ABSTRACT
B. Central process: Terminates in the spinal cord, usually at lamina II (substantia gelatinosa), synapsing to the second-order neurons in the spinal cord
C. Two types of important nerve transmission axons
i. Aδ-fibers: Myelinated, conduction velocities of 5-30 m/sec; respond to thermal and mechanical stimuli; detect sharp, localized pain
Figure 2.1 Pain pathway summary (modified) and possible interruption sites. First-order neurons (nociceptors; detect noxious stimulus → convert into electrical signals → synapse onto second-order neurons in spinal cord in lamina II → release substance P, glutamate, aspartate, somatostatin → second-order neurons (receive signals from nerve endings → cross midline → go through brain stem → synapse onto third-order neurons in thalamus → third-order neurons in thalamus relay signals to other brain regions (e.g., cerebral, prefrontal, singular, cingulate cortex).
