Proprioception is a complex interoception that informs the brain about the condition and movement of joints, tendons, and muscles. Impaired proprioception can be caused by medications and drugs, as well as neurological diseases and trauma.
What is proprioception?
Proprioception is a complex interoception that informs the brain about the condition and movement of joints, tendons, and muscles. The anatomical sensory structures are referred to as the perceptual apparatus. Mostly, perceptions are stimuli from the outside, which are received by the stimulus-specific organ by means of specialized receptors and transformed into bioelectrical excitation. After processing, they are projected into the central nervous system via afferent pathways. Only after the classification processes and interpretations of the central nervous system do perceptions pass into consciousness. This principle of receiving stimuli from the outside gives an organism a picture of its environment and is called exteroception. However, perception can also refer to stimulus reception from within. If the received stimuli originate from within the organism and thus enable self-perception, it is called interoception. Two perceptual structures characterize interoreception: visceroception and proprioception. Visceroception corresponds to the perception of organ activity. Proprioception, on the other hand, is the perception of one’s own body position and movement in space. This type of self-perception is also called depth sensitivity and is divided into the sense of position (position sense), the sense of movement and the sense of force (resistance sense). The main receptors of these perceptions are the muscle spindle, tendon spindle, and the sensitive receptors of the joint capsule, ligaments, and periosteum.
Function and task
Proprioception is facilitated by depth sensitivity and the vestibular organ. Surface sensitivities play a minor role. The vestibular organ of the inner ear is the human organ of equilibrium, which can perceive linear acceleration and angular acceleration via sensory cells on so-called statoliths. Rotational movements are perceived as inertial masses by a fluid in the tubular system of the inner ear. Depth sensitivity, on the other hand, is located in muscle tissue. Its receptors are the muscle spindle, the tendon spindle, and the sensitive receptors of the joints, bones, and ligaments. Proprioceptive stimuli are mediated by the organelles of the proprioceptors and the interoceptors. These are mostly mechanoreceptors. They detect mechanical stimuli and thus correspond to sensitive end organs that respond to a state or change of state in the musculoskeletal system. Via proprioception, humans perceive both the current state and state changes of their own body. The position sense serves the sensation of current initial positions. The sense of movement provides continuous feedback on the extent of one’s own movement and permanently determines the body position during movement. The sense of force or resistance is used for the dosage and mediation between traction and pressure, as required for any movement. The proprioceptive nerve pathways are located in the sensory cortex. The main field of this structure is its posterior central turn, where fibers of the trigeminal and ascending posterior cord pathways cross in. In its somatotopic organization, the close proximity of this structure corresponds to the spinal cord. When sensitive regions of the body are stimulated, the central nervous system automatically keeps the motor areas and thalamic nuclei of the structures on standby. This makes it easier for the human body to deliver purposeful reactive movements. Some afferent pathways to the praecentral gyrus are also thought to serve proprioceptive processing. Depth sensitivity, in particular, is a mandatory requirement of regulated motor activity and originates in the cerebellum (cerebellum). Some proprioceptive fibers originate from bones, visceral organs, or vessels and first reach the hypothalamus. In the hypothalamus, they are coupled with the impulses of the endocrine system and are thus involved in the regulation of vegetative and animal body functions. The information from the proprioceptors reaches the brain through two different pathways. The information of the conscious depth sensibility reaches the somatosensory pathway of the thalamus and the parietal lobe in the cortex (cerebral cortex).Unconscious information of depth perception, on the other hand, travels via the tractus spinocerebellaris to the cerebellum and thus reaches the center for movement control. Proprioception differs from person to person in its expression. Thus, a general proprioception does not exist, only a specific one.
Diseases and complaints
A foot that has fallen asleep currently suppresses proprioception in the lower limb. This is a commonplace phenomenon, usually preceded by malalignment or entrapment. In most cases, the phenomenon has no direct pathological value. Sometimes, however, when extreme and chronic, it indicates diseases of the central nervous system, such as multiple sclerosis. Proprioception in the sense of depth sensitivity also shows reactions to various medications, drugs and alcohol. Even the simplest movements are suddenly difficult for a drunk person, for example. Proprioception is distorted and causes a variety of posture problems, mobility disorders and coordination problems. A disorder of proprioreception can thus be caused by disorders of the vestibular organ as well as by those of the muscle spindle or tendon spindle and bone receptors. Lesions of the mediating neural pathways can also disable proprioception. Such neuronal lesions may be autoimmunologic in origin and caused by inflammation, as is the case in multiple sclerosis. However, they can just as easily be due to accidents and thus trauma. Other possibilities include space-occupying lesions or hemorrhages in the involved nerve areas or the responsible brain regions. The cause of impaired or abolished proprioception is determined by means of imaging procedures. MRI, for example, ideally allows the localization of a given lesion to be determined. Both the hypothalamus and the cerebellum or the respective afferent pathways can be the site of damage in cases of impaired proprioception. Sometimes, problems with depth sensitivity are also located in the inner ear, because when proprioception can no longer access correct information from the vestibular organ, it also no longer functions properly.
