Somatosensory receptors

Receptors

STIMULUS	RECEPTOR	LOCATION	RECEPTIVE FIELD (small = well localized)	ADAPTATION
Mechanoreception
Touch, pressure	Free nerve ending	Hair root	Small	Variable
Steady pressure, texture	Merkel receptor	Superficial		Slow
Flutter, stroking	Meissner corpuscle	Superficial		Rapid
Vibration	Pacinian corpuscle	Deep	Large	Extremely rapid
Stretch	Ruffini ending	Deep	Large	Slow
Thermoreception
Cold	Free nerve ending	Superficial	Small	Rapid
Warm	Free nerve ending	Superficial	Small	Rapid
Nociception
Thermal	Free nerve ending	Superficial	Small	Rapid
Mechanical			Large	Slow
Polymodal (esp. chemical)			Large	Slow

discriminative touch receptors (Meissner and Pacinian corpuscles, as well as Merkel discs and Ruffini endings) have specialized secondary structures that give them their physiological properties (e.g., it is the onion-like connective tissue lamellae that enable Pacinian corpuscles to respond to vibration)
in the table, the various receptors within each submodality are sorted by receptive field size
- among touch/pressure receptors, superficial sensations are well-localized, while deep sensations are not
- temperature is well-localized, and these receptors (whether nociceptive or not) adapt rapidly
- other types of nociception are not well localized and their receptors slowly adapt

another way to think about discriminative touch receptors is to sort them according to speed of adaptation rather than receptive field size:
- Meissner and Pacinian corpuscles, which encode flutter and vibration, adapt rapidly (they'll respond when something first touches your skin)
- Merkel discs and Ruffini endings, which encode steady pressure and stretch adapt slowly (they'll continue to respond if something stays in contact with your skin)