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 FIBRESA-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 FIBRESC-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

• Neurotransmitter - P-Substance

• 80% of pain conduction

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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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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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‘FACIAL PAIN’

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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

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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

– Vagus nerve

– Accessory Nerve

– Hypoglossal Nerve

– Cervical Spinal Nerves

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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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HERPES ZOSTER

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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’

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VISCERAL PAIN PATHWAY

Pain - Aδ and fibersTravel 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-Pathways

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