Pathway of Pain

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‘PATHWAY OF PAIN’
ORAL BIOLOGY
PRESENTATION

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PRESENTED BY:
DR.TEHRIM NASEER

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‘PAIN’
An unpleasant sensory and emotional
experience which we primarily associate with
tissue damage or describe in terms of such
damage, or both.

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‘NOCICEPTION’
The detection of tissue damage by
specialized transducers connected to A-
delta and C-fibers.

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CHARACTERISTICS OF
PRIMARY
AFFERENT FIBRES
A-DELTA FIBER:
• Myelinated
• Diameter fine 2 - 5 μm
• 12 - 30 m/sec. conduction velocity
• Terminated at I and V layer
• Fast pain, rapid, pricking and well localized
• Neurotransmitter - Glutamate
• 20% pain conduction

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CHARACTERISTICS OF PRIMARY
AFFERENT FIBRES
C-FIBER:
• Non-Myelinated
• Diameter less than 2 films
• -0.5 to 2 m/s conduction velocity
• Terminate in I and n layers
• Slow, diffuse, dull, aching

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CLASSIFICATION OF PAIN NOCICEPTION
• Proportionate to the stimulation of the nociceptor.
• When acute
•Physiologic pain
•Serves a protective function
•Normal pain
• when chronic
•Pathologic pain

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‘CLASSIFICATION OF PAIN’

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NEUROPATHIC PAIN:
• Sustained by aberrant processes in
PNS or CNS
• Disproportionate to the stimulation of
nociceptor
• Serves no protective function
• Pathologic pain

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MIXED PAIN:
• Nociceptive components
• Neuropathic components
• Examples:
• Failed low-back-surgery syndrome
• Complex regional pain syndrome

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IDIOPATHIC PAIN:
• No underlying lesion found yet, despite
investigation
• Pain disproportionate to the degree of
clinically discernible tissue injury

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‘NORMAL CENTRAL PAIN
MECHANISMS’

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Ascending Tracts Descending Tracts
CORTEX
MIDBRAIN
PONS
MEDULLA
SPINAL CORD
THALAMUS

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‘ASCENDING AND DESCENDING PAIN
PATHWAYS’

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‘PAIN INHIBITORY AND PAIN
FACILITATORY MECHANISMS
WITHIN DORSAL HORN’

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DORSAL HORN GATING MECHANISM

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Neuronal circuitry within the dorsal horn.
Primary afferent neuron axons synapse onto
spinothalmic neurons and onto inhibitory and
excitatory neurons.

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CAUSES OF FACIAL PAIN

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CAUSES OF FACIAL
PAIN
Facial pain can be caused by anything, from an infection to nerve damage in the face.
Common causes for facial pain include:
• oral infections
• ulcers (open sores)
• abscess (collection of pus under the surface tissue in the mouth, for example)
• skin abscess (collection of pus under the skin)
• headache
• facial injury
• toothache

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More serious causes for facial pain include:
• herpes zoster (shingles)
• migraine
• sinusitis (sinus infection)
• nerve disorder

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CHRONIC OROFACIAL
PAIN

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TRIGEMINAL
NEURALGIA
• Tic douloureux / fothergill’s neuralgia
• Paroxysms of fleeting ,excruciating u/l facial pain, usually
lasting less than a minute.
• Usually V2/V3 , rarely V1
• MC – adv age, women , rt side
• Stimulation of trigger zone – pain
• Pain – by activities like talking, chewing, brushing teeth,
exposure to cold, by wind on face

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• Trigeminal / gasserian / semilunar ganglion
• Situated just beside pons in a shallow
depression in petrous apex – meckel’s cave
• Sensory root enters the pons course
dorsomedially & terminate within brainstem:
Nucleus of spinal tract of Vth N
Main/Principal sensory nucleus
Mesencephalic nucleus

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• Fibres – pain & temp – enter spinal tract of
trigeminal & descend to various levels
depending on their somatotropic origin, then
synapse in adjacent nucleus of spinal tract.
• The axons of second order neurons cross
midline, aggregate as trigeminothalamic
tract & ascend to VPM
• From VPM , fibres project through thalamic
radiations to sensory cortex in post central
gyrus

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• B/L Weakness of
muscles of
mastication with
inability to close the
mouth ( dangling
jaw ) – motor neuron
ds, neuromuscular
transmission
disorder, myopathy
Clinical examination
motor functions

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Clinical examination
SENSORY FUNCTIONS
• Pain, touch, heat, cold – tested on face &
mucous membranes
• Each of the 3 divisions of Vth.N is tested
individually and compared with the opposite
side.

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Stimulate Direct
corneal
reflex
Consensual
corneal
reflex
Complete
VthN
lesion
Involved eye Absent Absent
Opposite eye Normal Normal
Complete
VIIthN
lesion
Involved eye Absent Normal
Opposite eye Normal Absent

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Second-Order Neuron; Some times is called a
transmission neuron since it transfer the
impulse on to higher center .
The synapse of the primary afferent and
second-order neuron occurs in the dorsal
horn of the spinal cord .

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Afferent (Sensory) Somatic
Nerves
• – Trigeminal Nerve
• – Facial Nerve
• – Glossopharyngeal Nerve
• – Vagus Nerve
• – Cervical Spinal Nerves

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Efferent (Motor) Somatic
Nerves
– Occulomotor, and abducent Nerves
– Trigeminal Nerve
– Facial Nerve
– Glossopharyngeal nerve

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TYPES OF PAIN
• Myofascial Pain
• Myositis
• Myospasm and Dystonia
• Protective Muscle Splinting
• Contracture
• Neoplasia
• Fibromyalgia

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LEISIONS AND
DISORDERS OF
NERVES

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Supranuclear lesions
• Lesions affecting corticobular pathway -
Contralateral trigeminal motor paresis
(deviation of jaw away from the lesion)
• B/L UMN lesions ( pseudobulbar palsy ) –
trigeminal motor paresis , exaggerated jaw
jerk.Mastication markedly impaired.
• Thalamic lesions – anaesthesia of c/l face
• Parietal lesions – depression of c/l corneal
reflex

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NUCLEAR LEISIONS
• Motor , sensory nuclei – primary/met .
tumours
AV malformations
demyelinating ds
infarction/h’age
syringobulbia
that affect pons, medulla and upper cervical
cord.

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Lesions affecting preganglionic
trigeminal nerve roots
• Tumour ( meningioma, schwannoma, metastasis,
nasopharyngeal ca )
• Infection ( granulomatous, infectious ,
carcinomatous meningitis )
• Trauma
• Aneurysm
Char i/p facial pain, parasthesias, numbness,
sensory loss, corneal reflex depressed, trigeminal
motor paresis.

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Lesions affecting peripheral branches
of VthCranial Nerve
• Ophthalmic div : in middle cranial fossa , at
temporal bone apex, lat wall of cavernous
sinus, sup.orbital fissure, distally in face
• Maxillary div : lower lateral wall of cavernous
sinus, at foramen rotundum, in
pterygopalatine fossa, in floor of orbit, at
infraorbital foramen, in face

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Raeder’s paratrigeminal
syndrome
• U/l oculosympathetic paresis – miosis ,
ptosis (without facial anhydrosis)
• Evidence of trigeminal involvement on same
side.
• d/t lesions in middle cranial fossa ( b/w
trigeminal ganglion & int.carotid.a, near
petrous apex)
• Lesions of gasserain ganglion – tumour,
aneurysm, trauma, infection

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Lesions affecting Gasserian ganglion
• Lesions of middle cranial fossa ( tumour, herpes zoster, sarcoidosis,
syphilis, tuberculosis, arachnoiditis, trauma, abscess )
• Pain – severe & paroxysmal
• Hemifacial / selective div of Vth CN
( esp V2,V3 )
 Parasthesias , numbness may also occur
 Sensory loss depends on div involved
 u/l pterygoid & masseter paresis may occur.

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VISCERAL PAIN PATHWAY
Pain - Aδ and fibers
Travel with autonomic afferent
Spinal cord
(Dorsal Horn)
Lat. spinothalmic tract
Thalamus
Somatosensory Cortex

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‘REFERENCES’
• Guyton and Hall textbook of Medical Physiology
• http://science.howstuffworks.com/life/inside-the-mind/human-
brain/pain3.htm
• http://www.docstoc.com/docs/
• http://www.google.fr/imgres
• www.ksums.net
• www.authorstream.com
• http://www.docstoc.com/docs/70291468/Pain-Terminology-and-Pain-

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