZO2 have been related to mechanotransduction and have been detected in proprioceptors innervating muscle spindles and Golgi tendon organs in mice. Also, mice lacking Piezo2 showed severely uncoordinated body movements and abnormal limb positions.
Finally, the lesion of the proprioception receptors, proprioceptors or the nerve center and pathways related to proprioception result in poor proprioception. Importantly, age-related changes also affect proprioception due to a combination of natural age-related changes to the central nervous system, nerves, joints, and muscles. Acute and long-term impairment can be related to toxicological, medical or injury conditions, but also with neuromuscular and central nervous system diseases.
Based on the above comments this book intends to provide a comprehensive update an overview of the anatomical, structural and molecular basis of proprioception as well as of the main causes of proprioception impairment and possible treatments.