Pain sensations in the skin, muscles, tendons and joints that are carried on large nerve fibers

Proprioception, or kinesthesia, is the sense that lets us perceive the location, movement, and action of parts of the body. It encompasses a complex of sensations, including perception of joint position and movement, muscle force, and effort. These sensations arise from signals of sensory receptors in the muscle, skin, and joints, and from central signals related to motor output. Proprioception enables us to judge limb movements and positions, 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.

Proprioception

4.6.7 Unstable Surface Training (Proprioception Training)

Proprioception comes from a Latin word meaning unconscious perception of movement. It allows the body to control its position for optimal locomotion. It is carried out by internal sensors such as the muscle spindle stretch receptor and Golgi tendon organ. The vestibular system in the brain is a key component in proprioception and also in maintaining static, mixed, or dynamic balance. Proprioception training improves balancing, movement sensing, and, naturally, proprioception.

Proprioception is present in every muscle movement, therefore proprioception training may be misleading. Unstable surface training is a more expressive name for this type of method. Proprioception is extremely important in motor learning, smooth motor learning, and preventing injury (Verhagen et al., 2004). The latter observation made unstable surface training very popular, where movements are carried out in a position that needs constant balancing. Exercises on a wobble board improve ankle and knee functional stability and prevent injuries (Cloak et al., 2013; Sparkes and Behm, 2010). A balance board or unstable straps push-up exercises used for shoulder joint training give different EMG signals compared to push-ups executed on a stable surface. On a stable surface, an EMG indicates lower muscle activity (Snarr and Esco, 2013). Unstable surface training is recommended for injury prevention, rehabilitation, and improving physical performance.

10.20.4.1 Proprioception

Proprioception not only allows humans to detect position and motion of limbs and joints (Lephart et al., 1998; Lord et al., 2003; Sturnieks et al., 2004), but also provides sensation of force generation to allow for better regulation of force output (Baker et al., 2002; Hurley and Scott, 1998; Williams et al., 2001). Furthermore, Hurley et al. (1997), Hurley and Scott (1998), and Sharma (1999) have reported that proprioception is closely related to functional performance and walking speed. We have demonstrated that non-weight-bearing proprioception training (Figures 19 and 20) and strength training exercise interventions were effective in improving pain, function, walking speed on different terrains, and knee strength in patients with knee OA. Proprioception training was found to be superior to enhance neuromuscular function, most notably joint reposition sense and walking speed on a spongy surface. As well documented in the literature, the integrity and control of sensorimotor systems, including those involved in proprioception and muscle action, are essential for the maintenance of balance and production of a smooth stable gait. As thus proprioception training should be more emphasized in our physiotherapy practice to maximize the treatment effect (Lin et al., 2009). As thus proprioception training shoulder should be stressed in our day-to-day practice of orthopedic physiotherapy.

General Proprioception

Proprioception means “sense of position.” The clinical sign of proprioception dysfunction is ataxia (incoordination). General proprioception describes the position of muscles, joints, and tendons because proprioceptors are located in neuromuscular spindles and Golgi tendon organs. Axons project within peripheral nerves and enter the spinal cord via dorsal roots. Neurons are located in the spinal ganglia. On entering the spinal cord, axons may (1) synapse directly on alpha motor neurons for initiation of extensor reflexes such as the patellar or knee jerk reflex (monosynaptic reflex arc) (Figure 1-14), (2) synapse on interneurons to indirectly influence alpha motor neurons, or (3) synapse on interneurons and then send afferent fibers via the spinal cord to the brainstem, cerebellum, and cerebrum (Figure 1-15).

Proprioception is transmitted to the cerebellum via spinocerebellar tracts. This information is used by the cerebellum to regulate muscle tone, posture, locomotion, and equilibrium. Lesions involving these tracts have a profound effect on gait and may create clinical signs similar to cerebellar dysfunction (i.e., truncal swaying, hypermetria). Spinocerebellar tracts activate Purkinje neurons in the cerebellum that inhibit protraction (flexion) of limbs. This facilitates limb extension for weight bearing. Lesions in spinocerebellar tracts result in overflexion of limbs, known as hypermetria. Clinical signs are ipsilateral to lesions.

Conscious proprioception is carried to the medulla via the dorsal columns (fasciculus gracilis [from pelvic limbs] and cuneatus [from thoracic limbs]), whose fibers first synapse in medullary nuclei (nuclei gracilis and cuneatus, respectively). Axons from these nuclei cross to the opposite side via the deep arcuate fibers and then traverse the brainstem in the medial lemniscus to the thalamus. Ultimately, fibers are projected to the contralateral parietal lobe of the cerebral cortex.

Lesions of these pathways are associated with general proprioceptive ataxia and delayed responses in the initiation of postural reactions (hopping, knuckling-paw placement). Lesions rostral and caudal to the midbrain create deficits in contralateral and ipsilateral limbs, respectively.

Pathway of postural reactions/general proprioception/upper motor neurons

Proprioception, the “ability to know where the legs are in space,” is perhaps the most sensitive and sophisticated sensory system in the body. Without visual confirmation, the degree of tension and stretch of the muscles and joints send constant relays to the somatosensory cortex, which in turn facilitates descending motor signals from the motor cortex to the muscles to make near-instantaneous movements. The speed and precision with which this occurs is extremely rapid and is seen in the grace with which animals move. As proprioceptive testing requires both sensory perception and motor corrections, both the ascending and descending tracts are assessed at once.

To assess proprioception, postural reaction testing (specifically knuckling and hopping testing) is performed. The impulses originate when a limb is placed in an abnormal knuckled position, stretching the muscle spindles and Golgi tendon organs. The stimulates the dorsal and ventral spinocerebellar tracts of the pelvic limbs and the cuneocerebellar and cranial spinocerebellar tracts in the thoracic limbs.

Proprioception

Proprioception refers to the sense of limb position and movement, where the latter is specifically referred to as kinesthesia. Proprioceptive feedback is critical for proper balance and motor control. Innervated by fast-conducting Aα fibers, muscles have receptors involved in proprioception. Muscle spindles comprise a bundle of thin muscle fibers that are enclosed within a capsule. Mechanosensitive afferents wrap around the muscle fibers and are activated by stretching such that their firing rate is proportional to muscle length. Contraction of the thin (intrafusal) muscle fibers, which are innervated by motoneurons, can effectively modulate the sensitivity of the muscle spindles. Golgi tendon organs, which are located between muscle and tendons, sense muscle force rather than length, and are an important component of reflex circuits. Joints are endowed with joint-capsule receptors that sense tension but, interestingly, individuals with artificial joints can still sense the angle and movement of their artificial joint reasonably well on the basis of input from muscle spindles.

The proprioceptive system

Proprioception can be divided into conscious and unconscious proprioception. Both are mediated by muscle and joint afferents. The former travels in the DCML and deals with aspects such as judging the weight of an object or where a person’s limbs are in space. Unconscious proprioception serves as an important backup to conscious proprioception, and is the sensation of limb and joint position and range and direction of limb movement. It is involved in the acquisition and maintenance of complex, skilled movements such as walking, talking and writing. Unconscious proprioception is mediated by the SCBT, whose primary function is to monitor and modify movements.

The proprioceptive system axons from muscle and joint receptors travel in the dorsal columns. Within a few segments, however, axons responsible for the proprioceptive information concerned with postural adjustments that occur unconsciously, leave the white matter and synapse in Clarke’s nucleus (nucleus dorsalis), located at the base of the dorsal horn on the medial side from T1 to L1 of the spinal cord. The second-order neurones then enter the dorsal SCBT on the lateral edge of the cord. This pathway ascends without crossing to the cerebellum and is also somatotopically organized. The SCBT remains at the lateral margin of the brainstem through the medulla, where it enters the cerebellum via the inferior cerebellar peduncle (ICP) to terminate on Purkinje cells. Purkinje cells relay the information to the deep cerebellar nuclei, and from there it is passed to other motor areas of the thalamus, brainstem and basal ganglia. Because Clarke’s column only extends from T1 to L1, it only carries information from the lower body and trunk. Information from the upper body is relayed by the cuneocerebellar tract to the accessory cuneate nucleus, and from there to the cerebellum via the ICP. Similarly, information from the face travels in the trigeminocerebellar tract to the cerebellum (Fig. 4.9).

A second spinocerebellar pathway exists and travels in the lateral white matter, just ventral to the dorsal SCBT. The axons of this pathway arise from cells in lamina VII of the spinal cord and receive a diverse input from proprioceptors, nociceptors and descending pathway tracts such as the vestibulospinal and reticulospinal tracts. The ventral SCBT seems to defy the ipsilaterality of the cerebellum, because the fibres cross over in the cord. However, they cross back before entering the cerebellum via the superior cerebellar peduncle. Therefore, the cerebellum still receives information from the ipsilateral side of the body. Ventral SCBT cells have large RFs and appear to act as comparators of descending inputs and other inputs to motor neurones.

3.6 Proprioception

Proprioception, the awareness of deep pressure and the position and movement of limbs, is mediated through receptors in muscles, tendons, and joints. They relay information to the spinal cord and brain via large Aα and Aβ myelinated fibers. Proprioceptive information is used to adapt body position and gait, and defects in the proprioceptive system may lead to ataxia. The lack of position sense in a limb may be demonstrated by placing the limb in an abnormal position. Unimpaired animals will correct this abnormal position directly. Commonly used tests are dorsal placement of the feet (Fig. 39.6A, Table 39.5) and crossing of limbs (Fig. 39.6B, Table 39.5).

Proprioception

Proprioception is altered in space because of the absence of static muscle tension required to support the weight of a limb, but accurate pointing is quickly learned. The proprioceptive feedback signaling ankle, knee, and hip flexion is disturbed during extended weightlessness and is likely a significant source of the inability of some astronauts to walk and run normally following return to earth. The ability to estimate the mass of objects, in the absence of their weight, is also reduced. The otolith–spinal reflex, which normally prepares one for a landing from a fall, is also reduced in space, as well as is the Hoffman reflex measurement of spinal cord excitability during transient acceleration.