Proprioception: an introduction
The proprioceptive sense interprets information from our muscles and joints to allow us to coordinate our body to achieve tasks.
Possibly one of the most widely misunderstood, misdescribed and misinterpreted senses, proprioception is our awareness of our external body. Although this is highly involved in the placement and coordination of our body parts, because we need to know where they are to do this, proprioception is not the same as a sense of movement.
Proprioception interprets messages, consciously and unconsciously, from the edges of our body parts to perceive our body position, and the forces that are acting upon our bodies, at any given moment. It enables us to judge our limb movements and position, force, heaviness, stiffness and viscosity. It combines with other senses to locate external objects relative to the body and contributes to body image. Proprioception is closely tied to the control of movement without being a sense of movement.
An example of proprioception, is our senses giving us enough information to be able to move our arm and finger to touch our nose, without looking at all, and being able to press our nose gently. Another might be that when running, if we change from a concrete surface to a grass surface, we notice, and then we do little conscious thinking about how we adapt how we use our body to maintain our movement.
Sensation versus sense
Proprioceptive sensations are confusing because we are largely unaware of them. They are distinguishable from exteroceptors such as the eye and the ear in that they are not associated with specific, recognisable sensations. However, when we are not looking at our limbs, we are able to indicate with reasonable accuracy their positions and whether they are moving. Part of the explanation for this lack of identifiable sensation relates to the predictability of proprioceptive signals. We are aware that we are making a willed movement and so anticipate the sensory input that it generates. A general concept in sensory physiology is that what we feel commonly represents the difference between what is expected and what has actually occurred.
On that basis, if a movement goes to plan and there is no mismatch between the expected signals and those actually generated, no definable sensation is produced, yet the subject still knows precisely the location of their limb.
Aspects of the proprioceptive sense
In order to continually “sense” our body position, and within that, all our body parts, even when we are moving them, there are a number of different aspects that our brain needs messages about.
Joint and limb position sense
Joint position sense determines the ability of a person to perceive a presented joint angle and then, after the limb has been moved, to actively or passively reproduce the same joint angle.
Sense of force
Also known as sense of effort / heaviness / tension or the force matching sense. It is our ability to interpret forces on our body, and the ability to reproduce (or match) a desired level of force (push a heavy door enough to open it).
Kinaesthesia sense
Kinaesthesia is the awareness of the motion or movement of our body parts, not to be confused with our general sense of movement and balance (vestibular sense). This motion sense refers to the ability to appreciate joint movement, including the duration, direction, amplitude, speed, acceleration and timing of movements.
Proprioceptive sense function
Proprioception allows the body to plan and react so that we position our movements correctly and smoothly without needing to rely on our vision sense. People use their sense of proprioception for most motor actions.
We need our sense of proprioception to look where we are going when we walk, to pick up a glass of water, to walk in the sand, to wave hello, to avoid knocking into other people and the list goes on and on.
A diminished sense of proprioception can result in clumsiness, poor coordination, improper posture, using too much or too little force, decreased body awareness, motor planning deficits and more. Here are some general function examples:
Reflexes
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.
Stabilisation
For a person to walk or stand upright, they must continuously monitor their posture and adjust muscle activity as needed. Adjusting to slight changes in terrain when walking means adjusting limb position and force output to prevent tripping.
Planning and refining movement
When planning complex movements such as reaching or eating we must consider the current position and velocity of our limb and use it to adjust dynamics to target a final position. Furthermore, proprioception is crucial in refining the movement if it deviates from the trajectory.
Proprioceptive sense regulation
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Hyper-sensitive proprioception
People who experience the proprioceptive sense more intensely, or who have a low need for proprioceptive input, may:
- Be reluctant to be picked up, carried or hugged
- Only like loose clothing, or prefer to be naked (though this may indicate tactile sensitivity)
- Not enjoy people leaning on them, placing a hand on them, or holding hands
- Prefer to sleep separately from their partner
- Prefer a lot of space around them.
Hypo-sensitive proprioception
People who experience the proprioceptive sense less intensively, or who have a high need for proprioceptive input, may:
- Pull, twist, or chew objects
- Accidentally break toys, belongings or equipment
- Hurt people unintentionally
- Lean on or bump into people by accident
- Struggle with tasks that require fine manipulation
- Stomp when they walk
- Kick or bash their feet against furniture legs
- Enjoy and crave rough and tumble play
- Prefer clothes and fastenings that are snug or tight
- Enjoy being wrapped in blankets or swaddled
- Needs to be hugged, carried and contained more than most.
Neurobiology of the proprioceptive sense
Proprioception can be neurologically defined as the cumulative neural input to the Central Nervous System from specialised nerve endings called mechanoreceptors and proprioceptors, which are located in joints, capsules, ligaments, muscles, tendons, and the skin.
Receptors
Current knowledge indicates that proprioception is primarily signalled by muscle receptors, namely muscle spindles, whereas joint receptors seem to play a lesser role in very specific functions such as determining the very end ranges of motion. Similarly, cutaneous (skin) receptors have been hypothesised to respond only in extremes. Muscle afferents receptors allow for the identification of limb position and movement via neural signalling of a change in muscle, skin or joint stretch. Hence, proprioception is basically a continuous loop of feedforward and feedback inputs between sensory receptors throughout your body and your nervous system. In contrast, muscle spindles have been almost unanimously described as able to provide potent afferent information across the entire range of motion.
Neurology
The proprioceptive sensory inputs received from receptors are integrated and appreciated at three distinct levels of the Central Nervous System: the spinal level, the brain stem level, and in the higher parts of the brain such as the cerebral cortex and cerebellum. The spinal level can contribute to functional joint stability by providing direct motor responses in the form of reflexes. At the brain stem, afferent information is integrated with visual and vestibular inputs in order to control automatic and stereotypical movement patterns, balance, and posture. The cerebral cortex and cerebellum, elicit the conscious awareness of proprioception, contributing to voluntary and purposeful movement, resistance, and position.
