Orofacial sensations Flashcards
(27 cards)
Classification of sensory receptors
- Exteroceptors - provide info frm external env:
- Touch, pressure, temp, taste, smell, light, sound
- Enteroceptors /interoceptors, visceroceptors) - provide info on internal env
- BP, plasma osmolality, blood pH
- Proprioceptors - info on musculoskeletal system - position sense
- Muscles, tendons, joints
Kinaesthesia
Suddenly lowering the back of the dental chair causes pt disorientment/ momentary panic
Exteroceptors in eye, ear and skin detect touch and pressure
Proprioceptors in muscles, tendons and joints
Together sense the mvmts and position of the parts of body.
Why is it that some patients can adapt to dental
occlusal changes and
learn quickly how to function again appropriately,
whereas other patients cannot?
Some patients are more neuroplastic than others and thus able to adapt better to changes.
Neuroplasticity is dependent on the ability of sensorimotor cortex to develop central sensitisation after the procedure.
For that to happen, Tissue injury & inflammation + peripheral nerve injury activates C fibres.
Summation of slow synaptic potentials → alteration in 2nd messengers
→ activates protein kinases
Increases excitability and synaptic efficacy
→ central sensitisation
What is Pre-emptive analgesia
The treatment of post-op pain by preventing the establishment of central sensitisation.
E.g. prior to extraction of impacted 3rd molar under GA
Administer long-acting local analgesia and anti-inflammatory drugs at time of surgery
Reduces risk of long-lasting post-op pain
Factors affecting pain perception
Intensity of the stimulation/tissue damage
Emotions
Past experience and memories of pain
Other concomitant sensory experiences
Gender, ethnicity and age
Placebo effect
Double pain sensation comes from
2 different fibres which conduct the impulses at different velocities
Fast pain:
Sharp, well-localised, short duration
Thermal and mechanical nociceptors
Adelta fibres
Slow pain:
Aching, burning pain
Poorly localised
Long duration
Polymodal nociceptors
Unmyelinated C fibres
Nerve fibres that process pain
A fibres: Myelinated, fast-conducting fibres at periphery of pulp and inner dentine along the odontoblast processes
A delta fibres - temp and sensation, prickling pain
Large A (A-alpha, A-beta) fibres - touch and pressure (not anaesthetised by LA)
C fibres: Smaller diameter, unmyelinated fibres in body of the pulp and slower conduction velocity
Burning pain sensation
Larger diameter → less resistance → faster conduction
Hot pulp syndrome
Peripheral sensitisation
In response to stimulus, Antidromic activation of pulp nociceptors and sensory endings occurs, stimulating surrounding nociceptors
1) Prostaglandins and substance P sensitise surrounding nociceptors
Mast cells degranulate and release histamine
Plasma extravasation leads to oedema, releasing bradykinin
2) K, bradykinin, serotonin, histamine activate nociceptors
3) Release of CGRP (Calcitonin Gene Related Peptide) causes dilation of peripheral blood vessels
=> Lowers pain threshold, Increase in pain sensitivity (hyperalgesia)
Allodynia and hyperalgesia
Allodynia = pain response to stimulus that normally doesn’t cause pain
Hyperalgesia = increased response to stimulus that normally causes pain
Referred pain
Dental Pain occurs when sensory information from the teeth and periodontal structures are transmitted to the brain via trigeminal nerve, ascending the ipsilateral trigeminal brainstem sensory nuclear complex.
Several primary neurons of nociceptors converge into the same secondary neuron onto the same pain pathway, causing pain to be felt elsewhere from the source.
Masseter refer pain to posterior teeth, eyes ears
Deep masseter trigger points are associated with tinnitus
Temporalis refers pain to the maxillary teeth, back of head
Theories of pain
Gate control theory:
Nerve impulses descend from brain
S fibres facilitate transmission by opening the gate
L fibres inhibit transmission by closing the gate
Hydrodynamic theory of pain:
Inward dentinal flow - caused by hot liquids
Outward dentinal flow - caused by air, drilling, osmotic changes (sugar)
Neuromatrix theory:
Input from brain’s memories, emotions + sensory sinalling systems → pain perception, action and stress-regulation mechanisms
Susceptibility to LA depends on
1 - Size of nerve fibre (smaller diameter is penetrated more easily by LA)
2 - Myelination (myelin blocked first)
3- Rate of firing - rapidly firing blocked first (higher affinity for LA)
Taste and smell pathways
Chemosensation occurs in sensory epithelia in the nose and mouth
Detection of pungent chemicals is mediated by both oral and nasal afferents of the trigeminal nerve
Taste signals are transmitted when tastant molecules bind to receptors on microvilli at top of taste cells.
Electrical changes release transmitter onto the nerve ending at bottom of cell.
Nerve carries taste messages to the brain.
Anterior ⅔ of tongue - Chorda tympani - VII
Posterior ⅓ and pharynx - glossopharyngeal IX
Anterior to epiglottis, larynx- vagus - X
Basis of common taste and smell disorders
Ageusia
Dysgeusia
Hypergeusia
Hypogeusia
Phantom taste perception
Physiology:
Tranport loss
- Inflammation from poor OH, xerostomia, interferes with access of a tastant to tastebud
Sensory loss
- Drugs, radiotherapy, diseases injure the receptor cell
Neural loss
- Nerve injury to gustatory afferent nerves and central gustatory pathways
Types of muscle fibres
Type I Fibres
1st to activate
smallest
Prolonged activity
Aerobic
Low power - slow, tonic contracting,
Low fatigability
Type IIa Fibres
Intermediate
Type IIb Fibres
largest
Very short term
Anaerobic
High Power - powerful, fast contracting
Quick to fatigue
MyHC1
Large
Aerobic
Slow contracting
Slow fatigue
Prolonged use
MyHC2
Small
Anaerobic
Fast contracting
Quick fatigue
Powerful
Jaw closing: 40% hybrid, 70% type 1: because jaw closers prolonged activity (maintain rest posn mandible/prolonged chewing) so more MyHC-1 fibres in both pure and hybrid forms
Jaw opening: 10% hybrid, 45% type 1
Jaw muscles
Having more MS in jaw closers vs jaw openers is important because
Muscle spindles = stretch receptors detect changes in muscle length + velocity at which it occrs
Jaw-closing muscles = many muscle spindles
(70% Type I - responsible for prolonged activity)
Higher + well-controlled levels of forces
Jaw-opening muscles
few to none. 45% Type I
Jaw opening is mainly by inhibition of jaw-closing muscles
Eg biting into fishbone, muscle spindle in jaw closers stretch are picked up by afferent fibres → efferent fibres frm trigeminal ganglion → oppose jaw-closing action
Having more MS in jaw closers vs jaw openers is important because
Stretch reflex - to detect muscle length & changes in muscle length
Jaw opening is limited by max opening while jaw closing runs risk of biting down too hard → smashing teeth.
Jaw reflexes
1) Jaw-closing/Jaw Jerk reflex
Receptor: muscle spindles
Primary afferent: Spindle Ia afferent
Cell body: Mesencephalic nucleus V
Stretch of jaw-closer muscle spindle mediates monosynaptic reflex excitation of muscle of origin.
→ tap on chin with mouth sl open stretches masseter → trigger masseter contraction → jaw snaps upward
Possibly Maintains head in rest position
2) Jaw Unloading reflex: During chewing when texture of food changes unexpectedly eg biting nut - disynaptic reflex decrease in JC muscle activity to adjust for decreased resistance
3) Jaw-opening reflex
Painful oral and perioral stimuli inhibit jaw-closing muscles
Disynaptic inhibition of JC muscles
Protective role - fishbone in gingiva
4) Periodontal reflexes
Disynaptic inhibition of JC muscles
Strong pressure/Tapping on tooth (stone in sandwich - rapid increase in load force) → reflex inhibition of jawcloser muscles
Protective role
Weak pressure on tooth → reflex excitation of jawclosers
Keep food btw teeth
Gag reflex
Spasmodic and abortive respiratory movements with the glottis closed
Stimulation of faucial pillar, posterior pharyngeal wall, base of tongue, S/P
How is chewing coordinated
Reflex theory (JC → JO → JC)
2. Pattern generator theory
3. Peripheral input + Cortical input + Central Pattern Generator
CPG sets rhythm for mastication
Receptors in and around the mouth alter strength, duration, rate of force dvpt by their connections w motorneurons of the jaw muscles
Chewing strokes are weaker and faster for soft food vs hard food.
Painful stimuli and conscious decisions can interrupt the activity of the CPG.
Change in synaptic potentials of receptors of teeth/gingiva/lips/jaws confirms modulation of synaptic input during chewing
Receptors involved in jaw reflexes: Muscle spindles, GTO, TMJ receptors
Gamma motor innervates MS only
Compensates sudden changes in the force dvped btw teeth
Alpha-Gamma co-stimulation maintains stretch sensitivity
Tendon organ receptors are activated by increased stress on the tendons of the muscles.
Muscles of mastication
Masseter - bilateral: elevates, unilateral: medial
Deep head
Originates zygomatic arch
Inserts angle of mandible
Superficial head (larger)
Originates Mx process of zygoma
Inserts angle of mandible
Temporalis - elevates and retrudes
Temporal fossa on skull
Coronoid process
Medial Pterygoid - elevate, side to side and protrudes
Deep head
Medial of LatPt plate
Medial aspect of Angle of mandible
Superficial head
Mx tuberosity, pyramidal process of the palatine
Medial aspect of Angle of mandible
Lateral Pterygoid - side to side and depresses
Upper head
Greater wing of sphenoid (infratemporal crest)
Joint capsule of TMJ
Lower head
Lateral of LatPt plate
Pterygoid fovea on neck of condyle
Swallowing phases
1) Oral phase - voluntary
Bolus created by mastication and tongue
Tongue elevates to hard palate and propels bolus back into the pharynx
2) Pharyngeal phase
Tongue blocks off oral cavity
Soft palate elevates blocking off the nasopharynx
Epiglottis folds back to close glottis
Larynx elevates to prevent aspiration
Upper oesophageal sphincter relaxes to allow bolus to enter oesophagus
3) Oesophageal phase
Once bolus is in oesophagus, UOS contracts to prevent regurgitation.
Constrictor muscle of pharynx contracts to force food inferiorly
Peristalsis of the oesophagus transports the bolus down toward the stomach
Lower oesophageal sphincter relaxes to allow bolus to exit oesophagus
Periodontal mechanoreceptors
Periodontal mechanoreceptors regulate the forces applied by the teeth in occlusion and mastication.
- Ruffini type receptors directly sensitive to stimulus
- Responses vary with the force applied to the tooth—greater sensitivity at low force levels
- Contribute to oral stereognosis (tactile sensitivity of teeth)
- Enables a patient to detect new restorations and changes in occlusion
Basis of swallowing and masticatory disorders
Poliomyelitis
Multiple sclerosis
Myasthenia Gravis
Muscular dystrophy
Poliomyelitis - kills motorneurons in anterior ventral spinal cord
Multiple sclerosis - demyelination of motor axons
Myasthenia Gravis - blockage of ACh receptors
Muscular dystrophy - contraction of muscle fibres inhibited
What is osseoperception?
Osseoperception is mechanoreception in the absence of a functional PMR
- Seen in implants
- Is related to TMJ, muscle and mucosal periosteal contributions
