Somatosensory receptors

Receptor proteins

recall that the transduction process couples a stimulus detector (i.e., a receptor protein) to an ion channel, in order to generate a receptor potential
in many sensory systems, the transduction channel is a member of the transient receptor potential (TRP) superfamily - TRP channels incorporate the receptor protein with the channel structure

there are 2 types of thermoreceptors:
1. COLD: respond to temperatures between 5 and 35^oC, AND greater than 45^oC ("paradoxical cold")
2. WARM: respond to temperatures between 30 and 45 ^oC
both types of thermoreceptor are rapidly adapting, i.e., they respond best when the temperature is changing
temperature detection is built into the structure of the channel

McKemy et al. (2002)

Mechanoreceptors

the actual process by which a deformation of the cell membrane causes the opening of a mechanotransduction channel is not known
proposed mechanisms include:
1. direct activation due to lipid tension
2. direct linkage via intracellular and extracellular proteins (see also the gating spring theory of auditory transduction)
3. indirect activation via a second messenger system that activates the channel
TRP channels have been proposed as mammalian mechanoreceptors, but not conclusively established

Mechanoreceptor theories

Lin and Corey (2005)

Nociceptors

TRPV1 is a known nociceptive channel
chemical stimuli that activate this channel include heat, protons, bradykinin and prostaglandins

TRPV1 structure