Where is the first synapse in the spinal cord? There is a differential projection of small-diameter and large-diameter primary afferent fibers to the spinal cord dorsal horn. The largest diameter Ia primary afferents arise from muscle spindles and make monosynaptic connection with motoneurons in the ventral horn. Large-diameter, non-nociceptive primary afferents synapse on neurons in …
Where do nociceptive fibers enter the spinal cord? Nociceptive primary afferent fibers have their cell bodies in dorsal root ganglia (or trigeminal ganglia for the face). The central branches of these afferents enter the spinal cord through the dorsal root and ascend or descend a few segments in the tract of Lissauer. The central branches …
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How are nociceptors altered by tissue injury? When there is tissue injury (e.g., an arthritic joint), the nociceptor is exposed to an inflammatory “soup” containing a host of molecules that influence the properties of the nociceptor. These molecules include prostaglandin products of arachidonic acid metabolism, bradykinin, cytokines, serotonin, and growth factors (notably nerve growth factor). …
What are TRP channels? TRP channels are a large family of transient receptor potential channels that allow ions to flow in response to a variety of stimuli, including temperature, many plant-derived compounds, and endogenous molecules. Different TRP channels cover the range of temperatures sensed by afferent fibers. For example, the threshold for TRPV1 is approximately …
What is NaV1.7? There are 9 different subtypes of voltage-gated Na channels. Of particular interest is the selective expression of a tetrodotoxin-sensitive voltage-gated Na channel, namely NaV1.7, in sensory neurons. Loss of function of this channel is associated with the condition of congenital insensitivity/indifference to pain. Conversely, gain of function of the channel underlies the …
What are some of the molecules that are unique to the nociceptor? All nociceptors use glutamate as their primary excitatory neurotransmitter. However, several other transmitters coexist with glutamate, and the differences in transmitters define the two major classes of nociceptors: The peptidergic class expresses calcitonin gene-related peptide (CGRP) and substance P. The non-peptide class is …
Differences between first and second pain First and second pain refers to the immediate and delayed pain responses to noxious stimulation. Other terms that denote these pains are fast and slow pain or sharp/pricking and dull/burning pain. The stimuli that generate first pain are transmitted by A delta, small, myelinated afferents. Second pain results from …