NS 9 and 10 Flashcards
define touch
the sensory experience when mechanoreceptors are excited
define mechanoreception
detection of mechanical stimuli
define exteroception
give information about things coming into contact with the body
define proprioception
awareness of position
mechanoreceptors and PDL mechanorecepors are what type of receptors?
exteroceptors
list the proprioceptors
- PDL mechanoreceptors
- muscle spindles
- joint receptors
- golgi tendon organs
- inner ear
what do the oro-facial mechanoreceptors in the mucosa detect?
food texture etc
it is important for mastication
the PDL mechnoreceptor is there for the…
forces on teeth
what do muscle spindles detect?
muscle length
what do joint receptors detect?
joint position and movement
what is the effect of stimulation of mechanoreceptors?
- sensation of touch
- reflexes ;
- jaw muscle reflex and salivary reflex - chewing gum
- interact/modulate other sensory modalities ie the effect of rubbing a painful area
rapidly adapting stimulus
few action potentials
slow adapting stimulus
many action potentials
what is the receptive field?
the area/space where a stimulus will affect the receptor
what is RA I and RA II?
- RA I = rapid adaptive, small receptive field
- RA II = rapid adaptive and large receptive field
What is SA I and SA II?
- SA I = slowly adapting and small receptive field
- SA II = slowly adapting and large receptive field
the meissner corpuscles belongs to which receptors?
RA I
List the features of the meissner corpuscles
small receptive field low threshold present in: - oral mucosa - vermilion border hard palate
name an RA II receptor?
pacinian corpuscle
features of the Pacinian corpuscles
- deep in mucosa
- large receptive field
- very low threshold
- rare in oral mucosa
name an SA I receptor
merkel cell
how low is the threshold in merkel cells?
as low as 1mg
where are merkel cells present?
tongue, lips and cheeks
raffini endings are which type of receptors?
SA II
features of the SA II receptors
deep large RF respond to tension low threshold PDL
what happens in transduction?
- mechanical energy –> electrical energy
- stimulus causes depolarisation
- if reaches threshold –> action potential
what type of fibres is present in the parent axon?
A - beta large myelinated fibres - fast (33-75 m/s)
what is the touch threshold of lips and oral mucosa?
10 mg
what is the touch threshold of teeth?
0.01N
The PDLM is an important ‘‘sensory’’ organ, which roles does it play?
exteroceptive and proprioceptive
what is the nerve endings of the PDLM?
ruffini
what are the afferents of the PDLMs?
A-beta axons and they have around 300 per tooth
list the cell bodies of the PDLMs
- V ganglion
- mesencephalic nucleus
how were animals used to study PDLM properties?
- cat canine preparation
- localise individual receptors
- single fibre recordings
how were humans used to study PDLM properties?
- recordings from inferior alveolar nerve
- discrete forces applied to teeth
how is pain with in the pdls easy to localise?
no branched axons between adjacent teeth
innervation density is higher at apex
list properties of the PDLM
amount of PDLM activity depends on:
- direction of applied force
- magnitude of force
- adaptation properties
- threshold of the receptors
- position of receptors in PDL
PDLM properties: if you have the same receptor then why is there a difference in properties?
- linked to position of fulcrum
- smaller stimulus nearer the fulcrum
tooth movement of how much results in a reflex effect in masseter muscle
8.5 microns
describe the sensory pathway
stage 1 : mechanoreception
- transduction of stimulus
- propagation along primary afferent nerve
stage 2: processing at first synapse - trigeminal nuclei
stage 3 : processing in thalamus
stage 4: conscious perception
in trigeminal pathways where would the fibres synapse?
- mainly in main sensory nucleus
- can project to spinal V nuclei as well
