the body to "detect and protect". Nociceptors detect different kinds of noxious stimuli indicating potential for damage, then initiate neural responses to withdraw from the stimulus. Thermal nociceptors are activated by noxious heat or cold at various temperatures. Mechanical nociceptors respond to excess pressure or mechanical deformation, such as a pinch. Chemical nociceptors respond to a wide variety of chemicals, some of which signal a response. They are involved in the detection of some spices in food, such as the pungent ingredients in Brassica and Allium plants, which target the sensory neural receptor to produce acute pain and subsequent pain hypersensitivity. Connection with the central nervous system Information coming from the sensory neurons in the head enters the central nervous system (CNS) through cranial nerves. Information from the sensory neurons below the head enters the spinal cord and passes towards the brain through the 31 spinal nerves. The sensory information traveling through the spinal cord follows well-defined pathways. The nervous system codes the differences among the sensations in terms of which cells are active. Classification Adequate stimulus A sensory receptor's adequate stimulus is the stimulus modality for which it possesses the adequate sensory transduction apparatus. Adequate stimulus can be used to classify sensory receptors: Baroreceptors respond to pressure in blood vessels Chemoreceptors respond to chemical stimuli Electromagnetic radiation receptors respond to electromagnetic radiation Infrared receptors respond to infrared radiation Photoreceptors respond to visible light Ultraviolet receptors respond to ultraviolet radiation Electroreceptors respond to electric fields Ampullae of Lorenzini respond to electric fields, salinity, and to temperature, but function primarily as electroreceptors Hydroreceptors respond to changes in humidity Magnetoreceptors respond to magnetic fields Mechanoreceptors respond to mechanical stress or mechanical strain Nociceptors respond to damage, or threat of damage, to body tissues, leading (often but not always) to pain perception Osmoreceptors respond to the osmolarity of fluids (such as in the hypothalamus) Proprioceptors provide the sense of position Thermoreceptors respond to temperature, either heat, cold or both Location Sensory receptors can be classified by location: Cutaneous receptors are sensory receptors found in the dermis or epidermis. Muscle spindles contain mechanoreceptors that detect stretch in muscles. Morphology Somatic sensory receptors near the surface of the skin can usually be divided into two groups based on morphology: Free nerve endings characterize the nociceptors and thermoreceptors and are called thus because the terminal branches of the neuron are unmyelinated and spread throughout the dermis