Proprioception
Proprioception (/ˌproʊpri.oʊˈsɛpʃən, -ə-/[1][2] PROH-pree-oh-SEP-shən, -ə-) is the sense of self-movement, force, and body position.[3][4]
Proprioception is mediated by proprioceptors, mechanosensory neurons located within muscles, tendons, and joints.[3] Most animals possess multiple subtypes of proprioceptors, which detect distinct kinematic parameters, such as joint position, movement, and load. Although all mobile animals possess proprioceptors, the structure of the sensory organs can vary across species.
Proprioceptive signals are transmitted to the central nervous system, where they are integrated with information from other sensory systems, such as the visual system and the vestibular system, to create an overall representation of body position, movement, and acceleration. In many animals, sensory feedback from proprioceptors is essential for stabilizing body posture and coordinating body movement.
System overview
In vertebrates, limb movement and velocity (muscle length and the rate of change) are encoded by one group of sensory neurons (
To determine the load on a limb, vertebrates use sensory neurons in the Golgi tendon organs:[7] type Ib afferents. These proprioceptors are activated at given muscle forces, which indicate the resistance that muscle is experiencing. Similarly, invertebrates have a mechanism to determine limb load: the Campaniform sensilla.[8] These proprioceptors are active when a limb experiences resistance.[citation needed]
A third role for proprioceptors is to determine when a joint is at a specific position. In vertebrates, this is accomplished by
Reflexes
The sense of proprioception is ubiquitous across mobile animals and is essential for the motor coordination of the body. Proprioceptors can form reflex circuits with motor neurons to provide rapid feedback about body and limb position. These mechanosensory circuits are important for flexibly maintaining posture and balance, especially during locomotion. For example, consider the stretch reflex, in which stretch across a muscle is detected by a sensory receptor (e.g., muscle spindle, chordotonal neurons), which activates a motor neuron to induce muscle contraction and oppose the stretch. During locomotion, sensory neurons can reverse their activity when stretched, to promote rather than oppose movement.[10][11]
Conscious and nonconscious
In humans, a distinction is made between conscious proprioception and nonconscious proprioception:
- Conscious proprioception is communicated by the
- Nonconscious proprioception is communicated primarily via the ventral spinocerebellar tract,[14] to the cerebellum.
- A nonconscious reaction is seen in the human proprioceptive reflex, or righting reflex—in the event that the body tilts in any direction, the person will cock their head back to level the eyes against the horizon.[15] This is seen even in infants as soon as they gain control of their neck muscles. This control comes from the cerebellum, the part of the brain affecting balance.[citation needed]
Mechanisms
Proprioception is mediated by mechanically sensitive proprioceptor neurons distributed throughout an animal's body. Most vertebrates possess three basic types of proprioceptors: muscle spindles, which are embedded in skeletal muscles, Golgi tendon organs, which lie at the interface of muscles and tendons, and joint receptors, which are low-threshold mechanoreceptors embedded in joint capsules. Many invertebrates, such as insects, also possess three basic proprioceptor types with analogous functional properties: chordotonal neurons, campaniform sensilla, and hair plates.[3]
The initiation of proprioception is the activation of a proprioceptor in the periphery.
Members of the
Although it was known that finger kinesthesia relies on skin sensation, recent research has found that kinesthesia-based haptic perception relies strongly on the forces experienced during touch.[24] This research allows the creation of "virtual", illusory haptic shapes with different perceived qualities.[25]
Anatomy
Proprioception of the head stems from the muscles innervated by the
Function
Stability
An important role for proprioception is to allow an animal to stabilize itself against perturbations.[28] For instance, for a person to walk or stand upright, they must continuously monitor their posture and adjust muscle activity as needed to provide balance. Similarly, when walking on unfamiliar terrain or even tripping, the person must adjust the output of their muscles quickly based on estimated limb position and velocity. Proprioceptor reflex circuits are thought to play an important role to allow fast and unconscious execution of these behaviors, To make control of these behaviors efficient, proprioceptors are also thought to regulate reciprocal inhibition in muscles, leading to agonist-antagonist muscle pairs.
Planning and refining movements
When planning complex movements such as reaching or grooming, an animal must consider the current position and velocity of its limb and use that information to adjust dynamics to target a final position. If the animal's estimate of its limb's initial position is wrong, then a deficiency in the movement can result. Furthermore, proprioception is crucial in refining the movement if it deviates from the trajectory.
Development
In adult fruit flies, each proprioceptor class arises from a specific cell lineage (i.e. each chordotonal neuron is from the chordotonal neuron lineage, although multiple lineages give rise to sensory bristles). After the last cell division, proprioceptors send out axons toward the central nervous system and are guided by hormonal gradients to reach stereotyped synapses. [29] The mechanisms underlying axon guidance are similar across invertebrates and vertebrates.[citation needed]
In mammals with longer gestation periods,
Mathematical models
Proprioceptors transfer the mechanical state of the body into patterns of neural activity. This transfer can be modeled mathematically, for example to better understand the internal workings of a proprioceptor[31][32][33] or to provide more realistic feedback in neuromechanical simulations.[34][35]
Various proprioceptor models of complexity have been developed. They range from simple phenomenological models to complex structural models, in which the mathematical elements correspond to anatomical features of the proprioceptor. The focus has been on muscle spindles,[31][32][33][36] but Golgi tendon organs[37][38] and insects' hair plates[39] have been modeled too.
Muscle spindles
Poppelle and Bowman [40] used linear system theory to model mammalian muscle spindles Ia and II afferents. They obtained a set of de-afferented muscle spindles, measured their response to a series of sinusoidal and step function stretches, and fit a transfer function to the spike rate. They found that the following Laplace transfer function describes the firing rate responses of the primary sensory fibers for a change in length:
The following equation describes the response of secondary sensory fibers:
More recently, Blum et al.[41] showed that the muscle spindle firing rate is modeled better as tracking the force of the muscle, rather than the length. Furthermore, muscle spindle firing rates show history dependence which cannot be modeled by a linear time-invariant system model.
Golgi tendon organs
Houk and Simon [38] provided one of the first mathematical models of a Golgi tendon organ receptor, modeling the firing rate of the receptor as a function of the muscle tension force. Just as for muscle spindles, they find that, as the receptors respond linearly to sine waves of different frequencies and has little variance in response over time to the same stimulus, Golgi tendon organ receptors may be modeled as linear time-invariant systems. Specifically, they find that the firing rate of a Golgi tendon organ receptor may be modeled as a sum of 3 decaying exponentials:
where is the firing rate and is a step function of force.
The corresponding Laplace transfer function for this system is:
For a soleus receptor, Houk and Simon obtain average values of K=57 pulses/sec/kg, A=0.31, a=0.22 sec−1, B=0.4, b=2.17 sec−1, C=2.5, c=36 sec−1 .
When modeling a stretch reflex, Lin and Crago[42] improved upon this model by adding a logarithmic nonlinearity before the Houk and Simon model and a threshold nonlinearity after.
Impairment
Chronic
Proprioception, a sense vital for rapid and proper body coordination,
In rare cases, viral infections result in a loss of proprioception. Ian Waterman and Charles Freed are two such people that lost their sense of proprioception from the neck down from supposed viral infections (i.e. gastric flu and a rare viral infection). After losing their sense of proprioception, Ian and Charles could move their lower body, but could not coordinate their movements. However, both individuals regained some control of their limbs and body by consciously planning their movements and relying solely on visual feedback. Interestingly, both individuals can still sense pain and temperature, indicating that they specifically lost proprioceptive feedback, but not tactile and nociceptive feedback. The impact of losing the sense of proprioception on daily life is perfectly illustrated when Ian Waterman stated, "What is an active brain without mobility".[48][49]
Proprioception is also permanently lost in people who lose a limb or body part through injury or amputation. After the removal of a limb, people may have a confused sense of that limb's existence on their body, known as phantom limb syndrome. Phantom sensations can occur as passive proprioceptive sensations of the limb's presence, or more active sensations such as perceived movement, pressure, pain, itching, or temperature. There are a variety of theories concerning the etiology of phantom limb sensations and experience. One is the concept of "proprioceptive memory", which argues that the brain retains a memory of specific limb positions and that after amputation there is a conflict between the visual system, which actually sees that the limb is missing, and the memory system which remembers the limb as a functioning part of the body.[50] Phantom sensations and phantom pain may also occur after the removal of body parts other than the limbs, such as after amputation of the breast, extraction of a tooth (phantom tooth pain), or removal of an eye (phantom eye syndrome).
Acute
Proprioception is occasionally impaired spontaneously, especially when one is tired. Similar effects can be felt during the
Temporary impairment of proprioception has also been known to occur from an overdose of vitamin B6 (pyridoxine and pyridoxamine)[citation needed]. Most of the impaired function returns to normal shortly after the amount of the vitamin in the body returns to a level that is closer to that of the physiological norm. Impairment can also be caused by cytotoxic factors such as chemotherapy.
It has been proposed that even common tinnitus and the attendant hearing frequency-gaps masked by the perceived sounds may cause erroneous proprioceptive information to the balance and comprehension centers of the brain, precipitating mild confusion.
Temporary loss or impairment of proprioception may happen periodically during growth, mostly during adolescence. Growth that might also influence this would be large increases or drops in bodyweight/size due to fluctuations of fat (liposuction, rapid fat loss or gain) and/or muscle content (bodybuilding, anabolic steroids, catabolisis/starvation)[citation needed]. It can also occur in those that gain new levels of flexibility, stretching, and contortion. A limb's being in a new range of motion never experienced (or at least, not for a long time since youth perhaps) can disrupt one's sense of location of that limb. Possible experiences include suddenly feeling that feet or legs are missing from one's mental self-image; needing to look down at one's limbs to be sure they are still there; and falling down while walking, especially when attention is focused upon something other than the act of walking.
Diagnosis
Impaired proprioception may be diagnosed through a series of tests, each focusing on a different functional aspect of proprioception.
The Romberg's test is often used to assess balance. The subject must stand with feet together and eyes closed without support for 30 seconds. If the subject loses balance and falls, it is an indicator for impaired proprioception.
For evaluating proprioception's contribution to motor control, a common protocol is joint position matching.[52] The patient is blindfolded while a joint is moved to a specific angle for a given period of time and then returned to neutral. The subject is then asked to move the joint back to the specified angle. Recent investigations have shown that hand dominance, participant age, active versus passive matching, and presentation time of the angle can all affect performance on joint position matching tasks.[citation needed]
For passive sensing of joint angles, recent studies have found that experiments to probe psychophysical thresholds produce more precise estimates of proprioceptive discrimination than the joint position matching task.[53] In these experiments, the subject holds on to an object (such as an armrest) that moves and stops at different positions. The subject must discriminate whether one position is closer to the body than another. From the subject's choices, the tester may determine the subject's discrimination thresholds.
Proprioception is tested by American
Training
Proprioception is what allows someone to learn to walk in complete darkness without losing balance. During the learning of any new skill, sport, or art, it is usually necessary to become familiar with some proprioceptive tasks specific to that activity. Without the appropriate integration of proprioceptive input, an artist would not be able to brush paint onto a canvas without looking at the hand as it moved the brush over the canvas; it would be impossible to drive an automobile because a motorist would not be able to steer or use the pedals while looking at the road ahead; a person could not
Oliver Sacks reported the case of a young woman who lost her proprioception due to a viral infection of her spinal cord.[54] At first she could not move properly at all or even control her tone of voice (as voice modulation is primarily proprioceptive). Later she relearned by using her sight (watching her feet) and inner ear only for movement while using hearing to judge voice modulation. She eventually acquired a stiff and slow movement and nearly normal speech, which is believed to be the best possible in the absence of this sense. She could not judge effort involved in picking up objects and would grip them painfully to be sure she did not drop them.
The proprioceptive sense can be sharpened through study of many disciplines. Juggling trains reaction time, spatial location, and efficient movement.[citation needed] Standing on a wobble board or balance board is often used to retrain or increase proprioceptive abilities, particularly as physical therapy for ankle or knee injuries. Slacklining is another method to increase proprioception.
Standing on one leg (stork standing) and various other body-position challenges are also used in such disciplines as yoga, Wing Chun and tai chi.[55] The vestibular system of the inner ear, vision and proprioception are the main three requirements for balance.[56] Moreover, there are specific devices designed for proprioception training, such as the exercise ball, which works on balancing the abdominal and back muscles.
History of study
In 1557, the position-movement sensation was described by Julius Caesar Scaliger as a "sense of locomotion".[57]
In 1826, Charles Bell expounded the idea of a "muscle sense",[58] which is credited as one of the first descriptions of physiologic feedback mechanisms.[59] Bell's idea was that commands are carried from the brain to the muscles, and that reports on the muscle's condition would be sent in the reverse direction.
In 1847, the London neurologist
At around the same time, Moritz Heinrich Romberg, a Berlin neurologist, was describing unsteadiness made worse by eye closure or darkness, now known as the eponymous Romberg's sign, once synonymous with tabes dorsalis, that became recognised as common to all proprioceptive disorders of the legs.[citation needed]
In 1880, Henry Charlton Bastian suggested "kinaesthesia" instead of "muscle sense" on the basis that some of the afferent information (back to the brain) comes from other structures, including tendons, joints, and skin.[61]
In 1889, Alfred Goldscheider suggested a classification of kinaesthesia into three types: muscle, tendon, and articular sensitivity.[62]
In 1906, the term proprio-ception (and also intero-ception and extero-ception) is attested in a publication by Charles Scott Sherrington involving receptors.[63] He explains the terminology as follows:[64]
The main fields of distribution of the receptor organs fundamentally distinguishable seem, therefore, to be two, namely, a surface field constituted by the surface layer of the organism, and a deep field constituted by the tissues of the organism beneath the surface sheet.
[...]
the stimulations occurring in [the] deep field is that the stimuli are traceable to actions of the organism itself, and are so in much greater measure than are the stimulations of the surface field of the organism. Since in the deep field the stimuli to the receptors are delivered by the organism itself,[b] the deep receptors may be termed proprio-ceptors, and the deep field a field of proprio-ception.
Today, the "exteroceptors" are the organs that provide information originating outside the body, such as the eyes, ears, mouth, and skin. The
Primary endings of muscle spindles "respond to the size of a muscle length change and its speed" and "contribute both to the sense of limb position and movement".[65] Secondary endings of muscle spindles detect changes in muscle length, and thus supply information regarding only the sense of position.[65] Essentially, muscle spindles are stretch receptors.[66] It has been accepted that cutaneous receptors also contribute directly to proprioception by providing "accurate perceptual information about joint position and movement", and this knowledge is combined with information from the muscle spindles.[67]
Etymology
Proprioception is from Latin proprius, meaning "one's own", "individual", and capio, capere, to take or grasp. Thus to grasp one's own position in space, including the position of the limbs in relation to each other and the body as a whole.[citation needed]
The word kinesthesia or kinæsthesia (kinesthetic sense) refers to movement sense, but has been used inconsistently to refer either to proprioception alone or to the brain's integration of proprioceptive and vestibular inputs. Kinesthesia is a modern medical term composed of elements from Greek; kinein "to set in motion; to move" (from PIE root *keie- "to set in motion") + aisthesis "perception, feeling" (from PIE root *au- "to perceive").
Plants and bacteria
Although they lack neurons, systems responding to stimuli (analogous to the sensory system in animals with a nervous system, which includes the proprioception) have also been described in some plants (
Further studies have shown that the cellular mechanism of proprioception in plants involves myosin and actin, and seems to occur in specialized cells.[71] Proprioception was then found to be involved in other tropisms and to be central also to the control of nutation.[72]
The discovery of proprioception in plants has generated an interest in the popular science and generalist media.[73][74] This is because this discovery questions a long-lasting a priori that we have on plants. In some cases this has led to a shift between proprioception and self-awareness or self-consciousness. There is no scientific ground for such a semantic shift. Indeed, even in animals, proprioception can be unconscious; so it is thought to be in plants.[69][74]
Recent studies suggest that bacteria have control systems that may resemble proprioception.[75]
See also
- Balance disorder – Physiological disturbance of perception
- Body image – Aesthetic perception of one's own body
- Body schema – Postural model that keeps track of limb position
- Broken escalator phenomenon – Illusion when stepping onto a broken escalator
- Dizziness – Neurological condition causing impairment in spatial perception and stability
- Equilibrioception– Physiological sense regarding posture
- Hand–eye coordination– Coordination between the eyes and hand
- Ideomotor phenomenon – Concept in hypnosis and psychological research
- Illusions of self-motion – Misperception of one's location or movement
- Instinctive aiming– Shooting method where the weapon's sights are not used or relied on
- Kinaesthetics – Study of body motion, and preception of motion
- Kinesthetic learning – Learning by physical activities
- List of distinct cell types in the adult human body
- Motion sickness – Nausea caused by motion or perceived motion
- Motor control – Regulation of movement within organisms possessing a nervous system
- Multisensory integration – Study of senses and nervous system
- Seasickness– Motion sickness occurring at sea
- Spatial disorientation – Inability of a person to correctly determine their body position in space
- Theory of multiple intelligences – Theory of multiple types of human intelligence proposed by Howard Gardner
- Vertigo – Type of dizziness where a person has the sensation of moving or surrounding objects moving
Notes
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External links
- Proprioception at the U.S. National Library of Medicine Medical Subject Headings (MeSH)