Where do the large (L, Aβ) and small (S, A-δ, and C) fibers synapse?

The large (L, Aβ) and small (S, A-δ, and C) fibers synapse in the spinal cord, specifically in the dorsal horn. This is where the primary afferent fibers, which carry sensory information from the body, enter the spinal cord and make connections with interneurons or projection neurons.

Large fibers, which are primarily responsible for transmitting sensations such as touch and pressure, synapse with neurons in the dorsal horn that send signals up to the brain. Small fibers, on the other hand, transmit sensations such as pain and temperature. Their synaptic connections in the spinal cord are crucial for the modulation and processing of pain signals before they ascend to higher brain centers.

This synaptic interaction in the spinal cord is an essential part of the pain pathway, allowing for the integration of different sensory modalities and contributing to the perception of pain. The other locations mentioned do not serve as sites for this specific synapsing of sensory fibers. For instance, while peripheral nerve endings are responsible for the reception of sensory stimuli, they do not serve as synaptic sites for these fibers entering the central nervous system. Similarly, the brainstem is involved in further processing and modulation of signals after they have already synapsed in the spinal