pain & touch

Receptors

• Afferent neurons have sensory receptors associated with them.

• These receptors detect a stimulus.

• Stimuli lead to receptor potentials in the receptor. 

• This is called sensory transduction and leads to action potentials in the afferent neuron. 

Photoreceptors

light

Mechanoreceptors

mechanical energy

Thermoreceptors

heat

Osmoreceptors

concentration changes

Chemoreceptors

certain chemicals

Nociceptors (pain receptors)

tissue damage

Tactile (touch) receptors

type of mechanoreceptor in the skin

subtypes of tactile receptors

• Light touch sustained touch (braille)

• Pressure (massage)

• Hair movement

• Vibrations

• Light fluttering tough (tickle)

Touch (tonic and phasic)

Different receptors respond differently to sustained stimuli

Tonic receptors

do not adapt or adapt slowly

Phasic receptors

adapt rapidly

• Many tactile receptors are phasic.

Pain

• A protective mechanism in response to stimulation of nociceptors.

• Also includes behavioral and emotional reactions.

• Pain is subjective and influenced by past experiences.

what are the types of nocireceptors?

mechanical, thermal, and polymodal

mechanical nocireceptor

mechanical damage (cutting, slashing, pinching)

thermal nocireceptor

Temperature extremes

polymodal nocireceptor

All kinds of stimuli including irritating chemicals

what are the 2 pathways pain signals travel on?

fast delta-A fibers and slow C fibers

fast delta-A fibers

Sends immediate sharp pain; short lived

slow C fibers

Sends delayed dull pain; persists longer

The Brain’s Analgesic System

• Built in system to suppress pain.

  • Endorphins, Endogenous opioids, endocannabinoids.

• Activation pathway unclear.

• Exercise, stress, acupuncture have all been shown to induce this system