and perceive self-motion. However, the vestibular inputs alone cannot help the CNS distinguish the environmental context in which motion is occurring to determine if the body is moving through the environment (e.g., walking) Visual system The visual system provides information to the CNS regarding head and body motion and position with respect to the environment, as well as referencing verticality. It also contributes to maintaining postural control during quiet stance, as is seen with the occurrence of increased postural sway when the eyes are closed as compared with eyes open. Another example of the influence of visual inputs for postural control comes from an experiment by Lee and Lishman (1975) where they provided continual environmental oscillations (movement of walls and ceiling) and noted that the neurologically intact subjects Somatosensory system The somatosensory system provides the CNS with information regarding body position and motion with respect to the supporting surface. It also provides information about the relative position and relationship of body segments to one another. Somatosensory inputs register body and segment motion when moving along a horizontal surface, to detect changes in the conditions or motion of the surface to maintain verticality with respect to the surface. An example of this is walking along a cobblestone path or sandy beach, where ankle motion
versus moving with the environment (e.g., riding in a train), in order to elicit the appropriate postural responses. For that, the CNS requires information from the visual and somatosensory systems. exhibited an increased sway in response to movement of the environment. Consider a familiar example of standing on a train platform and watching a moving train pass in front of you. There is a sense that you are moving, despite maintaining a static standing position on the platform, which comes from the visually mediated sway that is occurring. This example also illustrates that the visual system is unable to accurately distinguish self-motion from motion of the environment. Thus, making that distinction requires additional information from the other sensory systems associated with postural control. accommodates the uneven or compliant, shifting surface. However, when surface conditions change so that they are not horizontal, such as with a rocking ship or a ramp, orienting the body relative to the supporting surface is no longer effective. Rather, orienting with reference to gravity becomes the effective strategy, such as is mediated by the vestibular system. Examination of somatosensation relative to postural control should include proprioception and kinesthesia of the feet, especially in older individuals and those with diabetes or peripheral neuropathy.
SENSORY INTEGRATION
not change the net movement we are perceiving since we are not in motion. That information is fed back to the CNS (no change), and sensory inputs are reinterpreted. Although the visual system is sending information to the CNS that movement is taking place, since we are not moving relative to the surface the somatosensory system is not detecting movement, and since there is no head movement the vestibular system is also sending information to the CNS that we are not moving. Thus, the sensory inputs are being compared and “reweighted” to resolve this sensory conflict. As a result, the CNS shifts its reliance on information from the two corroborating sensory systems, and we quickly come to the realization that the car next to us is in motion. These adaptations, occurring in a fraction of a second, are essential to successfully maintaining postural control under changing task conditions, and are the basis for the rehabilitation of peripheral vestibular deficits.
Understanding the role of the vestibular, visual, and somatosensory systems in detecting motion and position elucidates their relative contributions to the CNS to create a schema, or map, of the body with respect to the environment, which underlies postural control. We share many experiences where we have discovered how these systems work together. A common example of sensory integration is one where you are sitting in your car next to another car at the red light. Suddenly, the car next to you starts to move forward to get a jump on the green light. Your peripheral vision picks this up as net motion, but it cannot distinguish whether you are rolling backward or the car next to you is moving forward. Since we tend to rely on visual information, despite its inaccuracies relative to movement, our brain misinterprets this information as self- motion and drives the motor response of pushing your foot down harder on the brake pedal. Unfortunately, that does
TYPES OF PERIPHERAL VESTIBULAR DISORDERS
categorize the pathologic basis of the patient’s symptoms. This is achieved by gaining an accurate description of the frequency, onset, and duration of episodes of dizziness through systematic differential questioning on intake interview. Determining the category of pathology plays an important role in guiding intervention and indicating whether referral for additional services may be required. than 60 seconds, and brought on by stereotypical head positions relative to gravity. The pathological mechanism that underlies BPPV is caused by otoconia that have been dislodged from the macula in the utricle either through natural degenerative changes or by trauma, such as a fall. The displaced otoconia eventually find their way to the semicircular canals, resulting in free-floating debris within the canal, or debris that has adhered to the cupula.
Causes of peripheral vestibular dysfunction can arise from pathology of the semicircular canals, otoliths, or the CN VIII. Peripheral vestibular pathology is classified into three categories: distorted function, reduced function, and fluctuating function. Establishing the nature and character of complaints of dizziness is an essential first step in the differential clinical examination process; it helps to Distorted function Benign paroxysmal positional vertigo (BPPV) is the sole pathology that falls into this category. BPPV is the most common cause of dizziness symptoms in the older adult (van Leeuwen & Bruintjes, 2014). The incidence of BPPV is greater for adults 60 years of age as compared to younger adults, with the incidence of BPPV peaking in the sixth and seventh decades of life (Hilton & Pinder, 2003; von Brevern et al., 2007). Symptoms associated with BPPV are characterized as brief periods of vertigo, lasting less
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