Physiology, Vibratory Sense

Issues of Concern

The most significant concern related to vibration sensation is the peripheral neuropathy of diabetes mellitus, which affects the peripheral nerves and results in the loss of pain, temperature, and vibration sensations. Better glycemic control is the only way to prevent this pathology.[4]

Cellular Level

Pacinian corpuscles (PCs) are highly specialized corpuscles found in the dermis of glabrous skin. This specialization is partly due to the adventitial tissue surrounding the corpuscles. PCs have a large, ellipsoid shape, ranging up to 3 to 4mm in the digits. Their shape and size vary depending upon the location in the body and area of skin of their residence. PCs have a large myelinated centrally located nerve fiber called neurite, running along their long axis. Bilaterally arranged glial lamellae immediately surround the neurites, and perineural (collagenous) lamellae further surround them on the outer aspect. Inner core cells are derived from Schwann cells and are involved in the conduction of signals. These lamellar layers are separated from each other by a fluid-filled layer, kept in between due to the presence of tight junctions found between adjacent lamellar cells. A capsule surrounds the outer lamellar layer. When a vibratory stimulus deforms skin, this stimulus reaches the dermis where it transmits to the external capsule of PCs. This distortion travels through the external and internal core until it reaches the central neurite. As a result, stretch-gated cation channels (voltage-gated and non-voltage gated) on the neuronal membrane open and conduct a neural response.[5]

Development

The development of Pacinian corpuscles (PCs) starts at the gestational age of 13 weeks and is completed at the age of 4 months postnatal. The inner core forms from a compact network of Schwann cells and outer core, and the surrounding mesenchyme forms the capsule. The development of Meissner corpuscles (MCs) starts at 22 weeks and attains complete morphology by 8 months of life. The developing MCs have a complex relationship of their axons with the epidermis and are covered by Schwann cells until late maturity. The present data suggest that there is an asynchronous relationship between the development and immunohistochemical maturation of MCs and PCs.[6] The alar and basal plates of neural tube give origin to dorsal (sensory) and ventral (motor) horns of the spinal cord, respectively. The dorsal horn makes the sensory pathway of the posterior column, which carries the vibratory signals.

Organ Systems Involved

The sense of vibration is perceived and conducted to the brain via integumentary and nervous systems. Skin is involved in the conduction of distortion from the environment to the external capsule of PCs in the dermis, and from the central neurite of PCs, the neuronal signal transmits via the dorsal column-medial lemniscus to the VPL nucleus of the thalamus. From the VPL nucleus, the final transmission is to the somatosensory area of the cerebral cortex.[7]

Function

The function of vibratory receptors is to make us aware of different frequencies of external stimuli. Meissner corpuscles detect frequencies between 30 and 50 Hz; Pacinian corpuscles are sensitive to frequencies between 100 and 400 Hz. The dorsal column-medial lemniscus pathway appreciates fine touch, 2-point discrimination, and vibration sensations from all the body excluding the head.

Mechanism

Pacinian and Meissner corpuscles are located in the deep dermis and detect distortion of skin from external stimuli and transmit it to the central neurite. Stretch gated ion channels open and conduct a neural response; this is the underlying mechanism of vibration perception. Trigeminal nerve transmits the vibrotactile signals from the facial area, and the dorsal column–medial lemniscus (DCML) pathway carries vibratory signals from the rest of the body. The signals get relayed via the thalamus to the primary somatosensory area of the postcentral gyrus.[8][1]

Related Testing

The Romberg test assesses the integrity of the posterior column pathway, which carries vibratory sensations. The examiner asks the patient to close his/her eyes while standing.  If the patient can not maintain his/her balance with eyes closed, the problem lies in the posterior column, and not in the cerebellum.

Pathophysiology

The pathophysiology of vibration perception and its pathways is related to the diseases affecting the dorsal column. Any factor which disrupts the neuronal transmission from vibratory sensors in the deep dermis to the somatosensory area in the cortex affects the vibratory sensations. The explanation of several of these mechanisms is in the clinical significance section below.

Clinical Significance

The clinical significance of vibratory sensation lies in its carrier pathway (DCML), which also carries position sense and fine touch. Several diseases affect the DCML pathway and thus manifest as loss of position, vibration, and touch sensations.

Most common in developed countries is subacute combined degeneration of the spinal cord due to vitamin B12 deficiency. Vitamin B12 primarily exists in animal products, including meat, fish, poultry, and milk. Our bodies have extensive reserves of B12 and symptoms of deficiency appear after several years of a diet devoid of B12, explaining why vegetarians are mostly the victims of vitamin B12 deficiency if they don’t substitute it with other sources.

Another example is tabes dorsalis, a late manifestation of tertiary syphilis. It causes degenerative joints disease (Charcot joints), Argyll Robertson pupils (light reflex lost but accommodation reflex retained), and affects dorsal column. Tabes dorsalis incidence is reduced dramatically after the introduction of penicillin in the treatment of syphilis.

An infarction of the posterior spinal artery also affects the posterior column pathway resulting in the loss of vibration, proprioception, and light touch below the level of the lesion.

Hemisection of the spinal cord, known as Brown-Sequard syndrome, also affects the dorsal column along with other pathways. It is commonly the result of trauma, tumors, and abscesses.[9][10][11]