This document provides an overview of pain pathways and mechanisms. It defines pain and discusses the different types of pain receptors and fibers that detect and transmit nociceptive signals. It describes the dual pain pathway and outlines the pathways from peripheral receptors to the central nervous system. It also discusses theories of pain and the three systems (sensory-discriminative, motivational-affective, cognitive-evaluative) that interact to produce the pain experience. Finally, it provides details on the nerve supply and innervation of maxillary and mandibular teeth.

2. • Introduction
• Definition
• Classification
• Pain receptors
• Neural pain pathways
• Sensory neurons
• Theories of pain
• Pain pathways
Dual pain pathway
Pain pathway of Maxillofacial Region

3. • Pain is a sensory experience of
special significance to physicians
and basic scientists.
• Pain is the commonest symptom
which physicians are called upon
to treat.
• Apart from its obvious applied
value, study of physiology of pain
has taught us a lot about neural
function in general.
• Pain is an intensely subjective
experience, and is therefore
difficult to describe.

4. The International Association for the Study
of Pain
Pain is "an unpleasant sensory and
emotional experience associated with
actual or potential tissue damage, or
described in terms of such damage"
• Monheim : “An unpleasant emotional
experience usually initiated by noxious
stimulus and transmitted over a specialized
neural network to the CNS where it is
interpreted as such.”

5. PAIN
Somatic
(somasthetic)
Visceral (from viscera)
e.g. angina pectoris,
peptic ulcer, intestinal
colic, renal colic, etc.
Superficial (from skin &
subcutaneous tissue) e.g.
superficial cuts/burns, etc.
Deep (from
muscles/bones/fascia/periosteum)
e.g. fractures/arthritis/fibrositis,
rupture of muscle belly

6. The experience of painThe experience of pain
Three systems interact usually to produce pain:Three systems interact usually to produce pain:
1.1. sensory - discriminativesensory - discriminative
2. motivational - affective2. motivational - affective
3. cognitive - evaluative3. cognitive - evaluative
1. Sensory - discriminative system1. Sensory - discriminative system processes informationprocesses information
aboutabout
the strength, intensity, quality and temporal and spatialthe strength, intensity, quality and temporal and spatial
aspects of painaspects of pain
2. Motivational - affective system2. Motivational - affective system determines the individual´sdetermines the individual´s
approach-avoidance behavioursapproach-avoidance behaviours
3. Cognitive - evaluative system3. Cognitive - evaluative system overlies the individualsoverlies the individuals
learnedlearned
behaviour concerning the experience of pain. It maybehaviour concerning the experience of pain. It may

8. • Sensory input from various external stimuli is thought
to be received by specific peripheral receptors that act
as transducers and transmit by nerve action potentials
along specific nerve pathways toward the central
nervous system.
• Termed first–order afferents, these peripheral terminals
of afferent nerve fibers differ in the form of energy to
which they respond at their respective lowest stimulus
intensity, that is, are differentially sensitive.
• The impulse interpreted is nociceptive (causing pain)
if it exceeds the pain threshold, that is, the intensity of
the stimulus is so great that the receptor is no longer
differentially sensitive.

9. GENERAL
SENSES
SPECIAL
SOMATIC VISCERAL
SUPERFICIAL DEEP
Touch-pressure
Thermal
Pain
Pain
Proprioception
Pain
Baroreception
Chemoreception
Visual
Audition
Olfaction
Gustation

10. • A nerve ending that responds to noxious stimuli that
can actually or potentially produce tissue damage.
• Free nerve endings i.e., they are not enclosed in a
capsule. The receptors for fast pain are sensitive to
mechanical or thermal stimuli of noxious strength. The
receptors for slow pain are sensitive not only to
noxious mechanical and thermal stimuli but also to a
wide variety of chemicals associated with
inflammation.
• These substances include histamine, serotonin,
bradykinin, acetylcholine, potassium ions and
hydrogen ions. It is possible that noxious
mechanical and thermal stimuli also act through the
release of some of these chemicals.

11. • Since pain receptors respond to a wide
variety of stimuli, they are called
polymodal.
• Types of nociceptors :
Aδ Mechanical Nociceptors
C Polymodal Nociceptors
C fibre mechanical nociceptors
High threshold cold nociceptors

12. • Mechanoreceptors, which respond to tactile non
painful stimuli, can be assessed psychophysically
by the ability of a human subject to discriminate
whether application of a two blunt-point stimuli is
perceived as one or two points.
• These receptors are divided into two functional
groups (rapidly or slowly adapting) depending on
their response during stimuli.
• Rapidly adapting mechanoreceptors respond at the
onset and offset of the stimuli, while slowly
adapting mechanoreceptors respond throughout
the stimuli duration.

13. • Mechanoreceptors can be divided into those
expressed in:
 Hairy skin (hair follicle receptors):
• Low threshold, rapidly adapting.
• Three major subtypes: ‘down’, ‘guard’,
tylotrich’.
 Glabrous (hairless) skin:
• Small receptive fields.
• Two major subtypes: ‘Meissener’s capsule’
(rapidly adapting) and ‘Merkel’s disc’
(slowly adapting).

14. • Proprioception (limb position sense), which
refers tooth position and movement of the
limbs (kinaesthesia), is determined by
mechanoreceptors located in skin, joint
capsules and muscle spindles.
• The CNS integrates information received
from these receptors, while keeping track of
previous motor responses that initiated limb
movement – a process known as efferent copy
or corollary discharge (reviewed by
Matthews, 1982).

16. • Nociception is the neural mechanism by which an individual
detects the presence of a potentially tissue harming stimulus.
There is no implication of (or requirement for) awareness of this
stimulus.
• The nociceptive mechanism (prior to the perceptive event)
consists of a multitude of events as follows:
• Transduction:
• This is the conversion of one form of energy to another. It occurs
at a variety of stages along the nociceptive pathway from:
– Stimulus events to chemical tissue events.
– Chemical tissue and synaptic cleft events to
- Electrical events in neurones.
– Electrical events in neurones to chemical events at synapses.

17. • Transmission:
• Electrical events are transmitted along
neuronal pathways, while molecules in the
synaptic cleft transmit information from
one cell surface to another.
• Modulation:
• The adjustment of events, by up- or down
regulation. This can occur at all levels of
the nociceptive pathway, from tissue,
through primary (1°) afferent neurone and
dorsal horn, to higher brain centres.
• Thus, the pain pathway as described
by Descartes has had to be adapted
with time.

18. SENSORY NEURONS
First Order Second Order Third Order

20. • According to this view, pain is produced when any
sensory nerve is stimulated beyond a certain level.
• In other words pain is supposed to be a non-specific
sensation and depends only on high intensity
stimulation.
• But the trigeminal system provides an example
against this theory. In case of trigeminal neuralgia
the patient can suffer excruciating pain from a
stimulus no greater than a gentle touch provided it is
applied to a trigger zone.
• Although, the intensity theory is not accepted, it
remains true to say that intensity of stimulation is a
factor in causing pain.

21.  (Johannes Muller, 1842):
• According to this view, pain is a specific modality
equivalent to vision and hearing etc.
• Just as there are Meissner corpuscles for the sensation of
touch, Ruffini end organs supposedly for warmth and
Krause end organs supposedly for cold, so also pain is
mediated by free nerve endings.
• Certain psychophysical studies have been regarded as
supporting specificity theory. Specialization is known to
exist in nervous system and there are well known tracts.
• But concept of specific nerve ending is no long tenable.
The Krause and Ruffini endings are absent from the dermis
of about all hairy skin, so it is certain that these structures
cannot be receptors for cold and warmth.

22. • Head and Rivers (1908) postulated the existence of
two cutaneous sensory nerves extending from the
periphery to the CNS.
• The protopathic system is primitive, yielding diffuse
impression of pain, including extremes of
temperature and is upgraded.
• The epicritic system is concerned with tough
discrimination and small changes in temperature and
is phylogenetically a more recent acquisition.

24. • This theory proposed by Melzack and Wall in
1965 and recently re-evaluated is receiving
considerable attention.
• This theory of pain takes into account the
relative in put of neural impulses along large and
small fibers, the small nerve fibers reach the
dorsal horn of spinal cord and relay impulses to
further cells which transmit them to higher
levels.
• The large nerve fibers have collateral branches,
which carry impulses to substantia gelatinosa
where they stimulate secondary neurons.

27. The role of the afferent and efferent pathwaysThe role of the afferent and efferent pathways
inin
processing of pain informationprocessing of pain information
Nociceptive painNociceptive pain
Nociceptors:Nociceptors: Endings of small unmyelinated and lightlyEndings of small unmyelinated and lightly
myelinated afferent neuronsmyelinated afferent neurons
Stimulators:Stimulators: Chemical, mechanical and thermal noxaeChemical, mechanical and thermal noxae
Mild stimulationMild stimulation →→ positive, pleasurable sensationpositive, pleasurable sensation
(e.g. tickling)(e.g. tickling)
Strong stimulationStrong stimulation →→ painpain
These differences are a result of the frequencyThese differences are a result of the frequency
and amplitude of the afferent signal transmittedand amplitude of the afferent signal transmitted
from the nerve endings to the CNSfrom the nerve endings to the CNS
Location:Location: In muscles, tendons, epidermis, subcutanous tissue,In muscles, tendons, epidermis, subcutanous tissue,
visceral organsvisceral organs
-- they are not evenly distributed in the bodythey are not evenly distributed in the body
(in skin more then in internal structures(in skin more then in internal structures ))

28. Afferent pathways:Afferent pathways:
•• From nociceptorsFrom nociceptors →→ transmittedtransmitted by small A-delta fibers andby small A-delta fibers and
C- fibersC- fibers to the spinal cordto the spinal cord →→ form synapses with neuronsform synapses with neurons
in the dorsal horn(DH)in the dorsal horn(DH)
•• From DHFrom DH →→ transmitted to higher parts of the spinal cordtransmitted to higher parts of the spinal cord
and to the rest of the CNS by spinothalamic tractsand to the rest of the CNS by spinothalamic tracts
**TheThe small unmyelinated C- neuronssmall unmyelinated C- neurons are responsible for theare responsible for the
transmission oftransmission of diffuse burning or aching sensationsdiffuse burning or aching sensations
**Transmission through the larger, myelinated A- delta fibersTransmission through the larger, myelinated A- delta fibers
occurs much more quickly. A - fibers carryoccurs much more quickly. A - fibers carry well-localized,well-localized,
sharp pain sensationssharp pain sensations

29. Efferent analgesic systemEfferent analgesic system
Its role: - inhibition of afferent pain signalsIts role: - inhibition of afferent pain signals
Mechanisms:Mechanisms:
- pain afferents stimulates the neurons- pain afferents stimulates the neurons in periaqueductalin periaqueductal
graygray ((PAG) -PAG) - gray matter surrounding the cerebralgray matter surrounding the cerebral
aqueductaqueduct in the midbrain results inin the midbrain results in activation of efferentactivation of efferent
(descendent) anti-nociceptive pathways(descendent) anti-nociceptive pathways
-- from there the impulses are transmitted throughfrom there the impulses are transmitted through
the spinalthe spinal cord tocord to the dorsal hornthe dorsal horn
-- there thaythere thay inhibit or block transmission of nociceptiveinhibit or block transmission of nociceptive
signals at the level of dorsal hornsignals at the level of dorsal horn

30. The role of the spinal cord in pain processingThe role of the spinal cord in pain processing
•• MostMost afferent pain fibersafferent pain fibers terminate in the dorsal hornterminate in the dorsal horn of theof the
spinal segment that they enter. Some, howeverspinal segment that they enter. Some, however ,, extendextend
toward the head or the foot for several segments beforetoward the head or the foot for several segments before
terminatingterminating
•• The A-The A- ββ fibers, some large A-delta fibers and small C- fibersfibers, some large A-delta fibers and small C- fibers
terminate in the laminae of dorsal hornterminate in the laminae of dorsal horn and in the substantiaand in the substantia
gelatinosagelatinosa
•• The laminaeThe laminae than transmit specific information (aboutthan transmit specific information (about
burned or crushed skin, about gentle pressure)burned or crushed skin, about gentle pressure) to 2ndto 2nd
afferent neuronafferent neuron

31. •• 22ndnd
afferent neuronsafferent neurons transmit the impulse from the substantiatransmit the impulse from the substantia
gelatinosa (SG) and laminaegelatinosa (SG) and laminae through the ventral and lateralthrough the ventral and lateral
hornhorn,,
crossing in the same or adjacent spinal segmentcrossing in the same or adjacent spinal segment ,, to the otherto the other
sideside
of the cordof the cord.. From there theFrom there the impulse is carried through theimpulse is carried through the
spinothalamic tractspinothalamic tract to the brain. Theto the brain. The two divisions oftwo divisions of
spinothalamic tract are known:spinothalamic tract are known:
1.1. the neospinothalamic tractthe neospinothalamic tract -- it carries information to the midit carries information to the mid
brain, thalamus and post central gyrus (where pain isbrain, thalamus and post central gyrus (where pain is
perceived)perceived)
2.2. the paleospinothalamic tractthe paleospinothalamic tract -- it carries information to theit carries information to the
reticular formation, pons, limbic system, and mid brainreticular formation, pons, limbic system, and mid brain
(more synapses to different structures of brain)(more synapses to different structures of brain)

33. NERVE SUPPLY FOR MAXILARY
TEETH

34. • Anterior superior alveolar nerve :
• Supplies
• 1- The Pulp &
• 2- Investing structure &
• 3- labial mucoperiosteum
• of anterior teeth ( 1 , 2 , 3 ) .
• Middle superior alveolar nerve :
• Supplies
• 1- The Pulp &
• 2- Investing structure &
• 3- Buccal mucoperiosteum
• Of premolars ( 4 , 5 ) & MB root of 1st molar ( 6 ) .

35. • Posterior superior alveolar nerve :
• Supplies
• 1- The Pulp &
• 2- Investing structure &
• 3- Buccal mucoperiosteum
• Of upper molars except MesioBuccal root of 1st molar ( 6 )
• Greater ( anterior ) palatine nerve :
• Supplies
• 1- palatal mucoperiosteum
• of maxillary molars ( 6 , 7 , 8 ) & premolars ( 4 , 5 ) .
• Nasopalatine nerve:
• Supplies
• 1- palatal mucoperiosteum
• of Maxillary anterior teeth ( 1 , 2 , 3 )

36. NERVE SUPPLY FOR MANDIBULAR
TEETH

37. • Incisive nerve :
•
• Supplies
• 1- The Pulp &
• 2- Investing structure
• Of the lower anterior teeth ( 1 , 2 , 3 ) .
• inferior alveolar nerve :
•
• supplies
• 1- The Pulp &
• 2- Investing structure &
• Of the lower premolars ( 4 , 5 ) & molars teeth ( 6 , 7 , 8 ) .

38. • inferior dental plexus "cutaneous colli nerve " :
•
• supplies
• 1- Labial or Buccal mucoperiosteum
• of the anterior teeth ( 1 , 2 , 3 ) & premolar ( 4 , 5 ) .
• long buccal nerve :
•
• supplies
• 1- Buccal mucoperiosteum of the lower molars ( 6 ,7 , 8 )
• Lingual nerve :
•
• Supplies
• 1- Lingual mucoperiosteum of the all lower teeth ( 1 , 2 , 3 , 4 , 5 , 6 , 7 ,8 )
.