A<unk>  ("pain receptor") is a sensory neuron that responds to damaging or potentially damaging stimuli by sending “possible threat” signals to the spinal cord and the brain. If the brain perceives the threat as credible, it creates the sensation of pain to direct attention to the body part, so the threat can hopefully be mitigated; this process is called nociception.
Nociceptor
Efferent nerve fiber
Sensory nerve
Muscle spindle
Gamma motor neuron
Thermoreceptor
Postganglionic nerve fibers
Special somatic afferent fiber