page_title: Pallesthesia
section_title: Pathway
hierarchical_section_title: Pallesthesia / Pathway
caption_attribution_description: English: Illustration from Anatomy &amp; Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013.
context_page_description: Pallesthesia, or vibratory sensation, is the ability to perceive vibration. This sensation, often conducted through skin and bone, is usually generated by mechanoreceptors such as Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles. All of these receptors stimulate an action potential in afferent nerves found in various layers of the skin and body. The afferent neuron travels to the spinal column and then to the brain where the information is processed. Damage to the peripheral nervous system or central nervous system can result in a decline or loss of pallesthesia.
  A diminished sense of vibration is known as pallhypesthesia. To determine whether a patient has diminished or absent pallesthesia, testing can be conducted using a tuning fork at 128 Hz by placing it on the skin overlying a bone. This works because bones are good resonators of vibrations.
context_section_description: The sensory conduction pathway that allows for cognitive recognition of vibration occurs through afferent neurons, also known as sensory neurons. The outside stimulus is a vibration that activates one of the three encapsulated nerve endings based upon where the sensation is felt. The intensity of the vibration must cause the neuron(s) to reach or surpass a threshold in order for an action potential to be propagated. From here, the signal travels through the dorsal column–medial lemniscus pathway.
  The pathway is composed of the dorsal column within the spinal cord and the medial lemniscus in the brain stem. Collectively, the ascending sensory fibers are called the dorsal column because ascending fibers gather at the dorsal funiculus in the spinal cord. The dorsal funiculus is located between the dorsal horn and the medial line in the spinal cord.
  There are three types of neurons in the pathway: first-, second-, and third-order neurons. The first-order neuron is the afferent neuron. It enters the spinal cord through the dorsal root ganglia and branches in the spinal cord. Some neurons terminate in the spinal cord, where they contribute to a reflex response. Other neurons continue ipsilaterally, same side, to the medulla oblongata. If the neurons are coming from the lower limbs, they are carried by the fasciculus gracilis into the medulla. If the neurons are coming from the upper limbs; they are carried by the fasciculus cuneatus. In the medulla, at the dorsal column, nuclei of the first-order neuron synapse with the second-order neuron, which then decussates (crosses over to the other side of the central nervous system) into the medial lemniscus. The second-order neuron then carries the information to the ventral posterolateral nucleus of the thalamus and then the somatosensory cortex in the parietal lobe. Immediately, the posterior parietal lobe synthesizes the information into a recognizable pattern. The coded information is then sent to the prefrontal cortex to devise a motor response to the stimulation. The motor information is sent through efferent neurons.
caption: The image on the left side depicts the dorsal column pathway for vibration perception.
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