A sensory receptor detects a stimulus and converts it into neural signaling. Afferent pathways carry information toward the CNS, where processing contributes to perception. Sensation is not created by the receptor alone.
Mechanoreceptors respond to deformation such as pressure, stretch and vibration. Thermoreceptors respond to temperature. Nociceptors respond to potentially tissue-threatening stimuli. Proprioceptors provide information about body position and movement.
Skin contains multiple receptor endings with different receptive fields and adaptation rates. Rather than memorizing touch as one single sense, understand that pressure, vibration, skin stretch and light contact are encoded differently and integrated by the nervous system.
Muscle spindles provide information about muscle length and change in length. Golgi tendon organs respond to tension/force. Joint and cutaneous receptors also contribute to position sense.
Light enters through cornea → aqueous humor → pupil → lens → vitreous body → retina. Rods are highly sensitive in dim light; cones support color and high-acuity vision. The optic nerve carries retinal output toward the brain.
Sound travels through external ear → tympanic membrane → ossicles → cochlea, where hair cells transduce mechanical vibration. The vestibular apparatus, including semicircular canals and otolith organs, contributes to balance and head-motion sensing.
Taste receptors detect dissolved chemicals; olfactory receptors detect airborne molecules. Both are chemical senses and interact strongly in flavor perception.
Nociception is neural encoding/processing of potentially harmful stimuli. Pain is a personal sensory and emotional experience influenced by biological, psychological and social context. Massage therapists should not equate pain intensity directly with tissue damage.
Altered sensation from neuropathy, nerve injury or neurological disease changes pressure and temperature safety. New numbness, tingling, burning, electrical or radiating symptoms during massage are reasons to stop or modify and reassess, not to press harder.