sensory transduction: peripheral receptors for somatosensory and pain pathways

somatosensory

includes sensations arising from stimuli impinging on

1. skin (cutaneous)

2. muscles and joints

3. internal organs

GANGLION

the cell bodies of all first order neurons involved in processing of sensory information are located in a BLANK located in the periphery

somatosensory system

collective category for all sensations that are not the special senses

• touch

• body position

• pain

• temperature

mechanoceptors 

low threshold, detec minute vibration forces impinging on skin - sensitive to physical distortion (bending, stretching, pressure and vibration) 

proprioceptors

low threshold, detect small changes in muscle tension

dorsal root ganglion

trigeminal ganglion

cell body location of mechanoreceptors/proprioceptors

stretch-sensitive ion channels

receptors of skin (mechanoreceptors) and muscle (proprioceptors)

dorsal root ganglion

dendrites

periphery 

spinal cord 

cell body with NO BLANK 

a single axonal process emerges from the cell body, splits into 2 parts - one goes to the BLANK and the other enters the BLANK BLANK 

sensory transduction type 1

mechanosenitive receptors are on the terminal of the peripheral process of dorsal root ganglion

sensory transduction type 2

a receptor cell is activated by a physical/chemical stimulus, this cell releases a neurotransmitter that activates the terminal end of the (dorsal root) ganglion neuron and generates action potentials

antidromaical

action potential travels to the cell body

orthodromical 

action potential travels to the CNS 

transduce

ion channel

sensory receptors BLANK a physical stimulus into an electrical signal - involves opening of an BLANK BLANK

generator potential

somatosensory receptors induce action potentials in the peripheral process of the dorsal root ganglion neuron

• created in response to skin distortion

schwann cells

myelination in the PNS

oligodendrocytes

myelination in the CNS 

alpha-beta

myelinated, large diameter fibers that conduct information at high speeds

• mechanoreceptors of skin

merkel’s disks

meissner’s corpuscles

superficial - limited branching and densly packed

ruffini’s ending

pacinian corpsule

deep - and sparse

receptive field

area of skin innervated by peripheral axon of the dorsal root ganglion neuron

• convey information of the location of a stimulus

smaller

greater

BLANK the receptive field, the BLANK the discrimination of two points

two point discrimination

measure of spatial resolution

areas with finest discrimination:

• have higher density of mechanoreceptors in the skin

• are enriched with receptors with a small receptive field

pacian corpuscle

meisnner’s corpuscle

encapsulated endings - connective tissue capsule formed by schwann cells

merkel’s disks

ruffini endings

non-encapsulated endings

ruffini ending

least understood mechanoreceptor

• sensitive to strecthing of skin produced by finger and limb movement 

  • finger position and conformation of hand 

merkel cell

receptor cell that is activated by sensory stimuli and releases excitatory neurotransmitter to merkel’disk - depolarizes the distal end of DRG and initiates an action potential

• merkel’s disk receptor cell; example of signal transduction type 2

adaptation

firing pattern of receptive endings in response to sustained stimulation

slow adapation

continues to respond as long as the stimulus is present; very little change in firing rate and detects static position

• ruffini ending

• merkel’s disks

fast adaptation

receptors are activated at the start of the stimulus, but then they shut down until the stimulus is removed; detect change in movement of stimuli

• pacian corpuscle

• meissner’s corpuscle 

merkel’s disk

underlie tactile form perception; texture

• small receptive field

• non-encapsulated

• slow adaptation

meissner’s corpuscle

transduce information when textured objects are moved across skin; grip control

• small receptive field

• encapsulated

• fast adaptation

pacician corpsucle

underlie perception of vibration

• large receptive field

• encapsulated

• fast adaptation

noiciceptors

separate group of DRG cells that code for painful sensations; free nerve endings

alpha-delta

C

two types of nociceptors

alpha delta

small, myelinated

• higher threshold of activation and conduct slightly slower than those carrying touch information from the skin

• respond almost immediately following application of noxious stimulus - primary pain (sharp and quick)

• critical for localization of input and initail interpretor for stimulus intensity; detects initial painful insult

C fibers

small and unmyelinated - slow conduction

• transmit secondary pain (diffused and achy)

• majority of nociceptors

polymodal

c-fibers have this characteristics - a majority of C-fibers respond to noxious mechanical, heat and cold stimuli

TRPV1

important nociceptor transduction of painful heat stimuli

sensitization

nociceptor has an increased response to the same painful stimulus overtime, especially is there is tissue injury

hyperalgesia

stimuli that were perceived as mild but now are perceived as intense

allodynia

stimuli that were not painful, now induce pain